Wuschel (WUS) Gene Homologs
This invention relates to isolated polynucleotides encoding WUS polypeptides. The invention further provides isolated WUS polypeptides. The invention also provides methods of using the polynucleotides to modulate the level of WUS, improve transformation efficiency, to stimulate plant cell growth, including stem cells, to stimulate organogenesis, to stimulate somatic embryogenesis, to induce apomixis, and to provide a positive selection for cells comprising the polynucleotide. The invention also relates to cells, plants and seeds comprising the polynucleotides of the invention or produced by the methods of the invention.
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This application is a Continuation of co-pending U.S. application Ser. No. 10/744,572 filed Dec. 23, 2003, which is a Continuation-In-Part of co-pending U.S. application Ser. No. 09/807,946 filed Apr. 20, 2001, which is a national application that claims the benefit of PCT International Application No. PCT/US00/26648, filed Sep. 28, 2000, which in turn claims the benefit of U.S. Provisional Application No. 60/157,216 filed Oct. 1,1999. The entire contents of the above applications are herein incorporated by reference.
FIELD OF THE INVENTIONThis invention is in the field of plant molecular biology. More specifically, this invention pertains to nucleic acid fragments encoding Wuschel (WUS) proteins in plants and seeds.
BACKGROUND OF THE INVENTIONOrgan formation in plants occurs via the activity of apical meristems. Plant meristems contain a pool of stem cells, which are able to self-maintain, and give rise to a variety of cell types including cells required for organ initiation. The initiation and maintenance of stem cells and their integration into organ-forming meristems are thus the basis for continuous plant development.
The Wuschel protein, designated hereafter as WUS, plays a key role in the initiation and maintenance of the apical meristem, which contains a pool of pluripotent stem cells (Endrizzi et al., 1996, Plant Journal 10:967-979; Laux et al., 1996, Development 122:87-96; and Mayer et al., 1998, Cell 95:805-815). Arabidopsis plants mutant for the WUS gene contain stem cells that are misspecified and that appear to undergo differentiation. WUS encodes a novel homeodomain protein, which presumably functions as a transcriptional regulator (Mayer et al., 1998, Cell 95:805-815). The stem cell population of Arabidopsis shoot meristems is believed to be maintained by a regulatory loop between the CLAVATA (CLV) genes which promote organ initiation and the WUS gene which is required for stem cell identity, with the CLV genes repressing WUS at the transcript level, and WUS expression being sufficient to induce meristem cell identity and the expression of the stem cell marker CLV3 (Brand et al. (2000) Science 289:617-619; Schoof et al. (2000) Cell 100:635-644). Constitutive expression of WUS in Arabidopsis has been recently shown to lead to adventitious shoot proliferation from leaves (in planta) (Laux, T., talk presented at the XVI International Botanical Congress Meeting, Aug. 1-7,1999, St. Louis, Mo.).
There is a great deal of interest in identifying the genes that encode proteins involved in development in plants, generally toward the objective of altering plant growth and architecture. WUS represents one such gene. However, the WUS gene can also be used for the novel application of stimulating in vitro growth of plant tissue and improving transformation. In this manner, this gene can expand the range of tissues types targeted for transformation. Specifically, the WUS gene may be used to improve meristem transformation frequencies and could result in genotype independent transformation of many important crops such as maize, soybean and sunflower. Furthermore, transformation into meristems would stimulate the formation of new apical initials reducing the chimeric nature of the transgenic events. Lastly, ectopic expression into non-meristematic cells would stimulate adventive meristem formation. This could lead to transformation of non-traditional tissues such as leaves, leaf bases, stem tissue, etc. Alternatively, transformation of a more traditional target such as callus or the scutellum of immature embryos could promote a “non-traditional” growth response, i.e. meristems in place of somatic embryos. In addition, WUS may also be used as a genetic marker for meristems.
Modulation of WUS is expected to modulate plant and/or plant tissue phenotype including cell growth stimulation, organogenesis, and somatic embryogenesis. WUS may also be used to improve transformation via somatic embryogenesis. Expression of Arabidopsis WUS can induce stem cells in vegetative tissues, which can differentiate into somatic embryos (Zuo, et al. (2002) Plant J 30:349-359). The ability to stimulate organogenesis and/or somatic embryogenesis may be used to generate an apomictic plant. Apomixis has economic potential because it can cause any genotype, regardless of how heterozygous, to breed true. It is a reproductive process that bypasses female meiosis and syngamy to produce embryos genetically identical to the maternal parent. With apomictic reproduction, progeny of specially adaptive or hybrid genotypes would maintain their genetic fidelity throughout repeated life cycles. In addition to fixing hybrid vigor, apomixis can make possible commercial hybrid production in crops where efficient male sterility or fertility restoration systems for producing hybrids are not available. Apomixis can make hybrid development more efficient. It also simplifies hybrid production and increases genetic diversity in plant species with good male sterility.
Accordingly, the availability of nucleic acid sequences encoding all or a portion of a WUS protein would facilitate studies to better understand programmed development in plants, provide genetic tools to enhance the efficiency of gene transfer into meristem tissue and help provide alternative transformation methods in several important crops.
SUMMARY OF THE INVENTIONThis invention relates to isolated polynucleotides encoding WUS polypeptides. The invention further provides isolated WUS polypeptides. The invention also provides methods of using the polynucleotides to modulate the level of WUS, improve transformation efficiency, to stimulate plant cell growth, including stem cells, to stimulate organogenesis, to stimulate somatic embryogenesis, to induce apomixis, and to provide a positive selection for cells comprising the polynucleotide. The invention also relates to cells, plants and seeds comprising the polynucleotides of the invention or produced by the methods of the invention.
BRIEF DESCRIPTION OF THE DRAWING AND SEQUENCE LISTINGSThe invention can be more fully understood from the following detailed description and the accompanying drawing and Sequence Listing, which form a part of this application.
The present invention concerns isolated polynucleotides comprising nucleotide sequences which encode polypeptides involved in the initiation and maintenance of stem cells in plants, i.e., polypeptides having Wuschel activity. The invention also provides isolated polypeptides having Wuschel activity.
The present invention concerns an isolated polynucleotide comprising a nucleotide sequence selected from the group consisting of: (a) a first nucleotide sequence encoding a polypeptide of at least 50 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, and 12, (b) a second nucleotide sequence encoding a polypeptide of at least 100 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs:14, 16, 18, and 20, (c) a third nucleotide sequence encoding a polypeptide of at least 180 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO:24, (d) a fourth nucleotide sequence encoding a polypeptide of at least 230 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO:22, (e) a fifth nucleotide sequence encoding a polypeptide of at least 100 amino acids having at least 80% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs:6, 8, and 10, and (f) a sixth nucleotide sequence comprising the complement of (a), (b), (c), (d), or (e).
In a second embodiment, it is preferred that the isolated polynucleotide of the claimed invention comprises a first nucleotide sequence which comprises a nucleic acid sequence selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 that codes for the polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
In a third embodiment, this invention concerns an isolated polynucleotide comprising a nucleotide sequence of at least one of 60 (or at least one of 40, or at least one of 30) contiguous nucleotides derived from a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 and the complement of such nucleotide sequences.
In a fourth embodiment, this invention relates to a chimeric gene comprising an isolated polynucleotide of the present invention operably linked to at least one suitable regulatory sequence.
In a fifth embodiment, the present invention concerns an isolated host cell comprising a chimeric gene of the present invention or an isolated polynucleotide of the present invention. The host cell may be eukaryotic, such as a yeast or a plant cell, or prokaryotic, such as a bacterial cell. The present invention also relates to a virus, for example a baculovirus or a plant virus, comprising an isolated polynucleotide of the present invention or a chimeric gene of the present invention.
In a sixth embodiment, the invention also relates to a process for producing an isolated host cell comprising a chimeric gene of the present invention or an isolated polynucleotide of the present invention, the process comprising either transforming or transfecting an isolated compatible host cell with a chimeric gene or isolated polynucleotide of the present invention.
In a seventh embodiment, the invention concerns an isolated WUS polypeptide selected from the group consisting of: (a) a polypeptide of at least 50 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, and 12, (b) a polypeptide of at least 100 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 14, 16, 18, and 20, (c) a polypeptide of at least 180 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO: 24, (d) a polypeptide of at least 230 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO: 22, and (e) a polypeptide of at least 100 amino acids having at least 80% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs:6, 8, and 10.
In an eighth embodiment, the invention relates to a method of selecting an isolated polynucleotide that affects the level of expression of a WUS polypeptide or enzyme activity in a host cell, for example a plant cell, the method comprising the steps of: (a) constructing an isolated polynucleotide of the present invention or an isolated chimeric gene of the present invention; (b) introducing the isolated polynucleotide or the isolated chimeric gene into a host cell; (c) measuring the level of the WUS polypeptide or enzyme activity in the host cell containing the isolated polynucleotide; and (d) comparing the level of the WUS polypeptide or enzyme activity in the host cell containing the isolated polynucleotide with the level of the WUS polypeptide or enzyme activity in the host cell that does not contain the isolated polynucleotide.
In a ninth embodiment, the invention concerns a method of obtaining a nucleic acid fragment encoding a substantial portion of a WUS polypeptide, such as a plant WUS polypeptide, comprising the steps of: synthesizing an oligonucleotide primer comprising a nucleotide sequence of at least one of 60 (or at least one of 40, or at least one of 30) contiguous nucleotides derived from a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23, and the complement of such nucleotide sequences; and amplifying a nucleic acid fragment (for example, a cDNA inserted in a cloning vector) using the oligonucleotide primer. Optionally, the amplified nucleic acid fragment will encode a substantial portion of a WUS amino acid sequence.
In a tenth embodiment, this invention relates to a method of obtaining a nucleic acid fragment encoding all or a substantial portion of the amino acid sequence encoding a WUS polypeptide comprising the steps of: probing a cDNA or genomic library with an isolated polynucleotide of the present invention; identifying a DNA clone that hybridizes with an isolated polynucleotide of the present invention; isolating the identified DNA clone; and sequencing the cDNA or genomic fragment that comprises the isolated DNA clone.
In an eleventh embodiment, this invention concerns a composition, such as a hybridization mixture, comprising an isolated polynucleotide of the present invention.
In a twelfth embodiment, this invention concerns a method for positive selection of a transformed cell comprising: (a) transforming a host cell with the chimeric gene of the present invention or an expression cassette of the present invention; and (b) growing the transformed host cell, for example a plant cell, such as a monocot or a dicot, under conditions which allow expression of the WUS polynucleotide, and identifying transformed cells.
In a thirteenth embodiment, this invention relates to a method of altering the level of expression of a WUS protein in a host cell comprising: (a) transforming a host cell with a chimeric gene of the present invention; and (b) growing the transformed host cell under conditions that are suitable for expression of the chimeric gene wherein expression of the chimeric gene results in production of altered levels of the WUS protein in the transformed host cell.
In another embodiment, the invention relates to isolated polynucleotides, having at least 70%, 75%, 80%, 85%, 90%, 95%, 97% or up to and including 100% identity over their entire length to at least one of the nucleic acid sequences selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80, which encode polypeptides having WUS activity. The invention also relates to isolated polynucleotides which are fully complementary to the nucleic acid sequences of this embodiment.
In another embodiment, the invention relates to isolated polynucleotides comprising at least a minimum whole integer number of contiguous nucleotides ranging from at least 30 contiguous nucleotides up to and including the full-length of the sequence. For example, the isolated polynucleotide comprises at least 30, 40, 50, 60, 75, 100, 150, 300, 500, 1000 contiguous nucleotides, up to and including the full-length of a nucleic acid sequence selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. Optionally, the isolated polynucleotide is a full-length polynucleotide encoding a polypeptide having WUS activity, which comprises at least 30, 40, 50, 60, 75, 100, 150, 300, 500, 1000 contiguous nucleotides, up to and including the full-length of a nucleic acid sequence selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. The invention also relates to isolated polynucleotides which are fully complementary to the nucleic acid sequences of this embodiment.
In another embodiment, the invention relates to isolated polynucleotides, or the complement thereof, which encode a polypeptide having WUS activity, wherein the encoded polypeptide has at least 70%, 75%, 80%, 85%, 90%, 95%, 97% or up to and including 100% identity to at least one of the amino acid sequences selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. The invention also relates to isolated polynucleotides which are fully complementary to the nucleic acid sequences of this embodiment.
In another embodiment, the invention relates to isolated polynucleotides which encode a polypeptide comprising a minimum whole integer number of contiguous amino acids from at least one polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81, wherein the number of contiguous amino acids is selected from the range of 20 amino acids up to and including the full length of the polypeptide. For example, the isolated polynucleotide encodes a polypeptide comprising at least 20, 25, 30, 40, 50, 75,100, 200 contiguous amino acids, up to and including the full-length of at least one amino acid sequence selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. The invention also relates to isolated polynucleotides which are fully complementary to the nucleic acid sequences of this embodiment.
In another embodiment, the invention relates to isolated polynucleotides comprising primers capable of amplifying WUS polynucleotides from a nucleic acid library. In some embodiments, isolated polynucleotide amplification primers are selected from the group consisting of SEQ ID NOS: 82, 83, 84, 85, 86 and 87.
In another embodiment, the invention relates to DNA constructs, host cells, plants, and seeds comprising the isolated polynucleotides of the invention, or the complement thereof, particularly isolated polynucleotides having a certain percent identity to at least one nucleic acid sequence selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80, or encoding a polypeptide having a certain percent identity to at least one amino acid sequence selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. Also included are isolated polynucleotides comprising at least a minimum whole integer number of contiguous nucleotides, or encoding a polypeptide comprising a minimum whole integer number of contiguous amino acids, as described above, of the sequences of the invention.
In another embodiment, the invention relates to isolated polynucleotides encoding polypeptides having WUS activity, which comprise conserved domains or consensus amino acid sequences. The isolated polynucleotides comprise nucleic acid sequences which encode a WUS polypeptide comprising at least one conserved polypeptide motif. The polypeptide motifs include the homeodomain motif, the (E/R)TLPLFP motif, and the A(A/S)LEL(ST)L motif. Amino acid variations within these motifs are known, and included in this embodiment. Also included is a 25 amino acid motif located between the (E/R)TLPLFP and the A(A/S)LEL(ST)L motifs. In some embodiments, the isolated polynucleotides have a certain percent sequence identity to the polynucleotides of the present invention, wherein the sequence identity in the region of the polynucleotide encoding a conserved motif may be less than 100%. In some embodiments, the isolated polynucleotides are selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. Optionally, this embodiment includes polynucleotides which encode polypeptides in which a motif is absent, for example, polypeptides lacking the 25 amino acid motif (SEQ ID NO: 91 QPP(P/S)RPRHAVPVPAGE(T/P)IR(GN)GGG(S/G)S), the (E/R)TLPLFP motif or the A(A/S)LEL(ST)L motif. In some embodiments, the isolated polynucleotides have a certain percent sequence identity to the polynucleotides of the present invention, wherein at least one amino acid motif is absent. In some embodiments, the isolated polynucleotide is selected from the group consisting of SEQ ID NO: 30, 32, 39, 46, 49, 51, 53, 56, 58, 60, 63, 65, 67, 70, 72, 74, 77, and 80.
In another embodiment, the invention relates to isolated polynucleotides, or the complement thereof, which encode a polypeptide having WUS activity, wherein the encoded polypeptide has at least 70%, 75%, 80%, 85%, 90%, 95%, 97% or up to and including 100% identity to at least one of the consensus amino acid sequences selected from the group consisting of SEQ ID NOS: 88, 89, and 90. The invention also relates to isolated polynucleotides which are fully complementary to the nucleic acid sequences of this embodiment.
In another embodiment, the invention relates to isolated polypeptides having WUS activity, which comprise conserved domains or consensus amino acid sequences. The isolated polypeptides comprise at least one conserved polypeptide motif. The polypeptide motifs include the homeodomain motif, the (E/R)TLPLFP motif, and the A(A/S)LEL(ST)L motif. Amino acid variations within these motifs are known, and included in this embodiment. Also included is a 25 amino acid motif located between the (E/R)TLPLFP and the A(A/S)LEL(ST)L motifs. In some embodiments, the isolated polypeptides have a certain percent sequence identity to the polypeptides of the present invention, wherein the sequence identity in the region of the polynucleotide encoding a conserved motif may be less than 100%. In some embodiments, the isolated polypeptides are selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. Optionally, this embodiment includes polypeptides in which at least one motif is absent. This embodiment includes, for example, polypeptides lacking the 25 amino acid motif (SEQ ID NO: 91), the (E/R)TLPLFP motif or the A(A/S)LEL(ST)L motif. In some embodiments, the isolated polypeptides have a certain percent sequence identity to the polypeptides of the present invention, wherein at least one motif is absent. In some embodiments, the isolated polypeptide is selected from the group consisting of SEQ ID NO: SEQ ID NO: 31, 33, 40, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81.
In another embodiment, the invention relates to isolated polypeptides having WUS activity, wherein the encoded polypeptide has at least 70%, 75%, 80%, 85%, 90%, 95%, 97% or up to and including 100% identity to at least one of the consensus amino acid sequences selected from the group consisting of SEQ ID NOS: 88, 89, and 90.
In another embodiment, the invention relates to isolated polypeptides having WUS activity, wherein the polypeptide has at least 70%, 75%, 80%, 85%, 90%, 95%, 97% or up to and including 100% identity to at least one of the amino acid sequences selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81.
In another embodiment, the invention relates to isolated polypeptides having WUS activity, wherein the polypeptide comprises at least a minimum whole integer number of contiguous amino acids from at least one polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81, wherein the number of contiguous amino acids is selected from the range of 20 amino acids up to and including the full length of the polypeptide. For example, the isolated polypeptide comprises at least 20, 25, 30, 40, 50, 75,100, 200 contiguous amino acids, up to and including the full-length of at least one amino acid sequence selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81.
In another embodiment, the invention relates to a method to modulate the level of WUS in a cell, plant cell, or plant. The method comprises introducing into the cell an isolated polynucleotide of the invention, and expressing the polynucleotide in the cell, wherein the expression of the polynucleotide modulates the level of WUS in the cell. The introduced polynucleotide optionally comprises a DNA construct operably linked to a promoter active in the cell, in either sense or antisense orientation. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46,48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67,69, 70, 72, 74, 76, 77, 79, and 80. The cell is optionally cultured under conditions in order to generate a plant wherein the level of WUS is modulated. In other embodiments, the introduced polynucleotide optionally comprises an RNA molecule, which is introduced into the cell, plant cell, or plant. In another embodiment, the method to modulate the level of WUS in a cell, plant cell, or plant comprises introducing an isolated WUS polypeptide of the invention into the cell, plant cell, or plant. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polypeptide is selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
In another embodiment, the invention relates to a method to stimulate plant cell growth. In some embodiments, stimulation of plant cell growth can provide a positive selection means, stimulate organogenesis, stimulate embryogenesis, including the production of asexually derived embryos, such as somatic embryos, and/or apomictic embryos. The method comprises introducing into the cell an isolated polynucleotide of the invention, and expressing the polynucleotide in the cell, wherein the expression of the polynucleotide modulates the level of WUS in the cell, thereby stimulating plant cell growth. The introduced polynucleotide optionally comprises a DNA construct operably linked to a promoter active in the cell, in either sense or antisense orientation. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23. The cell is optionally cultured under conditions in order to generate a plant. In other embodiments, the introduced polynucleotide optionally comprises an RNA molecule, which is introduced into the cell, plant cell, or plant, thereby stimulating cell growth. In another embodiment, the method to plant cell growth comprises introducing an isolated WUS polypeptide of the invention into the cell, plant cell, or plant. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments, cells stimulated to proliferate by polynucleotides and/or polypeptides of the invention are subsequently transformed with another polynucleotide of interest. WUS stimulates growth in a non-cell autonomous manner, therefore in some embodiments proliferating cells stimulated by WUS, but not comprising stably incorporated WUS are used as the host cells for transformation with a polynucleotide of interest.
In another embodiment, the invention relates to a method of positive selection for transformed plant cells. The method comprises introducing into a plant cell an isolated polynucleotide which encodes a polypeptide having WUS activity, expressing the polynucleotide, and culturing the transformed cells under conditions which provide positive selection for cells comprising the polynucleotide. Optionally, the culture conditions comprise conditions in which neither exogenous plant hormones, nor chemical selection agents are provided. The conditions may also comprise the addition of exogenous plant hormones, in any range of lower concentration up to the normal plant cell culture concentration. If the plant cell comprises another selectable marker, the conditions may comprise the addition of the selecting agent or method. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42,44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23.
In another embodiment, the invention relates to a method to produce asexually derived embryos. The method comprises introducing into the cell an isolated polynucleotide of the invention, and expressing the polynucleotide in the cell, wherein the expression of the polynucleotide produces an asexually derived embryo. The introduced polynucleotide optionally comprises a DNA construct operably linked to a promoter active in the cell, in either sense or antisense orientation. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23. The produced embryo is optionally cultured under conditions in order to generate a plant. In other embodiments, the introduced polynucleotide optionally comprises an RNA molecule, which results in the production of an asexually derived embryo. In another embodiment, the method to produce asexually derived embryos comprises introducing an isolated WUS polypeptide of the invention into the cell, plant cell, or plant. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the asexually derived embryos are somatic embryos or apomictic embryos. In some embodiments, the plant regenerated from the embryo has an apomictic phenotype.
In another embodiment, the invention relates to a method to generate an apomictic plant. The method comprises introducing into a plant cell an isolated polynucleotide which encodes a polypeptide having WUS activity, regenerating a plant comprising the polynucleotide, wherein the plant has an apomictic phenotype. The introduced polynucleotide optionally comprises a DNA construct operably linked to a promoter active in the cell. Optionally, the promoter active in the cell is an inducible promoter, a tissue-preferred promoter, a developmentally regulated promoter, or a promoter, or combination of promoters, having more than one of these properties. In one embodiment, the promoter is a nucellus-preferred promoter, such as the barley nuc-1 promoter, or an inducible promoter, like In2. In some embodiments, WUS expression may be further regulated by having another gradient, temporal or spatial, super-imposed by separating the coding region or encoded polypeptide into at least two segments which are separably regulated. In some embodiments, the coding region is interrupted by a recombinase flanked spacer region, which is excised when the appropriate recombinase is provided in a controlled manner. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4,6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41,42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23. In other embodiments a polypeptide having WUS activity is reconstituted via intein splicing. Only cells comprising both segments that have been expressed and combined will comprise a polypeptide having WUS activity.
In another embodiment, the invention relates to a method to increase transformation frequency. The method comprises introducing into a plant cell an isolated polynucleotide of the invention which encodes a polypeptide having WUS activity, and expressing the polynucleotide in the cell, wherein the expression of the polynucleotide increases transformation frequency. Transformation frequency is measured relative to a wild-type or control plant cell that does not contain and/or express the polynucleotide of the invention. The introduced polynucleotide optionally comprises a promoter active in the cell operably linked to the isolated polynucleotide. In some embodiments, the introduced polynucleotide further comprises a polynucleotide of interest, which may be operably linked to a promoter active in the cell, or a polynucleotide of interest may be separately introduced. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23. Optionally, a transformed cell produced by the method is further cultured under conditions in order to generate a plant. In other embodiments, the introduced polynucleotide optionally comprises an RNA molecule which is introduced into the cell, plant cell, or plant. In another embodiment, the method comprises introducing an isolated WUS polypeptide of the invention into the cell, plant cell, or plant. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In certain embodiments, the plant cell is a typically non-transformable and/or recalcitrant plant cell.
In another embodiment, the invention relates to a method to stimulate organogenesis in a plant. The method comprises introducing into a plant cell an isolated polynucleotide of the invention which encodes a polypeptide having WUS activity, and expressing the polynucleotide in the cell, wherein the expression of the polynucleotide stimulates organogenesis. The introduced polynucleotide optionally comprises a promoter active in the cell operably linked to the isolated polynucleotide. In some embodiments, the introduced polynucleotide further comprises a polynucleotide of interest, which may be operably linked to a promoter active in the cell, or a polynucleotide of interest may be separately introduced. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23. Optionally, a transformed cell produced by the method is further cultured under conditions in order to generate a plant. In other embodiments, the introduced polynucleotide optionally comprises an RNA molecule which is introduced into the cell, plant cell, or plant. In another embodiment, the method comprises introducing an isolated WUS polypeptide of the invention into the cell, plant cell, or plant. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
In another embodiment, the invention relates to a method to stimulate somatic embryogenesis in a plant. The method comprises introducing into a plant cell an isolated polynucleotide of the invention which encodes a polypeptide having WUS activity, and expressing the polynucleotide in the cell, wherein the expression of the polynucleotide stimulates somatic embryogenesis. The introduced polynucleotide optionally comprises a promoter active in the cell operably linked to the isolated polynucleotide. In some embodiments, the introduced polynucleotide further comprises a polynucleotide of interest, which may be operably linked to a promoter active in the cell, or a polynucleotide of interest may be separately introduced. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments, the isolated polynucleotide encodes a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24. In some embodiments the isolated polynucleotide is selected from the group consisting of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, and 80. In some embodiments the polynucleotide is selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23. Optionally, a transformed cell produced by the method is further cultured under conditions in order to generate a plant. In other embodiments, the introduced polynucleotide optionally comprises an RNA molecule which is introduced into the cell, plant cell, or plant. In another embodiment, the method comprises introducing an isolated WUS polypeptide of the invention into the cell, plant cell, or plant. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOS: 27, 29, 31, 33, 36, 38, 40, 43, 45, 47, 50, 52, 54, 57, 59, 61, 64, 66, 68, 71, 73, 75, 78, and 81. In some embodiments the isolated polypeptide is selected from the group consisting of SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
In another embodiment, the invention relates to any transgenic host cell, plant cell, plant, and/or seed produced by the methods of the invention. This embodiment includes those instances wherein the host cell, plant cell, plant, and/or seed is transgenic and comprises a polynucleotide of the invention. This embodiment also includes those instances wherein a polynucleotide or polypeptide of the invention was used in a transient manner in order to generate host cells, plant cells, plants and/or seeds having the desired traits. In certain embodiments, the host cell, plant cell, plant, and/or seed produced by the methods of the invention may further comprise other polynucleotides of interest.
Table 1 lists the polypeptides that are described herein, the designation of the cDNA clones that comprise the nucleic acid fragments encoding polypeptides representing all or a substantial portion of these polypeptides, and the corresponding identifier (SEQ ID NO:) as used in the attached Sequence Listing. Table 1 also identifies the cDNA clones as individual ESTs (“EST”), the sequences of the entire cDNA insert comprising the indicated cDNA clone (“full insert sequence” or “FIS”), contigs assembled from two or more EST, FIS, and/or PCR sequences (“Contig”), or sequences encoding the entire protein derived from an EST, an FIS, a contig, or an FIS and PCR fragment sequence (“complete gene sequence” or “CGS”). Nucleotide SEQ ID NOs: 1, 5,11, and 15 correspond to nucleotide SEQ ID NOs: 1, 3, 5, and 7, respectively, presented in U.S. Provisional Application No. 60/157216, filed Oct. 1, 1999. Amino acid SEQ ID NOs: 2, 6, 12, and 16 correspond to amino acid SEQ ID NOs: 2, 4, 6, and 8, respectively, presented in U.S. Provisional Application No. 60/157216, filed Oct. 1, 1999. Nucleotide SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 20, 21, and 23, and amino acid SEQ ID NOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 and 25 retain the same sequence identifiers as presented in PCT International Application No. PCT/US00/26648 filed Sep. 28, 2000. The sequence descriptions and Sequence Listing attached hereto comply with the rules governing nucleotide and/or amino acid sequence disclosures in patent applications as set forth in 37 C.F.R. §1.821-1.825.
The Sequence Listing contains the one letter code for nucleotide sequence characters and the three letter codes for amino acids as defined in conformity with the IUPAC-IUBMB standards described in Nucleic Acids Res. 13:3021-3030 (1985) and in the Biochemical J. 219(2):345-373 (1984) which are herein incorporated by reference. The symbols and format used for nucleotide and amino acid sequence data comply with the rules set forth in 37 C.F.R. §1.822.
In the context of this disclosure, a number of terms shall be utilized. The terms “polynucleotide”, “polynucleotide sequence”, “nucleic acid sequence”, and “nucleic acid fragment”/“isolated nucleic acid fragment” are used interchangeably herein. These terms encompass nucleotide sequences and the like. A polynucleotide may be a polymer of RNA or DNA that is single- or double-stranded, that optionally contains synthetic, non-natural or altered nucleotide bases. A polynucleotide in the form of a polymer of DNA may be comprised of one or more segments of cDNA, genomic DNA, synthetic DNA, or mixtures thereof. An isolated polynucleotide of the present invention may include a polynucleotide comprising at least 60 contiguous nucleotides, or at least 40 contiguous nucleotides, and optionally at least 30 contiguous nucleotides derived from SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, or 23, or the complement of such sequences.
The length of the polynucleotide is given as an integer selected from the group consisting of from at least 30 to the length of the nucleic acid sequence from which the polynucleotide is a subsequence of. Therefore, an isolated polynucleotide of the present invention also includes polynucleotides comprising contiguous nucleotides of at least 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, 175, 200, 250, 300, 500 or up to and including the full-length of the polynucleotides of SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, or 23 and the polynucleotides of SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46,48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, or 80. Optionally, the number of such subsequences encoded by a polynucleotide of the instant embodiment can be any integer selected from the group consisting of from 1 to 20, such as 2, 3, 4, or 5. The subsequences can be separated by any integer of nucleotides from 1 to the number of nucleotides in the sequence such as at least 5, 10, 15, 25, 50, 100, or 200 nucleotides. The subsequences of the present invention can comprise structural characteristics of the sequence from which it is derived, for example including but not limited to, signal sequences, translational start sites, polyadenylation sites, conserved motifs, introns, exons, UTR's, and the like.
As used herein “fully complementary” refers to a nucleic acid sequence which is 100% complementary to a reference nucleic acid sequence.
The term “apomixis” is used to describe asexual reproduction that replaces or substitutes for sexual methods of reproduction. When apomixis occurs, embryos are produced from maternal tissue and use only the maternal genome, and are referred to as “apomictic embryos”. A plant capable of producing embryos in the absence of fertilization is referred to as an “apomictic plant”, or a plant that has an “apomictic phenotype”.
As used herein, “Wuschel polynucleotide” or “WUS polynucleotide” means a polynucleotide encoding a polypeptide with Wuschel activity, or a polynucleotide capable of modulating the expression of mRNA or protein in a host cell. The term is also inclusive of fragments, variants, homologues, alleles or precursors with the any one of the above stated functions.
A “protein” or “polypeptide” is a chain of amino acids arranged in a specific order determined by the coding sequence in a polynucleotide encoding the polypeptide. Each protein or polypeptide has a unique function. As used herein, “polypeptide” means proteins, protein fragments, modified proteins (e.g., glycosylated, phosphorylated, or other modifications), amino acid sequences and synthetic amino acid sequences. The polypeptide can be modified or not.
As used herein, “Wuschel polypolypeptide” or “WUS polypeptide” means a polypeptide having Wuschel activity, i.e., involved in the initiation and maintenance of stem cells in plants. Wuschel activity stimulates cell growth, including stem cells. Wuschel is a plant homeodomain protein, comprising an ‘atypical’ (compared to the animal homeodomain motif) helix-loop-helix-turn-helix homeodomain motif comprising extra amino acid residues in the loop and/or turn of the domain. Wuschel proteins may further comprise other conserved motifs, such as the two conserved Wuschel C-terminal domains, the (E/R)TLPLFP and A(A/S)LEL(S/T)L domains. The term is also inclusive of fragments, variants, homologues, with the any one of the above stated functions.
The term “isolated” refers to material, such as a nucleic acid or a protein, which is: (1) substantially or essentially free from components which normally accompany or interact with the material as found in its naturally occurring environment or (2) if the material is in its natural environment, the material has been altered by deliberate human intervention to a composition and/or placed at a locus in the cell other than the locus native to the material. The term “isolated” polynucleotide refers to a polynucleotide that is substantially free from other nucleic acid sequences, such as other chromosomal and extrachromosomal DNA and RNA, that normally accompany or interact with it as found in its naturally occurring environment. Isolated polynucleotides may be purified from a host cell in which they naturally occur. Conventional nucleic acid purification methods known to skilled artisans may be used to obtain isolated polynucleotides. The term also embraces recombinant polynucleotides and chemically synthesized polynucleotides.
The term “recombinant” means, for example, that a nucleic acid sequence is made by an artificial combination of two otherwise separated segments of sequence, e.g., by chemical synthesis or by the manipulation of isolated nucleic acids by genetic engineering techniques.
As used herein, “contig” refers to a nucleotide sequence that is assembled from two or more constituent nucleotide sequences that share common or overlapping regions of sequence homology. For example, the nucleotide sequences of two or more nucleic acid fragments can be compared and aligned in order to identify common or overlapping sequences. Where common or overlapping sequences exist between two or more nucleic acid fragments, the sequences (and thus their corresponding nucleic acid fragments) can be assembled into a single contiguous nucleotide sequence.
As used herein, “substantially similar” refers to nucleic acid fragments wherein changes in one or more nucleotide bases results in substitution of one or more amino acids, but do not affect the functional properties of the polypeptide encoded by the nucleotide sequence. “Substantially similar” also refers to nucleic acid fragments wherein changes in one or more nucleotide bases does not affect the ability of the nucleic acid fragment to mediate alteration of gene expression by gene silencing through for example antisense or co-suppression technology. “Substantially similar” also refers to modifications of the nucleic acid fragments of the instant invention such as deletion or insertion of one or more nucleotides that do not substantially affect the functional properties of the resulting transcript vis-à-vis the ability to mediate gene silencing or alteration of the functional properties of the resulting protein molecule. It is therefore understood that the invention encompasses more than the specific exemplary nucleotide or amino acid sequences and includes functional equivalents thereof. The terms “substantially similar” and “corresponding substantially” are used interchangeably herein.
Substantially similar nucleic acid fragments may be selected by screening nucleic acid fragments representing subfragments or modifications of the nucleic acid fragments of the instant invention, wherein one or more nucleotides are substituted, deleted and/or inserted, for their ability to affect the level of the polypeptide encoded by the unmodified nucleic acid fragment in a plant or plant cell. For example, a substantially similar nucleic acid fragment representing at least one of 30 contiguous nucleotides derived from the instant nucleic acid fragment can be constructed and introduced into a plant or plant cell. The level of the polypeptide encoded by the unmodified nucleic acid fragment present in a plant or plant cell exposed to the substantially similar nucleic fragment can then be compared to the level of the polypeptide in a plant or plant cell that is not exposed to the substantially similar nucleic acid fragment.
For example, it is well known in the art that silencing of gene expression may be accomplished using nucleic acid fragments representing less than the entire coding region of a gene, and by using nucleic acid fragments that do not share 100% sequence identity with the gene to be suppressed. Moreover, alterations in a nucleic acid fragment which result in the production of a chemically equivalent amino acid at a given site, but do not affect the functional properties of the encoded polypeptide, are well known in the art. Thus, a codon for the amino acid alanine, a hydrophobic amino acid, may be substituted by a codon encoding another less hydrophobic residue, such as glycine, or a more hydrophobic residue, such as valine, leucine, or isoleucine. Similarly, changes which result in substitution of one negatively charged residue for another, such as aspartic acid for glutamic acid, or one positively charged residue for another, such as lysine for arginine, can also be expected to produce a functionally equivalent product. Nucleotide changes which result in alteration of the N-terminal and C-terminal portions of the polypeptide molecule would also not be expected to alter the activity of the polypeptide. Each of the proposed modifications is well within the routine skill in the art, as is determination of retention of biological activity of the encoded products. Consequently, an isolated polynucleotide comprising a nucleotide sequence of at least one of 60 (or at least one of 40, or at least one of 30) contiguous nucleotides derived from a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23, and the complement of such nucleotide sequences may be used in methods of selecting an isolated polynucleotide that affects the expression of a WUS polypeptide in a host cell. A method of selecting an isolated polynucleotide that affects the level of expression of a polypeptide in a virus or in a host cell (eukaryotic, such as plant or yeast, prokaryotic such as bacterial) may comprise the steps of: constructing an isolated polynucleotide of the present invention or an isolated chimeric gene of the present invention; introducing the isolated polynucleotide or the isolated chimeric gene into a host cell; measuring the level of a polypeptide or enzyme activity in the host cell containing the isolated polynucleotide; and comparing the level of a polypeptide or enzyme activity in the host cell containing the isolated polynucleotide with the level of a polypeptide or enzyme activity in a host cell that does not contain the isolated polynucleotide.
Moreover, substantially similar nucleic acid fragments may also be characterized by their ability to hybridize. Estimates of such homology are provided by either DNA-DNA or DNA-RNA hybridization under conditions of stringency as is well understood by those skilled in the art (Hames and Higgins, Eds. (1985) Nucleic Acid Hybridisation, IRL Press, Oxford, U.K.). Stringency conditions can be adjusted to screen for moderately similar fragments, such as homologous sequences from distantly related organisms, or to screen for highly similar fragments, such as genes that duplicate functional enzymes from closely related organisms. Post-hybridization washes determine stringency conditions. One set of conditions uses a series of washes starting with 6×SSC, 0.5% SDS at room temperature for 15 min, then repeated with 2×SSC, 0.5% SDS at 45° C. for 30 min, and then repeated twice with 0.2×SSC, 0.5% SDS at 50° C. for 30 min. More stringent conditions may use higher temperatures in which the washes are identical to those above except for the temperature of the final two 30 min washes in 0.2×SSC, 0.5% SDS was increased to 60° C. Another set of highly stringent conditions uses two final washes in 0.1×SSC, 0.1% SDS at 65° C.
Substantially similar nucleic acid fragments of the instant invention may also be characterized by the percent identity of the amino acid sequences that they encode to the amino acid sequences disclosed herein, as determined by algorithms commonly employed by those skilled in this art. Suitable nucleic acid fragments (isolated polynucleotides of the present invention) encode polypeptides that are at least about 70% identical, or at least about 80% identical to the amino acid sequences reported herein. Nucleic acid fragments that encode amino acid sequences that are about 85% identical to the amino acid sequences are reported herein. Nucleic acid fragments encode amino acid sequences that are at least about 90% identical to the amino acid sequences are also reported herein. Nucleic acid fragments that encode amino acid sequences that are at least about 95% identical to the amino acid sequences are reported herein. Suitable nucleic acid fragments not only have the above identities but typically encode a polypeptide having at least 50 amino acids, at least 100 amino acids, at least 150 or 180 amino acids, at least 200 or 230 amino acids, or at least 250 amino acids.
Methods of alignment of sequences for comparison are well known in the art. Thus, the determination of percent sequence identity between any two sequences can be accomplished using a mathematical algorithm. Non-limiting examples of such mathematical algorithms are the algorithm of Myers & Miller (1988) CABIOS 4:11-17; the local alignment algorithm of Smith et al. (1981) Adv. Appl. Math. 2:482; the global alignment algorithm of Needleman & Wunsch (1970) J. Mol. Biol. 48:443-453; the search-for-local alignment method of Pearson & Lipman (1988) PNAS 85:2444-2448; the algorithm of Karlin & Altschul (1990) PNAS 87:2264-2268, modified as in Karlin & Altschul (1993) PNAS 90:5873-5877.
Computer implementations of these mathematical algorithms can be utilized for comparison of sequences to determine sequence identity. Such implementations include, but are not limited to: CLUSTAL in the PC/Gene program (available from Intelligenetics, Mountain View, Calif.); the ALIGN program (Version 2.0) and GAP, BESTFIT, PILEUP, PRETTY, BLAST, FASTA, and TFASTA in the GCG Wisconsin Genetics Software Package, Version 10 (Accelrys Inc., 9685 Scranton Road, San Diego, Calif., USA). Alignments using these programs can be performed using the default parameters. The CLUSTAL program is well described by Higgins et al. (1988) Gene 73:237-244 (1988); Higgins et al. (1989) CABIOS 5:151-153; Corpet et al. (1988) Nucl. Acids Res. 16:10881-90; Huang et al. (1992) CABIOS 8:155-65; and Pearson et al. (1994) Meth. Mol. Biol. 24:307-331.
Sequence alignments and percent identity calculations, particularly for sequences selected from the group consisting of SEQ ID NOS: 1-25, were performed using the Megalign program of the LASERGENE bioinformatics computing suite (DNASTAR Inc., Madison, Wis.). Percent sequence identity can also be calculated over the entire length of the sequences compared using the alignment algorithm of Needleman & Wunsch, J. Mol. Biol. 48:443 (1970), for example as implemented in the GAP algorithm in the GCG™ software package (Accelrys, San Diego, Calif.). GAP Version 10 uses the following default parameters: % identity for a nucleotide sequence using GAP Weight of 50 and Length Weight of 3;% identity for an amino acid sequence using the BLOSUM62 scoring matrix (Henikoff & Henikoff, PNAS 89:10915-10919 (1992)), GAP Weight of 8 and Length Weight of 2.
Multiple alignment of the sequences, particularly for sequences selected from the group consisting of SEQ ID NOS: 1-25, was performed using the Clustal method of alignment (Higgins and Sharp (1989) CABIOS. 5:151-153) with the default parameters (GAP PENALTY=10, GAP LENGTH PENALTY=10). Default parameters for pairwise alignments using the Clustal method were KTUPLE 1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5. Multiple alignments of polynucleotide and polypeptide sequences can also be generated using the PileUp program (Feng & Doolittle, J. Mol. Evol. 25:351-360 (1987)) in the GCG™ software package (Accelrys, San Diego, Calif.), which uses the following default parameters for amino acid sequences of the BLOSUM62 scoring matrix (Henikoff & Henikoff, PNAS 89:10915-10919 (1992)), GAP Weight=8 and Length Weight=2. For polynucleotide sequences, PILEUP uses the default parameters of GAP Weight=5, and Length Weight=1.
Optionally, one of skill can use the PRETTY program for alignment of polynucleotide and polypeptide sequences, as found in the GCG™ software package (Accelrys, San Diego, Calif.), which uses the following default parameters for amino acid sequences of the BLOSUM62 scoring matrix (Henikoff & Henikoff, PNAS 89:10915-10919 (1992)), GAP Weight=8 and Length Weight=2, and which also generates a consensus sequence for the alignment. For polynucleotide sequences, PRETTY uses the default parameters of GAP Weight=5, and Length Weight=1.
Substantially similar polynucleotides of the instant invention may also be characterized by the percent identity of the nucleic acid sequences to the polynucleotides disclosed herein, as determined by algorithms commonly employed by those skilled in this art. Isolated polynucleotides of the present invention comprise nucleic acids sequences that have at least 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% identity to the polynucleotides disclosed, e.g., SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 19, 21, or 23, or SEQ ID NOS: 26, 28, 30, 32, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 77, 79, or 80. Sequence alignments and percent identity calculations may be performed using standard methods and algorithms, as described above.
As used herein, “substantially similar” in reference to polypeptides and amino acid sequences refers to polypeptides wherein changes (e.g., modification, substitution, deletion, insertion) in one or more amino acids do not affect the functional properties of the polypeptide, i.e., at least one activity of the polypeptide is retained, such as a protein-protein interaction, antibody binding, or enzymatic and/or biological activity. It is therefore understood that the invention encompasses more than the specific exemplary amino acid sequences and includes functional equivalents thereof. The terms “substantially similar” and “corresponding substantially” are used interchangeably herein. For these purposes, substantially similar polypeptides normally comprise amino acid sequences having a sequence identity of at least 60%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, or greater.
A “substantial portion” of an amino acid or nucleotide sequence comprises an amino acid or a nucleotide sequence that is sufficient to afford putative identification of the protein or gene that the amino acid or nucleotide sequence comprises. Amino acid and nucleotide sequences can be evaluated either manually by one skilled in the art, or by using computer-based sequence comparison and identification tools that employ algorithms such as BLAST (Basic Local Alignment Search Tool; Altschul et al. (1993) J. Mol. Biol. 215:403-410; see also NCBI BLAST website). In general, a sequence of ten or more contiguous amino acids or thirty or more contiguous nucleotides is necessary in order to putatively identify a polypeptide or nucleic acid sequence as homologous to a known protein or gene. Moreover, with respect to nucleotide sequences, gene-specific oligonucleotide probes comprising 30 or more contiguous nucleotides may be used in sequence-dependent methods of gene identification (e.g., Southern hybridization) and isolation (e.g., in situ hybridization). In addition, short oligonucleotides of 12 or more nucleotides may be used as amplification primers in PCR in order to obtain a particular nucleic acid fragment comprising the primers. Accordingly, a “substantial portion” of a nucleotide sequence comprises a nucleotide sequence that will afford specific identification and/or isolation of a nucleic acid fragment comprising the sequence. The instant specification teaches amino acid and nucleotide sequences encoding polypeptides that comprise one or more particular plant proteins. The skilled artisan, having the benefit of the sequences as reported herein, may now use all or a substantial portion of the disclosed sequences for purposes known to those skilled in this art. Accordingly, the instant invention comprises the complete sequences as reported in the accompanying Sequence Listing, as well as substantial portions of those sequences as defined above.
“Codon degeneracy” refers to divergence in the genetic code permitting variation of the nucleotide sequence without affecting the amino acid sequence of an encoded polypeptide. Accordingly, the instant invention relates to any nucleic acid fragment comprising a nucleotide sequence that encodes all or a substantial portion of the amino acid sequences set forth herein. The skilled artisan is well aware of the “codon-bias” exhibited by a specific host cell in usage of nucleotide codons to specify a given amino acid. Therefore, when synthesizing a nucleic acid fragment for improved expression in a host cell, it is desirable to design the nucleic acid fragment such that its frequency of codon usage approaches the frequency of preferred codon usage of the host cell.
“Synthetic nucleic acid fragments” can be assembled from oligonucleotide building blocks that are chemically synthesized using procedures known to those skilled in the art. These building blocks are ligated and annealed to form larger nucleic acid fragments which may then be enzymatically assembled to construct the entire desired nucleic acid fragment. “Chemically synthesized”, as related to a nucleic acid fragment, means that the component nucleotides were assembled in vitro. Manual chemical synthesis of nucleic acid fragments may be accomplished using well established procedures, or automated chemical synthesis can be performed using one of a number of commercially available machines. Accordingly, the nucleic acid fragments can be tailored for optimal gene expression based on optimization of the nucleotide sequence to reflect the codon bias of the host cell. The skilled artisan appreciates the likelihood of successful gene expression if codon usage is biased towards those codons favored by the host. Determination of preferred codons can be based on a survey of genes derived from the host cell where sequence information is available.
“Gene” refers to a polynucleotide that expresses a specific protein, including regulatory sequences preceding (5′ non-coding sequences) and following (3′ non-coding sequences) the coding sequence. “Native” refers to a polynucleotide as found in nature with its own regulatory sequences. “Chimeric” refers any polynucleotide that is not a native gene, comprising regulatory and coding sequences that are not found together in nature. Accordingly, a chimeric gene may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that found in nature. “Endogenous gene” refers to a native gene in its natural location in the genome of an organism. A “foreign gene” refers to a gene not normally found in the host organism, but that is introduced into the host organism by gene transfer. Foreign genes can comprise native genes inserted into a non-native organism, or chimeric genes. A “transgene” is a gene that has been introduced into the genome by a transformation procedure.
As used herein, “heterologous” in reference to a nucleic acid is a nucleic acid that originates from a foreign species, or, if from the same species, is substantially modified from its native form in composition and/or genomic locus by deliberate human intervention. For example, a promoter operably linked to a heterologous structural gene is from a species different from that from which the structural gene was derived, or, if from the same species, one or both are substantially modified from their original form. A heterologous protein may originate from a foreign species or, if from the same species, is substantially modified from its original form by deliberate human intervention.
“Coding sequence” refers to a nucleotide sequence that codes for a specific amino acid sequence. “Regulatory sequences” refer to nucleotide sequences located upstream (5′ non-coding sequences), within, or downstream (3′ non-coding sequences) of a coding sequence, and which influence the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory sequences may include promoters, translation leader sequences, introns, and polyadenylation recognition sequences.
“Promoter” refers to a nucleotide sequence capable of controlling the expression of a coding sequence or functional RNA. In general, a coding sequence is located 3′ to a promoter sequence. The promoter sequence consists of proximal and more distal upstream elements, the latter elements often referred to as enhancers. Accordingly, an “enhancer” is a nucleotide sequence which can stimulate promoter activity and may be an innate element of the promoter or a heterologous element inserted to enhance the level or tissue-specificity of a promoter. Promoters may be derived in their entirety from a native gene, or may be composed of different elements derived from different promoters found in nature, or may even comprise synthetic nucleotide segments. It is understood by those skilled in the art that different promoters may direct the expression of a gene in different tissues or cell types, or at different stages of development, or in response to different environmental conditions. Promoters which cause a nucleic acid fragment to be expressed in most cell types at most times are commonly referred to as “constitutive promoters”. New promoters of various types useful in plant cells are constantly being discovered; numerous examples may be found in the compilation by Okamuro and Goldberg (1989) Biochemistry of Plants 15:1-82. It is further recognized that since in most cases the exact boundaries of regulatory sequences have not been completely defined, nucleic acid fragments of different lengths may have identical promoter activity.
“Translation leader sequence” refers to a nucleotide sequence located between the promoter sequence of a gene and the coding sequence. The translation leader sequence is present in the fully processed mRNA upstream of the translation start sequence. The translation leader sequence may affect processing of the primary transcript to mRNA, mRNA stability or translation efficiency. Examples of translation leader sequences have been described (Turner and Foster (1995) Mol. Biotechnol. 3:225-236).
“3′ non-coding sequences” refer to nucleotide sequences located downstream of a coding sequence and include polyadenylation recognition sequences and other sequences encoding regulatory signals capable of affecting mRNA processing or gene expression. The polyadenylation signal is usually characterized by affecting the addition of polyadenylic acid tracts to the 3′ end of the mRNA precursor. The use of different 3′ non-coding sequences is exemplified by Ingelbrecht et al. (1989) Plant Cell 1:671-680.
“RNA transcript” refers to the product resulting from RNA polymerase-catalyzed transcription of a DNA sequence. When the RNA transcript is a perfect complementary copy of the DNA sequence, it is referred to as the primary transcript or it may be a RNA sequence derived from posttranscriptional processing of the primary transcript and is referred to as the mature RNA. “Messenger RNA (mRNA)” refers to the RNA that is without introns and that can be translated into polypeptides by the cell. “cDNA” refers to DNA that is complementary to and derived from an mRNA template. The cDNA can be single-stranded or converted to double stranded form using, for example, the Klenow fragment of DNA polymerase 1. “Sense-RNA” refers to an RNA transcript that includes the mRNA and so can be translated into a polypeptide by the cell. “Antisense RNA” refers to an RNA transcript that is complementary to all or part of a target primary transcript or mRNA and that blocks the expression of a target gene (see U.S. Pat. No. 5,107,065, incorporated herein by reference). The complementarity of an antisense RNA may be with any part of the specific nucleotide sequence, i.e., at the 5′ non-coding sequence, 3′ non-coding sequence, introns, or the coding sequence. “Functional RNA” refers to sense RNA, antisense RNA, ribozyme RNA, or other RNA that may not be translated but yet has an effect on cellular processes.
The term “operably linked” refers to the association of two or more nucleic acid fragments on a single polynucleotide so that the function of one is affected by the other. For example, a promoter is operably linked with a coding sequence when it is capable of affecting the expression of that coding sequence (i.e., that the coding sequence is under the transcriptional control of the promoter). Coding sequences can be operably linked to regulatory sequences in sense or antisense orientation. The term is also inclusive of protein trans-splicing events (e.g. inteins) which produce a single functional polypeptide.
The term “expression”, as used herein, refers to the transcription and stable accumulation of sense (mRNA) or antisense RNA derived from the nucleic acid fragment of the invention. Expression may also refer to translation of mRNA into a polypeptide. “Antisense inhibition” refers to the production of antisense RNA transcripts capable of suppressing the expression of the target protein.
“Overexpression” refers to the production of a gene product in transgenic organisms that exceeds levels of production in normal or non-transformed organisms.
“Co-suppression” refers to the production of sense RNA transcripts capable of suppressing the expression of identical or substantially similar foreign or endogenous genes (U.S. Pat. No. 5,231,020, incorporated herein by reference).
“Altered levels” or “altered expression” refers to the production of gene product(s) in transgenic organisms in amounts or proportions that differ from that of normal or non-transformed organisms.
“Null mutant” refers here to a host cell which either lacks the expression of a certain polypeptide or expresses a polypeptide which is inactive or does not have any detectable expected enzymatic function.
“Mature protein” or the term “mature” when used in describing a protein refers to a post-translationally processed polypeptide; i.e., one from which any pre- or propeptides present in the primary translation product have been removed.
“Precursor protein” or the term “precursor” when used in describing a protein refers to the primary product of translation of mRNA; i.e., with pre- and propeptides still present. Pre- and propeptides may be but are not limited to intracellular localization signals.
A “chloroplast transit peptide” is an amino acid sequence which is translated in conjunction with a protein and directs the protein to the chloroplast or other plastid types present in the cell in which the protein is made. “Chloroplast transit sequence” refers to a nucleotide sequence that encodes a chloroplast transit peptide. A “signal peptide” is an amino acid sequence which is translated in conjunction with a protein and directs the protein to the secretory system (Chrispeels (1991) Ann. Rev. Plant Phys. Plant Mol. Biol. 42:21-53). If the protein is to be directed to a vacuole, a vacuolar targeting signal (supra) can further be added, or if to the endoplasmic reticulum, an endoplasmic reticulum retention signal (supra) may be added. If the protein is to be directed to the nucleus, any signal peptide present should be removed and instead a nuclear localization signal included (Raikhel (1992) Plant Phys. 100:1627-1632).
“Transformation” refers to the transfer of a nucleic acid fragment into the genome of a host organism. Host organisms containing the transformed nucleic acid fragments are referred to as “transgenic” organisms. Examples of methods of plant transformation include Agrobacterium-mediated transformation (De Blaere et al. (1987) Meth. Enzymol. 143:277) and particle-accelerated or “gene gun” transformation technology (Klein et al. (1987) Nature (London) 327:70-73; U.S. Pat. No. 4,945,050, incorporated herein by reference). Thus, isolated polynucleotides of the present invention can be incorporated into recombinant constructs, typically DNA constructs, capable of introduction into and replication in a host cell. Such a construct can be a vector that includes a replication system and sequences that are capable of transcription and translation of a polypeptide-encoding sequence in a given host cell. A number of vectors suitable for stable transfection of plant cells or for the establishment of transgenic plants have been described in, e.g., Pouwels et al., Cloning Vectors: A Laboratory Manual, 1985, supp. 1987; Weissbach and Weissbach, Methods for Plant Molecular Biology, Academic Press, 1989; and Flevin et al., Plant Molecular Biology Manual, Kluwer Academic Publishers, 1990. Typically, plant expression vectors include, for example, one or more cloned plant genes under the transcriptional control of 5′ and 3′ regulatory sequences and a dominant selectable marker. Such plant expression vectors also can contain a promoter regulatory region (e.g., a regulatory region controlling inducible or constitutive, environmentally- or developmentally-regulated, or cell- or tissue-specific expression), a transcription initiation start site, a ribosome binding site, an RNA processing signal, a transcription termination site, and/or a polyadenylation signal.
“Stable transformation” refers to the transfer of a nucleic acid fragment into a genome of a host organism, including both nuclear and organellar genomes, resulting in genetically stable inheritance. In contrast, “transient transformation” refers to the transfer of a nucleic acid fragment into the nucleus, or DNA-containing organelle, of a host organism resulting in gene expression without integration or stable inheritance. The term “transformation” as used herein refers to both stable transformation and transient transformation.
The terms “recombinant construct”, “expression construct” and “recombinant expression construct” are used interchangeably herein. These terms refer to a functional unit of genetic material that can be inserted into the genome of a cell using standard methodology well known to one skilled in the art. Such construct may be used by itself or may be used in conjunction with a vector. If a vector is used, the choice of vector is dependent upon the method that will be used to transform host plants as is well known to those skilled in the art.
In reference to transformation, particularly stable transformation, a “recalcitrant” cell or line is a cell or line wherein introduction of a polynucleotide of interest into the cell generally does not result in the recovery of stably transformed tissue that can be regenerated to produce a transformed plant. The term is inclusive of known recalcitrant genotypes, as well as older tissues, or tissue sources which generally do not respond and/or proliferate in standard culture conditions.
As used herein “transient transformation” refers to the transfer of a nucleic acid fragment or protein into the nucleus (or DNA-containing organelle) of a host organism resulting in gene expression without, necessarily, resulting in integration and stable inheritance.
As used herein, the term “positive selection” refers to any means by which a selectable phenotype or growth advantage is produced relative to control cells in the absence of chemical selection. The term is inclusive of positive selection.
Standard recombinant DNA and molecular cloning techniques used herein are well known in the art and are described more fully in Sambrook et al. Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory Press: Cold Spring Harbor, 1989 (hereinafter “Maniatis”). “Motifs” refers to short regions of conserved sequences of nucleic acids or amino acids that comprise part of a longer sequence. These conserved motifs may be associated with a specific function. These conserved motifs could be used to identify new homologues in plants. It is expected that some or all of the motifs may be found in a homologue. Also, it is expected that one or two of the conserved amino acids in any given motif may differ in a true homologue.
“PCR” or “polymerase chain reaction” is well known by those skilled in the art as a technique used for the amplification of specific DNA segments (U.S. Pat. Nos. 4,683,195 and 4,800,159).
As used herein, the term “plant” includes reference to whole plants, plant organs (e.g., leaves, stems, roots, etc.), plant tissue, seeds and plant cells, and progeny of the same. Plant cell, as used herein includes, without limitation, seeds, suspension cultures, embryos, meristematic regions, callus tissue, leaves, roots, shoots, gametophytes, sporophytes, pollen, and microspores.
As used herein, the term “organogenesis” refers to stem cell and/or meristematic activity that leads to the differentiation of organs.
As used herein, the term “asexually derived embryo” refers to any embryo generated in the absence of fertilization. The term is inclusive of apomictic and somatic embryos. As used herein, the term “somatic embryogenesis” refers to non-zygotic embryogenesis.
As used herein, the term “stem cells” refers to pleuripotent cells that give rise to both additional stem cells as well as cells that can differentiate into other cell types.
The present invention concerns isolated polynucleotides which encode polypeptides having WUS activity or that can modulate the level or activity of WUS in a cell, isolated polypeptides having WUS activity, and methods of using these sequences. Wuschel is involved in the initiation and maintenance of plant stem cells. Loss-of-function mutations in the WUS gene lead to shoot and floral meristems that fail to self-maintain. WUS mRNA expression is localized to a small group of cells in the central zone, below the L3 of the apical meristem, and affects stem cell fate in a non-cell autonomous manner (Mayer et al. (1998) Cell 95:805-815, herein incorporated by reference). Cells of the central zone divide relatively infrequently, while cells in the surrounding peripheral zone divide rapidly. Cell position in the meristem appears to regulate stem cell fate, via the interactions of many regulatory genes, including WUS, STM, CLV and the like (see, e.g., Byrne et al. (2003) Curr. Op. Gen. Dev. 13:551-557; Doerner (2000) Curr. Biol. 10:R826-R829; and Sharma, et al. (2003) PNAS 100:11823-11829, the contents of which are all herein incorporated by reference).
WUS encodes a homeodomain transcription factor polypeptide whose function is to bind a target DNA sequence and direct expression of the target gene. Binding of WUS to a DNA sequence was confirmed by Lohmann and co-workers (2001) Cell 105:793-803. The homeodomain region is approximately 61-64 amino acids with a substructure of alpha helix1-loop-alpha helix2-turn-alpha helix 3. Alpha helix3 makes the primary contact with the DNA sequence, although other substructures of the homeodomain polypeptide affect the level and specificity of interaction with the target DNA. The WUS homeodomain falls into a subcategory of homeodomain transcription factors depending on the presence and number of extra amino acids present in the loop and turn substructures relative to animal homeodomain transcription factors. One or two extra amino acids in the loop and four extra amino acids in the turn define the WUS family of transcription factors from other homeodomain transcription factors (“1+4” or “2+4'categories, Kamiya et al. (2003) Plant J 35:429-441). For example, WUS2 (p001 6.ctsas50r) is in the “2+4” category of homeodomain factors, like the Arabidopsis protein, whereas the other WUS sequences of the present invention belong to the “1+4” category (e.g., p0083.cldev71r, represented in SEQ ID NO: 33). Two secondary protein motifs have been identified (Stuurman et al. (2002) Genes Dev. 16:2213-2218) and include a highly conserved (E/R)TLPLFP and less conserved A(A/S)LEL(S/T)L amino acid sequences near the C-terminal end of the polypeptide. The role of these secondary motifs are not clear, but such leucine-rich motifs are generally involved in protein-protein interactions. The A(A/S)LEL(S/T)L shows significant similarity to C-terminal motifs identified in zn-finger proteins and ERFs, which have been implicated to act as a repressor domain via protein-protein interaction (Ohta, et al. (2001) Plant Cell 13:1959-1968; and Dinkins et al. (2003) Plant Science 165:33-41; herein incorporated by reference).
The present invention concerns an isolated polynucleotide comprising a nucleotide sequence selected from the group consisting of: (a) a first nucleotide sequence encoding a polypeptide of at least 50 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, and 12, (b) a second nucleotide sequence encoding a polypeptide of at least 100 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 14, 16, 18, and 20, (c) a third nucleotide sequence encoding a polypeptide of at least 180 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO: 24, (d) a fourth nucleotide sequence encoding a polypeptide of at least 230 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO: 22, (e) a fifth nucleotide sequence encoding a polypeptide of at least 100 amino acids having at least 80% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 6, 8, and 10, and (f) a sixth nucleotide sequence comprising the complement of (a), (b), (c), (d), or (e).
The first nucleotide sequence may comprise a nucleic acid sequence selected from the group consisting of SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23, that codes for the polypeptide selected from the group consisting of SEQ ID NOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
Nucleic acid fragments encoding at least a portion of several WUS proteins have been isolated and identified by comparison of random plant cDNA sequences to public databases containing nucleotide and protein sequences using the BLAST algorithms well known to those skilled in the art. The nucleic acid fragments of the instant invention may be used to isolate cDNAs and genes encoding homologous proteins from the same or other plant species. Isolation of homologous genes using sequence-dependent protocols is well known in the art. Examples of sequence-dependent protocols include, but are not limited to, methods of nucleic acid hybridization, and methods of DNA and RNA amplification as exemplified by various uses of nucleic acid amplification technologies (e.g., polymerase chain reaction, ligase chain reaction).
For example, genes encoding other WUS proteins, either as cDNAs or genomic DNAs, could be isolated directly by using all or a portion of the instant nucleic acid fragments as DNA hybridization probes to screen libraries from any desired plant employing methodology well known to those skilled in the art. Specific oligonucleotide probes based upon the instant nucleic acid sequences can be designed and synthesized by methods known in the art (Maniatis). Moreover, an entire sequence can be used directly to synthesize DNA probes by methods known to the skilled artisan such as random primer DNA labeling, nick translation, end-labeling techniques, or RNA probes using available in vitro transcription systems. In addition, specific primers can be designed and used to amplify a part or all of the instant sequences. The resulting amplification products can be labeled directly during amplification reactions or labeled after amplification reactions, and used as probes to isolate full length cDNA or genomic fragments under conditions of appropriate stringency.
In addition, two short segments of the instant nucleic acid fragments may be used in polymerase chain reaction protocols to amplify longer nucleic acid fragments encoding homologous genes from DNA or RNA. The polymerase chain reaction may also be performed on a library of cloned nucleic acid fragments wherein the sequence of one primer is derived from the instant nucleic acid fragments, and the sequence of the other primer takes advantage of the presence of the polyadenylic acid tracts to the 3′ end of the mRNA precursor encoding plant genes. Alternatively, the second primer sequence may be based upon sequences derived from the cloning vector. For example, the skilled artisan can follow the RACE protocol (Frohman et al. (1988) Proc. Natl. Acad. Sci. USA 85:8998-9002) to generate cDNAs by using PCR to amplify copies of the region between a single point in the transcript and the 3′ or 5′ end. Primers oriented in the 3′ and 5′ directions can be designed from the instant sequences. Using commercially available 3′ RACE or 5′ RACE systems (BRL), specific 3′ or 5′ cDNA fragments can be isolated (Ohara et al. (1989) Proc. Natl. Acad. Sci. USA 86:5673-5677; Loh et al. (1989) Science 243:217-220). Products generated by the 3′ and 5′ RACE procedures can be combined to generate full-length cDNAs (Frohman and Martin (1989) Techniques 1:165). Consequently, a polynucleotide comprising a nucleotide sequence of at least one of 60 (or at least 40, or at least 30) contiguous nucleotides derived from a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 and the complement of such nucleotide sequences may be used in such methods to obtain a nucleic acid fragment encoding a substantial portion of an amino acid sequence of a polypeptide.
The present invention relates to a method of obtaining a nucleic acid fragment encoding a substantial portion of a WUS polypeptide, optionally a substantial portion of a plant WUS polypeptide, comprising the steps of: synthesizing an oligonucleotide primer comprising a nucleotide sequence of at least one of 60 (or of at least 40, or at least one of 30) contiguous nucleotides derived from a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23, and the complement of such nucleotide sequences; and amplifying a nucleic acid fragment (e.g., cDNA inserted in a cloning vector) using the oligonucleotide primer. Optionally, the amplified nucleic acid fragment will encode a portion of a WUS polypeptide.
Availability of the instant nucleotide and deduced amino acid sequences facilitates immunological screening of cDNA expression libraries. Synthetic peptides representing portions of the instant amino acid sequences may be synthesized. These peptides can be used to immunize animals to produce polyclonal or monoclonal antibodies with specificity for peptides or proteins comprising the amino acid sequences. These antibodies can be then be used to screen cDNA expression libraries to isolate full-length cDNA clones of interest (Lerner (1984) Adv. Immunol. 36:1-34; Maniatis).
In another embodiment, this invention concerns viruses and host cells comprising either the chimeric genes of the invention as described herein or an isolated polynucleotide of the invention as described herein. Examples of host cells which can be used to practice the invention include, but are not limited to, yeast, bacteria, and plants.
As was noted above, the nucleic acid fragments of the instant invention may be used to create transgenic plants in which the disclosed polypeptides are present at higher or lower levels than normal or in cell types or developmental stages in which they are not normally found. This would have the effect of altering development (e.g., the initiation and maintenance of meristem apical initials) in those plants.
Overexpression of the proteins of the instant invention may be accomplished by first constructing a chimeric gene in which the coding region is operably linked to a promoter capable of directing expression of a gene in the desired tissues at the desired stage of development. The chimeric gene may comprise promoter sequences and translation leader sequences derived from the same genes. 3′ non-coding sequences encoding transcription termination signals may also be provided. The instant chimeric gene may also comprise one or more introns in order to facilitate gene expression.
It is well known in the art that silencing of gene expression may be accomplished using nucleic acid fragments representing less than the entire coding region of a gene, and by using nucleic acid fragments that do not share 100% sequence identity with the gene to be suppressed.
Reduction of the activity of specific genes (also known as gene silencing, or gene suppression) is desirable for several aspects of genetic engineering in plants. Many techniques for gene silencing are well known to one of skill in the art, including but not limited to antisense technology (see, e.g., Sheehy et al. (1988) PNAS USA 85:8805-8809; and U.S. Pat. Nos. 5,107,065; 5,453, 566; and 5,759,829); cosuppression (e.g., Taylor (1997) Plant Cell 9:1245; Jorgensen (1990) Trends Biotech. 8(12):340-344; Flavell (1994) PNAS USA 91:3490-3496; Finnegan et al. (1994) Bio/Technology 12: 883-888; and Neuhuber et al. (1994) Mol. Gen. Genet. 244:230-241); RNA interference (Napoli et al. (1990) Plant Cell 2:279-289; U.S. Pat. No. 5,034,323; Sharp (1999) Genes Dev. 13:139-141; Zamore et al. (2000) Cell 101:25-33; and Montgomery et al. (1998) PNAS USA 95:15502-15507), virus-induced gene silencing (Burton et al. (2000) Plant Cell 12:691-705; and Baulcombe (1999) Curr. Op. Plant Bio. 2:109-113); target-RNA-specific ribozymes (Haseloff et al. (1988) Nature 334: 585-591); hairpin structures (Smith et al. (2000) Nature 407:319-320; WO 99/53050; WO 02/00904; and WO 98/53083); ribozymes (Steinecke et al. ((1992) EMBO J. 11:1525; and Perriman et al. ((1993) Antisense Res. Dev. 3:253); oligonucleotide mediated targeted modification (e.g., WO 03/076574 and WO 99/25853); Zn-finger targeted molecules (e.g., WO 01/52620; WO 03/048345; and WO 00/42219); and other methods or combinations of the above methods known to those of skill in the art. The references cited above are herein incorporated by reference in their entirety.
Plasmid vectors comprising the instant isolated polynucleotide (or chimeric gene) may be constructed. The choice of plasmid vector is dependent upon the method that will be used to transform host plants. The skilled artisan is well aware of the genetic elements that must be present on the plasmid vector in order to successfully transform, select and propagate host cells containing the chimeric gene. The skilled artisan will also recognize that different independent transformation events will likely result in different levels and patterns of expression (Jones et al. (1985) EMBO J. 4:2411-2418; De Almeida et al. (1989) Mol. Gen. Genetics 218:78-86), and thus multiple events must be screened in order to obtain lines displaying the desired expression level and pattern. Such screening may be accomplished by Southern analysis of DNA, Northern analysis of mRNA expression, Western analysis of protein expression, or phenotypic analysis.
For some applications it may be useful to direct the instant polypeptides to different cellular compartments, or to facilitate its secretion from the cell. It is thus envisioned that the chimeric gene described above may be further supplemented by directing the coding sequence to encode the instant polypeptides with appropriate intracellular targeting sequences such as transit sequences (Keegstra (1989) Cell 56:247-253), signal sequences or sequences encoding endoplasmic reticulum localization (Chrispeels (1991) Ann. Rev. Plant Phys. Plant Mol. Biol. 42:21-53), or nuclear localization signals (Raikhel (1992) Plant Phys.100:1627-1632) with or without removing targeting sequences that are already present. While the references cited give examples of each of these, the list is not exhaustive and more targeting signals of use may be discovered in the future.
It may also be desirable to reduce or eliminate expression of genes encoding the instant polypeptides in plants for some applications. In order to accomplish this, a chimeric gene designed for co-suppression of the instant polypeptide can be constructed by linking a gene or gene fragment encoding that polypeptide to plant promoter sequences. Alternatively, a chimeric gene designed to express antisense RNA for all or part of the instant nucleic acid fragment can be constructed by linking the gene or gene fragment in reverse orientation to plant promoter sequences. Either the co-suppression or antisense chimeric genes could be introduced into plants via transformation wherein expression of the corresponding endogenous genes are reduced or eliminated.
Molecular genetic solutions to the generation of plants with altered gene expression have a decided advantage over more traditional plant breeding approaches. Changes in plant phenotypes can be produced by specifically inhibiting expression of one or more genes by antisense inhibition or cosuppression (U.S. Pat. Nos. 5,190,931, 5,107,065 and 5,283,323). An antisense or cosuppression construct would act as a dominant negative regulator of gene activity. While conventional mutations can yield negative regulation of gene activity these effects are most likely recessive. The dominant negative regulation available with a transgenic approach may be advantageous from a breeding perspective. In addition, the ability to restrict the expression of a specific phenotype to the reproductive tissues of the plant by the use of tissue specific promoters may confer agronomic advantages relative to conventional mutations which may have an effect in all tissues in which a mutant gene is ordinarily expressed.
The person skilled in the art will know that special considerations are associated with the use of antisense or cosuppression technologies in order to reduce expression of particular genes. For example, the proper level of expression of sense or antisense genes may require the use of different chimeric genes utilizing different regulatory elements known to the skilled artisan. Once transgenic plants are obtained by one of the methods described above, it will be necessary to screen individual transgenics for those that most effectively display the desired phenotype. Accordingly, the skilled artisan will develop methods for screening large numbers of transformants. The nature of these screens will generally be chosen on practical grounds. For example, one can screen by looking for changes in gene expression by using antibodies specific for the protein encoded by the gene being suppressed, or one could establish assays that specifically measure enzyme activity. A preferred method will be one which allows large numbers of samples to be processed rapidly, since it will be expected that a large number of transformants will be negative for the desired phenotype.
In certain embodiments the WUS nucleic acid sequences of the present invention can be stacked with any combination of polynucleotide sequences of interest in order to create plants with a desired phenotype. For example, the polynucleotides of the present invention may be stacked with any other polynucleotides of the present invention, such as any combination of WUS1 (SEQ ID NOS: 11,13, and 32), WUS2 (SEQ ID NOS: 5, 7, 26, 28, 30, 34, 35, 37, 39, 41, 42, 44, 46, 48, 49, 51, 53, 55, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, and, 74), WUS3 (SEQ ID NO: 3), WUS5 (SEQ ID NOS: 76, and 77), WUS6 (SEQ ID NOS: 79, and 80), and other WUS sequences (SEQ ID NOS: 1, 9, 15, 17, 19, 21, 23, 88, 89, and 90). The WUS polynucleotides of the present invention can also be combined with other genes implicated in transcriptional regulation, homeotic gene regulation, stem cell maintenance and proliferation, cell division, and/or cell differentiation such as other WUS homologues (see, e.g, Mayer et al. (1998) Cell 95:805-815); clavata (e.g., CLV1, CVL2, CLV3) (see, e.g., WO 03/093450; Clark et al. (1997) Cell 89:575-585; Jeong et al. (1999) Plant Cell 11:1925-1934; Fletcher et al. (1999) Science 283:1911-1914); Clavata and Embryo Surround region genes (e.g., CLE) (see, e.g., Sharma et al. (2003) Plant Mol. Biol. 51:415-425; Hobe et al. (2003) Dev Genes Evol 213:371-381; Cock & McCormick (2001) Plant Physiol 126:939-942; and Casamitjana-Martinez et al. (2003) Curr Biol 13:1435-1441); baby boom (e.g., BNM3, BBM) (see, e.g., WO 00/75530; Boutileir et al. (2002) Plant Cell 14:1737-1749); Zwille (Lynn et al. (1999) Dev 126:469-481); leafy cotyledon (e.g., Lec1, Lec2) (see, e.g., Lotan et al. (1998) Cell 93:1195-1205; WO 00/28058; Stone et al. (2001) PNAS 98:11806-11811; and U.S. Pat. No. 6,492,577); Shoot Meristem-less (STM) (Long et al. (1996) Nature 379:66-69); ultrapetala (ULT) (see, e.g., Fletcher (2001) Dev 128:1323-1333); mitogen activated protein kinase (MAPK) (see, e.g., Jonak et al. (2002) Curr Opin Plant Biol 5:415); kinase associated protein phosphatase (KAPP) (see, e.g., Williams et al. (1997) PNAS 94:10467-10472; and Trotochaud et al. (1999) Plant Cell 11:393-406); ROP GTPase (see, e.g., Wu et al. (2001) Plant Cell 13:2841-2856; and Trotochaud et al. (1999) Plant Cell 11:393-406); fasciata (e.g., FAS1, FAS2) (see, e.g., Kaya et al. (2001) Cell 104:131-142); cell cycle genes (see, e.g., U.S. Pat. No. 6,518,487; WO 99/61619; and WO 02/074909), Shepherd (SHD) (see, e.g., Ishiguro et al. (2002) EMBO J. 21:898-908); Poltergeist (see, e.g., Yu et al. (2000) Dev 127:1661-1670; Yu et al. (2003) Curr Biol 13:179-188); Pickle (PKL) (see, e.g., Ogas et al. (1999) PNAS 96:13839-13844); knox genes (e.g., KN1, KNAT1) (see, e.g., Jackson et al. (1994) Dev 120:405-413; Lincoln et al. (1994) Plant Cell 6:1859-1876; Venglat et al. (2002) PNAS 99:4730-4735); fertilization independent endosperm (FIE) (e.g., Ohad et al. (1999) Plant Cell 11:407-415), and the like, the disclosures of which are herein incorporated by reference. The combinations generated can also include multiple copies of any one of the polynucleotides of interest. The combinations may have any combination of up-regulating and down-regulating expression of the combined polynucleotides. The combinations may or may not be combined on one construct for transformation of the host cell, and therefore may be provided sequentially or simultaneously. The host cell may be a wild-type or mutant cell, in a normal or aneuploid state.
The polynucleotides of the present invention can also be stacked with any other gene or combination of genes to produce plants with a variety of desired trait combinations including but not limited to traits desirable for animal feed such as high oil genes (e.g., U.S. Pat. No. 6,232,529); balanced amino acids (e.g. hordothionins (U.S. Pat. Nos. 5,990,389; 5,885,801; 5,885,802; and 5,703,409); barley high lysine (Williamson et al. (1987) Eur. J. Biochem. 165:99-106; and WO 98/20122); and high methionine proteins (Pedersen et al. (1986) J. Biol. Chem. 261:6279; Kirihara et al. (1988) Gene 71:359; and Musumura et al. (1989) Plant Mol. Biol. 12: 123)); increased digestibility (e.g., modified storage proteins (U.S. application Ser. No. 10/053,410, filed Nov. 7, 2001); and thioredoxins (U.S. application Ser. No. 10/005,429, filed Dec. 3, 2001)), the disclosures of which are herein incorporated by reference. The polynucleotides of the present invention can also be stacked with traits desirable for insect, disease or herbicide resistance (e.g., Bacillus thuringiensis toxic proteins (U.S. Pat. Nos. 5,366,892; 5,747,450; 5,737,514; 5723,756; 5,593,881; Geiser et al. (1986) Gene 48:109); fumonisin detoxification genes (U.S. Pat. No. 5,792,931); avirulence and disease resistance genes (Jones et al. (1994) Science 266:789; Martin et al. (1993) Science 262:1432; Mindrinos et al. (1994) Cell 78:1089); acetolactate synthase (ALS) mutants that lead to herbicide resistance such as the S4 and/or Hra mutations; inhibitors of glutamine synthase such as phosphinothricin or basta (e.g., bar gene); and glyphosate resistance (EPSPS gene)); and traits desirable for processing or process products such as high oil (e.g., U.S. Pat. No. 6,232,529 ); modified oils (e.g., fatty acid desaturase genes (U.S. Pat. No. 5,952,544; WO 94/11516)); modified starches (e.g., ADPG pyrophosphorylases (AGPase), starch synthases (SS), starch branching enzymes (SBE) and starch debranching enzymes (SDBE)); and polymers or bioplastics (e.g., U.S. Pat. No. 5.602,321; beta-ketothiolase, polyhydroxybutyrate synthase, and acetoacetyl-CoA reductase (Schubert et al. (1988) J. Bacteriol. 170:5837-5847) facilitate expression of polyhydroxyalkanoates (PHAs)), the disclosures of which are herein incorporated by reference. One could also combine the polynucleotides of the present invention with polynucleotides providing agronomic traits such as male sterility (e.g., see U.S. Pat. No. 5.583,210), stalk strength, flowering time, or transformation technology traits such as cell cycle regulation or gene targeting (e.g. WO 99/61619; WO 00/17364; WO 99/25821), the disclosures of which are herein incorporated by reference.
These stacked combinations can be created by any method including but not limited to cross breeding plants by any conventional or TopCross methodology, or genetic transformation. If the traits are stacked by genetically transforming the plants, the polynucleotide sequences of interest can be combined at any time and in any order. For example, a transgenic plant comprising one or more desired traits can be used as the target to introduce further traits by subsequent transformation. The traits can be introduced simultaneously in a co-transformation protocol with the polynucleotides of interest provided by any combination of transformation cassettes. For example, if two sequences will be introduced, the two sequences can be contained in separate transformation cassettes (trans) or contained on the same transformation cassette (cis). Expression of the sequences can be driven by the same promoter or by different promoters. In certain cases, it may be desirable to introduce a transformation cassette that will suppress the expression of the polynucleotide of interest. This may be combined with any combination of other suppression cassettes or overexpression cassettes to generate the desired combination of traits in the plant.
In another embodiment, the present invention concerns an isolated polypeptide selected from the group consisting of: (a) a polypeptide of at least 50 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 2, 4, and 12, (b) a polypeptide of at least 100 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs: 14, 16, 18, and 20, (c) a polypeptide of at least 180 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO: 24, (d) a polypeptide of at least 230 amino acids having at least 70% identity based on the Clustal method of alignment when compared to a polypeptide of SEQ ID NO: 22, and (e) a polypeptide of at least 100 amino acids having at least 80% identity based on the Clustal method of alignment when compared to a polypeptide selected from the group consisting of SEQ ID NOs:6, 8, and 10.
The instant polypeptides (or portions thereof) may be produced in heterologous host cells, particularly in the cells of microbial hosts, and can be used to prepare antibodies to these proteins by methods well known to those skilled in the art. The antibodies are useful for detecting the polypeptides of the instant invention in situ in cells or in vitro in cell extracts. Preferred heterologous host cells for production of the instant polypeptides are microbial hosts. Microbial expression systems and expression vectors containing regulatory sequences that direct high level expression of foreign proteins are well known to those skilled in the art. Any of these could be used to construct a chimeric gene for production of the instant polypeptides. This chimeric gene could then be introduced into appropriate microorganisms via transformation to provide high level expression of the encoded WUS protein. An example of a vector for high level expression of the instant polypeptides in a bacterial host is provided (Example 12).
All or a substantial portion of the polynucleotides of the instant invention may also be used as probes for genetically and physically mapping the genes that they are a part of, and used as markers for traits linked to those genes. Such information may be useful in plant breeding in order to develop lines with desired phenotypes. For example, the instant nucleic acid fragments may be used as restriction fragment length polymorphism (RFLP) markers. Southern blots (Maniatis) of restriction-digested plant genomic DNA may be probed with the nucleic acid fragments of the instant invention. The resulting banding patterns may then be subjected to genetic analyses using computer programs such as MapMaker (Lander et al. (1987) Genomics 1:174-181) in order to construct a genetic map. In addition, the nucleic acid fragments of the instant invention may be used to probe Southern blots containing restriction endonuclease-treated genomic DNAs of a set of individuals representing parent and progeny of a defined genetic cross. Segregation of the DNA polymorphisms is noted and used to calculate the position of the instant nucleic acid sequence in the genetic map previously obtained using this population (Botstein et al. (1980) Am. J. Hum. Genet. 32:314-331).
The production and use of plant gene-derived probes for use in genetic mapping is described in Bernatzky and Tanksley (1986) Plant Mol. Biol. Reporter 4:37-41. Numerous publications describe genetic mapping of specific cDNA clones using the methodology outlined above or variations thereof. For example, F2 intercross populations, backcross populations, randomly mated populations, near isogenic lines, and other sets of individuals may be used for mapping. Such methodologies are well known to those skilled in the art.
Nucleic acid probes derived from the instant nucleic acid sequences may also be used for physical mapping (i.e., placement of sequences on physical maps; see Hoheisel et al. In: Nonmammalian Genomic Analysis: A Practical Guide, Academic press 1996, pp. 319-346, and references cited therein).
In another embodiment, nucleic acid probes derived from the instant nucleic acid sequences may be used in direct fluorescence in situ hybridization (FISH) mapping (Trask (1991) Trends Genet. 7:149-154). Although current methods of FISH mapping favor use of large clones (several to several hundred KB; see Laan et al. (1995) Genome Res. 5:13-20), improvements in sensitivity may allow performance of FISH mapping using shorter probes.
A variety of nucleic acid amplification-based methods of genetic and physical mapping may be carried out using the instant nucleic acid sequences. Examples include allele-specific amplification (Kazazian (1989) J Lab Clin Med 11:95-96), polymorphism of PCR-amplified fragments (CAPS; Sheffield et al. (1993) Genomics 16:325-332), allele-specific ligation (Landegren et al. (1988) Science 241:1077- 1080), nucleotide extension reactions (Sokolov (1990) Nucleic Acids Res 18:3671), Radiation Hybrid Mapping (Walter et al. (1994) Nat Genet 7:22-28) and Happy Mapping (Dear and Cook (1989) Nucleic Acids Res 17:6795-6807). For these methods, the sequence of a nucleic acid fragment is used to design and produce primer pairs for use in the amplification reaction or in primer extension reactions. The design of such primers is well known to those skilled in the art. In methods employing PCR-based genetic mapping, it may be necessary to identify DNA sequence differences between the parents of the mapping cross in the region corresponding to the instant nucleic acid sequence. This, however, is generally not necessary for mapping methods.
Loss of function mutant phenotypes may be identified for the instant cDNA clones either by targeted gene disruption protocols or by identifying specific mutants for these genes contained in a maize population carrying mutations in all possible genes (Ballinger and Benzer (1989) Proc. Natl. Acad. Sci USA 86:9402-9406; Koes et al. (1995) Proc. Natl. Acad. Sci USA 92:8149-8153; Bensen et al. (1995) Plant Cell 7:75-84). The latter approach may be accomplished in two ways. First, short segments of the instant nucleic acid fragments may be used in polymerase chain reaction protocols in conjunction with a mutation tag sequence primer on DNAs prepared from a population of plants in which Mutator transposons or some other mutation-causing DNA element has been introduced (see Bensen, supra). The amplification of a specific DNA fragment with these primers indicates the insertion of the mutation tag element in or near the plant gene encoding the instant polypeptide. Alternatively, the instant nucleic acid fragment may be used as a hybridization probe against PCR amplification products generated from the mutation population using the mutation tag sequence primer in conjunction with an arbitrary genomic site primer, such as that for a restriction enzyme site-anchored synthetic adaptor. With either method, a plant containing a mutation in the endogenous gene encoding the instant polypeptide can be identified and obtained. This mutant plant can then be used to determine or confirm the natural function of the instant polypeptides disclosed herein.
Using a chemical-inducible activation-tagging, Zuo et al. showed that induced overexpression of WUS in Arabidopsis caused somatic embryo formation in all tissues and organs tested, without any external plant hormones (Zuo et al. (2002) Plant J. 30:349-359; U.S. Patent Application Publication No. US 2003/0082813 A1). Somatic embryogenesis is a unique pathway for asexual propagation or somatic cloning in plants. The developmental process of somatic embryogenesis is believed to share considerable similarity with that of zygotic embryogenesis (Mordhorst et al. (1997) Crit. Rev. Plant Sci. 16:535-576; Zimmerman (1993) Plant Cell 5:1411-1423).
In another embodiment of the invention, embryogenesis is induced in haploid cells, such as pollen cells, egg cells, or cells from a haploid line such as RWS, to produce haploid plants. This can be achieved by stably transforming a plant cell or tissue with a WUS gene under the control of a tissue specific promoter that is active in a haploid cell or tissue, and expressing the WUS gene therein, or by introducing the WUS gene into a plant tissue or cell under the control of an inducible promoter and applying the inducer to cause expression of the WUS gene therein. In one embodiment, the WUS gene is under the control of a promoter that is both haploid- tissue specific and inducible. In another embodiment, a promoter is used that is both inducible and tissue-specific, giving greater control over the process. In another embodiment, WUS is operably linked to an inducible egg-specific promoter and used to induce embryogenesis. In another embodiment, a WUS gene linked to an inducible pollen-specific promoter is used to induce somatic embryogenesis in pollen cells. Expression of WUS in the haploid tissue or cell (for example, by application of the inducer specific for the inducible promoter) results in the formation of haploid somatic embryos, which can be grown into haploid plants using standard techniques.
When an inducible promoter is used (whether tissue specific or not), one embodiment comprises exposing excised transgenic tissue containing the haploid cells (e.g., pollen or female gametophytic cell, such as an egg) to the inducer for a time sufficient to induce somatic embryo formation, withdrawing the inducer, and then growing the somatic embryo into a transgenic haploid plant in the absence of the inducer.
Diploidization of the haploid plants to form dihaploids, either spontaneously or by treatment with the appropriate chemical (e.g. colchicine) can significantly expedite the process of obtaining homozygous plants as compared to a method of conventional genetic segregation. Further, besides facilitating breeding, this finds use in studies of mutagenesis and other genetic studies, because dihaploids are homozygous, containing the duplicated copies of each gene, expected to be identical.
Additionally, WUS genes may be used to induce apomixis in plants. Apomixis and methods of conferring apomixis into plants are discussed in several patents (see, e.g., U.S. Pat. Nos. 5,710,367; 5,811,636; 6,028,185; 6,229,064; and 6,239,327 as well as WO 00/24914 which are incorporated herein by reference). Reproduction in plants is ordinarily classified as sexual or asexual. The term apomixis is generally accepted as the replacement of sexual reproduction by various forms of asexual reproduction (Rieger et al., IN Glossary of Genetics and Cytogenetics, Springer-Verlag, New York, N.Y., 1976). In general, the initiation of cell proliferation in the embryo and endosperm are uncoupled from fertilization. Apomixis is a genetically controlled method of reproduction in plants where the embryo is formed without union of an egg and a sperm. There are three basic types of apomictic reproduction:
1) apospory—embryo develops from a chromosomally unreduced egg in an embryo sac derived from a somatic cell in the nucellus,
2) diplospory—embryo develops from an unreduced egg in an embryo sac derived from the megaspore mother cell, and
3) adventitious embryony—embryo develops directly from a somatic cell. In most forms of apomixis, pseudogamy or fertilization of the polar nuclei to produce endosperm is necessary for seed viability.
These types of apomixis have economic potential because they can cause any genotype, regardless of how heterozygous, to breed true. It is a reproductive process that bypasses female meiosis and syngamy to produce embryos genetically identical to the maternal parent. With apomictic reproduction, progeny of specially adaptive or hybrid genotypes would maintain their genetic fidelity throughout repeated life cycles. In addition to fixing hybrid vigor, apomixis can make possible commercial hybrid production in crops where efficient male sterility or fertility restoration systems for producing hybrids are not available. Apomixis can make hybrid development more efficient. It also simplifies hybrid production and increases genetic diversity in plant species with good male sterility.
It would be ideal to find genes controlling obligate or a high level of apomixis in the cultivated species and be able to readily hybridize cross-compatible sexual x apomictic genotypes to produce true-breeding F1 hybrids. To date, most desirable genes controlling apomixis are found in the wild species which are distantly related to the cultivated species. Although interspecific crosses may be possible between the cultivated and wild species, chromosome pairing between genomes is usually low or nonexistent.
Although apomixis is effectively used in Citrus to produce uniform and disease- and virus-free rootstock (Parlevliet et al. (1959) Citrus Proc. Am. Soc. Hort. Sci. 74:252-260) and in buffelgrass (Bashaw (1980) Crop Sci. 20:112) and Poa (Pepin et al. (1971) Crop Sci. 11:445-448) to produce improved cultivars, it has not been successfully transferred to a cultivated crop plant. The transfer of apomixis to important crops would make possible development of true-breeding hybrids and commercial production of hybrids without a need for cytoplasmic-nuclear male sterility and high cost, labor-intensive production processes. An obligately apomictic F1 hybrid would breed true through the seed indefinitely and could be considered a vegetative or clonal method of reproduction through the seed. The development of apomictically reproducing cultivated crops would also provide a major contribution toward the food security in developing nations.
Examples of promoters under developmental control include promoters that preferentially initiate transcription in certain tissues, such as leaves, roots, seeds, fibers, xylem vessels, tracheids, or sclerenchyma. Such promoters are referred to as tissue-preferred. Promoters that initiate transcription only or primarily in certain tissues are referred to as tissue-specific or tissue-preferred. A cell type specific promoter primarily drives expression in certain cell types in one or more organs, for example, vascular cells in roots or leaves. An inducible promoter is a promoter that is under environmental control. Examples of environmental conditions that may effect transcription by inducible promoters include anaerobic conditions or the presence of light. Tissue-specific, tissue-preferred, cell type specific, and inducible promoters constitute the class of non-constitutive promoters. A constitutive promoter is a promoter that is active under most environmental conditions.
Constitutive promoters include, for example, the core promoter of the Rsyn7 promoter and other constitutive promoters disclosed in WO 99/43838 and U.S. Pat. No. 6,072,050; the core CaMV 35S promoter (Odell et al. (1985) Nature 313:810-812); rice actin (McElroy et al. (1990) Plant Cell 2:163-171); ubiquitin (Christensen et al. (1989) Plant Mol. Biol. 12:619-632; and Christensen et al. (1992) Plant Mol. Biol. 18:675-689); pEMU (Last et al. (1991) Theor. Appl. Genet. 81:581-588); MAS (Velten et al. (1984) EMBO J. 3:2723-2730); ALS promoter (U.S. Pat. No. 5,659,026), and the like. Other constitutive promoters include, for example, U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; 5,608,142; and 6,177,611.
In some embodiments it will be beneficial to express the gene from an inducible promoter. Such promoters include those from pathogenesis-related proteins (PR proteins), which are induced following infection by a pathogen; e.g., PR proteins, SAR proteins, beta-1,3-glucanase, chitinase, etc. See, for example, Redolfi et al. (1983) Neth. J. Plant Pathol. 89:245-254; Uknes et al. (1992) Plant Cell 4:645-656; and Van Loon (1985) Plant Mol. Virol. 4:111-116. See also WO 99/43819, herein incorporated by reference. Promoters that are expressed locally at or near the site of pathogen infection are also available. See, for example, Marineau et al. (1987) Plant Mol. Biol. 9:335-342; Matton et al. (1989) Molecular Plant-Microbe Interactions 2:325-331; Somsisch et al. (1986) PNAS USA 83:2427-2430; Somsisch et al. (1988) Mol. Gen. Genet. 2:93-98; and Yang (1996) PNAS USA 93:14972-14977. See also, Chen et al. (1996) Plant J. 10:955-966; Zhang et al. (1994) PNAS USA 91:2507-2511; Warner et al. (1993) Plant J. 3:191-201; Siebertz et al. (1989) Plant Cell 1:961-968; U.S. Pat. No. 5,750,386 (nematode-inducible); and the references cited therein. The inducible promoter for the maize PRms gene is induced by the pathogen Fusarium moniliforme (see, for example, Cordero et al. (1992) Physiol. Mol. Plant Path. 41:189-200).
Additionally, as pathogens find entry into plants through wounds or insect damage, a wound-inducible promoter may be used in the constructions of the invention. Such wound-inducible promoters include potato proteinase inhibitor (pin 11) gene (Ryan (1990) Ann. Rev. Phytopath. 28:425-449; Duan et al. (1996) Nature Biotech. 14:494-498); wun1 and wun2, U.S. Pat. No. 5,428,148; win1 and win2 (Stanford et al. (1989) Mol. Gen. Genet. 215:200-208); systemin (McGurl et al. (1992) Science 225:1570-1573); WIP1 (Rohmeier et al. (1993) Plant Mol. Biol. 22:783-792; Eckelkamp et al. (1993) FEBS Letts 323:73-76); MPI gene (Corderok et al. (1994) Plant J. 6:141-150); and the like, herein incorporated by reference.
Chemical-regulated promoters can be used to modulate the expression of a gene in a plant through the application of an exogenous chemical regulator. Depending upon the objective, the promoter may be a chemical-inducible promoter, where application of the chemical induces gene expression, or a chemical-repressible promoter, where application of the chemical represses gene expression. Chemical-inducible promoters are known in the art and include, but are not limited to, the maize In2-2 promoter, which is activated by benzenesulfonamide herbicide safeners, the maize GST promoter, which is activated by hydrophobic electrophilic compounds that are used as pre-emergent herbicides, and the tobacco PR-1a promoter, which is activated by salicylic acid. Other chemical-regulated promoters of interest include steroid-responsive promoters (see, for example, the glucocorticoid-inducible promoter in Schena et al. (1991) PNAS USA 88:10421-10425 and McNellis et al. (1998) Plant J. 14:247-257) and tetracycline-inducible and tetracycline-repressible promoters (see, for example, Gatz et al. (1991) Mol. Gen. Genet. 227:229-237, and U.S. Patent Nos. 5,814,618 and 5,789,156), herein incorporated by reference.
Tissue-preferred promoters can be utilized to target enhanced expression of a sequence of interest within a particular plant tissue. Tissue-preferred promoters include those identified by Kawamata et al. (1997) Plant Cell Physiol. 38:792-803; Hansen et al. (1997) Mol. Gen Genet. 254:337-343; Russell et al. (1997) Transgenic Res. 6:157-168; Rinehart et al. (1996) Plant Physiol. 112:1331-1341; Van Camp et al. (1996) Plant Physiol. 112:525-535; Canevascini et al. (1996) Plant Physiol. 112:513-524; Yamamoto et al. (1994) Plant Cell Physiol. 35:773-778; Lam (1994) Results Probl. Cell Differ. 20:181-196; Orozco et al. (1993) Plant Mol Biol. 23:1129-1138; Matsuoka et al. (1993) PNAS USA 90:9586-9590; and Guevara-Garcia et al. (1993) Plant J. 4:495-505. Such promoters can be modified, if necessary, for weak expression.
Leaf-preferred promoters are known in the art. See, for example, Yamamoto et al. (1997) Plant J. 12:255-265; Kwon et al. (1994) Plant Physiol. 105:357-67; Yamamoto et al. (1994) Plant Cell Physiol. 35:773-778; Gotor et al. (1993) Plant J. 3:509-18; Orozco et al. (1993) Plant Mol. Biol. 23:1129-1138; and Matsuoka et al. (1993) PNAS USA 90:9586-9590. In addition, promoter of cab and ribisco can also be used. See, for example, Simpson et al. (1958) EMBO J 4:2723-2729 and Timko et al. (1988) Nature 318:57-58.
Root-preferred promoters are known and can be selected from the many available from the literature or isolated de novo from various compatible species. See, for example, Hire et al. (1992) Plant Mol. Biol. 20(2):207-218 (soybean root-specific glutamine synthetase gene); Keller and Baumgartner (1991) Plant Cell 3(10):1051-1061 (root-specific control element in the GRP 1.8 gene of French bean); Sanger et al. (1990) Plant Mol. Biol. 14(3):433-443 (root-specific promoter of the mannopine synthase (MAS) gene of Agrobacterium tumefaciens); and Miao et al. (1991) Plant Cell 3(1):11-22 (full-length cDNA clone encoding cytosolic glutamine synthetase (GS), which is expressed in roots and root nodules of soybean). Additional root-preferred promoters include the VfENOD-GRP3 gene promoter (Kuster et al. (1995) Plant Mol. Biol. 29(4):759-772); and rolB promoter (Capana et al. (1994) Plant Mol. Biol. 25(4):681-691. See also U.S. Pat. Nos. 5,837,876; 5,750,386; 5,633,363; 5,459,252; 5,401,836; 5,110,732; and 5,023,179.
Seed-preferred promoters include both promoters active during seed development such as promoters of seed storage proteins, as well as those promoters active during seed germination. See Thompson et al. (1989) BioEssays 10:108, herein incorporated by reference. Such seed-preferred promoters include, but are not limited to, Cim1 (cytokinin-induced message); cZ19B1 (maize 19 kDa zein); milps (myo-inositol-1-phosphate synthase) (WO 00/11177; and U.S. Pat. No. 6,225,529; herein incorporated by reference). Gamma-zein (27kDa zein) is an exemplary endosperm-preferred promoter. Globulin-1 and oleosin are exemplary embryo-preferred promoters. The barley nucellus-preferred promoter, nuc1, is also of interest. For dicots, seed-specific promoters include, but are not limited to, bean β-phaseolin, napin, β-conglycinin, soybean lectin, cruciferin, and the like. For monocots, seed-preferred promoters include, but are not limited to, maize 15 kDa zein, 22 kDa zein, 27 kDa gamma-zein, waxy, shrunken 1, shrunken 2, globulin 1, etc. See also WO 00/12733, where seed-preferred promoters from end1 and end2 genes are disclosed; herein incorporated by reference. Stalk-preferred promoter(s) include, for example, S2A (Abrahams et al. 1995 Plant Mol Biol 27:513-528).
Where low-level expression is desired, a weak promoter will be used, i.e., a promoter that drives expression of a coding sequence at a low level. Alternatively, it is recognized that weak promoters also encompasses promoters that are expressed in only a few cells and not in others to give a total low level of expression. Such weak constitutive promoters include, for example, the core promoter of the Rsyn7 promoter (WO 99/43838; and U.S. Pat. No. 6,072,050), the core 35S CaMV promoter, and the like. Other constitutive promoters include, for example, U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; and 5,608,142. See also, U.S. Patent No. 6,177,611, herein incorporated by reference.
The isolated polynucleotides or polypeptides may be introduced into the plant by one or more techniques typically used for direct delivery into cells. Such protocols may vary depending on the type of organism, cell, plant or plant cell, i.e. monocot or dicot, targeted for gene modification. Suitable methods of transforming plant cells include microinjection (Crossway et al. (1986) Biotechniques 4:320-334; and U.S. Pat. 6,300,543), electroporation (Riggs et al. (1986) Proc. Natl. Acad. Sci. USA 83:5602-5606, direct gene transfer (Paszkowski et al. (1984) EMBO J. 3:2717-2722), and ballistic particle acceleration (see, for example, Sanford et al., U.S. Pat. No. 4,945,050; WO 91/10725; and McCabe et al. (1988) Biotechnology 6:923-926). Also see, Tomes et al., Direct DNA Transfer into Intact Plant Cells Via Microprojectile Bombardment. pp.197-213 in Plant Cell, Tissue and Organ Culture, Fundamental Methods. eds. O. L. Gamborg & G. C. Phillips. Springer-Verlag Berlin Heidelberg New York, 1995; U.S. Pat. 5,736,369 (meristem); Weissinger et al. (1988) Ann. Rev. Genet. 22:421-477; Sanford et al. (1987) Particulate Science and Technology 5:27-37 (onion); Christou et al. (1988) Plant Physiol. 87:671-674 (soybean); Datta et al. (1990) Biotechnology 8:736-740 (rice); Klein et al. (1988) Proc. Natl. Acad. Sci. USA 85:4305-4309 (maize); Klein et al. (1988) Biotechnology 6:559-563 (maize); WO 91/10725 (maize); Klein et al. (1988) Plant Physiol. 91:440-444 (maize); Fromm et al. (1990) Biotechnology 8:833-839; and Gordon-Kamm et al. (1990) Plant Cell 2:603-618 (maize); Hooydaas-Van Slogteren & Hooykaas (1984) Nature (London) 311:763-764; Bytebier et al. (1987) Proc. Natl. Acad. Sci. USA 84:5345-5349 (Liliaceae); De Wet et al. (1985) In The Experimental Manipulation of Ovule Tissues, ed. G. P. Chapman et al., pp. 197-209. Longman, N.Y. (pollen); Kaeppler et al. (1990) Plant Cell Reports 9:415-418; and Kaeppler et al. (1992) Theor. Appl. Genet. 84:560-566 (whisker-mediated transformation); U.S. Pat. No. 5,693,512 (sonication); D'Halluin et al. (1992) Plant Cell 4:1495-1505 (electroporation); Li et al. (1993) Plant Cell Reports 12:250-255; and Christou & Ford (1995) Annals of Botany 75:407-413 (rice); Osjoda et al. (1996) Nature Biotech. 14:745-750; Agrobacterium mediated maize transformation (U.S. Pat. 5,981,840); silicon carbide whisker methods (Frame et al. (1994) Plant J. 6:941-948); laser methods (Guo et al. (1995) Physiologia Plantarum 93:19-24); sonication methods (Bao et al. (1997) Ultrasound in Medicine & Biology 23:953-959; Finer & Finer (2000) Lett Appl Microbiol. 30:406-10; Amoah et al. (2001) J Exp Bot 52:1135-42); polyethylene glycol methods (Krens et al. (1982) Nature 296:72-77); protoplasts of monocot and dicot cells can be transformed using electroporation (Fromm et al. (1985) Proc. Natl. Acad. Sci. USA 82:5824-5828) and microinjection (Crossway et al. (1986) Mol. Gen. Genet. 202:179-185); all of which are herein incorporated by reference.
The target for transformation could be in the form of plant cells, tissues, or organs such as embryo, callus, meristem, leaf, inflorescence, root, shoot or seed. In other methods plant gametes, microspores, pollen, mother cells, zygote, or nucellar cells can be used, or subcellular organelles such as chloroplasts and mitochondria.
Plants cells transformed with a plant expression vector can be regenerated, e.g., from single cells, callus tissue or leaf discs according to standard plant tissue culture techniques. Various cells, tissues, and organs from almost any plant can be successfully cultured to regenerate an entire plant. Plant regeneration from cultured protoplasts is described in Evans et al., Protoplasts Isolation and Culture, Handbook of Plant Cell Culture, Macmillan Publishing Company, New York, pp.124-176 (1983); and Binding, Regeneration of Plants, Plant Protoplasts, CRC Press, Boca Raton, pp. 21-73 (1985), all of which are herein incorporated by reference.
The regeneration of plants containing the foreign gene introduced by Agrobacterium can be achieved as described by Horsch et al. (1985) Science 227:1229-1231, and Fraley et al. (1983) Proc. Natl. Acad. Sci. USA. 80:4803. This procedure typically produces shoots within two to four weeks and these transformant shoots are then transferred to an appropriate root-inducing medium containing the selective agent and an antibiotic to prevent bacterial growth. Transgenic plants of the present invention may be fertile or sterile.
Regeneration can also be obtained from plant callus, explants, organs, or parts thereof. Such regeneration techniques are described generally in Klee et al. (1987) Ann. Rev. Plant Phys. 38:467-486. The regeneration of plants from either single plant protoplasts or various explants is well known in the art. See, for example, Methods for Plant Molecular Biology, A. Weissbach and H. Weissbach, eds., Academic Press, Inc., San Diego, Calif. (1988). For maize cell culture and regeneration see generally, The Maize Handbook, Freeling and Walbot, Eds., Springer, New York (1994); Corn and Corn Improvement, 3rd edition, Sprague and Dudley Eds., American Society of Agronomy, Madison, Wis. (1988).
The cells, which have been altered by any targeted gene modification method, may also be grown into plants in accordance with conventional ways. See, for example, McCormick et al. (1986) Plant Cell Reports 5:81-84; Gruber et al., 1993, “Vectors for Plant Transformation” In: Methods in Plant Molecular Biology and Biotechnology; Glick and Thompson, eds., CRC Press, Inc., Boca Raton, pages 89-119; and Gordon-Kamm et al. (1990) Plant Cell 2:603-618. These plants may then be grown, and either pollinated with the same transformed strain or different strains, and the resulting hybrid having the desired phenotypic characteristic identified. Two or more generations may be grown to ensure that the subject phenotypic characteristic is stably maintained and inherited.
The present invention may be used for transformation of any plant species of angiosperms and gymnosperms, particularly monocotyledonous and dicotyledonous plants including, but not limited to, corn (Zea mays), Brassica sp. (e.g., B. napus, B. juncea), particularly those Brassica species useful as sources of seed oil, alfalfa (Medicago sativa), rice (Oryza sativa), rye (Secale cereale), sorghum (Sorghum bicolor, S. vulgare), millet (e.g., pearl millet (Pennisetum glaucum), proso millet (Pnaicum miliaceum), foxtail millet (Setaria italica), and finger millet (Eleusine coracana)), sunflower (Helianthus annuus), safflower (Carthamus tinctorius), wheat (Triticum aestivum), soybean (Glycine max), tobacco (Nicotiana tabacum), potato (Solanum tuberosum), peanuts (Arachis hypogaea), cotton (e.g., Gossypium barbadense, and G. hirsutum), sweet potato (Ipomoea batatus), cassava (Manihot esculenta), coffee (Coffea spp.), coconut (Cocos nucifera), pineapple (Ananas comosus), citrus trees (Citrus spp.), cocoa (Theobroma cacao), tea (Camellia sinensis), banana (Musa spp.), avocado (Persea americana), fig (Ficus casica), guava (Psidium guajava), mango (Mangifera indica), olive (Olea europaea), papaya (Carica papaya), cashew (Anacardium occidentale), macadamia (Macadamia integrifolia), almond (Prunus amygdalus), sugar beets (Beta vulgaris), sugarcane (Saccharum spp.), oats (Avena), barley (Hordeum), vegetables, ornamentals, turf grass, and conifers.
Vegetables include tomatoes (Lycopersicon esculentum), lettuce (e.g., Lactuca sativa), green beans (Phaseolus vulgaris), lima beans (Phaseolus limensis), peas (Lathyrus spp.), and members of the genus Cucumis such as cucumber (C. sativus), cantaloupe (C. cantalupensis), and musk melon (C. melo). Ornamentals include azalea (Rhododendron spp.), hydrangea (Macrophylla hydrangea), hibiscus (Hibiscus rosasanensis), roses (Rosa spp.), tulips (Tulipa spp.), daffodils (Narcissus spp.), petunias (Petunia hybrida), carnation (Dianthus caryophyllus), poinsettia (Euphorbia pulcherrima), and chrysanthemum. Conifers that may be employed in practicing the present invention include, for example, pines such as loblolly pine (Pinus taeda), slash pine (Pinus elliotii), ponderosa pine (Pinus ponderosa), lodgepole pine (Pinus contorta), and Monterey pine (Pinus radiata); Douglas-fir (Pseudotsuga menziesii); Western hemlock (Tsuga canadensis); Sitka spruce (Picea glauca); redwood (Sequoia sempervirens); true firs such as silver fir (Abies amabilis) and balsam fir (Abies balsamea); and cedars such as Western red cedar (Thuja plicata) and Alaska yellow-cedar (Chamaecyparis nootkatensis). Plants of particular interest in the present invention include crop plants, for example, corn, alfalfa, sunflower, Brassica, soybean, cotton, safflower, peanut, sorghum, wheat, millet, tobacco, etc., particularly corn and soybean.
EXAMPLESThe present invention is further defined in the following Examples, in which parts and percentages are by weight and degrees are Celsius, unless otherwise stated. It should be understood that these Examples, while indicating preferred embodiments of the invention, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, various modifications of the invention in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.
The disclosure of each reference set forth herein is incorporated herein by reference in its entirety.
Example 1Composition of cDNA Libraries; Isolation and Sequencing of cDNA Clones
cDNA libraries representing mRNAs from various corn (Zea mays) and soybean (Glycine max) tissues were prepared. The characteristics of the libraries 5 are described below.
*Chemicals used included hydroxyurea, aphidicolin, HC-toxin, actinomycin D, all of which are commercially available from Calbiochem-Novabiochem Corp. (1-800-628-8470)
**Chemicals used included sorbitol, egosterol, taxifolin, methotrexate, D-mannose, D-glactose, alpha-amino adipic acid, ancymidol, all of which are commercially available from Calbiochem-Novabiochem Corp. (1-800-628-8470)
cDNA libraries may be prepared by any one of many methods available. For example, the cDNAs may be introduced into plasmid vectors by first preparing the cDNA libraries in Uni-ZAP™ XR vectors according to the manufacturer's protocol (Stratagene Cloning Systems, La Jolla, Calif.). The Uni-ZAP™ XR libraries are converted into plasmid libraries according to the protocol provided by Stratagene. Upon conversion, cDNA inserts will be contained in the plasmid vector pBluescript. In addition, the cDNAs may be introduced directly into precut Bluescript II SK(+) vectors (Stratagene) using T4 DNA ligase (New England Biolabs), followed by transfection into DH10B cells according to the manufacturer's protocol (GIBCO BRL Products). Once the cDNA inserts are in plasmid vectors, plasmid DNAs are prepared from randomly picked bacterial colonies containing recombinant pBluescript plasmids, or the insert cDNA sequences are amplified via polymerase chain reaction using primers specific for vector sequences flanking the inserted cDNA sequences. Amplified insert DNAs or plasmid DNAs are sequenced in dye-primer sequencing reactions to generate partial cDNA sequences (expressed sequence tags or “ESTs”; see Adams et al. (1991) Science 252:1651-1656). The resulting ESTs are analyzed using a Perkin Elmer Model 377 fluorescent sequencer.
Full-insert sequence (FIS) data is generated utilizing a modified transposition protocol. Clones identified for FIS are recovered from archived glycerol stocks as single colonies, and plasmid DNAs are isolated via alkaline lysis. Isolated DNA templates are reacted with vector primed M13 forward and reverse oligonucleotides in a PCR-based sequencing reaction and loaded onto automated sequencers. Confirmation of clone identification is performed by sequence alignment to the original EST sequence from which the FIS request is made.
Confirmed templates are transposed via the Primer Island transposition kit (PE Applied Biosystems, Foster City, Calif.) which is based upon the Saccharomyces cerevisiae Ty1 transposable element (Devine and Boeke (1994) Nucleic Acids Res. 22:3765-3772). The in vitro transposition system places unique binding sites randomly throughout a population of large DNA molecules. The transposed DNA is then used to transform DH10B electro-competent cells (Gibco BRL/Life Technologies, Rockville, Md.) via electroporation. The transposable element contains an additional selectable marker (dihydrofolate reductase (DHFR) Fling and Richards (1983) Nucleic Acids Res. 11:5147-5158), allowing for dual selection on agar plates of only those subclones containing the integrated transposon. Multiple subclones are randomly selected from each transposition reaction, plasmid DNAs are prepared via alkaline lysis, and templates are sequenced (ABI Prism dye-terminator ReadyReaction mix) outward from the transposition event site, utilizing unique primers specific to the binding sites within the transposon.
Sequence data is collected (ABI Prism Collections) and assembled using Phred/Phrap (P. Green, University of Washington, Seattle). Phrep/Phrap is a public domain software program which re-reads the ABI sequence data, re-calls the bases, assigns quality values, and writes the base calls and quality values into editable output files. The Phrap sequence assembly program uses these quality values to increase the accuracy of the assembled sequence contigs. Assemblies are viewed by the Consed sequence editor (D. Gordon, University of Washington, Seattle).
In some of the clones the cDNA does not cover the entire open reading frame, typically the 5′ region is absent. In order to obtain the upstream information one of two different protocols are used. The first of these methods results in the production of a fragment of DNA containing a portion of the desired gene sequence while the second method results in the production of a fragment containing the entire open reading frame. Both of these methods use two rounds of PCR amplification to obtain fragments from one or more libraries. The libraries can be chosen based on previous knowledge that the specific gene should be found in a certain tissue, and/or can be randomly chosen. Reactions to obtain the same gene may be performed on several libraries in parallel or on a pool of libraries. Library pools are normally prepared using from 3 to 5 different libraries and normalized to a uniform dilution. In the first round of amplification both methods use a vector-specific (forward) primer corresponding to a portion of the vector located at the 5′-terminus of the clone coupled with a gene-specific (reverse) primer. The first method uses a sequence that is complementary to a portion of the already known gene sequence while the second method uses a gene-specific primer complementary to a portion of the 3′-untranslated region (also referred to as UTR). In the second round of amplification, a nested set of primers is used for both methods. The resulting DNA fragment is ligated into a pBluescript vector using a commercial kit and following the manufacturer's protocol. This kit is selected from many available from several vendors including InVitrogen (Carlsbad, Calif.), Promega Biotech (Madison, Wis.), and Gibco-BRL (Gaithersburg, Md.). The plasmid DNA is isolated by the alkaline lysis method and submitted for sequencing and assembly using Phred/Phrap, as above.
Example 2 Identification of cDNA ClonescDNA clones encoding WUS protein were identified by conducting BLAST (Basic Local Alignment Search Tool; Altschul et al. (1993) J. Mol. Biol. 215:403-410; see also NCBI BLAST website) searches for similarity to sequences contained in the BLAST “nr” database (comprising all non-redundant GenBank CDS translations, sequences derived from the 3-dimensional structure Brookhaven Protein Data Bank, the last major release of the SWISS-PROT protein sequence database, EMBL, and DDBJ databases). The cDNA sequences obtained in Example 1 were analyzed for similarity to all publicly available DNA sequences contained in the “nr” database using the BLASTN algorithm provided by the National Center for Biotechnology Information (NCBI). The DNA sequences were translated in all reading frames and compared for similarity to all publicly available protein sequences contained in the “nr” database using the BLASTX algorithm (Gish and States (1993) Nat. Genet. 3:266-272) provided by the NCBI. For convenience, the P-value (probability) of observing a match of a cDNA sequence to a sequence contained in the searched databases merely by chance as calculated by BLAST are reported herein as “pLog” values, which represent the negative of the logarithm of the reported P-value. Accordingly, the greater the pLog value, the greater the likelihood that the cDNA sequence and the BLAST “hit” represent homologous sequences.
ESTs submitted for analysis are compared to the GenBank database as described above. ESTs that contain sequences more 5- or 3-prime can be found by using the BLASTN algorithm (Altschul et al. (1997) Nucleic Acids Res. 25:3389-3402) against the DuPont proprietary database comparing nucleotide sequences that share common or overlapping regions of sequence homology. Where common or overlapping sequences exist between two or more nucleic acid fragments, the sequences can be assembled into a single contiguous nucleotide sequence, thus extending the original fragment in either the 5 or 3 prime direction. Once the most 5-prime EST is identified, its complete sequence can be determined by Full Insert Sequencing as described in Example 1. Homologous genes belonging to different species can be found by comparing the amino acid sequence of a known gene (from either a proprietary source or a public database) against an EST database using the TBLASTN algorithm. The TBLASTN algorithm searches an amino acid query against a nucleotide database that is translated in all 6 reading frames. This search allows for differences in nucleotide codon usage between different species, and for codon degeneracy.
Example 3 Characterization of cDNA Clones Encoding WUS Protein Homologs The BLASTX search using the EST sequences from clones listed in Table 3 revealed similarity of the polypeptides encoded by the cDNAs to WUS proteins from Arabidopsis thaliana (NCBI GenBank Identifier (GI) No. 3785979) and Arabidopsis thaliana (NCBI GI No. 4090200; SEQ ID NO: 25). Shown in Table 3 are the BLAST results for individual ESTs (“EST”), the sequences of the entire cDNA inserts comprising the indicated cDNA clones (“FIS”), or contigs assembled from two or more ESTs (“Contig”).
The data in Table 4 represents a calculation of the percent identity of the amino acid sequences set forth in SEQ ID NOs: 2, 6, 12 and 16 and the Arabidopsis thaliana (NCBI No. 3785979) and (NCBI GI No. 4090200; SEQ ID NO: 25) sequences. The percent identity between the amino acid sequences set forth in SEQ ID NOs: 2, 6, 12 and 16 as compared to the Arabidopsis sequences ranged from 37-45%
The sequence of the entire cDNA insert in most of the clones listed in Table 3 was determined. Further sequencing and searching of the DuPont proprietary database allowed the identification of other corn and soybean clones encoding WUS protein. The BLASTX search using the EST sequences from clones listed in Table 5 revealed similarity of the polypeptides encoded by the cDNAs to WUS proteins from Arabidopsis thaliana (NCBI GI Nos. 3785979, 4090200, 4580396, 9294502 and 6091768) and Oryza sativa (NCBI GI No. 8099120). Shown in Table 5 are the BLAST results for individual ESTs (“EST”), the sequences of the entire cDNA inserts comprising the indicated cDNA clones (“FIS”), sequences of contigs assembled from two or more ESTs (“Contig”), sequences of contigs assembled from an FIS and one or more ESTs or PCR fragment sequence (“Contig*”), or sequences encoding the entire protein derived from an EST, an FIS, a contig, or an FIS and PCR fragment sequence (“CGS”):
FIGS. 1(A & B) presents an alignment of the amino acid sequences set forth in SEQ ID NOs: 4, 10, 20, 22, and 24 and the Arabidopsis thaliana sequence (NCBI GI No.4090200; SEQ ID NO: 25). The data in Table 6 represents a calculation of the percent identity of the amino acid sequences set forth in SEQ ID NOs: 4, 10, 20, 22, and 24 and the Arabidopsis thaliana sequence (NCBI GI No. 4090200; SEQ ID NO: 25).
Sequence alignments and percent identity calculations were performed using the Megalign program of the LASERGENE bioinformatics computing suite (DNASTAR Inc., Madison, Wis.). Multiple alignment of the sequences was performed using the Clustal method of alignment (Higgins and Sharp (1989) CABIOS. 5:151-153) with the default parameters (GAP PENALTY=10, GAP LENGTH PENALTY=10). Default parameters for pairwise alignments using the Clustal method were KTUPLE 1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5. Sequence alignments and BLAST scores and probabilities indicate that the nucleic acid fragments comprising the instant cDNA clones encode a substantial portion of a WUS protein. These sequences represent the first corn and soybean sequences encoding WUS proteins known to Applicant.
Example 4 Sunflower Meristem TransformationThere are a number of published examples of meristem transformation systems for dicot species including soybean (McCabe et al. (1988) BioTechnology 6:923-926), sunflower (Bidney et al. (1992) Plant Mol. Biol. 18:301-313), and cotton (Gould et al. (1998) Plant Mol. Biol. Rep. 16:283), where chimeric genes are delivered to cells of the meristem and then participate in formation of shoots, reproductive structures and ultimately seed. Transgene delivery is accomplished by both standard particle bombardment protocols as described for soybean or by T-DNA and Agrobacterium protocols as described for sunflower and cotton. The WUS gene could be delivered to dicot meristem targets for either stable or transient transformation to impact the transformation response. WUS could be delivered together with agronomic genes or be used as a conditioning treatment prior to or following the protocol for DNA delivery. The methods for sunflower meristem transformation follow.
Sunflower meristem transformation is achieved by a protocol for direct DNA delivery by particle bombardment or a protocol involving a combination of DNA-free particle bombardment followed by use of Agrobacterium inoculation for DNA delivery as described in Bidney et al. (supra). Sunflower line SMF3, described in Burrus et al. (1991, Plant Cell Rep. 10:161-166) is used. The explant source is dry sunflower seed that is imbibed and dissected into meristem explants. Seeds are dehulled and surface sterilized then placed in sterile petri plates on two layers of filter paper moistened with sterile distilled water for overnight imbibition in the dark at 26° C. in a Percival incubator. The next day, cotyledons and root radicle are removed and meristem explants transferred to 374E medium (MS salts, Shepard vitamins, 40 mg/l adenine sulfate, 3% sucrose, 0.5 mg/l 6-BAP, 0.25 mg/l IAA, 0.1 mg/l GA, pH 5.6, and 0.8% Phytagar). Explants are cultured for 24 hr on 374E medium in the dark at 26° C. Following this culture period, elongated primary leaves are removed to expose the apical meristem. The meristem explants are placed in the center of petri plates with 374M medium (374E with 1.2% Phytagar) in preparation for particle bombardment then back in the dark for another 24 hr period at 26° C.
Particle preparation for the Agrobacterium based protocol is done by suspending 18.8 mg of 1.8 μm tungsten particles or 21.6 mg of 2.0 μm gold particles in 200 μl absolute ethanol. Following particle resuspension by sonication and vigorous mixing, 10 μl of particle suspension is dropped on the center of the surface of macro-carrier. Plates of 374M medium containing sunflower meristem explants are shot twice by a DuPont Biolistics PDS1000 helium gun with vacuum drawn to 26 Hg, with 650 psi rupture discs, and at the top level in the gun. Following particle bombardment, explants are spread out on the 374M plates, inoculated with an Agrobacterium suspension and co-cultured in the light at 26° C. for 4d. The Agrobacterium inoculating suspension is prepared by first starting a 5 ml liquid culture in 60A medium with kanamycin (YEP medium—10 g/l Bactopeptone, 10 g/l yeast extract, 5 g/l sodium chloride, pH 7.0, and 50 mg/l kanamycin) grown to log phase (OD600 0.5-1.0). The log phase growth Agrobacterium suspension is centrifuged at 6K for 5 min and the supernatant discarded. The bacterial pellet is resuspended in inoculation medium (IM) (IM—12.5 mM MES, 1 g/l ammonium chloride, 0.3 g/l magnesium sulfate, pH 5.7) to a final calculated OD600 vis of 4.0. The inoculating Agrobacterium suspension is applied twice using a micro-pipette and 0.5 μl of suspension per explant. After the 4d co-cultivation of sunflower meristem explants, the expanded bases of explants are trimmed off and they are transferred to 374C medium (374E which lacks hormones, but adds 250 mg/l cefotaxime) and cultured for two weeks in the light under 18 hr day length at 26° C.
Alternatively, a direct DNA delivery protocol can be applied to sunflower meristem explants prepared as described above. Particles are prepared as follows: to 50 μL of a 15 mg/mL 0.6 μm gold particle suspension is added (in order): 10 μL DNA (0.1 μg/uL), 20 μL spermidine (0.1 M), and 50 μL CaCl2 (2.5 M). The particle preparation is then agitated for three minutes, spun in a microfuge for 10 seconds and the supernatant removed. The DNA-coated particles are then washed once in 500 μL 100% ethanol and resuspended in 30 μL of 100% ethanol. The DNA/particle suspension can be sonicated three times for one second each. Five μL of the DNA-coated gold particles are then loaded on each macro carrier disk. Meristem explants are bombarded as described in the previous paragraph, spread out on 374M medium, and cultured for 4d in a Percival incubator under 18 hr of daylength at 26° C. The expanded bases of the explant are then cut off and the explant transferred to 374C medium for 2 wk of culture under the long day conditions at 26° C.
After two weeks sunflower shoots emerge from the meristem explants on 374C medium. The shoots can be scored destructively or non-destructively for the frequency of transgenic sectors per experiment and the quality of sectors with longer, wider, and deeper transgenic sectors being more desirable. They can be scored and compared to control using scorable markers such as the GUS enzyme or green fluorescence protein (GFP). Transgenic plants and seed can be obtained by adding steps to the procedure as outlined below. An assay is required such as an enzyme assay or ELISA for an agronomic protein of interest. An example is provided using the enzyme oxalate oxidase as a scorable marker (see, for example, U.S. Pat. No. 6,166,291, herein incorporated by reference). Chemical selection is not required for this transformation process.
Primary shoots following two weeks of culture on 374C medium are screened using the oxalate oxidase enzyme assay. Oxalate oxidase enzyme assays are set up using fresh leaf or cotyledon tissue to identify transformants. The assay method is done according to the protocol of Suigura et al. (1979) Chem. Pharm. Bull. 27(9):2003-2007. The assay is a two step reaction in which hydrogen peroxide is generated by oxalate oxidase in the first step then detected quantitatively by a peroxidase linked color reaction in the second. The color reaction is then measured by spectrophotometer using visible light at 550 nm. The first step of the assay is initiated by grinding shoot derived leaf tissue, pooled leaf tips of 1 sample per shoot, in 0.1 M succinate buffer, pH 3.5. The extracts are centrifuged and supernatants are discarded because most of the enzyme activity is in the cell wall due to the signal peptide of oxalate oxidase. The pellet is resuspended in 0.1 M succinate buffer, pH 3.5, and 0.05 ml of an oxalic acid solution consisting of 10 mM oxalic acid dissolved in 0.1 M succinate buffer, pH 3.5. The oxalate oxidase enzyme reaction proceeds with mild agitation at room temperature (25° C.) for 4 hr. At the end of this time period the reactions are centrifuged and an aliquot of the supernatant removed and added to a volume of 1 M Tris, pH unadjusted, to adjust the samples to a final pH of 7.0 (Tris to 0.147 M) for the second reaction step of the assay. Color development is done by adding the following components in 0.2 M Tris HCl, pH 7.0, in a mixture such that listed final concentrations are achieved: horseradish peroxidase (20 μM), 4-aminoantipyrine (0.165 mM), and N,N-dimethylaniline (0.33 mM). Absorbance at 500 nm is read for samples of the color development reaction. Shoots positive for oxalate oxidase activity are moved into nodal culture for plant recovery and the negative shoots discarded.
Positive shoots are divided into nodal explants where each explant contains at least one node from which a shoot might be recovered. Nodal explants are cultured for 3d on 374G medium (374E plus 250 mg/l cefotaxime) in the light to release nodal meristems then transferred to 374C medium and cultured in the light at 26° C. for 4 weeks to allow nodal shoot development. Shoots derived from nodal culture are assayed for oxalate oxidase activity as described above. The oxalate oxidase positive shoots are moved to procedures for plant recovery in the greenhouse and the negatives discarded.
Assay positive shoots are recovered by grafting to Pioneer sunflower hybrid 6150 grown aseptically and in vitro on 48 P medium (½× MS salts, 0.5% sucrose, pH 5.0, 0.3% gelrite). Root-stock is prepared by surface sterilizing seed of 6150 as described above for SMF3 then imbibing in the light at 26° C. for 4 days. Following this initial germination step, seedlings are place in the dark on 48P medium for 4 d to elongate hypocotyls. The seedlings are then placed back into the light and can be used in the next 7-10 days for grafting. Grafting is done by first cutting the 6150 seedling in the hypocotyl region below the meristem, then slicing the hypocotyl longitudinally in half at the cut site. Transgenic shoots are cut at their base to separate from the originating explant and secured on the root-stock by using a Parafilm™ wrap. After about one week in vitro, the grafted plants are transferred to soil and maintained under humid conditions until they can survive in drier air in the greenhouse.
Transformed T0 plants are further characterized by oxalate oxidase activity assays to verify the continued presence of an active transgene and to determine if the transgene would be present in floral tissue. If there is a sector of transformation which does not develop into a new portion of the growing T0 plant, that plant portion is trimmed off to induce floral bud initiation from axillary meristems. TO flowers are selfed, T1 seed is recovered, and the T1 seed is germinated for T1 transgenic plant identification. Cotyledon or leaf tissue of T1 seedlings is sampled and used to assay for the scorable transgene.
Example 5 Sunflower Leaf Explant Transformation Ectopic Expression of Soybean WUS to Induce OrganogenesisIn addition to testing WUS in meristem transformation, other tissue explants can be tested for the formation of adventive meristems following stable or transient transformation by WUS. The explant types are well known in the art of dicot transformation and might include hypocotyl explants, leaf explants, cotyledon explants, or immature tissues such as embryo or primary leaf as described here for sunflower. As described for meristem explants, the DNA delivery can be done by either the direct delivery of particle bombardment or by Agrobacterium delivery by T-DNA. Using sunflower genotype SMF3 as an example, primary leaves are isolated from meristem explants prepared as described above. After the overnight culture of dissected seeds on 374E medium, the primary leaves have elongated. These are removed and placed in the center of sterile petri plates on filters moistened with 530 medium (MS salts, B5 vitamins, 3% sucrose, 4 mg/l p-chlorophenoxyacetic acid, pH 5.8) in preparation for particle bombardment. Primary leaf explants are spread out over the center of these plates such that none are overlapping others. Particle bombardment is done exactly as described above for direct DNA delivery to meristem explants except that a sterile 70 um nitex mesh is placed over the top of the explants to help prevent them from shifting during bombardment. The DNA delivered could include a chimeric gene, consisting of a constitutive promoter such as SCP1 combined with the selectable marker NPTII and the PINII 3′ region, that allows for the preferential growth of transformed tissue. Alternatively, the WUS gene may provide a growth advantage to the tissue such that a selectable marker is not required. Following particle bombardment, the explants are cultured for 3d on filters continuously moistened with 530 medium by adding 0.5 mL of additional liquid medium per 24 hr. They are cultured in the Percival growth chamber in the light under 18 hr daylength and at 26° C. Primary leaf explants that show growth are then transferred to 374E medium containing 50 mg/l kanamycin if the selectable marker gene was used and cultured for 2 to 3 wk to allow transgenic callus and shoot formation. Cultures that do not respond are transferred every two weeks to 374E with 50 mg/l kanamycin until recoverable shoots are formed. Shoots are sampled, selected, and recovered to the greenhouse as described for meristem explants above.
Sunflower primary leaves can be transformed using Agrobacterium by slight modifications to the protocols above. The explants on 530 medium are bombarded as described for meristem explants in the Agrobacterium procedure above. An Agrobacterium suspension is produced exactly as described for meristem explants except that the liquid culture is 25 ml instead of 5 ml. The Agrobacterium cells are centrifuged, the growth medium supernatant discarded, and the cells resuspended to a calculated OD600 of 0.6 in inoculation medium. Primary leaf explants are inoculated in this suspension for 10 min, then placed back on 530 medium and co-cultivated for 3d under the growth chamber conditions described above. The explants are then transferred to 374D medium (374E, 50 mg/l kanamycin, 250 mg/l cefotaxime) and cultured for 2-3 weeks. Explants can be transferred every two weeks to fresh 374D medium until shoots can be recovered.
Example 6 Expression of Chimeric Genes in Monocot CellsA chimeric gene comprising a cDNA encoding the instant polypeptide in sense orientation with respect to the maize 27 kD zein promoter that is located 5′ to the cDNA, and the 10 kD zein 3′ end that is located 3′ to the cDNA fragment, can be constructed. The cDNA fragment of this gene may be generated by polymerase chain reaction (PCR) of the cDNA clone using appropriate oligonucleotide primers. Cloning sites (NcoI or SmaI) can be incorporated into the oligonucleotides to provide proper orientation of the DNA fragment when inserted into the digested vector pML103 as described below. Amplification is then performed in a standard PCR. The amplified DNA is then digested with restriction enzymes NcoI and SmaI and fractionated on an agarose gel. The appropriate band can be isolated from the gel and combined with a 4.9 kb NcoI-SmaI fragment of the plasmid pML103. Plasmid pML103 has been deposited under the terms of the Budapest Treaty at ATCC (American Type Culture Collection, 10801 University Blvd., Manassas, Va. 20110-2209), and bears accession number ATCC 97366. The DNA segment from pML103 contains a 1.05 kb SalI-NcoI promoter fragment of the maize 27 kD zein gene and a 0.96 kb SmaI-SalI fragment from the 3′ end of the maize 10 kD zein gene in the vector pGem9Zf(+) (Promega). Vector and insert DNA can be ligated at 15° C. overnight, essentially as described in Maniatis. The ligated DNA may then be used to transform E. coli XL1-Blue (Epicurian Coli XL-1 Blue™; Stratagene). Bacterial transformants can be screened by restriction enzyme digestion of plasmid DNA and limited nucleotide sequence analysis using the dideoxy chain termination method (Sequenase™ DNA Sequencing Kit; U.S. Biochemical). The resulting plasmid construct would comprise a chimeric gene comprising, in the 5′ to 3′ direction, the maize 27 kD zein promoter, a cDNA fragment encoding the instant polypeptide, and the 10 kD zein 3′ region.
The chimeric gene described above can then be introduced into corn cells by the following procedure. Immature corn embryos can be dissected from developing caryopses derived from crosses of the inbred corn lines H99 and LH132. The embryos are isolated 10 to 11 days after pollination when they are 1.0 to 1.5 mm long. The embryos are then placed with the axis-side facing down and in contact with agarose-solidified N6 medium (Chu et al. (1975) Sci. Sin. Peking 18:659-668). The embryos are kept in the dark at 27° C. Friable embryogenic callus consisting of undifferentiated masses of cells with somatic proembryoids and embryoids borne on suspensor structures proliferates from the scutellum of these immature embryos. The embryogenic callus isolated from the primary explant can be cultured on N6 medium and sub-cultured on this medium every 2 to 3 weeks.
The plasmid, p35S/Ac (obtained from Dr. Peter Eckes, Hoechst Ag, Frankfurt, Germany) may be used in transformation experiments in order to provide for a selectable marker. This plasmid contains the Pat gene (see European Patent Publication 0 242 236) which encodes phosphinothricin acetyl transferase (PAT). The enzyme PAT confers resistance to herbicidal glutamine synthetase inhibitors such as phosphinothricin. The pat gene in p35S/Ac is under the control of the 35S promoter from Cauliflower Mosaic Virus (Odell et al. (1985) Nature 313:810-812) and the 3′ region of the nopaline synthase (nos) gene from the T-DNA of the Ti plasmid of Agrobacterium tumefaciens.
The particle bombardment method (Klein et al. (1987) Nature 327:70-73) may be used to transfer genes to the callus culture cells. According to this method, gold particles (1 μm in diameter) are coated with DNA using the following technique. Ten μg of plasmid DNAs are added to 50 μL of a suspension of gold particles (60 mg per mL). Calcium chloride (50 μL of a 2.5 M solution) and spermidine free base (20 μL of a 1.0 M solution) are added to the particles. The suspension is vortexed during the addition of these solutions. After 10 minutes, the tubes are briefly centrifuged (5 sec at 15,000 rpm) and the supernatant removed. The particles are resuspended in 200 μL of absolute ethanol, centrifuged again and the supernatant removed. The ethanol rinse is performed again and the particles resuspended in a final volume of 30 μL of ethanol. An aliquot (5 μL) of the DNA-coated gold particles can be placed in the center of a Kapton™ flying disc (Bio-Rad Labs). The particles are then accelerated into the corn tissue with a Biolistic™ PDS-1000/He (Bio-Rad Instruments, Hercules Calif.), using a helium pressure of 1000 psi, a gap distance of 0.5 cm and a flying distance of 1.0 cm.
For bombardment, the embryogenic tissue is placed on filter paper over agarose-solidified N6 medium. The tissue is arranged as a thin lawn and covers a circular area of about 5 cm in diameter. The petri dish containing the tissue can be placed in the chamber of the PDS-1000/He approximately 8 cm from the stopping screen. The air in the chamber is then evacuated to a vacuum of 28 inches of Hg. The macrocarrier is accelerated with a helium shock wave using a rupture membrane that bursts when the He pressure in the shock tube reaches 1000 psi.
Seven days after bombardment the tissue can be transferred to N6 medium that contains bialaphos (5 mg per liter) and lacks casein or proline. The tissue continues to grow slowly on this medium. After an additional 2 weeks the tissue can be transferred to fresh N6 medium containing bialaphos. After 6 weeks, areas of about 1 cm in diameter of actively growing callus can be identified on some of the plates containing the bialaphos-supplemented medium. These calli may continue to grow when sub-cultured on the selective medium.
Plants can be regenerated from the transgenic callus by first transferring clusters of tissue to N6 medium supplemented with 0.2 mg per liter of 2,4-D. After two weeks the tissue can be transferred to regeneration medium (Fromm et al. (1990) Bio/Technology 8:833-839).
Example 7 Transformation and Regeneration of Maize EmbryosImmature maize embryos from greenhouse donor plants are bombarded with a plasmid containing the gene of the invention operably linked to a promoter; this could be a weak promoter such as nos, a tissue-specific promoter, such as globulin-1, an inducible promoter such as In2, or a strong promoter such as ubiquitin plus a plasmid containing the selectable marker gene PAT (Wohlleben et al., 1988, Gene 70:25-37) that confers resistance to the herbicide Bialaphos. Transformation is performed as follows.
Maize ears are harvested 8-14 days after pollination and surface sterilized in 30% Chlorox bleach plus 0.5% Micro detergent for 20 minutes, and rinsed two times with sterile water. The immature embryos are excised and placed embryo axis side down (scutellum side up), 25 embryos per plate. These are cultured on 560L medium 4 days prior to bombardment in the dark. Medium 560L is an N6-based medium containing Eriksson's vitamins, thiamine, sucrose, 2,4-D, and silver nitrate. The day of bombardment, the embryos are transferred to 560Y medium for 4 hours and are arranged within the 2.5-cm target zone. Medium 560Y is a high osmoticum medium (560L with high sucrose concentration).
A plasmid vector comprising the gene of the invention operably linked to the selected promoter is constructed. This plasmid DNA plus plasmid DNA containing a PAT selectable marker is precipitated onto 1.1 μm (average diameter) tungsten pellets using a CaCl2 precipitation procedure as follows: 100 μl prepared tungsten particles in water, 10 μl (1 μg) DNA in TrisEDTA buffer (1 μg total), 100 μl 2.5M CaC12, 10 μl 0.1M spermidine.
Each reagent is added sequentially to the tungsten particle suspension, while maintained on the multitube vortexer. The final mixture is sonicated briefly and allowed to incubate under constant vortexing for 10 minutes. After the precipitation period, the tubes are centrifuged briefly, liquid removed, washed with 500 μl 100% ethanol, and centrifuged for 30 seconds. Again the liquid is removed, and 105 μl 100% ethanol is added to the final tungsten particle pellet. For particle gun bombardment, the tungsten/DNA particles are briefly sonicated and 10 μl spotted onto the center of each macrocarrier and allowed to dry about 2 minutes before bombardment.
The sample plates are positioned 2 levels below the stopping plate for bombardment in a DuPont Helium Particle Gun. All samples receive a single shot at 650 PSI, with a total of ten aliquots taken from each tube of prepared particles/DNA. As a control, embryos are bombarded with DNA containing the PAT selectable marker as described above without the gene of invention.
Following bombardment, the embryos are kept on 560Y medium, an N6 based medium, for 2 days, then transferred to 560R selection medium, an N6 based medium containing 3 mg/liter Bialaphos, and subcultured every 2 weeks. After approximately 10 weeks of selection, bialaphos-resistant callus clones are sampled for PCR and activity of the gene of interest. In treatments containing the WUS gene, it is expected that growth will be stimulated and transformation frequencies increased, relative to the control. Positive lines are transferred to 288J medium, an MS based medium with lower sucrose and hormone levels, to initiate plant regeneration. Following somatic embryo maturation (2-4 weeks), well-developed somatic embryos are transferred to medium for germination and transferred to the lighted culture room. Approximately 7-10 days later, developing plantlets are transferred to medium in tubes for 7-10 days until plantlets are well established. Plants are then transferred to inserts in flats (equivalent to 2.5″ pot) containing potting soil and grown for 1 week in a growth chamber, subsequently grown an additional 1-2 weeks in the greenhouse, then transferred to Classic™ 600 pots (1.6 gallon) and grown to maturity. Plants are monitored for expression of the gene of interest.
Example 8 Ectopic Expression of Maize WUS to Induce OrganogenesisUsing the genotype High type 11 as an example, embryos are isolated and cultured on 560P medium for 3-5 days. Twelve hours before bombardment these embryos are transferred to high osmotic 560Y medium. Expression cassettes containing the WUS cDNA are then co-introduced into the scutella of these embryos along with an expression cassette containing genes encoding selectable markers, such as Bar or Pat, or visual markers such as green fluorescent protein (GFP) or cyan fluorescent protein (CFP) using methods well described in the art for particle gun transformations. Twelve to 24 hours following bombardment, embryos are then transferred back to 560P culture medium and incubated in the dark at 26° C. After one week of culture these embryos are moved to 560R selection medium. Cultures are then transferred every two weeks until transformed colonies appear. It is expected that expression of WUS will stimulate adventive meristem (shoot) formation. This will be apparent when the cultures are compared to controls (transformed without the WUS cDNA or non-induced). Using either inducible expression cassettes, tissue specific promoters, or promoters of varying strengths it will be possible to control the levels of expression to maximize the formation of adventive meristems. Using either non-responsive genotypes or sub-optimal culture conditions with responsive genotypes, only the transformed cells expressing the WUS cDNA will form meristems and regenerate plants. For experiments in which WUS-induced shoot proliferation occurs via ectopic meristem formation, WUS can be used as a positive selective phenotype and no selection agent is required in the media. In this manner the WUS gene can be used as a positive selective marker (only the cells expressing the gene will form shoot meristems) and transformants can be recovered without a negative selective agent (i.e. bialaphos, basta, kanamycin, etc.).
Results
A. Ectopic Expression of Maize WUS1 to Stimulate Organogenesis.
Using the maize genotype High type II, immature embryos were isolated, cultured and transformed as described generally in Example 7 substituting 0.6 μm gold particles for tungsten and with the sample plate 7.5 cm below the stooping screen. DNA was delivered using co-transformation, a method where introduced DNA's are normally integrated in a single locus. As a control, embryos were shot with a 1:1 mixture of plasmids, the first plasmid containing a ubiquitin promoter-driven green fluorescence protein (GFP) and a second plasmid containing a ubiquitin driven uidA gene (GUS). In the WUSCHEL treatment, the embryos were bombarded with a 1:1 mixture of plasmids containing the ubiquitin promoter driving expression of GFP (Ubi:GFP) and a plasmid containing the WUS1 DNA (SEQ ID NO: 32) driven by the maize In2 promoter (In2:WUS1). The In2 promoter is induced by auxin-like compounds and is weakly expressed on callus maintenance medium. Each treatment contained 175 embryos. Embryos were allowed to callus on 560P medium without selection. After approximately 3 weeks, GFP-positive tissue was visually selected under a fluorescent microscope and transferred to fresh medium. After 8 weeks colony numbers and size were recorded. In the control, 4 small events (<1 cm2) were recovered along with 1 medium event (1-2 cm2) for a total of 5 events. In the WUS1 treatment, the colonies were both more numerous and larger. In this treatment 6 small events (<1 cm2) were recovered along with 2 medium size events (1-2 cm2) and 3 large events (>2 cm2) for a total of 11 events. Plants were regenerated and some unusual phenotypes were observed during the plant regeneration process in the In2:WUS1 treatment, most notable were somatic embryos derived from root tips, a phenomenon observed with ectopic WUS expression in Arabidopsis (Zuo et al. (2002) Plant J. 30:349-359) One WUS1 event was observed with a highly unusual phenotype. In this event, ectopic earshoots and leaf-like structures were formed in a radial pattern on the abaxile side of the vegetative leaves. This is a highly unusual placement for meristems in angiosperms but a similar phenotype has been observed in Arabidopsis plants over-expressing WUSCHEL (Lohmann et al. (2001) Cell 105:793-803). All other regenerated plants were normal, as expected, since the In2 promoter is not on in the absence of auxin-like chemicals.
B. Ectopic Expression of Maize WUS in an Inbred to Stimulate Organogenesis.
Immature embryos were transformed as described in Example 7 with media alterations done to adapt the procedure for use with inbred germplasm and visual selection. Using the maize inbred 581, a tissue culture recalcitrant line, immature embryos from greenhouse grown plants were isolated 12 days after pollination and cultured on 605J medium (a medium containing both full strength MS salts (macro and micronutrient) and 0.6× N6 macronutrient salts plus additional B5 micronutrients, with a mixture of SH and Eriksson's vitamin, L-proline and casamino acids, silver nitrate, 0.3 mg/l 2,4-D and 1.2 mg/l Dicamba, 2% sucrose and 0.06% glucose, solidified with agar). The embryos were incubated in the dark at 28° C. overnight. The embryos were then transferred to a high osmoticum medium similar to 605J with the addition of 15% sucrose prior to particle bombardment. Embryos were shot in a method similar to that in Example 7 substituting 0.6 μm gold particles for tungsten. DNA was delivered using co-transformation, as noted above. As a control, embryos were shot with a 1:1 mixture of plasmid DNA's containing a Ubiquitin driven yellow fluorescence protein (YFP) and a plasmid containing a Ubiquitin driven uidA gene (GUS). In the WUSCHEL treatment the embryos were bombarded with a 1:1 mixture of plasmid DNA's containing the Ubiquitin promoter driving expression of YFP (Ubi:YFP) and a plasmid containing WUS2 (SEQ ID NO: 62) driven by the maize In2 promoter (In2:WUS2). Immediately following bombardment embryos were transferred back to low osmoticum 605J medium. Each treatment contained 90 embryos. Embryos were observed 3 days after bombardment and differences were observed between the treatments.
In the control treatment, hundreds of cells transiently expressing the YFP protein were visible under a fluorescent microscope, and in this population of fluorescing cells, cell division was very rare. Cells transiently expressing YFP were also apparent in the WUS2 treatment. However, in the WUS2 treatment, cell division was apparent in the cells surrounding the YFP positive cells, resulting in the appearance of a mound of cells with discrete YFP positive cells at the apex. Over the next few weeks these embryo/shoot-like outgrowths continued to elongate with the YFP expressing cells maintaining their position at the apex of projections or a few cells beneath the apex reminiscent of endogenous WUS expression in Arabidopsis apical meristems (Mayer et al. (1998) Cell 95:805-815). Embryos and embryogenic calli were transferred every two weeks. After approximately two months only YFP expressing calli were transferred. After 3 months, YFP tissue was transferred to regeneration medium lacking 2, 4-D. No embryogenic YFP positive events were recovered from the control treatment. In contrast, over 24 YFP positive events with embryogenic callus were obtained from the WUS2 treatment. Plants were regenerated from the WUS2 treatment and sent to the greenhouse. This experiment was repeated with similar results, the control transformation frequency was 2%, while the transformation frequency in the In2:WUS2 treatment transformation frequency was 19%.
C. Ectopic Expression of Maize WUS2 is Sufficient to Stimulate Oorganogenesis/Embryogenesis in Recalicitrant Tissues
There exists only a small developmental window in which maize embryos are amenable to tissue culture growth, a prerequisite for transformation. Normally this occurs between 9-12 days after pollination when the immature embryos are between 1.0-1.5 mm in length. Older, larger embryos fail to produce embryogenic callus and thus cannot be transformed. To demonstrate that WUS2 can be used to induce organogenesis/embryogenesis, embryos were isolated 17-18 days after pollination and used for transformation experiments. Using the maize inbreds 581, N46, and P38, immature embryos from greenhouse grown plants were isolated 17-18 days after pollination and cultured on 605J medium. Immature embryos were transformed and visually selected as described in Example 8B. DNA was delivered using co-transformation as described above. As a control, embryos were shot with a 1:1 mixture of plasmid DNA's containing a Ubiquitin driven YFP (Ubi:YFP) and a plasmid containing a Ubiquitin driven uidA gene (Ubi:uidA). In the WUSCHEL treatment the embryos were bombarded with a 1:1 mixture of plasmid DNA's containing the Ubiquitin promoter driving expression of the YFP (Ubi:YFP) and a plasmid containing the WUS2 DNA (SEQ ID NO: 62) driven by the maize Oleosin promoter (Ole:WUS2). Immediately following bombardment embryos were transferred back to low osmoticum 605J medium. Each bombarded plate contained 10 embryos. In the control, each genotype was represented by 2 plates. In the WUS2 treatment, 581 and N46 had 2 plates each while the P38 treatment had only 1 plate (10 embryos). Embryos were observed 5 days after bombardment and hundreds of YFP positive cells were seen in both treatments under the fluorescent microscope. When observed under visible light, embryo-like protuberances were visible in the WUS2 treatment. No embryo-like protuberances were observed in the control treatment. When observed under the fluorescent microscope each of the embryo-like protuberances in the WUS2 treatment was associated with YFP fluorescence demonstrating that WUS2 is sufficient to induce organogenesis from tissues that are normally unresponsive. These embryos are currently being cultured to obtain transformants. As observed in the WUS2 treatment in Example 8B, cell division was apparent in the cells surrounding the YFP positive cells, resulting in the appearance of a mound of cells with discrete YFP positive cells at the apex (SEE
It may be desirable to “kick start” meristem formation by transiently expressing the WUS genes product. This can be done by delivering WUS 5′ capped polyadenylated RNA, expression cassettes containing WUS DNA, or WUS protein. All of these molecules can be delivered using a biolistics particle gun. For example, 5′ capped polyadenylated WUS RNA can easily be made in vitro using Ambion's mMessage mMachine kit. Following a delivery procedure outlined above, RNA is co-delivered along with DNA containing an agronomically useful expression cassette. It is expected that cells receiving WUS will form shoot meristems and a large portion of these will have integrated the agronomic gene. Plants regenerated from these embryos can then be screened for the presence of the agronomic gene.
Example 10 Maize Meristem TransformationMeristem transformation protocols rely on the transformation of apical initials or cells that can become apical initials following reorganization due to injury or selective pressure. The progenitors of these apical initials differentiate to form the tissues and organs of the mature plant (i.e., leaves, stems, ears, tassels, etc.). The meristems of most angiosperms are layered with each layer having its own set of initials. Normally in the shoot apex these layers rarely mix. In maize the outer layer of the apical meristem, the L1, differentiates to form the epidermis while descendents of cells in the inner layer, the L2, give rise to internal plant parts including the gametes. The initials in each of these layers are defined solely by position and can be replaced by adjacent cells if they are killed or compromised. Meristem transformation frequently targets a subset of the population of apical initials and the resulting plants are chimeric. If for example, 1 of 4 initials in the L1 layer of the meristem are transformed only ¼ of epidermis would be transformed. Selective pressure can be used to enlarge sectors but this selection must be non-lethal since large groups of cells are required for meristem function and survival.
Transformation of a meristem cell with a WUS sequence under the expression of a promoter active in the apical meristem (either meristem-specific or constitutive) would allow the transformed cells to re-direct the initiation of new apical initials driving the meristem towards homogeneity and minimizing the chimeric nature of the plant body. To demonstrate this, the WUS sequence is cloned into a cassette with a promoter that is active within the meristem (i.e. either a strong constitutive maize promoter such as the ubiquitin promoter including the first ubiquitin intron, or a promoter active in meristematic cells such as the maize histone, cdc2 or actin promoter). Coleoptilar stage embryos are isolated and plated meristem-up on a high sucrose maturation medium (see Lowe et al., 1997, In Genetic Biotechnology and Breeding of Maize and Sorghum, A S Tsaftaris, ed., Royal Society of Chemistry, Cambridge, UK, pp 94-97). The WUS expression cassette along with a reporter construct such as Ubi:GUS:pinII can then be co-delivered (preferably 24 hours after isolation) into the exposed apical dome using conventional particle gun transformation protocols. As a control, the WUS construct can be replaced with an equivalent amount of pUC plasmid DNA. After a week to 10 days of culture on maturation medium the embryos can be transferred to a low sucrose hormone-free germination medium. Leaves from developing plants can be sacrificed for GUS staining. Transient expression of the WUS sequence in meristem cells, through formation of new apical initials, will result in broader sectors or completely transformed meristems increasing the probability of germ-line transformation. Integration and expression of the WUS sequence will impart a competitive advantage to expressing cells resulting in a progressive enlargement of the transgenic sector. Due to the WUS-induced maintenance of apical initials and growth of their transformed derivatives, they will supplant wild-type meristem cells as the plant continues to grow. The result will be both enlargement of transgenic sectors within a given cell layer (i.e. periclinal expansion) and into adjacent cell layers (i.e. anticlinal invasions). As cells expressing the WUS gene occupy an increasingly large proportion of the meristem, the frequency of transgene germline inheritance goes up accordingly. Using WUS in this manner to target meristems will increase transformation rates, relative to control treatments. Coleoptilar-stage embryos used as a source of meristems is used an example, but other meristem sources could be used as well, for example immature influorescences.
Example 11 Expression of Chimeric Genes in Dicot CellsA seed-specific expression cassette composed of the promoter and transcription terminator from the gene encoding the β subunit of the seed storage protein phaseolin from the bean Phaseolus vulgaris (Doyle et al. (1986) J. Biol. Chem. 261:9228-9238) can be used for expression of the instant polypeptides in transformed soybean. The phaseolin cassette includes about 500 nucleotides upstream (5′) from the translation initiation codon and about 1650 nucleotides downstream (3′) from the translation stop codon of phaseolin. Between the 5′ and 3′ regions are the unique restriction endonuclease sites NcoI (which includes the ATG translation initiation codon), SmaI, KpnI and XbaI. The entire cassette is flanked by HindIII sites.
The cDNA fragment of this gene may be generated by polymerase chain reaction (PCR) of the cDNA clone using appropriate oligonucleotide primers. Cloning sites can be incorporated into the oligonucleotides to provide proper orientation of the DNA fragment when inserted into the expression vector. Amplification is then performed as described above, and the isolated fragment is inserted into a pUC18 vector carrying the seed expression cassette.
Soybean embryos may then be transformed with the expression vector comprising sequences encoding the instant polypeptides. To induce somatic embryos, cotyledons, 3-5 mm in length dissected from surface sterilized, immature seeds of the soybean cultivar A2872, can be cultured in the light or dark at 26° C. on an appropriate agar medium for 6-10 weeks. Somatic embryos which produce secondary embryos are then excised and placed into a suitable liquid medium. After repeated selection for clusters of somatic embryos which multiplied as early, globular staged embryos, the suspensions are maintained as described below.
Soybean embryogenic suspension cultures can be maintained in 35 mL liquid media on a rotary shaker, 150 rpm, at 26° C. with fluorescent lights on a 16:8 hour day/night schedule. Cultures are subcultured every two weeks by inoculating approximately 35 mg of tissue into 35 mL of liquid medium.
Soybean embryogenic suspension cultures may then be transformed by the method of particle gun bombardment (Klein et al. (1987) Nature (London) 327:70-73; and U.S. Pat. No. 4,945,050). A DuPont Biolistic™ PDS1000/HE instrument (helium retrofit) can be used for these transformations.
A selectable marker gene which can be used to facilitate soybean transformation is a chimeric gene composed of the 35S promoter from Cauliflower Mosaic Virus (Odell et al. (1985) Nature 313:810-812), the hygromycin phosphotransferase gene from plasmid pJR225 (from E. coli; Gritz et al. (1983) Gene 25:179-188) and the 3′ region of the nopaline synthase (nos) gene from the T-DNA of the Ti plasmid of Agrobacterium tumefaciens. The seed expression cassette comprising the phaseolin 5′ region, the fragment encoding the instant polypeptide and the phaseolin 3′ region can be isolated as a restriction fragment. This fragment can then be inserted into a unique restriction site of the vector carrying the marker gene.
To 50 μL of a 60 mg/mL 1 μm gold particle suspension is added (in order): 5 μL DNA (1 μg/μL), 20 μL spermidine (0.1 M), and 50 μL CaCl2 (2.5 M). The particle preparation is then agitated for three minutes, spun in a microfuge for 10 seconds and the supernatant removed. The DNA-coated particles are then washed once in 400 μL 70% ethanol and resuspended in 40 μL of anhydrous ethanol. The DNA/particle suspension can be sonicated three times for one second each. Five μL of the DNA-coated gold particles are then loaded on each macro carrier disk.
Approximately 300-400 mg of a two-week-old suspension culture is placed in an empty 60×15 mm petri dish and the residual liquid removed from the tissue with a pipette. For each transformation experiment, approximately 5-10 plates of tissue are normally bombarded. Membrane rupture pressure is set at 1100 psi and the chamber is evacuated to a vacuum of 28 inches mercury. The tissue is placed approximately 3.5 inches away from the retaining screen and bombarded three times. Following bombardment, the tissue can be divided in half and placed back into liquid and cultured as described above.
Five to seven days post bombardment, the liquid media may be exchanged with fresh media, and eleven to twelve days post bombardment with fresh media containing 50 mg/mL hygromycin. This selective media can be refreshed weekly. Seven to eight weeks post bombardment, green, transformed tissue may be observed growing from untransformed, necrotic embryogenic clusters. Isolated green tissue is removed and inoculated into individual flasks to generate new, clonally propagated, transformed embryogenic suspension cultures. Each new line may be treated as an independent transformation event. These suspensions can then be subcultured and maintained as clusters of immature embryos or regenerated into whole plants by maturation and germination of individual somatic embryos.
Example 12 Expression of Chimeric Genes in Microbial CellsThe cDNAs encoding the instant polypeptides can be inserted into the T7 E. coli expression vector pBT430. This vector is a derivative of pET-3a (Rosenberg et al. (1987) Gene 56:125-135) which employs the bacteriophage T7 RNA polymerase/T7 promoter system. Plasmid pBT430 was constructed by first destroying the EcoRI and Hind III sites in pET-3a at their original positions. An oligonucleotide adaptor containing EcoRI and Hind III sites was inserted at the BamH I site of pET-3a. This created pET-3aM with additional unique cloning sites for insertion of genes into the expression vector. Then, the Nde I site at the position of translation initiation was converted to an Nco I site using oligonucleotide-directed mutagenesis. The DNA sequence of pET-3aM in this region, 5′-CATATGG, was converted to 5′-CCCATGG in pBT430.
Plasmid DNA containing a cDNA may be appropriately digested to release a nucleic acid fragment encoding the protein. This fragment may then be purified on a 1% low melting agarose gel. Buffer and agarose contain 10 μg/ml ethidium bromide for visualization of the DNA fragment. The fragment can then be purified from the agarose gel by digestion with GELase™ (Epicentre Technologies, Madison, Wis.) according to the manufacturer's instructions, ethanol precipitated, dried and resuspended in 20 μL of water. Appropriate oligonucleotide adapters may be ligated to the fragment using T4 DNA ligase (New England Biolabs (NEB), Beverly, Mass.). The fragment containing the ligated adapters can be purified from the excess adapters using low melting agarose as described above. The vector pBT430 is digested, dephosphorylated with alkaline phosphatase (NEB) and deproteinized with phenol/chloroform. The prepared vector pBT430 and fragment can then be ligated at 16° C. for 15 hours followed by transformation into DH5 electrocompetent cells (GIBCO BRL). Transformants can be selected on agar plates containing LB media and 100 μg/mL ampicillin. Transformants containing the gene encoding the instant polypeptide are then screened for the correct orientation with respect to the T7 promoter by restriction enzyme analysis.
For high level expression, a plasmid clone with the cDNA insert in the correct orientation relative to the T7 promoter can be transformed into E. coli strain BL21(DE3) (Studier et al. (1986) J. Mol. Biol. 189:113-130). Cultures are grown in LB medium containing ampicillin (100 mg/L) at 25° C. At an optical density at 600 nm of approximately 1, IPTG (isopropylthio-β-galactoside, the inducer) can be added to a final concentration of 0.4 mM and incubation can be continued for 3 h at 25° C. Cells are then harvested by centrifugation and re-suspended in 50 μL of 50 mM Tris-HCl at pH 8.0 containing 0.1 mM DTT and 0.2 mM phenylmethylsulfonyl fluoride (PMSF). A small amount of 1 mm glass beads can be added and the mixture sonicated 3 times for about 5 seconds each time with a microprobe sonicator. The mixture is centrifuged and the protein concentration of the supernatant determined. One μg of protein from the soluble fraction of the culture can be separated by SDS-polyacrylamide gel electrophoresis. Gels can be observed for protein bands migrating at the expected molecular weight.
Example 13 Use of FLP/Frt System to Excise the WUS CassetteIn cases where the WUS gene has been integrated and WUS expression is useful in the recovery of maize transgenics (i.e. under conditions where continuous expression of WUS promotes adventive meristem formation), but is ultimately not desired in the final product, the WUS expression cassette (or any portion thereof that is flanked by appropriate FRT recombination sequences) can be excised using FLP-mediated recombination (see, for example, PCT Publication WO 99/25841; and WO 99/25821).
Example 14 Identification of WUS2 Haplotypes from Various Inbred LinesPlant genomic DNA was isolated from 6 different inbred maize lines, 3DT, 09B, 07D, KW3, B73, and Mo17 using a standard CTAB extraction protocol (Doyle and Doyle, Focus, 1990). One gram of frozen immature leaf tissue was ground in liquid nitrogen using a pre-chilled mortar and pestle. The powdered tissue was transferred to a 50 mL Beckman centrifuge tube along with 100 mL of a pre-heated 60° C. CTAB isolation buffer (2% (w/v) cetyltrimethylammonium bromide; 1.4 M NaCl; 0.005% (v/v) 2-mercaptoethanol; 20 mM EDTA, pH 8.0; 100 mM Tris-HCl, pH 8.0). The samples were incubated for 1 hour at 60° C. with gently swirling every 10 minutes. The samples were then extracted once with 24:1 (v/v) chloroform:isoamyl alcohol. In order to concentrate the phases, the samples were centrifuged at 3750 rpm (2800×g) at room temperature. The aqueous phase was removed with a wide bore pipette and transferred to a sterile 50 mL Beckman tube. Nucleic acids were precipitated by the addition of a ⅔ volume of ice cold 2-propanol and incubated overnight at −20° C. Following the ethanol precipitation of the DNA, the tubes were centrifuged for 30 minutes at 3750 rpm (2800×g) at 4° C. The resultant pellet was rinsed in 20 mL of a wash solution (80% (v/v) ethanol, 15 mM ammonium acetate) for 30 minutes before being centrifuged for 10 minutes at 4500 rpm (1600×g). Following centrifugation, the supernatant was removed and the DNA pellet was air dried overnight on the bench top. The following day, the DNA was resuspended in 0.75 mL TE (10 mM Tris-HCl, pH 8.0; 1mM EDTA, pH 8.0).
Following genomic DNA isolation, gene specific primers were designed to amplify WUS2 (p001 6.ctsas50r) genomic fragments from maize inbred lines, 3DT, 09B, 07D, KW3, B73, and Mol7 using a polymerase chain reaction (PCR) technique. Three sets of gene specific primers were used that generated overlapping WUS2 genomic DNA fragments that together spanned the entire WUS2 coding sequence. WUS2 primer pairs 65505 (SEQ ID NO: 82) (5′GTCCGAGCTAGGTCACAGAAGCGCTCAGGA-3′); and 65506 (SEQ ID NO: 83) (5′TATCGTGTCCGACGACGCGAAGCGT-3′); 66571 (SEQ ID NO: 84) (5′-CCACCCTCGGCTTCTACGC-3′) and 65507 (SEQ ID NO: 85) (5′-ACCCCAGAACGGCAAGTAGCTGCTGCT-3′); 66577 (SEQ ID NO: 86) (5′-GCATTGCGCGCAGTT-3′) and 67447 (SEQ ID NO: 87) (5′-ACGCATGCAGTAGCTGGAGTCTAA-3′) amplified genomic DNA fragments that were approximately 757 bp, 512 bp, and 809 bp respectively. Amplified lengths should be taken as approximate since some variation within the WUS2 sequence between inbred lines was detected due to polymorphisms. PCR was performed using a three-step protocol that was preceded by an initial hotstart at 95° C. for 15 minutes: denaturation, 94° C. for 45 seconds; annealing, 60° C. for 45 seconds; extension, 72° C. for 1.5 minutes. Amplicons were separated on a 1% ethidium bromide stained agarose gel. Agarose gels were analyzed on a short wave (310 nm) UV transilluminator and captured using CCD imaging with the Quantity One image analysis/quantitation software from Bio-Rad (Hercules, Calif., USA). PCR products were gel purified, TA cloned into the pCR4.0 vector (InVitrogen, Carlsbad, Calif., USA), and submitted for sequencing. Consensus sequences for each inbred were generated using the Sequencher program version 4.1.4b7 (Gene Codes Corporation, Ann Arbor, Mich., USA). Approximately 1.4 kb of WUS2 sequence was derived from each inbred line and compared with one another. Any deviations between WUS2 sequence between the various inbred lines, such as insertion/deletions (indels) and/or single nucleotide polymorphisms (SNPs) were noted. Sequence ID numbers for genomic DNA sequences, and spliced products (see Example 18) that encompass the full-length WUS2 coding sequences are as follows:
- 3DT WUS2 nucleotide sequences, SEQ ID NOS: 62, 63, 65, and 67, and corresponding amino acid sequences, SEQ ID NO: 64, 66, and 68;
- 09B WUS2 nucleotide sequences, SEQ ID NOS: 69, 70, 72, and 74, and corresponding amino acid sequences, SEQ ID NOS: 71, 73, and 75;
- 07D WUS2 nucleotide sequences, SEQ ID NOS: 48, 49, 51, and 53, and corresponding amino acid sequences, SEQ ID NOS: 50, 52, and 54;
- KW3 WUS2 nucleotide sequences, SEQ ID NOS: 55, 56, 58, and 60, and corresponding amino acid sequences, SEQ ID NOS: 57, 59, and 61;
- B73 WUS2 nucleotide sequences, SEQ ID NOS: 34, 35, 37, and 39, and corresponding amino acid sequences, SEQ ID NOS: 36, 38, and 40; and
- Mo17 WUS2 nucleotide sequences, SEQ ID NOS: 41, 42, 44, and 46, and corresponding amino acid sequences, SEQ ID NOS: 43, 45, and 47.
The WUS gene can be placed under control of an inducible expression system, as described in Zuo et al. (2000) Plant J 24:265-273; and U.S. Patent Application Publication No. US 2003/0082813 A1, the entire contents of which are herein incorporated by reference. The G10-90 promoter in the XVE vector can be replaced with a tissue-specific promoter (e.g. a pollen-, root-stem- or leaf-specific promoter). A variety of tissue-specific promoters are well known to those of skill in the art. Because expression of a transgene is activated by the chimeric XVE gene which is controlled by a tissue-specific promoter in this Example, the OleXA-46 promoter controlling the WUS transgene is therefore tissue-specific in an inducer-dependent manner. This means that WUS will be induced only in the presence of an inducer and only in the specific tissue corresponding to the tissue specific promoter. Appropriate tissues or cell types, can then be collected from the transgenic plants and used for induction of somatic embryos and regeneration of plants.
When pollen derived from transgenic plants carrying a pollen-specific promoter-XVE/OlexA-46-WUS vector is used, progeny plants generated from pollen-derived somatic embryos should be haploid instead of diploid (see, e.g., Twell et al. (1989) Mol. Gen. Genet. 217(2-3):240-245; and Twell et al. (1990) Development 109(3):705-714 for pollen-specific promoters). In this embodiment of the invention, a transgenic plant having in its genome a WUS gene under the control of an inducible, pollen-specific promoter would not normally express the gene. Pollen from such a plant can be cultured in the presence of the inducer until somatic embryogenesis occurs, after which the inducer is removed and the haploid embryos are permitted to develop into haploid clones according to standard techniques.
Example 16 Generating an Apomictic PlantApomixis can be induced by introducing WUS into a plant cell in such a manner that the WUS gene is expressed in the appropriate tissues (e.g., nucellus tissue). This can be by means of, but is not limited to, placing the WUS gene under the control of a tissue-specific promoter (e.g., a nucellus-specific promoter), an inducible promoter, or a promoter that is both inducible and tissue-specific. Inducing expression of the WUS gene, e.g. in the nucellus, produces apomixis leading to an apomictic plant. This plant may then be used to establish a true-breeding plant line. Additionally, the vector utilized to transfer WUS into the plant cell can include any other desired heterologous gene in addition to WUS, including but not limited to, a marker gene or a gene to confer any desirable trait upon the plant, e.g., a gene resulting in larger plants, greater yield, stalk and/or root strength, cycle time, maturity zone, stress resistance(s), disease resistance(s), insect control and/or resistance(s), quality seed traits, added-value traits, etc. This would lead to the development of an apomictic line with the desired trait(s).
In a variation of the scheme, plant expression cassettes, including but not limited to monocot or dicot expression cassettes, directing WUS expression to the inner integument or nucellus can be constructed. An expression cassette directing expression of the WUS DNA sequences to the nucellus can be made using the barley Nuc1 promoter (Doan et al. (1996) Plant Mol. Biol. 31(4):877-886). Such an expression construct can be used for plant transformation. Other genes which confer desirable traits can also be included in the cassette, or provided on separate cassettes. For example, embryos can be co-bombarded with the selectable marker PAT fused to the GFP gene along with the nucellus specific WUS expression cassette.
It is anticipated that transgenic plants carrying the expression cassette will then be capable of producing de novo embryos from WUS expressing nucellar cells. In the case of maize, this is complemented by pollinating the ears to promote normal central cell fertilization and endosperm development. In another variation of this scheme, Nuc1:WUS transformations could be done using a FIE (fertility-independent endosperm)-null genetic background which would promote both de novo embryo development and endosperm development without fertilization (see Ohad et al. (1999) Plant Cell 11(3):407-415; and PCT publication WO 01/16325). Upon microscopic examination of the developing embryos it will be apparent that apomixis has occurred by the presence of embryos budding off the nucellus. In yet another variation of this scheme the WUS DNA sequences could be delivered as described above into a homozygous zygotic-embryo-lethal genotype, in this scenario, only the adventive embryos produced from somatic nucellus tissue would develop in the seed. Similarly, using Nuc1:WUS, to produce de novo embryos from the nucellus, in conjunction with a FIE suppression cassette would result in both embryo and endosperm development in the absence of fertilization.
WUS expression could be controlled by a simple tissue-specific promoter, in which case WUS would be expressed throughout the given tissue—for example throughout the nucellus in the case of the Nuc1 promoter. Or, WUS expression could be controlled in a way that confers a spatial gradient on top of the tissue specific localization, resulting in isolated pockets of expression. For example, using standard techniques as described above, plant tissue is transformed with the following: Nuc1:FRT1—spacer—:nos term:FRT1::WUS::pinII+In2::FLP::pinII
When FLP expression is induced by the addition of safener during late ovule development, it results in sporadic, cell-autonomous excision of the FRT1-flanked spacer, thus activating expression of WUS in these scattered single cells, but only for the single cells located in the nucellus, as controlled by the Nuc1 promoter.
Of course, there are variations on this theme depending on which promoters are used. For example, Nuc1 -driven FLP expression would activate WUS expression across a larger percentage of cells in the nucellus, and here you could use an inducible promoter (or even the nuc1 promoter again).
Another interesting variation on this theme that would confer a spatial gradient and a temporal gradient (a pulse) in a tissue-specific manner, by splitting the WUS coding region in two parts so the encoded products are made functional through intein splicing. Place the first half of the WUS gene in the nuc1/frt1-activated cassette and the second half of the WUS gene behind the In2 promoter. Upon adding a pulse of safener, for example through ear infusion, FLP activity would result in excision of the frt1-flanked spacer in scattered, single cells through the ear. However, only in the nucellus, where the first half of the WUS gene is being expressed, would intein splicing result in a functional WUS protein. Because the safener was added in a pulsed fashion, the second half of the WUS protein would only be encoded on a transient basis, resulting in pulsed expression of WUS in single cells within the nucellus.
Example 17 WUS expression for Positive SelectionIt is expected that transformants can be recovered using WUS expression to provide a positive selection means under reduced auxin levels or in the absence of auxins in the medium, and in the absence of herbicide or antibiotic selection.
To determine if WUS can be used in a positive selection scheme, transformation experiments, using any standard method including particle gun or Agrobacterium, can be performed. Transformants are selected on medium with normal auxin levels, or on medium with reduced or no auxin, or visually (using GFP) on medium without bialaphos. Transformation frequencies are based on numbers of embryos with one or more multicellular GFP positive cell clusters. For example, one can test this concept using two treatment variables. The first is that immature embryos are bombarded with a control plasmid (UBI:PAT˜GFP) or with UBI:PAT˜GFP+In2:WUS. The second variable is that the bombarded embryos are divided onto either normal bialaphos-containing selection medium (with normal auxin levels of 2 mg/L 2,4-D), or medium with no bialaphos and reduced 2,4-D levels (0.5 mg/L). It is expected from previous studies of positive selection that on bialaphos selection the WUS treatment will result in higher transformation frequency than the control. It is also anticipated that the low auxin medium (0.5 mg/L 2,4-D) will result in reduced growth rates. Consistent with this, it is expected that for the control plasmid treatment (UBI:PAT˜GFP), recovery of GFP-expressing (fluorescent) colonies will be reduced relative to highly effective bialaphos selection treatment. In contrast, it is expected that WUS expression, through its stimulation of embryogenesis, may compensate for the low auxin environment, providing a growth advantage to the transgenic colonies, and maintaining the efficiency of transformant recovery at approximately the same range as the WUS/bialaphos-selected treatment.
On medium completely devoid of auxin, it is expected that colonies will only be observed in the WUS treatment. In this experiment, immature embryos are transformed with either the control plasmid (UBI:PAT˜GFP) or with UBI:PAT˜GFP+In2:WUS, and then plated either onto 3.0 mg/L bialaphos, 2.0 mg/L 2,4-D medium or onto no-bialaphos, no 2,4-D medium (in this latter treatment, wild-type maize callus will not exhibit embryonic growth). Again, it is expected that the WUS polynucleotide express will increase transformation significantly over the control plasmid value on normal auxin-containing, bialaphos selection medium. Also, it is expected that no transformants will be recovered with the control plasmid on medium devoid of exogenous auxin.
Even on auxin-containing medium, the WUS polynucleotide in combination with GFP+ expression can be used to recover transformants without chemical selection. For example, under these conditions it is expected that the recovery of transformants will be relatively efficient, but may require more diligence than the low- or no-auxin treatments above to separate the GFP-expressing colonies from the growing callus population.
Example 18 Splicing Variants of Genomic WUS Sequences The polynucleotides generated in Example 14 are further evaluated and alternative splice sites are identified in the genomic sequences. Two introns are identified in the sequences, which can generate three alternately spliced products, a spliced sequence in which the first intron is spliced and the second intron remains, a spliced sequence in which the first and second introns are completely spliced, and a spliced sequence in which the first intron is spliced and the second intron is spliced in an alternate way. Of these products, the spliced sequence in which both introns are completely spliced is most likely to be the sequence which encodes the major protein product (Table 9). The polypeptides encoded by the alternatively spliced polynucleotide sequences are shown below, in Tables 7-9 in alignments generated using the CLUSTALW program under default parameters (VNTI software, Informax, Gaithersburg, Md.). Consensus sequences are also provided in the alignment. The consensus sequence generated by alignment of the WUS2 sequences with the 1st intron spliced is presented as SEQ ID NO: 88. The consensus sequence generated by alignment of the WUS2 sequences with the 1st intron and 2nd intron spliced is presented as SEQ ID NO: 89. The consensus sequence generated by alignment of the WUS2 sequences with the 1st intron and alternate splicing of the 2nd intron is presented as SEQ ID NO: 90. Conserved amino acid motifs are shown in bold, the 25 amino acid motif is in italicized bold.
New full-length Wuschel sequences from Zea mays genomic sequences, denoted as WUS5 and WUS6, have been identified in the GSS database of NCBI GenBank, assembled, and analyzed using the fgenesh exon/intron prediction algorithm (Salamov & Solovyev (2000) Genome Res. 10:516), in a commercially available software implementation (Softberry, Mount Kisco, N.Y.). WUS5 genomic polynucleotide sequence is presented as SEQ ID NO: 76. Analysis using fgenesh predicts the presence of one intron, the spliced product is presented as SEQ ID NO: 77. The predicted WUS5 polypeptide is shown as SEQ ID NO: 78, as encoded by the polynucleotide of SEQ ID NO: 77. The WUS6 genomic polynucleotide sequence is presented as SEQ ID NO: 79. Analysis using fgenesh predicts the presence of two introns, the spliced product is presented as SEQ ID NO: 80. The predicted WUS6 polypeptide is shown as SEQ ID NO: 81, as encoded by SEQ ID NO: 80.
Example 20 Homeodomain and Conserved Domain Structure of Wuschel PolypeptidesWuschel polypeptides typically comprise three conserved amino acid motifs, the N-terminal homeodomain region, and two conserved Wuschel C-terminal domains, the (E/R)TLPFLP and A(A/S)LEL(S/T)L domains. The A(A/S)LEL(S/T)L shows significant similarity to C-terminal motifs identified in zn-finger proteins and ERFs, which have been implicated to act as a repressor domain via protein-protein interaction (Ohta et al. (2001) Plant Cell 13:1959-1968; and Dinkins et al. (2003) Plant Science 165:33-41; herein incorporated by reference).
The homeodomain region of the Wuschel polypeptides is involved in making contact with target DNA. The homeodomain region consists of a helix1-loop-helix2-tum-helix3 structure where a fixed number of amino acids are present in the loop and turn regions in animal homeodomain polypeptides. Plant homeodomain polypeptides have extra amino acids in the loop, turn or both loop and turn regions of the homeodomain. Plant homeodomain polypeptides can be further classified into subgroups based on the number of extra amino acids present in the loop and turn regions. (Kamiya et al. (2003) Plant J 35:429-441). The helix3 generally makes the contact with target DNA sequences. Differences in the number of amino acids in the loop and turn regions may affect target site specificities, therefore different subgroups would interact with unique DNA target sites. The Wuschel subgroup has one to two extra amino acids in the loop region and four extra amino acids in the turn region (“2+4”). WUS2 is the only one of the five maize Wuschel polypeptides that has two extra amino acids in the loop region (“2+4”). The other Wuschel polypeptides have one extra amino acid in the loop and four extra amino acids in the turn relative to animal homeodomain polypeptide sequences (“1+4”). Not to be limited to any particular theory, these subgroups are expected to have different functions controlling the meristems in the plant. It is expected that the “2+4” subgroup would influence embryo development and control shoot and floral meristem function whereas the “1+4” would impact both root and floral meristems.
A search of public domain sequences which give significant hits to the WUS sequences of the invention, and which comprise a homeodomain region yielded 64 sequences. Of these 64 sequences, only seven sequences, representing six plant species, have the 2+4 homeodomain. The 2+4 homeodomain structure appears to be unique in the homeodomain transcription factor family. Of the seven 2+4 sequences, two are from Arabidopsis (may represent landrace variants), and one each from Petunia, Antirrhinum, Lycopersicon, Zea, and Oryza. Also detected were 6 sequences with a homeodomain-ZIP structure, wherein the homeodomain has a 0+4 structure. The remaining sequences fall into the 1+4 homeodomain category, and are represented by sequences from wheat, sorghum, soybean, and Brassica. The top 25 hits have a (E/R)TLPFLP-like motif, and represent both 2+4 and 1+4 homeodomains. All seven sequences having the 2+4 homeodomain also comprise the A(A/S)LEL(S/T)L motif. WUS3 (SEQ ID NO: 4) and rice QHB (Kamiya et al. (2003) Plant J 35:429-441) both have a motif similar to A(A/S)LEL(S/T)L, therefore a total of nine sequences have all three identified motifs.
Highlighted in bold are the protein sequence motifs that are conserved in WUS homologues. The second tyrosine (Y—shown in bold and italics) distinguishes WUS2 (p0016.ctsas50r) as being in the “2+4” category of homeodomain factors just like the Arabidopsis protein, whereas all of the other WUS sequences lack this tyrosine and thus belong to the “1+4” category (e.g., p0083.cldev71r represented in SEQ ID NO: 33); you will note that SEQ ID NO: 31 also lacks the second and third motifs due to the altered splicing event. (see Kamiya et al. (2003) Plant J 35:429-441 for homeodomain categorization).
Based on sequences for the ZmWUS2 sequences from several proprietary maize inbred lines and public lines (line B73, SEQ ID NOS: 34, 35, 37, and 39; line Mo17, SEQ ID NOS: 41, 42, 44, and 46; line 07D, SEQ ID NOS: 48, 49, 51, and 53; line KW3, SEQ ID NOS: 55, 56, 58, and 60; line 3DT, SEQ ID NOS: 62, 63, 65, and 67; and line 09B, SEQ ID NOS: 69, 70, 72, and 74), the public lines (B73 and Mo17) contain an extra 75 nucleotides that encode an extra 25 amino acids relative to the sequences of the proprietary lines (07D, KW3, 3DT, and 09B). This 25 amino acid difference resides in between two conserved Wuschel C-terminal domains, the (E/R)TLPFLP and A(A/S)LEL(S/T)L domains. The A(A/S)LEL(S/T)L shows significant similarity to C-terminal motifs identified in zn-finger proteins and ERFs, which have been implicated to act as a repressor domain via protein-protein interaction (Ohta et al. (2001) Plant Cell 13:1959-1968; and Dinkins et al. (2003) Plant Science 165:33-41; herein incorporated by reference). The presence or absence of these 25 amino acids may change the orientation of these two domains in the mature polypeptide and thus may affect the interactive nature of these Wuschel polypeptides with other host factors. In other words, this sequence may function as a spacer that affects the relative orientation of these two motifs in the context of the whole protein structure. It is of note that the two public lines come from very different pedigrees, therefore the likelihood of inheriting this polymorphism from a common source is low. The inbred lines also represent different pedigrees, and different heterotic groups. The consistency of this difference is suggestive, possibly indicating that this polymorphism was somehow selected during the breeding of elite inbred lines. A Wuschel polynucleotide encoding a polypeptide from a proprietary maize inbred line noted above was used in transformation experiments, the results of which are shown in Example 8B.
Example 22 Comparison of Wuschel Polypeptide Sequences The GCG (Accelrys, San Diego, Calif.) software implementation of the GAP algorithm (Needleman & Wunsch) was used to compare the polypeptides encoded by the full-length genomic or cDNA polynucleotides from maize to known Wuschel polypeptides from the model plant, Arabidopsis thaliana. Two Arabidopsis polypeptide sequences were used, represented by NCBI GI 4090200 (SEQ ID NO: 25); and NCBI 20197404 (which replaced GI 3785979 on 4/18/02). All comparisons were done using default parameters, namely the BLOSUM62 scoring matrix, Gap Creation Penalty =8, and Gap Extension Penalty=2. All percent sequence identities less than 70% have been rounded up to the nearest whole integer, all others are presented to the nearest tenth of a percent. Table 12 summarizes the results of these comparisons.
The GCG (Accelrys, San Diego, Calif.) software implementation of the GAP algorithm (Needleman & Wunsch) was further used to compare the polypeptides encoded by the full-length genomic, cDNA, or EST polynucleotides of the present invention. All comparisons were done using default parameters, namely the BLOSUM62 scoring matrix, Gap Creation Penalty=8, and Gap Extension Penalty=2. All percent sequence identities less than 70% have been rounded up to the nearest whole integer, all others are presented to the nearest tenth of a percent. Table 13 summarizes the results of these comparisons.
The GCG (Accelrys, San Diego, Calif.) software implementation of the GAP algorithm (Needleman & Wunsch) was further used to compare the full-length genomic, cDNA, or EST polynucleotides of the present invention. All comparisons were done using default parameters, namely Gap Creation Penalty =50, and Gap Extension Penalty =3. All percent sequence identities less than 70% have been rounded up to the nearest whole integer, all others are presented to the nearest tenth of a percent. Table 14 summarizes the results of these comparisons.
The above examples are provided to illustrate the invention but not to limit its scope. Other variants of the invention will be readily apparent to one of ordinary skill in the art and are encompassed by the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated in their entirety by reference.
Claims
1. An isolated polynucleotide comprising a nucleotide sequence encoding a WUSCHEL polypeptide containing a 1+4 homeodomain, wherein the polypeptide has at least 80% sequence identity over its entire length to SEQ ID NO: 14 based on the CLUSTAL alignment method using default parameters of KTUPLE 1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5, and wherein the polypeptide is capable of stimulating in vitro growth of plant tissue.
2. An isolated polynucleotide fully complementary to the polynucleotide of claim 1.
3. The isolated polynucleotide of claim 1, wherein the WUSCHEL polypeptide has at least 85% sequence identity over its entire length to SEQ ID NO: 14.
4. The isolated polynucleotide of claim 1, wherein the WUSCHEL polypeptide has at least 90% sequence identity over its entire length to SEQ ID NO: 14.
5. The isolated polynucleotide of claim 1, wherein the WUSCHEL polypeptide has at least 95% sequence identity over its entire length to SEQ ID NO: 14.
6. The isolated polynucleotide of claim 1, wherein the nucleotide sequence comprises SEQ ID NO: 13.
7. A chimeric gene comprising the polynucleotide of claim 1, operably linked to a regulatory sequence functional in a host cell.
8. A transgenic plant comprising the polynucleotide of claim 1.
9. A seed from the transgenic plant of claim 8, wherein the seed comprises the polynucleotide.
10. The seed of claim 9, wherein the seed is from a plant selected from the group consisting of corn, soybean, wheat, rice, alfalfa, sunflower, canola, or cotton.
11. A method for inducing meristem proliferation in a plant cell comprising:
- (a) transforming a plant cell with a polynucleotide of claim 1 operably linked to a regulatory sequence operable in the plant cell; and,
- (b) expressing the polynucleotide for a time sufficient to induce meristem proliferation.
12. The method of claim 11 wherein the polynucleotide is integrated into the plant cell genome to produce a transformed plant cell comprising the polynucleotide.
13. The method of claim 12 further comprising growing the transformed plant cell under plant growing conditions to produce a regenerated plant.
14. A plant produced by the method of claim 13.
15. A method for positive selection of a transformed cell, comprising:
- (a) transforming a plant cell with a polynucleotide of claim 1 operably linked to a regulatory sequence operable in the plant cell; and,
- (b) expressing the polynucleotide for a time sufficient to induce organogenesis and provide a positive selection means.
16. The method of claim 15 wherein the polynucleotide is integrated into the plant cell genome to produce a transformed plant cell comprising the polynucleotide.
17. The method of claim 16 further comprising growing the transformed plant cell under plant growing conditions to produce a regenerated plant.
18. A plant produced by the method of claim 17.
19. A method for transforming a plant cell comprising introducing the polynucleotide of claim 1 into the cell.
20. A transformed plant cell produced by the method of claim 19, wherein the cell comprises the polynucleotide.
21. A transformed plant regenerated from the plant cell of claim 20, wherein the plant comprises the polynucleotide.
22. A method to increase transformation frequency comprising:
- (a) introducing into a plant cell the isolated polynucleotide of claim 1 operably linked to a regulatory sequence operable in the plant cell; and,
- (b) expressing the polynucleotide in the plant cell;
- wherein plant cells expressing the polynucleotide have an increased transformation frequency as compared to control plant cells that do not have or express the polynucleotide.
23. A method to stimulate plant cell growth, wherein the method comprises:
- (a) introducing into a plant cell the isolated polynucleotide of claim 1 operably linked to a regulatory sequence operable in the plant cell; and,
- (b) expressing the polynucleotide in the plant cell;, wherein plant cells expressing the polynucleotide show stimulated plant cell growth as compared to control plant cells that do not have or express the polynucleotide.
Type: Application
Filed: May 29, 2007
Publication Date: Nov 22, 2007
Applicants: PIONEER HI-BRED INTERNATIONAL, INC. (Johnston, IA), E.I. DU PONT DE NEMOURS AND COMPANY (Wilmington, DE)
Inventors: Keith Lowe (Johnston, IA), Rebecca Cahoon (Webster Groves, MO), Christopher Scelonge (Ankeny, IA), Yumin Tao (Fremont, CA), William Gordon-Kamm (Urbandale, IA), Wesley Bruce (Raleigh, NC), Lisa Newman (Urbandale, IA)
Application Number: 11/754,389
International Classification: A01H 5/00 (20060101); C07H 21/00 (20060101); C07H 21/04 (20060101); C12N 15/82 (20060101); C12N 5/02 (20060101);
