INSECT RESISTANT INIR6 TRANSGENIC MAIZE PLANTS LACKING A SELECTABLE MARKER AND JUNCTION
Transgenic INIR6 maize plants comprising modifications of the DP-4114 maize locus which provide for facile excision of the modified DP-4114 transgenic locus or portions thereof, methods of making such plants, and use of such plants to facilitate breeding are disclosed.
The sequence listing contained in the file named “10086WO1_ST25.txt”, which was created on Aug. 2, 2021 and electronically filed herewith, is incorporated herein by reference in its entirety.
BACKGROUNDTransgenes which are placed into different positions in the plant genome through non-site specific integration can exhibit different levels of expression (Weising et al., 1988, Ann. Rev. Genet. 22:421-477). Such transgene insertion sites can also contain various undesirable rearrangements of the foreign DNA elements that include deletions and/or duplications. Furthermore, many transgene insertion sites can also comprise selectable or scoreable marker genes which in some instances are no longer required once a transgenic plant event containing the linked transgenes which confer desirable traits are selected.
Commercial transgenic plants typically comprise one or more independent insertions of transgenes at specific locations in the host plant genome that have been selected for features that include expression of the transgene(s) of interest and the transgene-conferred trait(s), absence or minimization of rearrangements, and normal Mendelian transmission of the trait(s) to progeny. An examples of a selected transgenic corn event which confers lepidopteran and coleopteran insect pest tolerance is the DP-4114 transgenic maize event disclosed in U.S. Pat. No. 8,575,434. DP-4114 transgenic maize plants express a Cry1F protein which can confer resistance to European corn borer (ECB, Ostrinia nubilalis) infestations as well as cry34Ab1 and cry35Ab1 proteins which can confer resistance to corn rootworm (CRW; Diabrotica sp. Including Diabrotica virgifera virgifera) infestations. DP-4114 transgenic maize plants also express a phosphinotricin acetyl transferase (PAT) protein which confers tolerance to the herbicide glufosinate.
Methods for removing selectable marker genes and/or duplicated transgenes in transgene insertion sites in plant genomes involving use of site-specific recombinase systems (e.g., cre-lox) as well as for insertion of new genes into transgene insertion sites have been disclosed (Srivastava and Ow; Methods Mol Biol, 2015, 1287:95-103; Dale and Ow, 1991, Proc. Natl Acad. Sci. USA 88, 10558-10562; Srivastava and Thomson, Plant Biotechnol J, 2016; 14(2):471-82). Such methods typically require incorporation of the recombination site sequences recognized by the recombinase at particular locations within the transgene.
SUMMARYTransgenic maize plant cells comprising an INIR6 transgenic locus comprising an originator guide RNA recognition site (OgRRS) in a first DNA junction polynucleotide of a DP-4114 transgenic locus and a cognate guide RNA recognition site (CgRRS) in a second DNA junction polynucleotide of the DP-4114 transgenic locus are provided. Transgenic maize plant cells comprising an INIR6 transgenic locus comprising an insertion and/or substitution in a DNA junction polynucleotide of a DP-4114 transgenic locus of DNA comprising a cognate guide RNA recognition site (CgRRS) are provided. In certain embodiments, the DP-4114 transgenic locus is set forth in SEQ ID NO:1, is present in seed deposited at the ATCC under accession No. PTA-11506 is present in progeny thereof, is present in allelic variants thereof, or is present in other variants thereof. INIR6 transgenic maize plant cells, transgenic maize plant seeds, and transgenic maize plants all comprising a transgenic locus set forth in SEQ ID NO: 2, 3, 20, 22, 23, 25, 26, 29, 30, 31, or an allelic variant thereof are provided. Transgenic maize plant parts including seeds and transgenic maize plants comprising the maize plant cells are also provided.
Methods for obtaining a bulked population of inbred seed comprising selfing the aforementioned transgenic maize plants and harvesting seed comprising the INIR6 transgenic locus from the selfed maize plant are also provided.
Methods of obtaining hybrid maize seed comprising crossing the aforementioned transgenic maize plants to a second maize plant which is genetically distinct from the first maize plant and harvesting seed comprising the INIR6 transgenic locus from the cross are provided. Methods for obtaining a bulked population of seed comprising selfing a transgenic maize plant of comprising SEQ ID NO: 2, 3, 20, 22, 23, 25, 26, 29, 30, 31, or an allelic variant thereof and harvesting transgenic seed comprising the transgenic locus set forth in SEQ ID NO: 2, 3, 20, 22, 23, 25, 26, 29, 30, 31, or an allelic variant thereof are provided.
A DNA molecule comprising SEQ ID NO: 2, 3, 8, 9, 10, 19, 20, 22, 23, 25, 26, 27, 29, 30, 31, 32-35, or an allelic variant thereof is provided. Processed transgenic maize plant products and biological samples comprising the DNA molecules are provided. Nucleic acid molecules adapted for detection of genomic DNA comprising the DNA molecules, wherein said nucleic acid molecule optionally comprises a detectable label are provided. Methods of detecting a maize plant cell comprising an INIR6 transgenic locus comprising the step of detecting a DNA molecule comprising SEQ ID NO: 2, 3, 8, 9, 10, 19, 20, 22, 23, 25, 26, 27, 29, 30, 31, 32-35, or an allelic variant thereof are provided.
Methods of excising the INIR6 transgenic locus from the genome of the aforementioned maize plant cells comprising the steps of: (a) contacting the INIR6 transgenic locus comprising the OgRRS and the CgRRS with: (i) an RNA dependent DNA endonuclease (RdDe); and (ii) a guide RNA (gRNA) capable of hybridizing to the guide RNA hybridization site of the OgRRS and the CgRRS; wherein the RdDe recognizes a OgRRS/gRNA and a CgRRS/gRNA hybridization complex; and, (b) selecting a transgenic plant cell, transgenic plant part, or transgenic plant wherein the INIR6 transgenic locus flanked by the OgRRS and the CgRRS has been excised.
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Unless otherwise stated, nucleic acid sequences in the text of this specification are given, when read from left to right, in the 5′ to 3′ direction. Nucleic acid sequences may be provided as DNA or as RNA, as specified; disclosure of one necessarily defines the other, as well as necessarily defines the exact complements, as is known to one of ordinary skill in the art.
Where a term is provided in the singular, the inventors also contemplate embodiments described by the plural of that term.
The term “about” as used herein means a value or range of values which would be understood as an equivalent of a stated value and can be greater or lesser than the value or range of values stated by 10 percent. Each value or range of values preceded by the term “about” is also intended to encompass the embodiment of the stated absolute value or range of values.
The phrase “allelic variant” as used herein refers to a polynucleotide or polypeptide sequence variant that occurs in a different strain, variety, or isolate of a given organism.
The term “and/or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. Thus, the term and/or” as used in a phrase such as “A and/or B” herein is intended to include “A and B,” “A or B,” “A” (alone), and “B” (alone). Likewise, the term “and/or” as used in a phrase such as “A, B, and/or C” is intended to encompass each of the following embodiments: A, B, and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B (alone); and C (alone).
As used herein, the phrase “approved transgenic locus” is a genetically modified plant event which has been authorized, approved, and/or de-regulated for any one of field testing, cultivation, human consumption, animal consumption, and/or import by a governmental body. Illustrative and non-limiting examples of governmental bodies which provide such approvals include the Ministry of Agriculture of Argentina, Food Standards Australia New Zealand, National Biosafety Technical Committee (CTNBio) of Brazil, Canadian Food Inspection Agency, China Ministry of Agriculture Biosafety Network, European Food Safety Authority, US Department of Agriculture, US Department of Environmental Protection, and US Food and Drug Administration.
The term “backcross”, as used herein, refers to crossing an F1 plant or plants with one of the original parents. A backcross is used to maintain or establish the identity of one parent (species) and to incorporate a particular trait from a second parent (species). The term “backcross generation”, as used herein, refers to the offspring of a backcross.
As used herein, the phrase “biological sample” refers to either intact or non-intact (e.g., milled seed or plant tissue, chopped plant tissue, lyophilized tissue) plant tissue. It may also be an extract comprising intact or non-intact seed or plant tissue. The biological sample can comprise flour, meal, syrup, oil, starch, and cereals manufactured in whole or in part to contain crop plant by-products. In certain embodiments, the biological sample is “non-regenerable” (i.e., incapable of being regenerated into a plant or plant part). In certain embodiments, the biological sample refers to a homogenate, an extract, or any fraction thereof containing genomic DNA of the organism from which the biological sample was obtained, wherein the biological sample does not comprise living cells.
As used herein, the terms “correspond,” “corresponding,” and the like, when used in the context of an nucleotide position, mutation, and/or substitution in any given polynucleotide (e.g., an allelic variant of SEQ ID NO: 1) with respect to the reference polynucleotide sequence (e.g., SEQ ID NO: 1) all refer to the position of the polynucleotide residue in the given sequence that has identity to the residue in the reference nucleotide sequence when the given polynucleotide is aligned to the reference polynucleotide sequence using a pairwise alignment algorithm (e.g., CLUSTAL O 1.2.4 with default parameters).
As used herein, the terms “Cpf1” and “Cas12a” are used interchangeably to refer to the same RNA dependent DNA endonuclease (RdDe). A Cas12a protein provided herein includes the protein of SEQ ID NO: 21.
The term “crossing” as used herein refers to the fertilization of female plants (or gametes) by male plants (or gametes). The term “gamete” refers to the haploid reproductive cell (egg or pollen) produced in plants by meiosis from a gametophyte and involved in sexual reproduction, during which two gametes of opposite sex fuse to form a diploid zygote. The term generally includes reference to a pollen (including the sperm cell) and an ovule (including the ovum). When referring to crossing in the context of achieving the introgression of a genomic region or segment, the skilled person will understand that in order to achieve the introgression of only a part of a chromosome of one plant into the chromosome of another plant, random portions of the genomes of both parental lines recombine during the cross due to the occurrence of crossing-over events in the production of the gametes in the parent lines. Therefore, the genomes of both parents must be combined in a single cell by a cross, where after the production of gametes from the cell and their fusion in fertilization will result in an introgression event.
As used herein, the phrases “DNA junction polynucleotide” and “junction polynucleotide” refers to a polynucleotide of about 18 to about 500 base pairs in length comprised of both endogenous chromosomal DNA of the plant genome and heterologous transgenic DNA which is inserted in the plant genome. A junction polynucleotide can thus comprise about 8, 10, 20, 50, 100, 200, 250, 500, or 1000 base pairs of endogenous chromosomal DNA of the plant genome and about 8, 10, 20, 50, 100, 200, 250, 500, or 1000 base pairs of heterologous transgenic DNA which span the one end of the transgene insertion site in the plant chromosomal DNA. Transgene insertion sites in chromosomes will typically contain both a 5′ junction polynucleotide and a 3′ junction polynucleotide. In embodiments set forth herein in SEQ ID NO: 1, the 5′ junction polynucleotide is located at the 5′ end of the sequence and the 3′ junction polynucleotide is located at the 3′ end of the sequence. In a non-limiting and illustrative example, a 5′ junction polynucleotide of a transgenic locus is telomere proximal in a chromosome arm and the 3′ junction polynucleotide of the transgenic locus is centromere proximal in the same chromosome arm. In another non-limiting and illustrative example, a 5′ junction polynucleotide of a transgenic locus is centromere proximal in a chromosome arm and the 3′ junction polynucleotide of the transgenic locus is telomere proximal in the same chromosome arm. The junction polynucleotide which is telomere proximal and the junction polynucleotide which is centromere proximal can be determined by comparing non-transgenic genomic sequence of a sequenced non-transgenic plant genome to the non-transgenic DNA in the junction polynucleotides.
The term “donor,” as used herein in the context of a plant, refers to the plant or plant line from which the trait, transgenic event, or genomic segment originates, wherein the donor can have the trait, introgression, or genomic segment in either a heterozygous or homozygous state.
As used herein, the term “DP-4114” is used to refer to any of a transgenic maize locus, transgenic maize plants and parts thereof including seed set forth in U.S. Pat. No. 8,575,434, which is incorporated herein by reference in its entirety. Representative DP-4114 transgenic maize seed have been deposited with American Type Culture Collection (ATCC, Manassas, Va. 20110-2209 USA) under Accession No. PTA-11506. DP-4114 transgenic loci include loci having the sequence of SEQ ID NO:1, the sequence of the DP-4114 locus in the deposited seed of Accession No. PTA-11506 and any progeny thereof, as well as allelic variants and other variants of SEQ ID NO:1
As used herein, the terms “excise” and “delete,” when used in the context of a DNA molecule, are used interchangeably to refer to the removal of a given DNA segment or element (e.g., transgene element or transgenic locus or portion thereof) of the DNA molecule.
As used herein, the phrase “elite crop plant” refers to a plant which has undergone breeding to provide one or more trait improvements. Elite crop plant lines include plants which are an essentially homozygous, e.g., inbred or doubled haploid. Elite crop plants can include inbred lines used as is or used as pollen donors or pollen recipients in hybrid seed production (e.g., used to produce F1 plants). Elite crop plants can include inbred lines which are selfed to produce non-hybrid cultivars or varieties or to produce (e.g., bulk up) pollen donor or recipient lines for hybrid seed production. Elite crop plants can include hybrid F1 progeny of a cross between two distinct elite inbred or doubled haploid plant lines.
As used herein, an “event,” “a transgenic event,” “a transgenic locus” and related phrases refer to an insertion of one or more transgenes at a unique site in the genome of a plant as well as to DNA fragments, plant cells, plants, and plant parts (e.g., seeds) comprising genomic DNA containing the transgene insertion. Such events typically comprise both a 5′ and a 3′ DNA junction polynucleotide and confer one or more useful traits including herbicide tolerance, insect resistance, male sterility, and the like.
As used herein, the phrases “endogenous sequence,” “endogenous gene,” “endogenous DNA,” “endogenous polynucleotide,” and the like refer to the native form of a polynucleotide, gene or polypeptide in its natural location in the organism or in the genome of an organism.
The terms “exogenous” and “heterologous” as are used synonymously herein to refer to any polynucleotide (e.g., DNA molecule) that has been inserted into a new location in the genome of a plant. Non-limiting examples of an exogenous or heterologous DNA molecule include a synthetic DNA molecule, a non-naturally occurring DNA molecule, a DNA molecule found in another species, a DNA molecule found in a different location in the same species, and/or a DNA molecule found in the same strain or isolate of a species, where the DNA molecule has been inserted into a new location in the genome of a plant.
As used herein, the term “F1” refers to any offspring of a cross between two genetically unlike individuals.
The term “gene,” as used herein, refers to a hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and that contains the genetic instruction for a particular characteristics or trait in an organism. The term “gene” thus includes a nucleic acid (for example, DNA or RNA) sequence that comprises coding sequences necessary for the production of an RNA, or a polypeptide or its precursor. A functional polypeptide can be encoded by a full length coding sequence or by any portion of the coding sequence as long as the desired activity or functional properties (e.g., enzymatic activity, pesticidal activity, ligand binding, and/or signal transduction) of the RNA or polypeptide are retained.
The term “identifying,” as used herein with respect to a plant, refers to a process of establishing the identity or distinguishing character of a plant, including exhibiting a certain trait, containing one or more transgenes, and/or containing one or more molecular markers.
As used herein, the term “INIR6” is used to refer either individually collectively to items that include any or all of the DP-4114 transgenic maize loci which have been modified as disclosed herein, modified DP-4114 transgenic maize plants and parts thereof including seed, and DNA obtained therefrom.
The term “isolated” as used herein means having been removed from its natural environment.
As used herein, the terms “include,” “includes,” and “including” are to be construed as at least having the features to which they refer while not excluding any additional unspecified features.
As used herein, the phrase “introduced transgene” is a transgene not present in the original transgenic locus in the genome of an initial transgenic event or in the genome of a progeny line obtained from the initial transgenic event. Examples of introduced transgenes include exogenous transgenes which are inserted in a resident original transgenic locus.
As used herein, the terms “introgression”, “introgressed” and “introgressing” refer to both a natural and artificial process, and the resulting plants, whereby traits, genes or DNA sequences of one species, variety or cultivar are moved into the genome of another species, variety or cultivar, by crossing those species. The process may optionally be completed by backcrossing to the recurrent parent. Examples of introgression include entry or introduction of a gene, a transgene, a regulatory element, a marker, a trait, a trait locus, or a chromosomal segment from the genome of one plant into the genome of another plant.
The phrase “marker-assisted selection”, as used herein, refers to the diagnostic process of identifying, optionally followed by selecting a plant from a group of plants using the presence of a molecular marker as the diagnostic characteristic or selection criterion. The process usually involves detecting the presence of a certain nucleic acid sequence or polymorphism in the genome of a plant.
The phrase “molecular marker”, as used herein, refers to an indicator that is used in methods for visualizing differences in characteristics of nucleic acid sequences. Examples of such indicators are restriction fragment length polymorphism (RFLP) markers, amplified fragment length polymorphism (AFLP) markers, single nucleotide polymorphisms (SNPs), microsatellite markers (e.g. SSRs), sequence-characterized amplified region (SCAR) markers, Next Generation Sequencing (NGS) of a molecular marker, cleaved amplified polymorphic sequence (CAPS) markers or isozyme markers or combinations of the markers described herein which defines a specific genetic and chromosomal location.
As used herein the terms “native” or “natural” define a condition found in nature. A “native DNA sequence” is a DNA sequence present in nature that was produced by natural means or traditional breeding techniques but not generated by genetic engineering (e.g., using molecular biology/transformation techniques).
The term “offspring”, as used herein, refers to any progeny generation resulting from crossing, selfing, or other propagation technique.
The phrase “operably linked” refers to a juxtaposition wherein the components so described are in a relationship permitting them to function in their intended manner. For instance, a promoter is operably linked to a coding sequence if the promoter affects its transcription or expression. When the phrase “operably linked” is used in the context of a PAM site and a guide RNA hybridization site, it refers to a PAM site which permits cleavage of at least one strand of DNA in a polynucleotide with an RNA dependent DNA endonuclease or RNA dependent DNA nickase which recognize the PAM site when a guide RNA complementary to guide RNA hybridization site sequences adjacent to the PAM site is present. A OgRRS and its CgRRS are operably linked to junction polynucleotides when they can be recognized by a gRNA and an RdDe to provide for excision of the transgenic locus or portion thereof flanked by the junction polynucleotides.
As used herein, the term “plant” includes a whole plant and any descendant, cell, tissue, or part of a plant. The term “plant parts” include any part(s) of a plant, including, for example and without limitation: seed (including mature seed and immature seed); a plant cutting; a plant cell; a plant cell culture; or a plant organ (e.g., pollen, embryos, flowers, fruits, shoots, leaves, roots, stems, and explants). A plant tissue or plant organ may be a seed, protoplast, callus, or any other group of plant cells that is organized into a structural or functional unit. A plant cell or tissue culture may be capable of regenerating a plant having the physiological and morphological characteristics of the plant from which the cell or tissue was obtained, and of regenerating a plant having substantially the same genotype as the plant. Regenerable cells in a plant cell or tissue culture may be embryos, protoplasts, meristematic cells, callus, pollen, leaves, anthers, roots, root tips, silk, flowers, kernels, ears, cobs, husks, or stalks. In contrast, some plant cells are not capable of being regenerated to produce plants and are referred to herein as “non-regenerable” plant cells.
The term “purified,” as used herein defines an isolation of a molecule or compound in a form that is substantially free of contaminants normally associated with the molecule or compound in a native or natural environment and means having been increased in purity as a result of being separated from other components of the original composition. The term “purified nucleic acid” is used herein to describe a nucleic acid sequence which has been separated from other compounds including, but not limited to polypeptides, lipids and carbohydrates.
The term “recipient”, as used herein, refers to the plant or plant line receiving the trait, transgenic event or genomic segment from a donor, and which recipient may or may not have the have trait, transgenic event or genomic segment itself either in a heterozygous or homozygous state.
As used herein the term “recurrent parent” or “recurrent plant” describes an elite line that is the recipient plant line in a cross and which will be used as the parent line for successive backcrosses to produce the final desired line.
As used herein the term “recurrent parent percentage” relates to the percentage that a backcross progeny plant is identical to the recurrent parent plant used in the backcross. The percent identity to the recurrent parent can be determined experimentally by measuring genetic markers such as SNPs and/or RFLPs or can be calculated theoretically based on a mathematical formula.
The terms “selfed,” “selfing,” and “self,” as used herein, refer to any process used to obtain progeny from the same plant or plant line as well as to plants resulting from the process. As used herein, the terms thus include any fertilization process wherein both the ovule and pollen are from the same plant or plant line and plants resulting therefrom. Typically, the terms refer to self-pollination processes and progeny plants resulting from self-pollination.
The term “selecting”, as used herein, refers to a process of picking out a certain individual plant from a group of individuals, usually based on a certain identity, trait, characteristic, and/or molecular marker of that individual.
As used herein, the phrase “originator guide RNA recognition site” or the acronym “OgRRS” refers to an endogenous DNA polynucleotide comprising a protospacer adjacent motif (PAM) site operably linked to a guide RNA hybridization site. In certain embodiments, an OgRRS can be located in an untransformed plant chromosome or in non-transgenic DNA of a DNA junction polynucleotide of both an original transgenic locus and a modified transgenic locus. In certain embodiments, an OgRRS can be located in transgenic DNA of a DNA junction polynucleotide of both an original transgenic locus and a modified transgenic locus. In certain embodiments, an OgRRS can be located in both transgenic DNA and non-transgenic DNA of a DNA junction polynucleotide of both an original transgenic locus and a modified transgenic locus (i.e., can span transgenic and non-transgenic DNA in a DNA junction polynucleotide).
As used herein the phrase “cognate guide RNA recognition site” or the acronym “CgRRS” refer to a DNA polynucleotide comprising a PAM site operably linked to a guide RNA hybridization site, where the CgRRS is absent from transgenic plant genomes comprising a first original transgenic locus that is unmodified and where the CgRRS and its corresponding OgRRS can hybridize to a single gRNA. A CgRRS can be located in transgenic DNA of a DNA junction polynucleotide of a modified transgenic locus, in transgenic DNA of a DNA junction polynucleotide of a modified transgenic locus, or in both transgenic and non-transgenic DNA of a modified transgenic locus (i.e., can span transgenic and non-transgenic DNA in a DNA junction polynucleotide).
As used herein, the phrase “a transgenic locus excision site” refers to the DNA which remains in the genome of a plant or in a DNA molecule (e.g., an isolated or purified DNA molecule) wherein a segment comprising, consisting essentially of, or consisting of a transgenic locus has been deleted. In a non-limiting and illustrative example, a transgenic locus excision site can thus comprise a contiguous segment of DNA comprising at least 10 base pairs of DNA that is telomere proximal to the deleted transgenic locus or to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal to the deleted transgenic locus or to the deleted segment of the transgenic locus.
As used herein, the phrase “transgene element” refers to a segment of DNA comprising, consisting essentially of, or consisting of a promoter, a 5′ UTR, an intron, a coding region, a 3′UTR, or a polyadenylation signal. Polyadenylation signals include transgene elements referred to as “terminators” (e.g., NOS, pinII, rbcs, Hsp17, TubA).
To the extent to which any of the preceding definitions is inconsistent with definitions provided in any patent or non-patent reference incorporated herein by reference, any patent or non-patent reference cited herein, or in any patent or non-patent reference found elsewhere, it is understood that the preceding definition will be used herein.
Genome editing molecules can permit introduction of targeted genetic change conferring desirable traits in a variety of crop plants (Zhang et al. Genome Biol. 2018; 19: 210; Schindele et al. FEBS Lett. 2018; 592(12):1954). Desirable traits introduced into crop plants such as maize and soybean include herbicide tolerance, improved food and/or feed characteristics, male-sterility, and drought stress tolerance. Nonetheless, full realization of the potential of genome editing methods for crop improvement will entail efficient incorporation of the targeted genetic changes in germplasm of different elite crop plants adapted for distinct growing conditions. Such elite crop plants will also desirably comprise useful transgenic loci which confer various traits including herbicide tolerance, pest resistance (e.g.; insect, nematode, fungal disease, and bacterial disease resistance), conditional male sterility systems for hybrid seed production, abiotic stress tolerance (e.g., drought tolerance), improved food and/or feed quality, and improved industrial use (e.g., biofuel). Provided herein are methods whereby targeted genetic changes are efficiently combined with desired subsets of transgenic loci in elite progeny plant lines (e.g., elite inbreds used for hybrid seed production or for inbred varietal production). Also provided are plant genomes containing modified transgenic loci which can be selectively excised with a single gRNA molecule. Such modified transgenic loci comprise an originator guide RNA recognition site (OgRRS) which is identified in non-transgenic DNA of a first junction polynucleotide of the transgenic locus and cognate guide RNA recognition site (CgRRS) which is introduced (e.g., by genome editing methods) into a second junction polynucleotide of the transgenic locus and which can hybridize to the same gRNA as the OgRRS, thereby permitting excision of the modified transgenic locus with a single guide RNA. An originator guide RNA recognition site (OgRRS) comprises endogenous DNA found in untransformed plants and in endogenous non-transgenic DNA of junction polynucleotides of transgenic plants containing a modified or unmodified transgenic locus. The OgRRS located in non-transgenic DNA of a first DNA junction polynucleotide is used to design a related cognate guide RNA recognition site (CgRRS) which is introduced (e.g., by genome editing methods) into the second junction polynucleotide of the transgenic locus. A CgRRS is thus present in junction polynucleotides of modified transgenic loci provided herein and is absent from endogenous DNA found in untransformed plants and absent from endogenous non-transgenic DNA found in junction sequences of transgenic plants containing an unmodified transgenic locus. Also provided are unique transgenic locus excision sites created by excision of such modified transgenic loci, DNA molecules comprising the modified transgenic loci, unique transgenic locus excision sites and/or plants comprising the same, biological samples containing the DNA, nucleic acid markers adapted for detecting the DNA molecules, and related methods of identifying the elite crop plants comprising unique transgenic locus excision sites.
Also provided herein are methods whereby targeted genetic changes are efficiently combined with desired subsets of transgenic loci in elite progeny plant lines (e.g., elite inbreds used for hybrid seed production or for inbred varietal production). Examples of such methods include those illustrated in
Also provided herein are allelic variants of any of the INIR6 transgenic loci or DNA molecules provided herein. In certain embodiments, such allelic variants of INIR6 transgenic loci include sequences having at least 85%, 90%, 95%, 98%, or 99% sequence identity across the entire length or at least 20, 40, 100, 500, 1,000, 2,000, 4,000, 6,000, 8,000, 9,000, 10,000, 12,000, 14,000, 16,000, or 16,752 nucleotides of SEQ ID NO: 2, 3, 20, 22, 23, 25, 26, 29, 30, or 31. In certain embodiments, such allelic variants of INIR6 DNA molecules include sequences having at least 85%, 90%, 95%, 98%, or 99% sequence identity across the entire length of SEQ ID NO: 2, 3, 8, 9, 10, 19, 20, 22, 23, 25, 26, 27, 29, 30, 31, or 32-35.
Also provided are unique transgenic locus excision sites created by excision of INIR6 transgenic loci or selectively excisable INIR6 transgenic loci, DNA molecules comprising the INIR6 transgenic loci or unique fragments thereof (i.e., fragments of an INIR6 locus which are not found in an DP-4114 transgenic locus). INIR6 plants comprising the same, biological samples containing the DNA, nucleic acid markers adapted for detecting the DNA molecules, and related methods of identifying maizew plants comprising unique INIR6 transgenic locus excision sites and unique fragments of a INIR6 transgenic locus. DNA molecules comprising unique fragments of an INIR6 transgenic locus are diagnostic for the presence of an INIR6 transgenic locus or fragments thereof in a maize plant, maize cell, maize seed, products obtained therefrom (e.g., seed meal or stover), and biological samples. DNA molecules comprising unique fragments of an INIR6 transgenic locus include DNA molecules comprising
Methods provided herein can be used to excise any transgenic locus where the first and second junction sequences comprising the endogenous non-transgenic genomic DNA and the heterologous transgenic DNA which are joined at the site of transgene insertion in the plant genome are known or have been determined. In certain embodiments provided herein, transgenic loci can be removed from crop plant lines to obtain crop plant lines with tailored combinations of transgenic loci and optionally targeted genetic changes. Such first and second junction sequences are readily identified in new transgenic events by inverse PCR techniques using primers which are complementary the inserted transgenic sequences. In certain embodiments, the first and second junction sequences of transgenic loci are published. An example of a transgenic locus which can be improved and used in the methods provided herein is the maize DP-4114 transgenic locus. The maize DP-4114 transgenic locus and its transgenic junction sequences are also depicted in
Sequences of the junction polynucleotides as well as the transgenic insert(s) of the DP-4114 transgenic locus which can be improved by the methods provided herein are set forth or otherwise provided in SEQ ID NO: 1, U.S. Pat. No. 8,575,434, the sequence of the DP-4114 locus in the deposited seed of ATCC accession No. PTA-11506, and elsewhere in this disclosure. In certain embodiments provided herein, the DP-4114 transgenic locus set forth in SEQ ID NO: 1 or present in the deposited seed of ATCC accession No. PTA-11506 is referred to as an “original DP-4114 transgenic locus.” Allelic or other variants of the sequence set forth SEQ ID NO: 1, the patent references set forth therein and incorporated herein by reference in their entireties, and elsewhere in this disclosure which may be present in certain variant DP-4114 transgenic plant loci (e.g., progeny of deposited seed of accession No. PTA-11506 which contain allelic variants of SEQ ID NO:1 or progeny originating from transgenic plant cells comprising the original DP4114 transgenic locus set forth in U.S. Pat. No. 8,575,434) can also be improved by identifying sequences in the variants that correspond to the SEQ ID NO: 1 by performing a pairwise alignment (e.g., using CLUSTAL O 1.2.4 with default parameters) and making corresponding changes in the allelic or other variant sequences. Such allelic or other variant sequences include sequences having at least 85%, 90%, 95%, 98%, or 99% sequence identity across the entire length or at least 20, 40, 100, 500, 1,000, 2,000, 4,000, 8,000, 10,000, 12,000, 14,350, 15,000, or 16,652 nucleotides of SEQ ID NO: 1. Also provided are plants, plant parts including seeds, genomic DNA, and/or DNA obtained from INIR6 plants which comprise one or more modifications (e.g., via insertion of a CgRRS in a junction polynucleotide sequence) which provide for selective excision of the INIR6 transgenic locus or a portion thereof. Also provided herein are methods of detecting plants, genomic DNA, and/or DNA obtained from plants comprising a INIR6 transgenic locus which contains one or more of a CgRRS, deletions of selectable marker genes, deletions of non-essential DNA, and/or a transgenic locus excision site. A first junction polynucleotide of a DP-4114 transgenic locus can comprise either one of the junction polynucleotides found at the 5′ end or the 3′ end of any one of the sequences set forth in SEQ ID NO: 1, allelic variants thereof, or other variants thereof. In certain embodiments, a 5′ junction polynucleotide of a DP-4114 transgenic locus can comprise DNA spanning the plant genomic DNA/transgene insert junction at nucleotides 2422 and 2423 of SEQ ID NO: 1. In certain embodiments, a 3′ junction polynucleotide of a DP-4114 transgenic locus can comprise DNA spanning the plant genomic DNA/transgene insert junction at nucleotides 14347 and 14348 of SEQ ID NO: 1. An OgRRS can be found within non-transgenic DNA, transgenic DNA, or a combination thereof in either one of the junction polynucleotides of any one of SEQ ID NO: 1, allelic variants thereof, or other variants thereof. A second junction polynucleotide of a transgenic locus can comprise either one of the junction polynucleotides found at the 5′ or 3′ end of any one of the sequences set forth in SEQ ID NO: 1, allelic variants thereof, or other variants thereof. A CgRRS can be introduced within transgenic, non-transgenic DNA, or a combination thereof of either one of the junction polynucleotides of any one of SEQ ID NO: 1, allelic variants thereof, or other variants thereof to obtain an INIR6 transgenic locus. In certain embodiments, the OgRRS is found in non-transgenic DNA or transgenic DNA of the 5′ junction polynucleotide of a transgenic locus of any one of SEQ ID NO: 1, allelic variants thereof, or other variants thereof and the corresponding CgRRS is introduced into the transgenic DNA, non-transgenic DNA, or a combination thereof in the 3′ junction polynucleotide of the DP-4114 transgenic locus of SEQ ID NO: 1, allelic variants thereof, or other variants thereof to obtain an INIR6 transgenic locus. In other embodiments, the OgRRS is found in non-transgenic DNA or transgenic DNA of the 3′ junction polynucleotide of the DP-4114 transgenic locus of any one of SEQ ID NO: 1, allelic variants thereof, or other variants thereof and the corresponding CgRRS is introduced into the transgenic DNA, non-transgenic DNA, or a combination thereof in the 5′ junction polynucleotide of the transgenic locus of SEQ ID NO: 1, allelic variants thereof, or other variants thereof to obtain an INIR6 transgenic locus.
In certain embodiments, the CgRRS is comprised in whole or in part of an exogenous DNA molecule that is introduced into a DNA junction polynucleotide by genome editing. In certain embodiments, the guide RNA hybridization site of the CgRRS is operably linked to a pre-existing PAM site in the transgenic DNA or non-transgenic DNA of the transgenic plant genome. In other embodiments, the guide RNA hybridization site of the CgRRS is operably linked to a new PAM site that is introduced in the DNA junction polynucleotide by genome editing. A CgRRS can be located in non-transgenic plant genomic DNA of a DNA junction polynucleotide of an INIR6 transgenic locus, in transgenic DNA of a DNA junction polynucleotide of an INIR6 transgenic locus or can span the junction of the transgenic and non-transgenic DNA of a DNA junction polynucleotide of an INIR6 transgenic locus. An OgRRS can likewise be located in non-transgenic plant genomic DNA of a DNA junction polynucleotide of an INIR6 transgenic locus, in transgenic DNA of a DNA junction polynucleotide of an INIR6 transgenic locus, or can span the junction of the transgenic and non-transgenic DNA of a DNA junction polynucleotide of an INIR6 transgenic locus
Methods provided herein can be used in a variety of breeding schemes to obtain elite crop plants comprising subsets of desired modified transgenic loci comprising an OgRRS and a CgRRS operably linked to junction polynucleotide sequences and transgenic loci excision sites where undesired transgenic loci or portions thereof have been removed (e.g., by use of the OgRRS and a CgRRS). Such methods are useful at least insofar as they allow for production of distinct useful donor plant lines each having unique sets of modified transgenic loci and, in some instances, targeted genetic changes that are tailored for distinct geographies and/or product offerings. In an illustrative and non-limiting example, a different product lines comprising transgenic loci conferring only two of three types of herbicide tolerance (e.g., glyphosate, glufosinate, and dicamba) can be obtained from a single donor line comprising three distinct transgenic loci conferring resistance to all three herbicides. In certain aspects, plants comprising the subsets of undesired transgenic loci and transgenic loci excision sites can further comprise targeted genetic changes. Such elite crop plants can be inbred plant lines or can be hybrid plant lines. In certain embodiments, at least two transgenic loci (e.g., transgenic loci including an INIR6 and another modified transgenic locus wherein an OgRRS and a CgRRS site is operably linked to a first and a second junction sequence and optionally a selectable marker gene and/or non-essential DNA are deleted) are introgressed into a desired donor line comprising elite crop plant germplasm and then subjected to genome editing molecules to recover plants comprising one of the two introgressed transgenic loci as well as a transgenic loci excision site introduced by excision of the other transgenic locus or portion thereof by the genome editing molecules. In certain embodiments, the genome editing molecules can be used to remove a transgenic locus and introduce targeted genetic changes in the crop plant genome. Introgression can be achieved by backcrossing plants comprising the transgenic loci to a recurrent parent comprising the desired elite germplasm and selecting progeny with the transgenic loci and recurrent parent germplasm. Such backcrosses can be repeated and/or supplemented by molecular assisted breeding techniques using SNP or other nucleic acid markers to select for recurrent parent germplasm until a desired recurrent parent percentage is obtained (e.g., at least about 95%, 96%, 97%, 98%, or 99% recurrent parent percentage). A non-limiting, illustrative depiction of a scheme for obtaining plants with both subsets of transgenic loci and the targeted genetic changes is shown in the
Hybrid plant lines comprising elite crop plant germplasm, at least one transgenic locus and at least one transgenic locus excision site, and in certain aspects, additional targeted genetic changes are also provided herein. Methods for production of such hybrid seed can comprise crossing elite crop plant lines where at least one of the pollen donor or recipient comprises at least the transgenic locus and a transgenic locus excision site and/or additional targeted genetic changes. In certain embodiments, the pollen donor and recipient will comprise germplasm of distinct heterotic groups and provide hybrid seed and plants exhibiting heterosis. In certain embodiments, the pollen donor and recipient can each comprise a distinct transgenic locus which confers either a distinct trait (e.g., herbicide tolerance or insect resistance), a different type of trait (e.g., tolerance to distinct herbicides or to distinct insects such as coleopteran or lepidopteran insects), or a different mode-of-action for the same trait (e.g., resistance to coleopteran insects by two distinct modes-of-action or resistance to lepidopteran insects by two distinct modes-of-action). In certain embodiments, the pollen recipient will be rendered male sterile or conditionally male sterile. Methods for inducing male sterility or conditional male sterility include emasculation (e.g., detasseling), cytoplasmic male sterility, chemical hybridizing agents or systems, a transgenes or transgene systems, and/or mutation(s) in one or more endogenous plant genes. Descriptions of various male sterility systems that can be adapted for use with the elite crop plants provided herein are described in Wan et al. Molecular Plant; 12, 3, (2019):321-342 as well as in U.S. Pat. No. 8,618,358; US 20130031674; and US 2003188347.
In certain embodiments, it will be desirable to use genome editing molecules to make modified transgenic loci by introducing a CgRRS into the transgenic loci, to excise modified transgenic loci comprising an OgRRS and a CgRRS, and/or to make targeted genetic changes in elite crop plant or other germplasm. Techniques for effecting genome editing in crop plants (e.g., maize) include use of morphogenic factors such as Wuschel (WUS), Ovule Development Protein (ODP), and/or Babyboom (BBM) which can improve the efficiency of recovering plants with desired genome edits. In some aspects, the morphogenic factor comprises WUS1, WUS2, WUS3, WOX2A, WOX4, WOX5, WOX9, BBM2, BMN2, BMN3, and/or ODP2. In certain embodiments, compositions and methods for using WUS, BBM, and/or ODP, as well as other techniques which can be adapted for effecting genome edits in elite crop plant and other germplasm, are set forth in US 20030082813, US 20080134353, US 20090328252, US 20100100981, US 20110165679, US 20140157453, US 20140173775, and US 20170240911, which are each incorporated by reference in their entireties. In certain embodiments, the genome edits can be effected in regenerable plant parts (e.g., plant embryos) of elite crop plants by transient provision of gene editing molecules or polynucleotides encoding the same and do not necessarily require incorporating a selectable marker gene into the plant genome (e.g., US 20160208271 and US 20180273960, both incorporated herein by reference in their entireties; Svitashev et al. Nat Commun. 2016; 7:13274).
In certain embodiments, edited transgenic plant genomes, transgenic plant cells, parts, or plants containing those genomes, and DNA molecules obtained therefrom, can comprise a desired subset of transgenic loci and/or comprise at least one transgenic locus excision site. In certain embodiments, a segment comprising an INIR6 transgenic locus comprising an OgRRS in non-transgenic DNA of a 1st junction polynucleotide sequence and a CgRRS in a 2nd junction polynucleotide sequence is deleted with a gRNA and RdDe that recognize the OgRRS and the CgRRS to produce an INIR6 transgenic locus excision site. In certain embodiments, the transgenic locus excision site can comprise a contiguous segment of DNA comprising at least 10 base pairs of DNA that is telomere proximal to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal to the deleted segment of the transgenic locus wherein the transgenic DNA (i.e., the heterologous DNA) that has been inserted into the crop plant genome has been deleted. In certain embodiments where a segment comprising a transgenic locus has been deleted, the transgenic locus excision site can comprise a contiguous segment of DNA comprising at least 10 base pairs DNA that is telomere proximal to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal DNA to the deleted segment of the transgenic locus wherein the heterologous transgenic DNA and at least 1, 2, 5, 10, 20, 50, or more base pairs of endogenous DNA located in a 5′ junction sequence and/or in a 3′ junction sequence of the original transgenic locus that has been deleted. In such embodiments where DNA comprising the transgenic locus is deleted, a transgenic locus excision site can comprise at least 10 base pairs of DNA that is telomere proximal to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal to the deleted segment of the transgenic locus wherein all of the transgenic DNA is absent and either all or less than all of the endogenous DNA flanking the transgenic DNA sequences are present. In certain embodiments where a segment consisting essentially of an original transgenic locus has been deleted, the transgenic locus excision site can be a contiguous segment of at least 10 base pairs of DNA that is telomere proximal to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal to the deleted segment of the transgenic locus wherein less than all of the heterologous transgenic DNA that has been inserted into the crop plant genome is excised. In certain aforementioned embodiments where a segment consisting essentially of an original transgenic locus has been deleted, the transgenic locus excision site can thus contain at least 1 base pair of DNA or 1 to about 2 or 5, 8, 10, 20, or 50 base pairs of DNA comprising the telomere proximal and/or centromere proximal heterologous transgenic DNA that has been inserted into the crop plant genome. In certain embodiments where a segment consisting of an original transgenic locus has been deleted, the transgenic locus excision site can contain a contiguous segment of DNA comprising at least 10 base pairs of DNA that is telomere proximal to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal to the deleted segment of the transgenic locus wherein the heterologous transgenic DNA that has been inserted into the crop plant genome is deleted. In certain embodiments where DNA consisting of the transgenic locus is deleted, a transgenic locus excision site can comprise at least 10 base pairs of DNA that is telomere proximal to the deleted segment of the transgenic locus and at least 10 base pairs of DNA that is centromere proximal to the deleted segment of the transgenic locus wherein all of the heterologous transgenic DNA that has been inserted into the crop plant genome is deleted and all of the endogenous DNA flanking the heterologous sequences of the transgenic locus is present. In any of the aforementioned embodiments or in other embodiments, the continuous segment of DNA comprising the transgenic locus excision site can further comprise an insertion of 1 to about 2, 5, 10, 20, or more nucleotides between the DNA that is telomere proximal to the deleted segment of the transgenic locus and the DNA that is centromere proximal to the deleted segment of the transgenic locus. Such insertions can result either from endogenous DNA repair and/or recombination activities at the double stranded breaks introduced at the excision site and/or from deliberate insertion of an oligonucleotide. Plants, edited plant genomes, biological samples, and DNA molecules (e.g., including isolated or purified DNA molecules) comprising the INIR6 transgenic loci excision sites are provided herein.
In other embodiments, a segment comprising a INIR6 transgenic locus (e.g., a transgenic locus comprising an OgRRS in non-transgenic DNA of a 1st junction sequence and a CgRRS in a 2nd junction sequence) can be deleted with a gRNA and RdDe that recognize the OgRRS and the CgRRS and replaced with DNA comprising the endogenous non-transgenic plant genomic DNA present in the genome prior to transgene insertion. A non-limiting example of such replacements can be visualized in
In certain embodiments, edited transgenic plant genomes and transgenic plant cells, plant parts, or plants containing those edited genomes, comprising a modification of an original transgenic locus, where the modification comprises an OgRRS and a CgRRS which are operably linked to a 1st and a 2nd junction sequence, respectively or irrespectively, and optionally further comprise a deletion of a segment of the original transgenic locus. In certain embodiments, the modification comprises two or more separate deletions and/or there is a modification in two or more original transgenic plant loci. In certain embodiments, the deleted segment comprises, consists essentially of, or consists of a segment of non-essential DNA in the transgenic locus. Illustrative examples of non-essential DNA include but are not limited to synthetic cloning site sequences, duplications of transgene sequences; fragments of transgene sequences, and Agrobacterium right and/or left border sequences. In certain embodiments, the non-essential DNA is a duplication and/or fragment of a promoter sequence and/or is not the promoter sequence operably linked in the cassette to drive expression of a transgene. In certain embodiments, excision of the non-essential DNA improves a characteristic, functionality, and/or expression of a transgene of the transgenic locus or otherwise confers a recognized improvement in a transgenic plant comprising the edited transgenic plant genome. In certain embodiments, the non-essential DNA does not comprise DNA encoding a selectable marker gene. In certain embodiments of an edited transgenic plant genome, the modification comprises a deletion of the non-essential DNA and a deletion of a selectable marker gene. The modification producing the edited transgenic plant genome could occur by excising both the non-essential DNA and the selectable marker gene at the same time, e.g., in the same modification step, or the modification could occur step-wise. For example, an edited transgenic plant genome in which a selectable marker gene has previously been removed from the transgenic locus can comprise an original transgenic locus from which a non-essential DNA is further excised and vice versa. In certain embodiments, the modification comprising deletion of the non-essential DNA and deletion of the selectable marker gene comprises excising a single segment of the original transgenic locus that comprises both the non-essential DNA and the selectable marker gene. Such modification would result in one excision site in the edited transgenic genome corresponding to the deletion of both the non-essential DNA and the selectable marker gene. In certain embodiments, the modification comprising deletion of the non-essential DNA and deletion of the selectable marker gene comprises excising two or more segments of the original transgenic locus to achieve deletion of both the non-essential DNA and the selectable marker gene. Such modification would result in at least two excision sites in the edited transgenic genome corresponding to the deletion of both the non-essential DNA and the selectable marker gene. In certain embodiments of an edited transgenic plant genome, prior to excision, the segment to be deleted is flanked by operably linked protospacer adjacent motif (PAM) sites in the original or unmodified transgenic locus and/or the segment to be deleted encompasses an operably linked PAM site in the original or unmodified transgenic locus. In certain embodiments, following excision of the segment, the resulting edited transgenic plant genome comprises PAM sites flanking the deletion site in the modified transgenic locus. In certain embodiments of an edited transgenic plant genome, the modification comprises a modification of a DP-4114 transgenic locus.
In certain embodiments, improvements in a transgenic plant locus are obtained by introducing a new cognate guide RNA recognition site (CgRRS) which is operably linked to a DNA junction polynucleotide of the transgenic locus in the transgenic plant genome. Such CgRRS sites can be recognized by RdDe and a single suitable guide RNA directed to the CgRRS and the originator gRNA Recognition Site (OgRRS) to provide for cleavage within the junction polynucleotides which flank an INIR6 transgenic locus. In certain embodiments, the CgRRS/gRNA and OgRRS/gRNA hybridization complexes are recognized by the same class of RdDe (e.g., Class 2 type II or Class 2 type V) or by the same RdDe (e.g., both the CgRRS/gRNA and OgRRS/gRNA hybridization complexes recognized by the same Cas9 or Cas 12 RdDe). Such CgRRS and OgRRS can be recognized by RdDe and suitable guide RNAs containing crRNA sufficiently complementary to the guide RNA hybridization site DNA sequences adjacent to the PAM site of the CgRRS and the OgRRS to provide for cleavage within or near the two junction polynucleotides. Suitable guide RNAs can be in the form of a single gRNA comprising a crRNA or in the form of a crRNA/tracrRNA complex. In the case of the OgRRS site, the PAM and guide RNA hybridization site are endogenous DNA polynucleotide molecules found in the plant genome. In certain embodiments where the CgRRS is introduced into the plant genome by genome editing, gRNA hybridization site polynucleotides introduced at the CgRRS are at least 17 or 18 nucleotides in length and are complementary to the crRNA of a guide RNA. In certain embodiments, the gRNA hybridization site sequence of the OgRRS and/or the CgRRS is about 17 or 18 to about 24 nucleotides in length. The gRNA hybridization site sequence of the OgRRS and the gRNA hybridization site of the CgRRS can be of different lengths or comprise different sequences so long as there is sufficient complementarity to permit hybridization by a single gRNA and recognition by a RdDe that recognizes and cleaves DNA at the gRNA/OgRRS and gRNA/CgRRS complex. In certain embodiments, the guide RNA hybridization site of the CgRRS comprise about a 17 or 18 to about 24 nucleotide sequence which is identical to the guide RNA hybridization site of the OgRRS. In other embodiments, the guide RNA hybridization site of the CgRRS comprise about a 17 or 18 to about 24 nucleotide sequence which has one, two, three, four, or five nucleotide insertions, deletions or substitutions when compared to the guide RNA hybridization site of the OgRRS. Certain CgRRS comprising a gRNA hybridization site containing has one, two, three, four, or five nucleotide insertions, deletions or substitutions when compared to the guide RNA hybridization site of the OgRRS can undergo hybridization with a gRNA which is complementary to the OgRRS gRNA hybridization site and be cleaved by certain RdDe. Examples of mismatches between gRNAs and guide RNA hybridization sites which allow for RdDe recognition and cleavage include mismatches resulting from both nucleotide insertions and deletions in the DNA which is hybridized to the gRNA (e.g., Lin et al., doi: 10.1093/nar/gku402). In certain embodiments, an operably linked PAM site is co-introduced with the gRNA hybridization site polynucleotide at the CgRRS. In certain embodiments, the gRNA hybridization site polynucleotides are introduced at a position adjacent to a resident endogenous PAM sequence in the junction polynucleotide sequence to form a CgRRS where the gRNA hybridization site polynucleotides are operably linked to the endogenous PAM site. In certain embodiments, non-limiting features of the OgRRS, CgRRS, and/or the gRNA hybridization site polynucleotides thereof include: (i) absence of significant homology or sequence identity (e.g., less than 50% sequence identity across the entire length of the OgRRS, CgRRS, and/or the gRNA hybridization site sequence) to any other endogenous or transgenic sequences present in the transgenic plant genome or in other transgenic genomes of the maize plant being transformed and edited; (ii) absence of significant homology or sequence identity (e.g., less than 50% sequence identity across the entire length of the sequence) of a sequence of a first OgRRS and a first CgRRS to a second OgRRS and a second CgRRS which are operably linked to junction polynucleotides of a distinct transgenic locus; (iii) the presence of some sequence identity (e.g., about 25%, 40%, or 50% to about 60%, 70%, or 80%) between the OgRRS sequence and endogenous sequences present at the site where the CgRRS sequence is introduced; and/or (iv) optimization of the gRNA hybridization site polynucleotides for recognition by the RdDe and guide RNA when used in conjunction with a particular PAM sequence. In certain embodiments, the first and second OgRRS as well as the first and second CgRRS are recognized by the same class of RdDe (e.g., Class 2 type II or Class 2 type V) or by the same RdDe (e.g., Cas9 or Cas 12 RdDe). In certain embodiments, the first OgRRS site in a first junction polynucleotide and the CgRRS introduced in the second junction polynucleotide to permit excision of a first transgenic locus by a first single guide RNA and a single RdDe. Such nucleotide insertions or genome edits used to introduce CgRRS in a transgenic plant genome can be effected in the plant genome by using gene editing molecules (e.g., RdDe and guide RNAs, RNA dependent nickases and guide RNAs, Zinc Finger nucleases or nickases, or TALE nucleases or nickases) which introduce blunt double stranded breaks or staggered double stranded breaks in the DNA junction polynucleotides. In the case of DNA insertions, the genome editing molecules can also in certain embodiments further comprise a donor DNA template or other DNA template which comprises the heterologous nucleotides for insertion to form the CgRRS. Guide RNAs can be directed to the junction polynucleotides by using a pre-existing PAM site located within or adjacent to a junction polynucleotide of the transgenic locus. Non-limiting examples of such pre-existing PAM sites present in junction polynucleotides, which can be used either in conjunction with an inserted heterologous sequence to form a CgRRS or which can be used to create a double stranded break to insert or create a CgRRS, include PAM sites recognized by a Cas12a enzyme. Non-limiting examples where a CgRRS are created in a DNA sequence are illustrated in Example 2.
Transgenic loci comprising OgRRS and CgRRS in a first and a second junction polynucleotides can be excised from the genomes of transgenic plants by contacting the transgenic loci with RdDe or RNA directed nickases, and a suitable guide RNA directed to the OgRRS and CgRRS. A non-limiting example where a modified transgenic locus is excised from a plant genome by use of a gRNA and an RdDe that recognizes an OgRRS/gRNA and a CgRRS/gRNA complex and introduces dsDNA breaks in both junction polynucleotides nd repaired by NHEJ is depicted in
In certain embodiments, edited transgenic plant genomes provided herein can lack one or more selectable and/or scoreable markers found in an original event (transgenic locus). Original DP-4114 transgenic loci (events), including those set forth in SEQ ID NO: 1), U.S. Pat. No. 8,575,434, the sequence of the DP-4114 locus in the deposited seed of accession No. PTA-11506 and progeny thereof, contain a selectable marker gene encoding a phosphinotricin acetyl transferase (PAT) protein which confers tolerance to the herbicide glufosinate. In certain embodiments provided herein, the DNA element comprising, consisting essentially of, or consisting of the PAT selectable marker gene of an DP-4114 transgenic locus is absent from an INIR6 transgenic locus. The PAT selectable marker cassette can be excised from an original DP-4114 transgenic locus by contacting the transgenic locus with one or more gene editing molecules which introduce double stranded breaks in the transgenic locus at the 5′ and 3′ end of the expression cassette comprising the PAT selectable marker transgene (e.g., an RdDe and guide RNAs directed to PAM sites located at the 5′ and 3′ end of the expression cassette comprising the PAT selectable marker transgene) and selecting for plant cells, plant parts, or plants wherein the selectable marker has been excised. Examples of an INIR6 transgenic locus comprising a deletion of a PAT selectable marker transgene and a 3′ border sequence include the INIR6 transgenic locus of SEQ ID NO: 25 and allelic variants thereof. Examples of an INIR6 transgenic locus comprising a deletion of a PAT selectable marker transgene and a CgRRS include the INIR6 transgenic locus of SEQ ID NO: 26 and variants thereof. In certain embodiments, a DNA fragment comprising, consisting essentially of, or consisting of the CaMV35S promoter and operably linked PAT coding region of the DP-4114 transgenic locus is deleted while leaving in place the CaMV35S terminator of the PAT selectable marker cassette in the INIR6 transgenic locus. In certain embodiments, the PinII terminator which is operably linked to Cry35Ab1 coding region is thus placed in tandem with the CaMV35S promoter in the INIR6 transgenic locus. Examples of an INIR6 transgenic locus comprising, consisting essentially of, or consisting of a deletion of the CaMV35S promoter and operably linked PAT coding region of a DP-4114 transgenic locus include am INIR6 transgenic locus which can be obtained with a Cas12a nuclease and a guide RNAs which cleave DNA located between the PinII terminator which is operably linked to the Cry35Ab1 coding region (e.g., guide RNA-4; SEQ ID NO: 24) and DNA located between the 3′ end of the PAT coding region and the 5′ end of the CaMV35S promoter (e.g., Guide RNA NO: 5; SEQ ID NO: 28). Examples of an INIR6 transgenic locus comprising a deletion of the CaMV35S promoter and operably linked PAT coding region of a DP-4114 transgenic locus include the INIR6 transgenic locus of SEQ ID NO: 29, 30, and variants thereof. Examples of an INIR6 transgenic locus comprising a CgRRS and a deletion of the CaMV35S promoter and operably linked PAT coding region of a DP-4114 transgenic locus include the INIR6 transgenic locus of SEQ ID NO: 31 and variants thereof. In certain embodiments, the selectable or scoreable marker transgene can be inactivated. Inactivation can be achieved by modifications including insertion, deletion, and/or substitution of one or more nucleotides in a promoter element, 5′ or 3′ untranslated region (UTRs), intron, coding region, and/or 3′ terminator and/or polyadenylation site of the selectable marker transgene. Such modifications can inactivate the selectable marker transgene by eliminating or reducing promoter activity, introducing a missense mutation, and/or introducing a pre-mature stop codon. In certain embodiments, the selectable PAT marker transgene can be replaced by an introduced transgene. In certain embodiments, an original transgenic locus that was contacted with gene editing molecules which introduce double stranded breaks in the transgenic locus at the 5′ and 3′ end of the expression cassette comprising the PAT selectable marker transgene can also be contacted with a suitable donor DNA template comprising an expression cassette flanked by DNA homologous to remaining DNA in the transgenic locus located 5′ and 3′ to the selectable marker excision site. In certain embodiments, a coding region of the PAT selectable marker transgene can be replaced with another coding region such that the replacement coding region is operably linked to the promoter and 3′ terminator or polyadenylation site of the PAT selectable marker transgene.
In certain embodiments, edited transgenic plant genomes provided herein can comprise additional new introduced transgenes (e.g., expression cassettes) inserted into the transgenic locus of a given event. Introduced transgenes inserted at the transgenic locus of an event subsequent to the event's original isolation can be obtained by inducing a double stranded break at a site within an original transgenic locus (e.g., with genome editing molecules including an RdDe and suitable guide RNA(s); a suitable engineered zinc-finger nuclease; a TALEN protein and the like) and providing an exogenous transgene in a donor DNA template which can be integrated at the site of the double stranded break (e.g. by homology-directed repair (HDR) or by non-homologous end-joining (NHEJ)). In certain embodiments, an OgRRS and a CgRRS located in a 1st junction polynucleotide and a 2nd junction polynucleotide, respectively, can be used to delete the transgenic locus and replace it with one or more new expression cassettes. In certain embodiments, such deletions and replacements are effected by introducing dsDNA breaks in both junction polynucleotides and providing the new expression cassettes on a donor DNA template (e.g., in
In certain embodiments, INIR6 plants provided herein, including plants with one or more transgenic loci, modified transgenic loci, and/or comprising transgenic loci excision sites can further comprise one or more targeted genetic changes introduced by one or more of gene editing molecules or systems. Also provided are methods where the targeted genetic changes are introduced and one or more transgenic loci are removed from plants either in series or in parallel (e.g., as set forth in the non-limiting illustration in
Gene editing molecules of use in methods provided herein include molecules capable of introducing a double-strand break (“DSB”) or single-strand break (“SSB”) in double-stranded DNA, such as in genomic DNA or in a target gene located within the genomic DNA as well as accompanying guide RNA or donor DNA template polynucleotides. Examples of such gene editing molecules include: (a) a nuclease comprising an RNA-guided nuclease, an RNA-guided DNA endonuclease or RNA directed DNA endonuclease (RdDe), a class 1 CRISPR type nuclease system, a type II Cas nuclease, a Cas9, a nCas9 nickase, a type V Cas nuclease, a Cas12a nuclease, a nCas12a nickase, a Cas12d (CasY), a Cas12e (CasX), a Cas12b (C2c1), a Cas12c (C2c3), a Cas12i, a Cas12j, a Cas14, an engineered nuclease, a codon-optimized nuclease, a zinc-finger nuclease (ZFN) or nickase, a transcription activator-like effector nuclease (TAL-effector nuclease or TALEN) or nickase (TALE-nickase), an Argonaute, and a meganuclease or engineered meganuclease; (b) a polynucleotide encoding one or more nucleases capable of effectuating site-specific alteration (including introduction of a DSB or SSB) of a target nucleotide sequence; (c) a guide RNA (gRNA) for an RNA-guided nuclease, or a DNA encoding a gRNA for an RNA-guided nuclease; (d) donor DNA template polynucleotides; and (e) other DNA templates (dsDNA, ssDNA, or combinations thereof) suitable for insertion at a break in genomic DNA (e.g., by non-homologous end joining (NHEJ) or microhomology-mediated end joining (MMEJ).
CRISPR-type genome editing can be adapted for use in the plant cells and methods provided herein in several ways. CRISPR elements, e.g., gene editing molecules comprising CRISPR endonucleases and CRISPR guide RNAs including single guide RNAs or guide RNAs in combination with tracrRNAs or scoutRNA, or polynucleotides encoding the same, are useful in effectuating genome editing without remnants of the CRISPR elements or selective genetic markers occurring in progeny. In certain embodiments, the CRISPR elements are provided directly to the eukaryotic cell (e.g., plant cells), systems, methods, and compositions as isolated molecules, as isolated or semi-purified products of a cell free synthetic process (e.g., in vitro translation), or as isolated or semi-purified products of in a cell-based synthetic process (e.g., such as in a bacterial or other cell lysate). In certain embodiments, genome-inserted CRISPR elements are useful in plant lines adapted for use in the methods provide herein. In certain embodiments, plants or plant cells used in the systems, methods, and compositions provided herein can comprise a transgene that expresses a CRISPR endonuclease (e.g., a Cas9, a Cpf1-type or other CRISPR endonuclease). In certain embodiments, one or more CRISPR endonucleases with unique PAM recognition sites can be used. Guide RNAs (sgRNAs or crRNAs and a tracrRNA) to form an RNA-guided endonuclease/guide RNA complex which can specifically bind sequences in the gDNA target site that are adjacent to a protospacer adjacent motif (PAM) sequence. The type of RNA-guided endonuclease typically informs the location of suitable PAM sites and design of crRNAs or sgRNAs. G-rich PAM sites, e.g., 5′-NGG are typically targeted for design of crRNAs or sgRNAs used with Cas9 proteins. Examples of PAM sequences include 5′-NGG (Streptococcus pyogenes), 5′-NNAGAA (Streptococcus thermophilus CRISPR1), 5′-NGGNG (Streptococcus thermophilus CRISPR3), 5′-NNGRRT or 5′-NNGRR (Staphylococcus aureus Cas9, SaCas9), and 5′-NNNGATT (Neisseria meningitidis). T-rich PAM sites (e.g., 5′-TTN or 5′-TTTV, where “V” is A, C, or G) are typically targeted for design of crRNAs or sgRNAs used with Cas12a proteins. In some instances, Cas12a can also recognize a 5′-CTA PAM motif. Other examples of potential Cas12a PAM sequences include TTN, CTN, TCN, CCN, TTTN, TCTN, TTCN, CTTN, ATTN, TCCN, TTGN, GTTN, CCCN, CCTN, TTAN, TCGN, CTCN, ACTN, GCTN, TCAN, GCCN, and CCGN (wherein N is defined as any nucleotide). Cpf1 (i.e., Cas12a) endonuclease and corresponding guide RNAs and PAM sites are disclosed in US Patent Application Publication 2016/0208243 A1, which is incorporated herein by reference for its disclosure of DNA encoding Cpf1 endonucleases and guide RNAs and PAM sites. Introduction of one or more of a wide variety of CRISPR guide RNAs that interact with CRISPR endonucleases integrated into a plant genome or otherwise provided to a plant is useful for genetic editing for providing desired phenotypes or traits, for trait screening, or for gene editing mediated trait introgression (e.g., for introducing a trait into a new genotype without backcrossing to a recurrent parent or with limited backcrossing to a recurrent parent). Multiple endonucleases can be provided in expression cassettes with the appropriate promoters to allow multiple genome site editing.
CRISPR technology for editing the genes of eukaryotes is disclosed in US Patent Application Publications 2016/0138008A1 and US2015/0344912A1, and in U.S. Pat. Nos. 8,697,359, 8,771,945, 8,945,839, 8,999,641, 8,993,233, 8,895,308, 8,865,406, 8,889,418, 8,871,445, 8,889,356, 8,932,814, 8,795,965, and 8,906,616. Cpf1 endonuclease and corresponding guide RNAs and PAM sites are disclosed in US Patent Application Publication 2016/0208243 A1. Other CRISPR nucleases useful for editing genomes include Cas12b and Cas12c (see Shmakov et al. (2015) Mol. Cell, 60:385-397; Harrington et al. (2020) Molecular Cell doi:10.1016/j.molcel.2020.06.022) and CasX and CasY (see Burstein et al. (2016) Nature, doi:10.1038/nature21059; Harrington et al. (2020) Molecular Cell doi:10.1016/j.molcel.2020.06.022), or Cas12j (Pausch et al, (2020) Science 10.1126/science.abb1400). Plant RNA promoters for expressing CRISPR guide RNA and plant codon-optimized CRISPR Cas9 endonuclease are disclosed in International Patent Application PCT/US2015/018104 (published as WO 2015/131101 and claiming priority to U.S. Provisional Patent Application 61/945,700). Methods of using CRISPR technology for genome editing in plants are disclosed in US Patent Application Publications US 2015/0082478A1 and US 2015/0059010A1 and in International Patent Application PCT/US2015/038767 A1 (published as WO 2016/007347 and claiming priority to U.S. Provisional Patent Application 62/023,246). All of the patent publications referenced in this paragraph are incorporated herein by reference in their entirety. In certain embodiments, an RNA-guided endonuclease that leaves a blunt end following cleavage of the target site is used. Blunt-end cutting RNA-guided endonucleases include Cas9, Cas12c, and Cas 12h (Yan et al., 2019). In certain embodiments, an RNA-guided endonuclease that leaves a staggered single stranded DNA overhanging end following cleavage of the target site following cleavage of the target site is used. Staggered-end cutting RNA-guided endonucleases include Cas12a, Cas12b, and Cas12e.
The methods can also use sequence-specific endonucleases or sequence-specific endonucleases and guide RNAs that cleave a single DNA strand in a dsDNA target site. Such cleavage of a single DNA strand in a dsDNA target site is also referred to herein and elsewhere as “nicking” and can be effected by various “nickases” or systems that provide for nicking. Nickases that can be used include nCas9 (Cas9 comprising a D10A amino acid substitution), nCas12a (e.g., Cas12a comprising an R1226A amino acid substitution; Yamano et al., 2016), Cas12i (Yan et al. 2019), a zinc finger nickase e.g., as disclosed in Kim et al., 2012), a TALE nickase (e.g., as disclosed in Wu et al., 2014), or a combination thereof. In certain embodiments, systems that provide for nicking can comprise a Cas nuclease (e.g., Cas9 and/or Cas12a) and guide RNA molecules that have at least one base mismatch to DNA sequences in the target editing site (Fu et al., 2019). In certain embodiments, genome modifications can be introduced into the target editing site by creating single stranded breaks (i.e., “nicks”) in genomic locations separated by no more than about 10, 20, 30, 40, 50, 60, 80, 100, 150, or 200 base pairs of DNA. In certain illustrative and non-limiting embodiments, two nickases (i.e., a CAS nuclease which introduces a single stranded DNA break including nCas9, nCas12a, Cas12i, zinc finger nickases, TALE nickases, combinations thereof, and the like) or nickase systems can directed to make cuts to nearby sites separated by no more than about 10, 20, 30, 40, 60, 80 or 100 base pairs of DNA. In instances where an RNA guided nickase and an RNA guide are used, the RNA guides are adjacent to PAM sequences that are sufficiently close (i.e., separated by no more than about 10, 20, 30, 40, 50, 60, 80, 100, 150, or 200 base pairs of DNA). For the purposes of gene editing, CRISPR arrays can be designed to contain one or multiple guide RNA sequences corresponding to a desired target DNA sequence; see, for example, Cong et al. (2013) Science, 339:819-823; Ran et al. (2013) Nature Protocols, 8:2281-2308. At least 16 or 17 nucleotides of gRNA sequence are required by Cas9 for DNA cleavage to occur; for Cpf1 at least 16 nucleotides of gRNA sequence are needed to achieve detectable DNA cleavage and at least 18 nucleotides of gRNA sequence were reported necessary for efficient DNA cleavage in vitro; see Zetsche et al. (2015) Cell, 163:759-771. In practice, guide RNA sequences are generally designed to have a length of 17-24 nucleotides (frequently 19, 20, or 21 nucleotides) and exact complementarity (i.e., perfect base-pairing) to the targeted gene or nucleic acid sequence; guide RNAs having less than 100% complementarity to the target sequence can be used (e.g., a gRNA with a length of 20 nucleotides and 1-4 mismatches to the target sequence) but can increase the potential for off-target effects. The design of effective guide RNAs for use in plant genome editing is disclosed in US Patent Application Publication 2015/0082478 A1, the entire specification of which is incorporated herein by reference. More recently, efficient gene editing has been achieved using a chimeric “single guide RNA” (“sgRNA”), an engineered (synthetic) single RNA molecule that mimics a naturally occurring crRNA-tracrRNA complex and contains both a tracrRNA (for binding the nuclease) and at least one crRNA (to guide the nuclease to the sequence targeted for editing); see, for example, Cong et al. (2013) Science, 339:819-823; Xing et al. (2014) BMC Plant Biol., 14:327-340. Chemically modified sgRNAs have been demonstrated to be effective in genome editing; see, for example, Hendel et al. (2015) Nature Biotechnol., 985-991. The design of effective gRNAs for use in plant genome editing is disclosed in US Patent Application Publication 2015/0082478 A1, the entire specification of which is incorporated herein by reference.
Genomic DNA may also be modified via base editing. Both adenine base editors (ABE) which convert A/T base pairs to G/C base pairs in genomic DNA as well as cytosine base pair editors (CBE) which effect C to T substitutions can be used in certain embodiments of the methods provided herein. In certain embodiments, useful ABE and CBE can comprise genome site specific DNA binding elements (e.g., RNA-dependent DNA binding proteins including catalytically inactive Cas9 and Cas12 proteins or Cas9 and Cas12 nickases) operably linked to adenine or cytidine deaminases and used with guide RNAs which position the protein near the nucleotide targeted for substitution. Suitable ABE and CBE disclosed in the literature (Kim, Nat Plants, 2018 March; 4(3):148-151) can be adapted for use in the methods set forth herein. In certain embodiments, a CBE can comprise a fusion between a catalytically inactive Cas9 (dCas9) RNA dependent DNA binding protein fused to a cytidine deaminase which converts cytosine (C) to uridine (U) and selected guide RNAs, thereby effecting a C to T substitution; see Komor et al. (2016) Nature, 533:420-424. In other embodiments, C to T substitutions are effected with Cas9 nickase [Cas9n(D10A)] fused to an improved cytidine deaminase and optionally a bacteriophage Mu dsDNA (double-stranded DNA) end-binding protein Gam; see Komor et al., Sci Adv. 2017 August; 3(8):eaao4774. In other embodiments, adenine base editors (ABEs) comprising an adenine deaminase fused to catalytically inactive Cas9 (dCas9) or a Cas9 D10A nickase can be used to convert A/T base pairs to G/C base pairs in genomic DNA (Gaudelli et al., (2017) Nature 551(7681):464-471.
In certain embodiments, zinc finger nucleases or zinc finger nickases can also be used in the methods provided herein. Zinc-finger nucleases are site-specific endonucleases comprising two protein domains: a DNA-binding domain, comprising a plurality of individual zinc finger repeats that each recognize between 9 and 18 base pairs, and a DNA-cleavage domain that comprises a nuclease domain (typically Fokl). The cleavage domain dimerizes in order to cleave DNA; therefore, a pair of ZFNs are required to target non-palindromic target polynucleotides. In certain embodiments, zinc finger nuclease and zinc finger nickase design methods which have been described (Urnov et al. (2010) Nature Rev. Genet., 11:636-646; Mohanta et al. (2017) Genes vol. 8, 12: 399; Ramirez et al. Nucleic Acids Res. (2012); 40(12): 5560-5568; Liu et al. (2013) Nature Communications, 4: 2565) can be adapted for use in the methods set forth herein. The zinc finger binding domains of the zinc finger nuclease or nickase provide specificity and can be engineered to specifically recognize any desired target DNA sequence. The zinc finger DNA binding domains are derived from the DNA-binding domain of a large class of eukaryotic transcription factors called zinc finger proteins (ZFPs). The DNA-binding domain of ZFPs typically contains a tandem array of at least three zinc “fingers” each recognizing a specific triplet of DNA. A number of strategies can be used to design the binding specificity of the zinc finger binding domain. One approach, termed “modular assembly”, relies on the functional autonomy of individual zinc fingers with DNA. In this approach, a given sequence is targeted by identifying zinc fingers for each component triplet in the sequence and linking them into a multifinger peptide. Several alternative strategies for designing zinc finger DNA binding domains have also been developed. These methods are designed to accommodate the ability of zinc fingers to contact neighboring fingers as well as nucleotide bases outside their target triplet. Typically, the engineered zinc finger DNA binding domain has a novel binding specificity, compared to a naturally-occurring zinc finger protein. Engineering methods include, for example, rational design and various types of selection. Rational design includes, for example, the use of databases of triplet (or quadruplet) nucleotide sequences and individual zinc finger amino acid sequences, in which each triplet or quadruplet nucleotide sequence is associated with one or more amino acid sequences of zinc fingers which bind the particular triplet or quadruplet sequence. See, e.g., U.S. Pat. Nos. 6,453,242 and 6,534,261, both incorporated herein by reference in their entirety. Exemplary selection methods (e.g., phage display and yeast two-hybrid systems) can be adapted for use in the methods described herein. In addition, enhancement of binding specificity for zinc finger binding domains has been described in U.S. Pat. No. 6,794,136, incorporated herein by reference in its entirety. In addition, individual zinc finger domains may be linked together using any suitable linker sequences. Examples of linker sequences are publicly known, e.g., see U.S. Pat. Nos. 6,479,626; 6,903,185; and 7,153,949, incorporated herein by reference in their entirety. The nucleic acid cleavage domain is non-specific and is typically a restriction endonuclease, such as Fokl. This endonuclease must dimerize to cleave DNA. Thus, cleavage by Fokl as part of a ZFN requires two adjacent and independent binding events, which must occur in both the correct orientation and with appropriate spacing to permit dimer formation. The requirement for two DNA binding events enables more specific targeting of long and potentially unique recognition sites. Fokl variants with enhanced activities have been described and can be adapted for use in the methods described herein; see, e.g., Guo et al. (2010) J Mol. Biol., 400:96-107.
Transcription activator like effectors (TALEs) are proteins secreted by certain Xanthomonas species to modulate gene expression in host plants and to facilitate the colonization by and survival of the bacterium. TALEs act as transcription factors and modulate expression of resistance genes in the plants. Recent studies of TALEs have revealed the code linking the repetitive region of TALEs with their target DNA-binding sites. TALEs comprise a highly conserved and repetitive region consisting of tandem repeats of mostly 33 or 34 amino acid segments. The repeat monomers differ from each other mainly at amino acid positions 12 and 13. A strong correlation between unique pairs of amino acids at positions 12 and 13 and the corresponding nucleotide in the TALE-binding site has been found. The simple relationship between amino acid sequence and DNA recognition of the TALE binding domain allows for the design of DNA binding domains of any desired specificity. TALEs can be linked to a non-specific DNA cleavage domain to prepare genome editing proteins, referred to as TAL-effector nucleases or TALENs. As in the case of ZFNs, a restriction endonuclease, such as Fokl, can be conveniently used. Methods for use of TALENs in plants have been described and can be adapted for use in the methods described herein, see Mahfouz et al. (2011) Proc. Natl. Acad. Sci. USA, 108:2623-2628; Mahfouz (2011) GM Crops, 2:99-103; and Mohanta et al. (2017) Genes vol. 8, 12: 399). TALE nickases have also been described and can be adapted for use in methods described herein (Wu et al.; Biochem Biophys Res Commun. (2014); 446(1):261-6; Luo et al; Scientific Reports 6, Article number: 20657 (2016)).
Embodiments of the donor DNA template molecule having a sequence that is integrated at the site of at least one double-strand break (DSB) in a genome include double-stranded DNA, a single-stranded DNA, a single-stranded DNA/RNA hybrid, and a double-stranded DNA/RNA hybrid. In embodiments, a donor DNA template molecule that is a double-stranded (e.g., a dsDNA or dsDNA/RNA hybrid) molecule is provided directly to the plant protoplast or plant cell in the form of a double-stranded DNA or a double-stranded DNA/RNA hybrid, or as two single-stranded DNA (ssDNA) molecules that are capable of hybridizing to form dsDNA, or as a single-stranded DNA molecule and a single-stranded RNA (ssRNA) molecule that are capable of hybridizing to form a double-stranded DNA/RNA hybrid; that is to say, the double-stranded polynucleotide molecule is not provided indirectly, for example, by expression in the cell of a dsDNA encoded by a plasmid or other vector. In various non-limiting embodiments of the method, the donor DNA template molecule that is integrated (or that has a sequence that is integrated) at the site of at least one double-strand break (DSB) in a genome is double-stranded and blunt-ended; in other embodiments the donor DNA template molecule is double-stranded and has an overhang or “sticky end” consisting of unpaired nucleotides (e.g., 1, 2, 3, 4, 5, or 6 unpaired nucleotides) at one terminus or both termini. In an embodiment, the DSB in the genome has no unpaired nucleotides at the cleavage site, and the donor DNA template molecule that is integrated (or that has a sequence that is integrated) at the site of the DSB is a blunt-ended double-stranded DNA or blunt-ended double-stranded DNA/RNA hybrid molecule, or alternatively is a single-stranded DNA or a single-stranded DNA/RNA hybrid molecule. In another embodiment, the DSB in the genome has one or more unpaired nucleotides at one or both sides of the cleavage site, and the donor DNA template molecule that is integrated (or that has a sequence that is integrated) at the site of the DSB is a double-stranded DNA or double-stranded DNA/RNA hybrid molecule with an overhang or “sticky end” consisting of unpaired nucleotides at one or both termini, or alternatively is a single-stranded DNA or a single-stranded DNA/RNA hybrid molecule; in embodiments, the donor DNA template molecule DSB is a double-stranded DNA or double-stranded DNA/RNA hybrid molecule that includes an overhang at one or at both termini, wherein the overhang consists of the same number of unpaired nucleotides as the number of unpaired nucleotides created at the site of a DSB by a nuclease that cuts in an off-set fashion (e.g., where a Cas12 nuclease effects an off-set DSB with 5-nucleotide overhangs in the genomic sequence, the donor DNA template molecule that is to be integrated (or that has a sequence that is to be integrated) at the site of the DSB is double-stranded and has 5 unpaired nucleotides at one or both termini). In certain embodiments, one or both termini of the donor DNA template molecule contain no regions of sequence homology (identity or complementarity) to genomic regions flanking the DSB; that is to say, one or both termini of the donor DNA template molecule contain no regions of sequence that is sufficiently complementary to permit hybridization to genomic regions immediately adjacent to the location of the DSB. In embodiments, the donor DNA template molecule contains no homology to the locus of the DSB, that is to say, the donor DNA template molecule contains no nucleotide sequence that is sufficiently complementary to permit hybridization to genomic regions immediately adjacent to the location of the DSB. In embodiments, the donor DNA template molecule is at least partially double-stranded and includes 2-20 base-pairs, e. g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 base-pairs; in embodiments, the donor DNA template molecule is double-stranded and blunt-ended and consists of 2-20 base-pairs, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 base-pairs; in other embodiments, the donor DNA template molecule is double-stranded and includes 2-20 base-pairs, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 base-pairs and in addition has at least one overhang or “sticky end” consisting of at least one additional, unpaired nucleotide at one or at both termini. In an embodiment, the donor DNA template molecule that is integrated (or that has a sequence that is integrated) at the site of at least one double-strand break (DSB) in a genome is a blunt-ended double-stranded DNA or a blunt-ended double-stranded DNA/RNA hybrid molecule of about 18 to about 300 base-pairs, or about 20 to about 200 base-pairs, or about 30 to about 100 base-pairs, and having at least one phosphorothioate bond between adjacent nucleotides at a 5′ end, 3′ end, or both 5′ and 3′ ends. In embodiments, the donor DNA template molecule includes single strands of at least 11, at least 18, at least 20, at least 30, at least 40, at least 60, at least 80, at least 100, at least 120, at least 140, at least 160, at least 180, at least 200, at least 240, at about 280, or at least 320 nucleotides. In embodiments, the donor DNA template molecule has a length of at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, or at least 11 base-pairs if double-stranded (or nucleotides if single-stranded), or between about 2 to about 320 base-pairs if double-stranded (or nucleotides if single-stranded), or between about 2 to about 500 base-pairs if double-stranded (or nucleotides if single-stranded), or between about 5 to about 500 base-pairs if double-stranded (or nucleotides if single-stranded), or between about 5 to about 300 base-pairs if double-stranded (or nucleotides if single-stranded), or between about 11 to about 300 base-pairs if double-stranded (or nucleotides if single-stranded), or about 18 to about 300 base-pairs if double-stranded (or nucleotides if single-stranded), or between about 30 to about 100 base-pairs if double-stranded (or nucleotides if single-stranded). In embodiments, the donor DNA template molecule includes chemically modified nucleotides (see, e.g., the various modifications of internucleotide linkages, bases, and sugars described in Verma and Eckstein (1998) Annu. Rev. Biochem., 67:99-134); in embodiments, the naturally occurring phosphodiester backbone of the donor DNA template molecule is partially or completely modified with phosphorothioate, phosphorodithioate, or methylphosphonate internucleotide linkage modifications, or the donor DNA template molecule includes modified nucleoside bases or modified sugars, or the donor DNA template molecule is labelled with a fluorescent moiety (e.g., fluorescein or rhodamine or a fluorescent nucleoside analogue) or other detectable label (e.g., biotin or an isotope). In another embodiment, the donor DNA template molecule contains secondary structure that provides stability or acts as an aptamer. Other related embodiments include double-stranded DNA/RNA hybrid molecules, single-stranded DNA/RNA hybrid donor molecules, and single-stranded donor DNA template molecules (including single-stranded, chemically modified donor DNA template molecules), which in analogous procedures are integrated (or have a sequence that is integrated) at the site of a double-strand break. Donor DNA templates provided herein include those comprising CgRRS sequences flanked by DNA with homology to a donor polynucleotide and include the donor DNA template set forth in SEQ ID NO: 14, SEQ ID NO: 27, and equivalents thereof with longer or shorter homology arms. Other DNA donor templates useful for effecting deletions in 3′ junction polynucleotides include those set forth in SEQ ID NO: 32 and 33 as well as equivalents thereof with longer and shorter homology arms. Other DNA donor templates useful for effecting deletions of a PAT selectable marker cassette and a 3′ junction polynucleotide include those set forth on SEQ ID NO: 34 and equivalents thereof with longer and shorter homology arms. Other DNA donor templates useful for effecting deletions of a CaMV35S promoter and PAT coding region of a PAT selectable marker cassette include those set forth on SEQ ID NO: 35 and equivalents thereof with longer and shorter homology arms. In certain embodiments, a donor DNA template can comprise an adapter molecule (e.g., a donor DNA template formed by annealing SEQ ID NO: 11 and 12 or by annealing SEQ ID NO: 11 and 13) with cohesive ends which can anneal to an overhanging cleavage site (e.g., introduced by a Cas12a nuclease and suitable gRNAs). In certain embodiments, integration of the donor DNA templates can be facilitated by use of a bacteriophage lambda exonuclease, a bacteriophage lambda beta SSAP protein, and an E. coli SSB essentially as set forth in US Patent Application Publication 20200407754, which is incorporated herein by reference in its entirety.
Donor DNA template molecules used in the methods provided herein include DNA molecules comprising, from 5′ to 3′, a first homology arm, a replacement DNA, and a second homology arm, wherein the homology arms containing sequences that are partially or completely homologous to genomic DNA (gDNA) sequences flanking a target site-specific endonuclease cleavage site in the gDNA. In certain embodiments, the replacement DNA can comprise an insertion, deletion, or substitution of 1 or more DNA base pairs relative to the target gDNA. In an embodiment, the donor DNA template molecule is double-stranded and perfectly base-paired through all or most of its length, with the possible exception of any unpaired nucleotides at either terminus or both termini. In another embodiment, the donor DNA template molecule is double-stranded and includes one or more non-terminal mismatches or non-terminal unpaired nucleotides within the otherwise double-stranded duplex. In an embodiment, the donor DNA template molecule that is integrated at the site of at least one double-strand break (DSB) includes between 2-20 nucleotides in one (if single-stranded) or in both strands (if double-stranded), e. g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides on one or on both strands, each of which can be base-paired to a nucleotide on the opposite strand (in the case of a perfectly base-paired double-stranded polynucleotide molecule). Such donor DNA templates can be integrated in genomic DNA containing blunt and/or staggered double stranded DNA breaks by homology-directed repair (HDR). In certain embodiments, a donor DNA template homology arm can be about 20, 50, 100, 200, 400, or 600 to about 800, or 1000 base pairs in length. In certain embodiments, a donor DNA template molecule can be delivered to a plant cell) in a circular (e.g., a plasmid or a viral vector including a geminivirus vector) or a linear DNA molecule. In certain embodiments, a circular or linear DNA molecule that is used can comprise a modified donor DNA template molecule comprising, from 5′ to 3′, a first copy of the target sequence-specific endonuclease cleavage site sequence, the first homology arm, the replacement DNA, the second homology arm, and a second copy of the target sequence-specific endonuclease cleavage site sequence. Without seeking to be limited by theory, such modified donor DNA template molecules can be cleaved by the same sequence-specific endonuclease that is used to cleave the target site gDNA of the eukaryotic cell to release a donor DNA template molecule that can participate in HDR-mediated genome modification of the target editing site in the plant cell genome. In certain embodiments, the donor DNA template can comprise a linear DNA molecule comprising, from 5′ to 3′, a cleaved target sequence-specific endonuclease cleavage site sequence, the first homology arm, the replacement DNA, the second homology arm, and a cleaved target sequence-specific endonuclease cleavage site sequence. In certain embodiments, the cleaved target sequence-specific endonuclease sequence can comprise a blunt DNA end or a blunt DNA end that can optionally comprise a 5′ phosphate group. In certain embodiments, the cleaved target sequence-specific endonuclease sequence comprises a DNA end having a single-stranded 5′ or 3′ DNA overhang. Such cleaved target sequence-specific endonuclease cleavage site sequences can be produced by either cleaving an intact target sequence-specific endonuclease cleavage site sequence or by synthesizing a copy of the cleaved target sequence-specific endonuclease cleavage site sequence. Donor DNA templates can be synthesized either chemically or enzymatically (e.g., in a polymerase chain reaction (PCR)). Donor DNA templates provided herein include those comprising CgRRS sequences flanked by DNA with homology to a donor polynucleotide.
INIR6 transgenic loci comprising deletions in a 5′ or a 3′ junction polynucleotide and/or deletions of all or a portion of the PAT selectable marker cassette are also provided herein. An INIR6-4 locus of SEQ ID NO: 22 comprising a deletion in a 3′ junction polynucleotide can be obtained by using a Cas12a nuclease, gRNA-1 (encoded by SEQ ID NO: 4), gRNA-2 (encoded by SEQ ID NO: 5), and the DNA donor template of SEQ ID NO: 32. An INIR6-5 locus of SEQ ID NO: 23 comprising a deletion in a 3′ junction polynucleotide deletion can be obtained by using a Cas12a nuclease, gRNA-2 (encoded by SEQ ID NO: 5), gRNA-3 (encoded by SEQ ID NO: 6), and the DNA donor template of SEQ ID NO: 33. An INIR6-6 locus of SEQ ID NO: 25 comprising a deletion in a 3′ junction polynucleotide and deletion of a PAT selectable marker cassette can be obtained by using a Cas12a nuclease, gRNA-1 (encoded by SEQ ID NO: 4), gRNA-4 (encoded by SEQ ID NO: 24), and the DNA donor template of SEQ ID NO: 34. An INIR6-8 locus of SEQ ID NO: 29 comprising a deletion of the CaMV35S promoter and PAT coding region of the PAT selectable marker cassette can be obtained by using a Cas12a nuclease, gRNA-4 (encoded by SEQ ID NO: 24), gRNA-5 (encoded by SEQ ID NO: 28), and the DNA donor template of SEQ ID NO: 35.
Various treatments are useful in delivery of gene editing molecules and/or other molecules to a DP-4114 or INIR6 plant cell. In certain embodiments, one or more treatments is employed to deliver the gene editing or other molecules (e.g., comprising a polynucleotide, polypeptide or combination thereof) into a eukaryotic or plant cell, e.g., through barriers such as a cell wall, a plasma membrane, a nuclear envelope, and/or other lipid bilayer. In certain embodiments, a polynucleotide-, polypeptide-, or RNP-containing composition comprising the molecules are delivered directly, for example by direct contact of the composition with a plant cell. Aforementioned compositions can be provided in the form of a liquid, a solution, a suspension, an emulsion, a reverse emulsion, a colloid, a dispersion, a gel, liposomes, micelles, an injectable material, an aerosol, a solid, a powder, a particulate, a nanoparticle, or a combination thereof can be applied directly to a plant, plant part, plant cell, or plant explant (e.g., through abrasion or puncture or otherwise disruption of the cell wall or cell membrane, by spraying or dipping or soaking or otherwise directly contacting, by microinjection). For example, a plant cell or plant protoplast is soaked in a liquid genome editing molecule-containing composition, whereby the agent is delivered to the plant cell. In certain embodiments, the agent-containing composition is delivered using negative or positive pressure, for example, using vacuum infiltration or application of hydrodynamic or fluid pressure. In certain embodiments, the agent-containing composition is introduced into a plant cell or plant protoplast, e.g., by microinjection or by disruption or deformation of the cell wall or cell membrane, for example by physical treatments such as by application of negative or positive pressure, shear forces, or treatment with a chemical or physical delivery agent such as surfactants, liposomes, or nanoparticles; see, e.g., delivery of materials to cells employing microfluidic flow through a cell-deforming constriction as described in US Published Patent Application 2014/0287509, incorporated by reference in its entirety herein. Other techniques useful for delivering the agent-containing composition to a eukaryotic cell, plant cell or plant protoplast include: ultrasound or sonication; vibration, friction, shear stress, vortexing, cavitation; centrifugation or application of mechanical force; mechanical cell wall or cell membrane deformation or breakage; enzymatic cell wall or cell membrane breakage or permeabilization; abrasion or mechanical scarification (e.g., abrasion with carborundum or other particulate abrasive or scarification with a file or sandpaper) or chemical scarification (e.g., treatment with an acid or caustic agent); and electroporation. In certain embodiments, the agent-containing composition is provided by bacterially mediated (e.g., Agrobacterium sp., Rhizobium sp., Sinorhizobium sp., Mesorhizobium sp., Bradyrhizobium sp., Azobacter sp., Phyllobacterium sp.) transfection of the plant cell or plant protoplast with a polynucleotide encoding the genome editing molecules (e.g., RNA dependent DNA endonuclease, RNA dependent DNA binding protein, RNA dependent nickase, ABE, or CBE, and/or guide RNA); see, e.g., Broothaerts et al. (2005) Nature, 433:629-633). Any of these techniques or a combination thereof are alternatively employed on the plant explant, plant part or tissue or intact plant (or seed) from which a plant cell is optionally subsequently obtained or isolated; in certain embodiments, the agent-containing composition is delivered in a separate step after the plant cell has been isolated.
In some embodiments, one or more polynucleotides or vectors driving expression of one or more genome editing molecules or trait-conferring genes (e.g., herbicide tolerance, insect resistance, and/or male sterility) are introduced into a DP-4114 or INIR6 plant cell. In certain embodiments, a polynucleotide vector comprises a regulatory element such as a promoter operably linked to one or more polynucleotides encoding genome editing molecules and/or trait-conferring genes. In such embodiments, expression of these polynucleotides can be controlled by selection of the appropriate promoter, particularly promoters functional in a eukaryotic cell (e.g., plant cell); useful promoters include constitutive, conditional, inducible, and temporally or spatially specific promoters (e.g., a tissue specific promoter, a developmentally regulated promoter, or a cell cycle regulated promoter). Developmentally regulated promoters that can be used in plant cells include Phospholipid Transfer Protein (PLTP), fructose-1,6-bi sphosphatase protein, NAD(P)-binding Rossmann-Fold protein, adipocyte plasma membrane-associated protein-like protein, Rieske [2Fe-2S] iron-sulfur domain protein, chlororespiratory reduction 6 protein, D-glycerate 3-kinase, chloroplastic-like protein, chlorophyll a-b binding protein 7, chloroplastic-like protein, ultraviolet-B-repressible protein, Soul heme-binding family protein, Photosystem I reaction center subunit psi-N protein, and short-chain dehydrogenase/reductase protein that are disclosed in US Patent Application Publication No. 20170121722, which is incorporated herein by reference in its entirety and specifically with respect to such disclosure. In certain embodiments, the promoter is operably linked to nucleotide sequences encoding multiple guide RNAs, wherein the sequences encoding guide RNAs are separated by a cleavage site such as a nucleotide sequence encoding a microRNA recognition/cleavage site or a self-cleaving ribozyme (see, e.g., Ferré-D'Amaré and Scott (2014) Cold Spring Harbor Perspectives Biol., 2:a003574). In certain embodiments, the promoter is an RNA polymerase III promoter operably linked to a nucleotide sequence encoding one or more guide RNAs. In certain embodiments, the RNA polymerase III promoter is a plant U6 spliceosomal RNA promoter, which can be native to the genome of the plant cell or from a different species, e.g., a U6 promoter from maize, tomato, or soybean such as those disclosed U.S. Patent Application Publication 2017/0166912, or a homologue thereof; in an example, such a promoter is operably linked to DNA sequence encoding a first RNA molecule including a Cas12a gRNA followed by an operably linked and suitable 3′ element such as a U6 poly-T terminator. In another embodiment, the RNA polymerase III promoter is a plant U3, 7SL (signal recognition particle RNA), U2, or U5 promoter, or chimerics thereof, e.g., as described in U.S. Patent Application Publication 20170166912. In certain embodiments, the promoter operably linked to one or more polynucleotides is a constitutive promoter that drives gene expression in eukaryotic cells (e.g., plant cells). In certain embodiments, the promoter drives gene expression in the nucleus or in an organelle such as a chloroplast or mitochondrion. Examples of constitutive promoters for use in plants include a CaMV 35S promoter as disclosed in U.S. Pat. Nos. 5,858,742 and 5,322,938, a rice actin promoter as disclosed in U.S. Pat. No. 5,641,876, a maize chloroplast aldolase promoter as disclosed in U.S. Pat. No. 7,151,204, and the nopaline synthase (NOS) and octopine synthase (OCS) promoters from Agrobacterium tumefaciens. In certain embodiments, the promoter operably linked to one or more polynucleotides encoding elements of a genome-editing system is a promoter from figwort mosaic virus (FMV), a RUBISCO promoter, or a pyruvate phosphate dikinase (PPDK) promoter, which is active in photosynthetic tissues. Other contemplated promoters include cell-specific or tissue-specific or developmentally regulated promoters, for example, a promoter that limits the expression of the nucleic acid targeting system to germline or reproductive cells (e.g., promoters of genes encoding DNA ligases, recombinases, replicases, or other genes specifically expressed in germline or reproductive cells). In certain embodiments, the genome alteration is limited only to those cells from which DNA is inherited in subsequent generations, which is advantageous where it is desirable that expression of the genome-editing system be limited in order to avoid genotoxicity or other unwanted effects. All of the patent publications referenced in this paragraph are incorporated herein by reference in their entirety.
Expression vectors or polynucleotides provided herein may contain a DNA segment near the 3′ end of an expression cassette that acts as a signal to terminate transcription and directs polyadenylation of the resultant mRNA and may also support promoter activity. Such a 3′ element is commonly referred to as a “3′-untranslated region” or “3′-UTR” or a “polyadenylation signal.” In some cases, plant gene-based 3′ elements (or terminators) consist of both the 3′-UTR and downstream non-transcribed sequence (Nuccio et al., 2015). Useful 3′ elements include: Agrobacterium tumefaciens nos 3′, tml 3′, tmr 3′, tms 3′, ocs 3′, and tr7 3′ elements disclosed in U.S. Pat. No. 6,090,627, incorporated herein by reference, and 3′ elements from plant genes such as the heat shock protein 17, ubiquitin, and fructose-1,6-biphosphatase genes from wheat (Triticum aestivum), and the glutelin, lactate dehydrogenase, and beta-tubulin genes from rice (Oryza sativa), disclosed in US Patent Application Publication 2002/0192813 A1. All of the patent publications referenced in this paragraph are incorporated herein by reference in their entireties.
In certain embodiments, the DP-4114 or INIR6 plant cells used herein can comprise haploid, diploid, or polyploid plant cells or plant protoplasts, for example, those obtained from a haploid, diploid, or polyploid plant, plant part or tissue, or callus. In certain embodiments, plant cells in culture (or the regenerated plant, progeny seed, and progeny plant) are haploid or can be induced to become haploid; techniques for making and using haploid plants and plant cells are known in the art, see, e.g., methods for generating haploids in Arabidopsis thaliana by crossing of a wild-type strain to a haploid-inducing strain that expresses altered forms of the centromere-specific histone CENH3, as described by Maruthachalam and Chan in “How to make haploid Arabidopsis thaliana”, protocol available at www[dot]openwetware[dot]org/images/d/d3/Haploid_Arabidopsis_protocol[dot]pdf; (Ravi et al. (2014) Nature Communications, 5:5334, doi: 10.1038/ncomms6334). Haploids can also be obtained in a wide variety of monocot plants (e.g., maize, wheat, rice, sorghum, barley) by crossing a plant comprising a mutated CENH3 gene with a wildtype diploid plant to generate haploid progeny as disclosed in U.S. Pat. No. 9,215,849, which is incorporated herein by reference in its entirety. Haploid-inducing maize lines that can be used to obtain haploid maize plants and/or cells include Stock 6, MHI (Moldovian Haploid Inducer), indeterminate gametophyte (ig) mutation, KEMS, RWK, ZEM, ZMS, KMS, and well as transgenic haploid inducer lines disclosed in U.S. Pat. No. 9,677,082, which is incorporated herein by reference in its entirety. Examples of haploid cells include but are not limited to plant cells obtained from haploid plants and plant cells obtained from reproductive tissues, e.g., from flowers, developing flowers or flower buds, ovaries, ovules, megaspores, anthers, pollen, megagametophyte, and microspores. In certain embodiments where the plant cell or plant protoplast is haploid, the genetic complement can be doubled by chromosome doubling (e.g., by spontaneous chromosomal doubling by meiotic non-reduction, or by using a chromosome doubling agent such as colchicine, oryzalin, trifluralin, pronamide, nitrous oxide gas, anti-microtubule herbicides, anti-microtubule agents, and mitotic inhibitors) in the plant cell or plant protoplast to produce a doubled haploid plant cell or plant protoplast wherein the complement of genes or alleles is homozygous; yet other embodiments include regeneration of a doubled haploid plant from the doubled haploid plant cell or plant protoplast. Another embodiment is related to a hybrid plant having at least one parent plant that is a doubled haploid plant provided by this approach. Production of doubled haploid plants provides homozygosity in one generation, instead of requiring several generations of self-crossing to obtain homozygous plants. The use of doubled haploids is advantageous in any situation where there is a desire to establish genetic purity (i.e., homozygosity) in the least possible time. Doubled haploid production can be particularly advantageous in slow-growing plants or for producing hybrid plants that are offspring of at least one doubled-haploid plant.
In certain embodiments, the DP-4114 or INIR6 plant cells used in the methods provided herein can include non-dividing cells. Such non-dividing cells can include plant cell protoplasts, plant cells subjected to one or more of a genetic and/or pharmaceutically-induced cell-cycle blockage, and the like.
In certain embodiments, the DP-4114 or INIR6 plant cells in used in the methods provided herein can include dividing cells. Dividing cells can include those cells found in various plant tissues including leaves, meristems, and embryos. These tissues include dividing cells from young maize leaf, meristems and scutellar tissue from about 8 or 10 to about 12 or 14 days after pollination (DAP) embryos. The isolation of maize embryos has been described in several publications (Brettschneider, Becker, and Lorz 1997; Leduc et al. 1996; Frame et al. 2011; K. Wang and Frame 2009). In certain embodiments, basal leaf tissues (e.g., leaf tissues located about 0 to 3 cm from the ligule of a maize plant; Kirienko, Luo, and Sylvester 2012) are targeted for HDR-mediated gene editing. Methods for obtaining regenerable plant structures and regenerating plants from the NHEJ-, MMEJ-, or HDR-mediated gene editing of plant cells provided herein can be adapted from methods disclosed in US Patent Application Publication No. 20170121722, which is incorporated herein by reference in its entirety and specifically with respect to such disclosure. In certain embodiments, single plant cells subjected to the HDR-mediated gene editing will give rise to single regenerable plant structures. In certain embodiments, the single regenerable plant cell structure can form from a single cell on, or within, an explant that has been subjected to the NHEJ-, MMEJ-, or HDR-mediated gene editing.
In some embodiments, methods provided herein can include the additional step of growing or regenerating an INIR6 plant from a INIR6 plant cell that had been subjected to the gene editing or from a regenerable plant structure obtained from that INIR6 plant cell. In certain embodiments, the plant can further comprise an inserted transgene, a target gene edit, or genome edit as provided by the methods and compositions disclosed herein. In certain embodiments, callus is produced from the plant cell, and plantlets and plants produced from such callus. In other embodiments, whole seedlings or plants are grown directly from the plant cell without a callus stage. Thus, additional related aspects are directed to whole seedlings and plants grown or regenerated from the plant cell or plant protoplast having a target gene edit or genome edit, as well as the seeds of such plants. In certain embodiments wherein the plant cell or plant protoplast is subjected to genetic modification (for example, genome editing by means of, e.g., an RdDe), the grown or regenerated plant exhibits a phenotype associated with the genetic modification. In certain embodiments, the grown or regenerated plant includes in its genome two or more genetic or epigenetic modifications that in combination provide at least one phenotype of interest. In certain embodiments, a heterogeneous population of plant cells having a target gene edit or genome edit, at least some of which include at least one genetic or epigenetic modification, is provided by the method; related aspects include a plant having a phenotype of interest associated with the genetic or epigenetic modification, provided by either regeneration of a plant having the phenotype of interest from a plant cell or plant protoplast selected from the heterogeneous population of plant cells having a target gene or genome edit, or by selection of a plant having the phenotype of interest from a heterogeneous population of plants grown or regenerated from the population of plant cells having a targeted genetic edit or genome edit. Examples of phenotypes of interest include herbicide resistance, improved tolerance of abiotic stress (e.g., tolerance of temperature extremes, drought, or salt) or biotic stress (e.g., resistance to nematode, bacterial, or fungal pathogens), improved utilization of nutrients or water, modified lipid, carbohydrate, or protein composition, improved flavor or appearance, improved storage characteristics (e.g., resistance to bruising, browning, or softening), increased yield, altered morphology (e.g., floral architecture or color, plant height, branching, root structure). In an embodiment, a heterogeneous population of plant cells having a target gene edit or genome edit (or seedlings or plants grown or regenerated therefrom) is exposed to conditions permitting expression of the phenotype of interest; e.g., selection for herbicide resistance can include exposing the population of plant cells having a target gene edit or genome edit (or seedlings or plants grown or regenerated therefrom) to an amount of herbicide or other substance that inhibits growth or is toxic, allowing identification and selection of those resistant plant cells (or seedlings or plants) that survive treatment. Methods for obtaining regenerable plant structures and regenerating plants from plant cells or regenerable plant structures can be adapted from published procedures (Roest and Gilissen, Acta Bot. Neerl., 1989, 38(1), 1-23; Bhaskaran and Smith, Crop Sci. 30(6):1328-1337; Ikeuchi et al., Development, 2016, 143: 1442-1451). Methods for obtaining regenerable plant structures and regenerating plants from plant cells or regenerable plant structures can also be adapted from US Patent Application Publication No. 20170121722, which is incorporated herein by reference in its entirety and specifically with respect to such disclosure. Also provided are heterogeneous or homogeneous populations of such plants or parts thereof (e.g., seeds), succeeding generations or seeds of such plants grown or regenerated from the plant cells or plant protoplasts, having a target gene edit or genome edit. Additional related aspects include a hybrid plant provided by crossing a first plant grown or regenerated from a plant cell or plant protoplast having a target gene edit or genome edit and having at least one genetic or epigenetic modification, with a second plant, wherein the hybrid plant contains the genetic or epigenetic modification; also contemplated is seed produced by the hybrid plant. Also envisioned as related aspects are progeny seed and progeny plants, including hybrid seed and hybrid plants, having the regenerated plant as a parent or ancestor. The plant cells and derivative plants and seeds disclosed herein can be used for various purposes useful to the consumer or grower. In other embodiments, processed products are made from the INIR6 plant or its seeds, including: (a) maize seed meal (defatted or non-defatted); (b) extracted proteins, oils, sugars, and starches; (c) fermentation products; (d) animal feed or human food products (e.g., feed and food comprising maize seed meal (defatted or non-defatted) and other ingredients (e.g., other cereal grains, other seed meal, other protein meal, other oil, other starch, other sugar, a binder, a preservative, a humectant, a vitamin, and/or mineral; (e) a pharmaceutical; (f) raw or processed biomass (e.g., cellulosic and/or lignocellulosic material); and (g) various industrial products.
EmbodimentsVarious embodiments of the plants, genomes, methods, biological samples, and other compositions described herein are set forth in the following sets of numbered embodiments.
1a. A transgenic maize plant cell comprising an INIR6 transgenic locus comprising an originator guide RNA recognition site (OgRRS) in a first DNA junction polynucleotide of a DP-4114 transgenic locus and a cognate guide RNA recognition site (CgRRS) in a second DNA junction polynucleotide of the DP-4114 transgenic locus.
1b. A transgenic maize plant cell comprising an INIR6 transgenic locus comprising an insertion and/or substitution of DNA in a DNA junction polynucleotide of a DP-4114 transgenic locus with DNA comprising a cognate guide RNA recognition site (CgRRS), a deletion of a 5′ or 3′ DNA junction polynucleotide of the DP-4114 transgenic locus, a deletion of a phosphinotricin acetyltransferase (PAT) selectable marker gene of the DP-4114 transgenic locus, and/or a deletion of DNA comprising, consisting essentially of, or consisting of the CaMV35S promoter and operably linked PAT coding region of the DP-4114 transgenic locus.
2. The transgenic maize plant cell of embodiment 1a or 1b, wherein said CgRRS comprises the DNA molecule set forth in SEQ ID NO: 8, 9, 10, or 19; and/or wherein said DP-4114 transgenic locus is set forth in SEQ ID NO: 1, is present in seed deposited at the ATCC under accession No. PTA-11506, is present in progeny thereof, is present in allelic variants thereof, or is present in other variants thereof.
3. The transgenic maize plant cell of embodiments 1a, 1b, or 2, wherein said INIR6 transgenic locus comprises the DNA molecule set forth in SEQ ID NO: 2, 3, 20, 22, 23, 25, 26, 29, 30, 31, or an allelic variant thereof.
4. A transgenic maize plant part comprising the maize plant cell of any one of embodiments 1a, 1b, 2, or 3, wherein said maize plant part is optionally a seed.
5. A transgenic maize plant comprising the maize plant cell of any one of embodiments 1a, 1b, 2, or 3.
6. A method for obtaining a bulked population of inbred seed comprising selfing the transgenic maize plant of embodiment 5 and harvesting seed comprising the INIR6 transgenic locus from the selfed maize plant.
7. A method of obtaining hybrid maize seed comprising crossing the transgenic maize plant of embodiment 5 to a second maize plant which is genetically distinct from the first maize plant and harvesting seed comprising the INIR6 transgenic locus from the cross.
8. A DNA molecule comprising SEQ ID NO: 2, 3, 8, 9, 10, 19, 20, 22, 23, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, or an allelic variant thereof.
9. A processed transgenic maize plant product comprising the DNA molecule of embodiment 8.
10. A biological sample containing the DNA molecule of embodiment 8.
11. A nucleic acid molecule adapted for detection of genomic DNA comprising the DNA molecule of embodiment 8, wherein said nucleic acid molecule optionally comprises a detectable label.
12. A method of detecting a maize plant cell comprising the INIR6 transgenic locus of any one of embodiments 1a, 1b, 2, or 3, comprising the step of detecting DNA molecule comprising SEQ ID NO: 2, 3, 8, 9, 10, 19, 20, 22, 23, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, or an allelic variant thereof.
13. A method of excising the INIR6 transgenic locus from the genome of the maize plant cell of any one of embodiments 1a, 1b, 2, or 3, comprising the steps of:
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- (a) contacting the edited transgenic plant genome of the plant cell of embodiment 5 with: (i) an RNA dependent DNA endonuclease (RdDe); and (ii) a guide RNA (gRNA) capable of hybridizing to the guide RNA hybridization site of the OgRRS and the CgRRS; wherein the RdDe recognizes a OgRRS/gRNA and a CgRRS/gRNA hybridization complex; and,
- (b) selecting a transgenic plant cell, transgenic plant part, or transgenic plant wherein the INIR6 transgenic locus flanked by the OgRRS and the CgRRS has been excised.
14. The method of embodiment 13, wherein the INIR6 transgenic locus of the maize plant cell comprises the CgRRS of SEQ ID NO: 26, 19, 8, 9, or 10 and the guide RNA comprises an RNA sequence encoded by SEQ ID NO: 16.
15. The method of embodiment 14, wherein the maize plant cell comprises the INIR6 transgenic locus of SEQ ID NO: 2, 3, 20, 26, 31, or an allelic variant thereof.
EXAMPLES Example 1. Introduction of a CgRRS in a 3′ Junction Polynucleotide of a DP-4114 Transgenic LocusTransgenic plant genomes containing one or more of the following transgenic loci (events) are contacted with:
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- (i) an ABE or CBE and guide RNAs which recognize the indicated target DNA sites (protospacer (guide RNA coding) plus PAM site) in the 5′ or 3′ junction polynucleotides of the event to introduce a CgRRS in the junction polynucleotide;
- (ii) an RdDe and guide RNAs which recognize the indicated target DNA site (guide RNA coding plus PAM site) in the 5′ or 3′ junction polynucleotides of the event as well as a donor DNA template spanning the double stranded DNA break site in the junction polynucleotide to introduce a CgRRS in a junction polynucleotide.
- Plant cells, callus, parts, or whole plants comprising the introduced CgRRS in the transgenic plant genome are selected.
Two plant gene expression vectors are prepared. Plant expression cassettes for expressing a bacteriophage lambda exonuclease, a bacteriophage lambda beta SSAP protein, and an E. coli SSB are constructed essentially as set forth in US Patent Application Publication 20200407754, which is incorporated herein by reference in its entirety. A DNA sequence encoding a tobacco c2 nuclear localization signal (NLS) is fused in-frame to the DNA sequences encoding the exonuclease, the bacteriophage lambda beta SSAP protein, and the E. coli SSB to provide a DNA sequence encoding the c2 NLS-Exo, c2 NLS lambda beta SSAP, and c2 NLS-SSB fusion proteins that are set forth in SEQ ID NO: 135, SEQ ID NO: 134, and SEQ ID NO: 133 of US Patent Application Publication 20200407754, respectively, and incorporated herein by reference in its entirety. DNA sequences encoding the c2 NLS-Exo, c2 NLS lambda beta SSAP, and c2NLS-SSB fusion proteins are operably linked to a OsUBI1, ZmUBI1, OsACT promoter and a OsUbi1, ZmUBI1, OsACT polyadenylation site respectively, to provide the exonuclease, SSAP, and SSB plant expression cassettes.
A DNA donor template sequence (SEQ ID NO: 14) that targets the 3′-T-DNA junction polynucleotide of the DP-4114 event (SEQ ID NO:1;
A plant expression cassette that provides for expression of the RNA-guided sequence-specific Cas12a endonuclease is constructed. A plant expression cassette that provides for expression of a guide RNA (e.g., encoded by SEQ ID NO: 5) complementary to sequences adjacent to the insertion site is constructed. An Agrobacterium superbinary plasmid transformation vector containing a cassette that provides for the expression of a suitable plant selectable marker (e.g., a glyphosate tolerant EPSPS, a neomycin phosphotransferase (nptII), a hygromycin phosphotransferase (hptII), or a phosphomannose isomerase (pmi)) is constructed. Once the cassettes, donor sequence and Agrobacterium superbinary plasmid transformation vector are constructed, they are combined to generate two maize transformation plasmids.
A maize transformation plasmid is constructed with the selectable marker cassette, the RNA-guided sequence-specific endonuclease cassette, the guide RNA cassette, and the DP-41145′-T_DNA junction sequence DNA donor sequence into the Agrobacterium superbinary plasmid transformation vector (the control vector).
A maize transformation plasmid is constructed with the selectable marker cassette, the RNA-guided sequence-specific endonuclease cassette, the guide RNA cassette, the SSB cassette, the lambda beta SSAP cassette, the Exo cassette, and the DP-4114 5′-DNA junction sequence donor DNA template sequence (e.g., SEQ ID NO: 14) into the Agrobacterium superbinary plasmid transformation vector (the lambda red vector).
All constructs are transformed into Agrobacterium strain LBA4404.
Maize transformations are performed based on published methods (e.g., Ishida et. al, Nature Protocols 2007; 2, 1614-1621; U.S. Pat. Nos. 7,064,248; 8,212,113; 8,450,561; 8,455,720; all incorporated herein by reference in their entireties). In certain instances, immature embryos approximately 1.8-2.2 mm in size, are isolated from surface sterilized ears 10-14 days after pollination. Embryos are placed in an Agrobacterium suspension made with infection medium at a concentration of OD 600=1.0. Acetosyringone (200 μM) is added to the infection medium at the time of use. Embryos and Agrobacterium are placed on a rocker shaker at slow speed for 15 minutes. Embryos are then poured onto the surface of a plate of co-culture medium. Excess liquid media is removed by tilting the plate and drawing off all liquid with a pipette. Embryos are flipped as necessary to maintain a scutelum up orientation. Co-culture plates are placed in a box with a lid and cultured in the dark at 22° C. for 3 days. Embryos are then transferred to resting medium, maintaining the scutellum up orientation. Embryos remain on resting medium for 7 days at 27-28° C. Embryos that produced callus are transferred to Selection 1 medium with a suitable concentration of the selection agent for the selectable marker gene selected and cultured for an additional, suitable time period (e.g. 7 days). In some instances, glyphosate is used as the selection agent for a glyphosate tolerant EPSPS selectable marker (e.g., as in U.S. Pat. No. 8,212,113, incorporated herein by reference in its entirety). In some instances, kanamycin, paromomycin, or G418 is used as the selection agent for a nptII selectable marker (e.g., as in U.S. Pat. No. 8,450,561, incorporated herein by reference in its entirety). In some instances, hygromycin is used as the selection agent for an hptII selectable marker (e.g., as in U.S. Pat. No. 7,064,248, incorporated herein by reference in its entirety). In some instances, media comprising mannose as a sole carbon source is used as the selection agent for a pmi selectable marker (as in U.S. Pat. No. 8,455,720, incorporated herein by reference in its entirety). Callused embryos are placed on Selection 2 medium with a suitable concentration of the selection agent and cultured for 14 days at 27-28° C. Growing calli resistant to the selection agent are transferred to Pre-Regeneration media with a suitable concentration of the selection agent to initiate shoot development. Calli remained on Pre-Regeneration media for a suitable time period (e.g., 7 days). Calli beginning to initiate shoots are transferred to Regeneration medium with a suitable concentration of the selection agent in Phytatrays and cultured in light at 27-28° C. Shoots that reached the top of the Phytatray with intact roots are isolated into Shoot Elongation medium prior to transplant into soil and gradual acclimatization to greenhouse conditions.
When a sufficient amount of viable tissue is obtained, it can be screened for insertion at the DP-4114 junction sequence, using a PCR-based approach. The PCR primer on the 5′-end is 5′-tacgctgggccctggaaggctagga-3′ (SEQ ID NO: 17). The PCR primer on the 3′-end is 5′-gatggacgagacgaggcggtggaga-3′ (SEQ ID NO: 18). The above primers that flank donor DNA homology arms are used to amplify the DP-4114 3′-junction polynucleotide sequence. The correct donor sequence insertion will produce a 1563 bp product. A unique DNA fragment comprising the CgRRS in the DP-4114 3′ junction polynucleotide is set forth in SEQ ID NO: 19. Amplicons can be sequenced directly using an amplicon sequencing approach or ligated to a convenient plasmid vector for Sanger sequencing. Those plants in which the DP-4114 junction sequence now contains the intended Cas12a recognition sequence are selected and grown to maturity. The T-DNA encoding the Cas12a reagents can be segregated away from the modified junction sequence in a subsequent generation. The resultant INIR6 transgenic locus (SEQ ID NO: 20) comprising the CgRRS and OgRRS (e.g., which each comprise SEQ ID NO: 7) can be excised using Cas12a and a suitable gRNA which hybridizes to DNA comprising SEQ ID NO: 7 at both the OgRRS and the CgRRS.
The breadth and scope of the present disclosure should not be limited by any of the above-described embodiments.
Claims
1. A transgenic maize plant cell comprising an INIR6 transgenic locus comprising the DNA molecule of SEQ ID NO: 34, the Cry1F, Cry34Ab1, and Cry35Ab1 genes of the DP-4114 transgenic locus and a deletion of both the 3′ DNA junction polynucleotide and phosphinotricin acetyltransferase (PAT) selectable marker gene of the DP-4114 transgenic locus.
2. The transgenic maize plant cell of claim 1, wherein the INIR6 transgenic locus comprises the DNA molecule of SEQ ID NO: 25.
3. (canceled)
4. A transgenic maize plant part comprising the maize plant cell of claim 1.
5. A The transgenic maize plant part of claim 4, wherein said maize plant part is a seed.
6. A transgenic maize plant comprising the maize plant cell of claim 1.
7. A method for obtaining a bulked population of inbred seed comprising selfing the transgenic maize plant of claim 6 and harvesting seed comprising the INIR6 transgenic locus from the selfed maize plant.
8. A method of obtaining hybrid maize seed comprising crossing the transgenic maize plant of claim 6 to a second maize plant which is genetically distinct from the first maize plant and harvesting seed comprising the INIR6 transgenic locus from the cross.
9.-22. (canceled)
Type: Application
Filed: Jul 24, 2023
Publication Date: Jan 4, 2024
Inventors: Michael Lee Nuccio (Salem, NH), Michael Andreas Kock (Rheinfelden), Joshua L. Price (Cambridge, MA)
Application Number: 18/357,624
