Peptides in Inhibiting Insects
The subject invention pertains to the use of peptide fragments of cadherins (including cadherin-like proteins). The subject invention includes a cell (and use thereof) comprising a polynucleotide that expresses the peptide fragment. The subject invention includes methods of feeding the peptides to insects. In preferred embodiments, the peptides are fed to target insects together with one or more insecticidal proteins, preferably (but not limited to) B.t. Cry proteins. When used in this manner, the peptide fragment can not only enhance the apparent toxin activity of the Cry protein against the insect species that was the source of the receptor but also against other insect species. Preferably, the cadherin is a Bacillus thuringiensis (B.t.) insecticidal crystal protein (Cry) toxin receptor. Preferably, the peptide fragment is a binding domain of the receptor. In some preferred embodiments, the peptide is the binding domain nearest to the membrane proximal ectodomain. Corresponding domains are identifiable in a variety of B.t. toxin receptors.
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This application is a continuation of U.S. Ser. No. 11/040,472, filed Jan. 21, 2005, which claims priority to provisional application Ser. No. 60/538,715, filed Jan. 22, 2004.
GOVERNMENTAL RIGHTSThis invention was made in part with government support under Grant No. AI 29092 awarded by the National Institutes of Health. The government may have certain rights in this invention.
BACKGROUND OF THE INVENTIONVarious receptors on insect cells for Bacillus thuringiensis (B.t.) insecticidal toxin proteins are known in the art. See, e.g., U.S. Pat. Nos. 6,586,197; 6,429,360; 6,137,033; and 5,688,691. However, no known prior art taught or suggested administering fragments of cadherin-like proteins, especially fragments of B.t. toxin receptors, to insects.
Bacillus thuringiensis as an Insecticide. Bacillus thuringiensis (B. A) is a facultative anaerobic, Gram-positive, motile, spore-forming bacterium. B.t. is accepted as a source of environment-friendly biopesticide. Farmers have applied B.t. as an insecticidal spray for control of lepidopteran and coleopteran pests for more than 30 years. The United States Environmental Protection Agency has considered B.t. sprays to be so safe that it has exempted them from the requirement of a tolerance (a standard for a maximum permissible residue limit on food).
There are other alternatives for delivery of B.t. toxin to target insects. B.t. toxin genes are inserted into microorganisms that are associated with the target insect habitat so that the transformed organisms will colonize and continue to produce enough quantities of toxin to prevent insect damage. Examples of these are the insertion of specific genes into bacteria that colonize plant leaf surface and roots externally, such as Pseudomonas cepacia, or internally, such as Clavibacter xyli. However, the release of living recombinant microorganisms causes many concerns and regulatory restrictions. Alternative methods of introducing genes into microorganisms have been developed to minimize potential horizontal gene flow to other bacterial species. These include using transposase-negative derivatives of Tn5 transposon, or suicide vectors that rely on homologous recombination for integration to be completed. There has also been a development of non-viable recombinant organisms that could increase toxin persistence in the field, such as products based on encapsulated B.t. toxins in P. fluorescens. This approach eliminates concerns associated with testing of living genetically engineered microorganisms.
B.t. proteins may be delivered in transgenic plants. Examples of such plants, called B.t. plants, protected from insect attack include cotton and corn. The U.S. Environmental Protection Agency has approved the commercial planting of B.t. cotton and corn since 1996.
The mechanism of action of the B.t. toxins proceeds through several steps that include solubilization of ingested crystal, proteolytic activation of the protoxins, binding of toxin to midgut receptors, and insertion of the toxin into the apical membrane to form ion channels or pores. Binding of the toxin to brush border membrane vesicles (BBMV) is supposed to be a two-step process involving reversible and irreversible steps. Multiple receptors may be involved in the process of toxin binding and membrane insertion.
Tabashnik et al. (Tabashnik 1992) described the phenomenon of synergy for B.t. Cry toxins and developed a formula for calculating synergy. Cry proteins are considered synergistic if the combined insecticidal potency is greater than the sum of the individual components. Cry1Aa and Cry1Ac are synergistic in bioassays against gypsy moth larvae (Lee and Dean, 1996). Other examples of B.t. synergy are reported for the Cry proteins of B.t. israelensis and combinations of spores and crystals against Plutella xylostella, the diamondback moth (Liu et al., 1998). Non-B.t. molecules are also known to synergize toxins. For example, ethylenediamine tetra acetic acid (EDTA) synergizes B.t. against P. xylostella. The synergy described herein is novel both in the nature of the synergistic molecule and the effect detected on important Lepidoptera larvae.
B.t. Toxin Receptors. Characterization of receptors from insect midgut and investigation of their interaction with Cry toxins provides an approach to elucidating toxin mode of action and designing improved Cry toxins for pest control. Most Cry toxin-binding midgut proteins identified to date belong to two main protein families: cadherin-like proteins and aminopeptidases. There is in vitro and in vivo evidence supporting the involvement of aminopeptidases in Cry1 toxicity against lepidopteran larvae. Aminopeptidases bind Cry toxins specifically allowing them to form pores in membranes (Masson et al., 1995; Sangadala et al., 2001; Sangadala et al., 1994). Recent studies provide evidence that aminopeptidase can function as receptors when expressed in cultured cells (Adang and Luo 2003) and insects (Gill and Ellar 2002; Rajagopal et al., 2002). Aminopeptidases do not always confer susceptibility to Cry toxins when expressed in heterologous systems (Banks et al., 2003; Simpson and Newcomb 2000).
Cadherin-like proteins are a class of Cry1 receptor proteins in lepidopteran larvae. Bombyx mori, the silkmoth, has a 175-kDa cadherin-like protein called BtR175 that functions as a receptor for Cry1Aa and Cry1Ac toxins on midgut epithelial cells (Hara et al., 2003; Nagamatsu et al., 1999). M. sexta has a 210-kDa cadherin-like protein, called Bt-R1, that serves as a receptor for Cry1A toxins (Bulla 2002a, b; Vadlamudi et al., 1993; Vadlamudi et al., 1995). Bt-R1 binds Cry1Aa, Cry1Ab, and Cry1Ac toxins on ligand blots (Francis and Bulla 1997). Purified membranes from COS cells expressing Bt-R1 bound all three Cry1A toxins in binding assays and ligand blots (Keeton and Bulla 1997). Furthermore, expression of Bt-R1 on the surface of COS7 cells led to toxin-induced cell toxicity as monitored by immunofluorescence microscopy with fixed cells (Dorsch et al., 2002).
Cadherin-like Bt-R1 protein has been suggested to induce a conformational change in Cry1Ab that allows the formation of a pre-pore toxin oligomer and increases binding affinity for aminopeptidase (Bravo et al. 2004). In Bombyx mori, the cadherin-like protein BtR175 serves as a Cry1Aa receptor (Nagamatsu et al., 1998). Sf9 cells expressing BtR175 swell after exposure to Cry1Aa toxin, presumably due to formation of ion channels in cell membranes (Nagamatsu et al. 1999). When expressed in mammalian COS7 cells, BtR175 induced susceptibility to Cry1Aa (Tsuda et al., 2003).
Hua et al. (Hua et al. 2004) developed a fluorescence-based assay using Drosophila S2 cells to analyze the function of Manduca sexta cadherin (Bt-R1a) as a Cry1 toxin receptor. Bt-R1a cDNA that differs from Bt-R1 by 37 nucleotides and two amino acids and expressed it transiently in Drosophila melanogaster, Schneider 2 (S2) cells (Hua et al. 2004). Cells expressing Bt-R1a bound Cry1Aa, Cry1Ab, and Cry1Ac toxins on ligand blots, and in saturation binding assays. More Cry1Ab was bound relative to Cry1Aa and Cry1Ac, though each Cry1A toxin bound with high-affinity (Kd values from 1.7 nM to 3.3 nM). Using fluorescent microscopy and flow cytometry assays, (Hua et al. 2004) showed that Cry1Aa, Cry1Ab and Cry1Ac, but not Cry1Ba, killed S2 cells expressing Bt-R1a cadherin. These results demonstrated that M. sexta cadherin Bt-R1a functions as a receptor for the Cry1A toxins in vivo and validates our cytotoxicity assay for future receptor studies.
Involvement of a cadherin-superfamily gene disruption in resistance to Cry1Ac has been described for a laboratory resistant strain of Heliothis virescens (Gahan et al., 2001). The encoded protein, called HevCaLP, has the binding properties expected for a Cry1A receptor (Jurat-Fuentes et al. 2004). Similarly, Pectinophora gossypiella larvae with resistance alleles in genes encoding a cadherin-like protein were resistant to Cry1A toxins (Morin et al., 2003).
B.t. toxins bind to specific regions on cadherin-like proteins. Regions of domain II of Cry1A toxins are involved in binding to Bt-R1 (Gomez et al., 2002; Gomez et al., 2001). The first toxin binding region identified in Bt-R1 was a stretch of seven amino acid residues located in the cadherin repeat seven (CR7) (Gomez et al. 2002; Gomez et al. 2001). (Dorsch et al. 2002) identified a second Cry1Ab binding region within cadherin repeat 11 (CR11) in Bt-R1. Recombinant and synthetic peptides containing both amino acid sequences inhibited Cry1Ab toxicity in vivo when fed to M. sexta larvae (Dorsch et al. 2002; Gomez et al. 2001), demonstrating their involvement in toxin action. Previously, two Bt-R1 toxin-binding regions in CR 7 (Gomez et al. 2001) and 11 (Dorsch et al. 2002) were proposed as functional receptor sites. U.S. Ser. No. 60/538,753 entitled “Novel Binding Domain of Cadherin-like Toxin Receptor,” by Adang et al., under Attorney Docket No. UGR-104P, identifies an additional binding site recognized by Cry toxins that functions as a receptor. This additional binding site, which is also a functional receptor region, is contained in the CR12—Membrane Proximal Extracellular Domain (MPED) of Bt-R1a (Hua et al. 2004). The HevCaLP protein of H. virescens has a Cry1Ac binding site at a comparable position (Xie et al. 2004), suggesting a conservation of binding sites between cadherins of different insect species.
There is no known report or suggestion of a B.t. toxin receptor or fragment thereof being fed, or otherwise administered, to an insect pest, with or without a B.t. protein, in order to kill or otherwise prevent the insect from feeding on a plant. Previous competitive-binding studies suggest that there would be no change in toxicity (Gomez et al. 2002) or a reduction in toxicity due to competitive binding (Gomez et al. 2001; Dorsch et al. 2002; Gomez et al. 2003; Xie et al. 2004).
BRIEF SUMMARY OF THE INVENTIONThe subject invention pertains to the use of peptide fragments of proteins for controlling insects. In preferred embodiments, the source protein is a cadherin (including cadherin-like proteins) and/or a Bacillus thuringiensis (B.t.) crystal protein (Cry) toxin receptors. Preferably, the peptide fragment is a binding domain of the receptor. In some preferred embodiments, the peptide is the binding domain nearest to the membrane proximal ectodomain. Corresponding domains are identifiable in a variety of B.t. toxin receptors. Thus, one aspect of the invention pertains to the use of an isolated polynucleotide that encodes a protein comprising (or consisting of) a fragment of a cadherin-like protein.
In preferred embodiments, the peptides are fed to target insects together with one or more insecticidal proteins, preferably (but not limited to) B.t. Cry proteins. When used in this manner, the peptide fragment can not only enhance the apparent toxin activity of the Cry protein against the insect species that was the source of the receptor but also against other insect species.
The subject invention includes a cell (and use thereof) carrying the polynucleotide and expressing the peptide fragment, including methods of feeding the peptide (preferably with B.t. Cry toxins) to insects.
SEQ ID NO:1 is a nucleotide sequence that encodes the CR12-MPED peptide.
SEQ ID NO:2 is the amino acid sequence of the CR12-MPED peptide. This peptide may be referred to as “B.t. Booster” or “BTB.”
SEQ ID NO:3 shows the nucleotide sequence of CR11-MPED truncated form of M. sexta cadherin Bt-R1a. CR11-MPED can be referred to as BtB2, which has 324 amino acid residues from Bacillus thuringiensis-R1a encoding an approximately 35,447 Dalton protein (theoretical pI=4.72).
SEQ ID NO:4 shows the amino acid sequence of CR11-MPED truncated form of M. sexta cadherin Bt-R1a. This peptide is as-produced by E. coli strain BL21/DE3/pRIL cloned with the pET-30a vector.
SEQ ID NO:5 shows the nucleotide sequence of CR1-3 from M. sexta BtR1a.
SEQ ID NO:6 shows the amino acid sequence of CR1-3 from M. sexta BtR1a. This peptide is as-produced by E. coli strain BL21/DE3/pRIL cloned with the pET-30a vector.
SEQ ID NO:7 (file Anof-PCAPseq.doc) shows the nucleotide sequence of the putative cell adhesion protein of Anopheles gambiae (NCBI LOCUS XM—321513).
SEQ ID NO:8 (file Anof-PCAPseq.doc) shows the amino acid sequence of the putative cell adhesion protein of Anopheles gambiae (NCBI LOCUS XM—321513).
SEQ ID NO:9 shows the nucleotide sequence encoding “PCAP”—the truncation from the Anopheles gambiae putative cell-adhesion protein (P CAP).
SEQ ID NO:10 shows the truncated PCAP (putative cell-adhesion protein) region of the Anopheles gambiae protein. This truncated peptide is referred to herein as PCAP or Ano-PCAP (213 amino acid residues—a 24416.56 Dalton protein, theoretical pI 4.96). This peptide is as-produced from the DNA being cloned into pET-30a vector and expressed in E. coli strain BL21/DE3/pRIL.
SEQ ID NO:11 shows the full-length Anopheles gambiae cDNA cadherein sequence. BLAST search with the sequence matches the DNA and predicted protein sequence for a partial Anopheles gambiae cDNA NCBI Locus XM—312086).
SEQ ID NO:12 shows the “Ano-Cad”-encoding fragment of SEQ ID NO:11 that was cloned into the pET-30A vector and expressed in E. coli strain BL21/DE3.
SEQ ID NO:13 shows the full-length Anopheles gambiae cadherin protein encoded by SEQ ID NO:11. Residues 1358-1569 of SEQ ID NO:13 correspond to the “Ano-Cad” peptide encoded by SEQ ID NO:12.
SEQ ID NO:14 shows the amino acid sequence of CR12-MPED truncated M. sexta cadherin Bt-R1a in pET-30a(+) (Novagen).
DETAILED DESCRIPTION OF THE INVENTIONThe subject invention concerns methods and materials used for controlling insects and other pests, particularly plant pests. More specifically, the subject invention pertains to the use of peptide fragments of a protein, preferably a cadherin (including cadherin-like proteins), for controlling insects. Alternatively or in addition, the protein is preferably a Bacillus thuringiensis (B.t.) crystal protein (Cry) toxin receptor. These peptide fragments are provided, or made available, to target pests for ingestion. This can be accomplished by a variety of means that are known in the art, some of which are discussed in more detail below.
Preferred are fragments of the ectodomains of cadherin proteins (the portion of the protein that is outside of the cell when part of the cadherin protein is embedded in the cellular membrane and part is exposed at the cell surface). Preferably, the cadherins can be Bacillus thuringiensis (B.t.) crystal protein (Cry) toxin receptors. Preferably, the peptide fragment is a binding domain of the receptor. In some preferred embodiments, the peptide is the binding domain nearest to the membrane proximal ectodomain. Corresponding domains are identifiable in a variety of B.t. toxin receptors.
In preferred embodiments, the peptides are fed to target insects together with one or more insecticidal proteins, preferably (but not limited to) B.t. Cry proteins. When used in this manner, the peptide fragment can not only enhance the apparent toxin activity of the Cry protein against the insect species that was the source of the receptor but also against other insect species.
A related aspect of the inventions pertains to the use of an isolated polynucleotide that encodes a protein comprising (or consisting of) a fragment of a cadherin-like protein. The subject invention includes a cell (and use thereof) carrying the polynucleotide and expressing the peptide fragment, including methods of feeding the peptide (preferably with B.t. Cry toxins) to insects. The nucleotide sequences can be used to transform hosts, such as plants, to express the receptor fragments (preferably cadherin fragments) of the subject invention. Transformation of plants with the genetic constructs disclosed herein can be accomplished using techniques well known to those skilled in the art. Thus, in some embodiments, the subject invention provides nucleotide sequences that encode fragments of receptors, preferably a Bt-R, cadherin-like protein.
The receptor used as the source of this domain(s) can be derived from various pests and insects, such as Manduca sexta, Heliothis virescens, Helicoverpa zea Spodoptera frugiperda and Plutella xylostella larvae. Many sequences of such receptors are publicly available. The subject peptide fragments can not only enhance a toxin's activity against the insect species that was the source of the receptor, but also against other insect species.
Various pests can be targeted, including but not limited to Manduca sexta, Heliothis virescens, Helicoverpa zea Spodoptera frugiperda and Plutella xylostella larvae. Because of the unique and novel approach of the subject invention, pests that were typically not susceptible to B.t. Cry proteins can now also be targeted. For example, hemipterans represent a major group of insects that have typically not been effectively controlled by B.t. δ-endotoxins. Numerous hemipteran pest species, most notably Lygus species, cause considerable plant damage and economic loss each year. The digestive system of hemipterans (including aphids) is unusual among the insects in several ways: certain hydrolytic digestive enzymes are absent such as trypsin; the midgut lacks a peritrophic membrane, and there is no crop. These features reflect the liquid diet and sucking mode of feeding, subject to evolutionary constraints. However, because of the subject novel approach, the subject invention offers new alternatives for pest control. The subject invention can be used to enhance and expand the spectrum (or insect range) of toxicity of a given insect-toxic protein.
In some preferred embodiments, these peptide fragments can be used to enhance the potency of B.t. toxins for controlling insects. In some preferred embodiments, the peptide fragments enhance the toxicity of Cry1 toxins, but as shown herein, the subject invention is not limited to use with such toxins.
Various types of plants and crops can be protected in a variety of ways by practicing the subject invention. Cotton and corn are the main crops that can be protected by peptides (and proteins) of the subject invention, as well as soybeans and rice. Preferred methods for protecting these crops include producing transgenic crops that are engineered to produce peptides (and proteins) according to the subject invention. Preferred uses for spray-on applications include, but are not limited to, protecting vegetables and targeting forest pests (protecting planted trees and the like). Preferred pests for targeting in this manner include but are not limited to lepidopterans.
Without being bound by a specific theory or theories of mechanism of action, one possibility is that these fragments work in conjunction with B.t. toxins and enhance the pesticidal activity of the toxin. When fed to insects with a Cry toxin, the peptide can change the effect of a toxin from a growth-inhibitory effect to an insecticidal effect. In addition or alternatively, the fragments can exert at least a partial toxic effect by a separate mechanism of action. Yet another possibility is that the fragments also, or alternatively, work indirectly to stabilize the B.t. toxin. Thus, said fragment can work independently from the Cry toxin (by another mechanism of action) and/or in conjunction with the Cry toxin to enhance the insecticidal potency of the Cry toxin. However, the mechanisms) of action are not important for practicing the subject invention. Based on the subject disclosure, one skilled in the art can practice various aspects of the subject invention in a variety of ways.
For example, the fragment of cadherin-like protein may be expressed as a fusion protein with a B.t. Cry toxin using techniques well known to those skilled in the art. As described herein, preferred fusions would be chimeric toxins produced by combining a toxin (including a fragment of a protoxin, for example) and a fragment of a cadherin-like protein. In addition, mixtures and/or combinations of toxins and cadherin-like protein fragments can be used according to the subject invention. These mixtures or chimeric proteins have the unexpected and remarkable properties of enhanced insecticidal potency.
It should similarly be noted that one skilled in the art, having the benefit of the subject disclosure, will recognize that the subject peptides potentially have a variety of functions, uses, and activities. As stated herein, the subject peptides can be administered together with a Cry protein. When used in this manner, peptides of the subject invention can effect a faster kill of the targeted insects, and/or they can enable less Cry protein to be required for killing the insects. Complete lethality, however, is not required. The ultimate preferred goal is to prevent insects from damaging plants. Thus, prevention of feeding is sufficient. Thus “inhibiting” the insects is all that is required. This can be accomplished by making the insects “sick” or by otherwise inhibiting (including killing) them so that damage to the plants being protected is reduced. Peptides of the subject invention can be used alone or in combination with another toxin to achieve this inhibitory effect, which can be referred to as “toxin activity.” Thus, the inhibitory function of the subject peptides can be achieved by any mechanism of action, directly or indirectly related to the Cry protein, or completely independent of the Cry protein.
In specific embodiments, the subject invention relates to the use of a cadherin repeat 12-MPED peptide of Manduca sexta Bt-R1a cadherin-like protein to enhance the potency of B.t. toxins. A region (i.e., fragment) of a cadherin-like protein was identified that synergizes the insecticidal potency of a B.t. Cry toxin. The receptor fragment binds toxin with high-affinity, catalyzes toxin-induced cell death when expressed on the surface of cultured insects cells, and enhances (i.e., synergizes) the insecticidal potency of a Cry toxin.
However, in light of the subject disclosure, it will be recognized that other peptides can be used in like manners. For example, a novel Cry1Ab-binding site on Bt-R1a was identified as described in U.S. Ser. No. 60/538,753 entitled “Novel Binding Domain of Cadherin-like Toxin Receptor,” by Adang et al., under Attorney Docket No. UGR-104P, which identifies an additional binding site recognized by Cry toxins that functions as a receptor. This additional binding site, which is also a functional receptor region, is contained in the CR12—Membrane Proximal Extracellular Domain (MPED) of Bt-R1a (Hua et al. 2004). The HevCaLP protein of H. virescens has a Cry1Ac binding site at a comparable position (Xie et al. 2004), suggesting a conservation of binding sites between cadherins of different insect species.
Full-length and truncated Bt-R1a fragments were genetically engineered and expressed in Drosophila S2 cells to test for Cry1Ab binding and cytotoxicity mediated by receptor fragments. See, e.g.,
The subject invention stemmed in part from the unexpected finding that a peptide comprising CR12 and the Membrane Proximal Ectodomain (MPED) (Dorsch et al. 2002) enhanced the toxicity of B.t. Cry1 toxins when fed as a mixture to insect larvae. This peptide, called CR12-MPED, is illustrated in
In preferred embodiments, the fragment of the receptor is a binding domain of the receptor. Without being bound by a specific theory regarding mechanism of action, binding of this domain to a B.t. toxin could induce a conformational change in the B.t. toxin, thus making it more toxic, more able to bind the toxin receptor, etc. In some preferred embodiments, the fragment comprises (or consists of) the CR12-MPED domain.
The peptides (such as CR12-MPED) and toxins can be fed or otherwise administered to the target (insect) pest in various ways, according to the subject invention. In one preferred embodiment, a transgenic plant produces the peptide (such as CR12-MPED) and one or more B.t. toxins. By consuming the peptide and B.t. protein produced by such plant (e.g., by eating plant tissues and cells containing the peptide and protein), the insect will thereby contact the peptide and protein. Together, they will exhibit the enhanced toxic effects in the insect gut.
Another preferred method of the subject invention is to spray the peptide (such as Cad12-MPED) onto transgenic B.t. plants (such as corn, cotton, soybeans, and the like). The peptide can be in a suitable carrier, as are known in the art. By spraying the peptide in this manner on plant tissues consumed by target pests, the pest will eat both the peptide (in the spray) and the B.t. protein (produced by and present in the plant).
Yet another preferred method is to spray both the peptide and the B.t. Cry protein onto plants and the like. Such methods are well-known in the art (but heretofore lacked the synergizing peptides of the subject invention). B.t. toxins, and/or the peptide of the subject invention, can be formulated with and agriculturally acceptable carrier, for example, that is suitable for spray application to plants and the like.
In one embodiment, the subject invention is drawn to the use of a polynucleotide that encodes a CR12 binding domain from M. sexta. In a preferred embodiment, such polynucleotides comprise (or consist of) a nucleotide sequence that encodes the CR12-MPED peptide of SEQ ID NO:2. (The N-terminal “G”—glycine residue—for example, can be removed and the remaining fragment of the exemplified sequence can be used, according to the subject invention.) One such nucleotide sequence is shown in SEQ ID NO:1.
In another embodiment the subject invention is drawn to the use of a cell or cells transfected with a polynucleotide molecule that comprises a nucleotide sequence encoding a CR12-MPED peptide, for example. Further, the protein is preferably, but not necessarily, anchored to and localized at the cell membrane, and is capable of binding a toxin. In a more preferred embodiment, said protein mediates an observable toxicity to said cell or cells, including death upon contacting a toxin.
While CR12-MPED is one example referred to above and elsewhere herein, several other peptides are exemplified herein. Some other such peptides are discussed below in the Examples. Thus, it should be understood that these other peptides, and variants thereof, can be referred to in the same manners as is CR12-MPED.
As described in the background of the invention, many B.t. toxins have been isolated and sequenced. Polynucleotides encoding any known B.t. toxins or those yet to be discovered and active fragments thereof (see, for example, U.S. Pat. No. 5,710,020) can be used in accord with the teachings herein. See Crickmore et al. (1998) for a description of other B.t. toxins. A list of Cry toxins from the Crickmore et al. website is attached as Appendix A. These include, but are not limited to, polynucleotides encoding Cry1A toxins such as Cry1Aa, Cry1Ab, Cry1Ac, preferably, as well as Cry1B, Cry1C, Cry1F, Cry1E, and Cry3A. Cry2 toxins are also preferred for co-administration with peptides of the subject invention. One can also select toxin(s) from the Crickmore list, for example, based on the type of pests being targeted. For example, rootworms were targeted in an Example as discussed below. Thus, anti-rootworm toxins (such as Cry34135 toxins) can preferably be used in such applications. The subject peptides can also be used to control mutant insects that are resistant to one or more B.t. toxins. Modified Cry toxins (such as those described in U.S. Pat. Nos. 6,825,006; 6,423,828; 5,914,318; and 5,942,664) can also be used according to the subject invention B.t. toxins other than Cry toxins (such as “Vip” toxins as categorized in another section of the Crickmore et al. website) are also contemplated for use. Insecticidal proteins from organisms other than B.t., such as Bacillus subtilis, are also contemplated for use.
In order to provide an understanding of a number of terms used in the specification and claims herein, the following definitions are provided.
An “isolated” nucleic acid or polynucleotide (or protein) is in a state or construct that would not be found in nature. Thus, it signifies the involvement of “the hand of man.” A polynucleotide encoding a peptide of the subject invention, to the extent that the peptide does not occur in the state of nature, would be an isolated polynucleotide. This polynucleotide in a plant genome would also be “isolated” as it is not occurring in its natural state. The term therefore covers, for example, (a) a DNA which has the sequence of part of a naturally occurring genomic DNA molecule but is not flanked by both of the coding or non-coding sequences that flank that part of the molecule in the genome of the organism in which it naturally occurs; (b) a nucleic acid incorporated into a vector or into the genomic DNA of a prokaryote or eukaryote in a manner such that the resulting molecule is not identical to any naturally occurring vector or genomic DNA; (c) a separate molecule such as a cDNA, a genomic fragment, a fragment produced by polymerase chain reaction (PCR), or a restriction fragment; and (d) a recombinant nucleotide sequence that is part of a hybrid gene, i.e., a gene encoding a fusion protein.
A nucleotide sequence is operably linked when it is placed into a functional relationship with another nucleotide sequence. For instance, a promoter is operably linked to a coding sequence if the promoter effects its transcription or expression. Generally, operably linked means that the sequences being linked are contiguous and, where necessary to join two protein coding regions, contiguous and in reading frame. However, it is well known that certain genetic elements, such as enhancers, may be operably linked even at a distance, i.e., even if not contiguous.
Polynucleotides of the subject invention include an isolated polynucleotide “consisting essentially of” a segment that encodes a CR12-MPED peptide, for example, attached to a label or reporter molecule and may be used to identify and isolate B.t. toxins and the like. Probes comprising synthetic oligonucleotides or other polynucleotides may be derived from naturally occurring or recombinant single or double stranded nucleic acids or be chemically synthesized. Polynucleotide probes may be labeled by any of the methods known in the art, e.g., random hexamer labeling, nick translation, or the Klenow fill-in reaction.
The polynucleotides may also be produced by chemical synthesis, e.g., by the phosphoramidite method described by Beaucage and Caruthers (1981) Tetra. Letts., 22:1859-1862 or the triester method according to Matteuci et al. (1981) J. Am. Chem. Soc., 103:3185, and may be performed on commercial automated oligonucleotide synthesizers. A double-stranded fragment may be obtained from the single stranded product of chemical synthesis either by synthesizing the complementary strand and annealing the strand together under appropriate conditions or by adding the complementary strand using DNA polymerase with an appropriate primer sequence.
DNA constructs prepared for introduction into a prokaryotic or eukaryotic host will typically comprise a replication system (i.e., vector) recognized by the host, including the intended DNA fragment encoding the desired polypeptide, and will preferably also include transcription and translational initiation regulatory sequences operably linked to the polypeptide-encoding segment. Expression systems (expression vectors) may include, for example, an origin of replication or autonomously replicating sequence (ARS) and expression control sequences, a promoter, an enhancer and necessary processing information sites, such as ribosome-binding sites, RNA splice sites, polyadenylation sites, transcriptional terminator sequences, and mRNA stabilizing sequences. Signal peptides may also be included where appropriate from secreted polypeptides of the same or related species, which allow the protein to cross and/or lodge in cell membranes or be secreted from the cell.
Expression and cloning vectors will likely contain a selectable marker, that is, a gene encoding a protein necessary for the survival or growth of a host cell transformed with the vector. Although such a marker gene may be carried on another polynucleotide sequence co-introduced into the host cell, it is most often contained on the cloning vector. Only those host cells into which the marker gene has been introduced will survive and/or grow under selective conditions. Typically selection genes encode proteins that (a) confer resistance to antibiotics or other toxic substances, e.g., ampicillin, neomycin, methotrexate, etc.; (b) complement auxotrophic deficiencies; or (c) supply critical nutrients not available from complex media. The choice of the proper selectable marker will depend on the host cell; appropriate markers for different hosts are known in the art.
It will be recognized by those skilled in the art that the DNA sequences may vary due to the degeneracy of the genetic code and codon usage. All DNA sequences which code for exemplified and/or suggested peptides (and proteins) are included. For example, the subject CR12 peptides are included in this invention, including the DNA of SEQ ID NO:1 (plus an ATG preceding the coding region), which encodes SEQ ID NO:2. The subject invention also includes polynucleotides having codons that are optimized for expression in plants, including any of the specific types of plants referred to herein. Various techniques for creating plant-optimized sequences are know in the art.
Additionally, it will be recognized by those skilled in the art that allelic variations may occur in the DNA sequences which will not significantly change activity of the amino acid sequences of the peptides which the DNA sequences encode. All such equivalent DNA sequences are included within the scope of this invention and the definition of the regulated promoter region. The skilled artisan will understand that exemplified sequences (such as the CR12-MPED sequence of SEQ ID NO:1) can be used to identify and isolate additional, non-exemplified nucleotide sequences which will encode functional equivalents to the sequences given in, or an amino acid sequence of greater than 90% identity thereto and having equivalent biological activity. DNA sequences having at least 90%, or at least 95% identity to a recited DNA sequence and encoding functioning peptides (such as CR12-MPED) are considered equivalent sequences and are included in the subject invention. Other numeric ranges for variant polynucleotides and amino acid sequences are provided below (e.g., 50-99%). Following the teachings herein and using knowledge and techniques well known in the art, the skilled worker will be able to make a large number of operative embodiments having equivalent DNA sequences to those listed herein without the expense of undue experimentation.
As used herein percent sequence identity of two nucleic acids is determined using the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87:2264-2268, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90:5873-5877. Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al. (1990) J. Mol. Biol. 215:402-410. BLAST nucleotide searches are performed with the NBLAST program, score=100, wordlength 12, to obtain nucleotide sequences with the desired percent sequence identity. To obtain gapped alignments for comparison purposes, Gapped BLAST is used as described in Altschul et al. (1997) Nucl. Acids. Res. 25:3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (NBLAST and XBLAST) are used. See ncbi.nih.gov website.
Polynucleotides (and the peptides and proteins they encode) can also be defined by their hybridization characteristics (their ability to hybridize to a given probe, such as the complement of a DNA sequence exemplified herein). Various degrees of stringency of hybridization can be employed. The more stringent the conditions, the greater the complementarity that is required for duplex formation. Stringency can be controlled by temperature, probe concentration, probe length, ionic strength, time, and the like. Preferably, hybridization is conducted under moderate to high stringency conditions by techniques well known in the art, as described, for example, in Keller, G. H., M. M. Manak (1987) DNA Probes, Stockton Press, New York, N.Y., pp. 169-170.
As used herein “moderate to high stringency” conditions for hybridization refers to conditions that achieve the same, or about the same, degree of specificity of hybridization as the conditions “as described herein.” Examples of moderate to high stringency conditions are provided herein. Specifically, hybridization of immobilized DNA on Southern blots with 32P-labeled gene-specific probes was performed using standard methods (Maniatis et al). In general, hybridization and subsequent washes were carried out under moderate to high stringency conditions that allowed for detection of target sequences with homology to sequences exemplified herein. For double-stranded DNA gene probes, hybridization was carried out overnight at 20-25° C. below the melting temperature (Tm) of the DNA hybrid in 6×SSPE, 5×Denhardt's solution, 0.1% SDS, 0.1 mg/ml denatured DNA. The melting temperature is described by the following formula from Beltz et al. (1983).
Tm=81.5° C.+16.6 Log [Na+]+0.41(%G+C)−0.61(%formamide)600/length of duplex in base pairs.
Washes are typically carried out as follows:
-
- (1) Twice at room temperature for 15 minutes in 1×SSPE, 0.1% SDS (low stringency wash).
- (2) Once at Tm-20° C. for 15 minutes in 0.2×SSPE, 0.1% SDS (moderate stringency wash).
For oligonucleotide probes, hybridization was carried out overnight at 10-20° C. below the melting temperature (Tm) of the hybrid in 6×SSPE, 5×Denhardt's solution, 0.1% SDS, 0.1 mg/ml denatured DNA. Tm for oligonucleotide probes was determined by the following formula from Suggs et al. (1981):
Tm(° C.)=2(number T/A base pairs)+4(number G/C base pairs)
Washes were typically carried out as follows:
-
- (1) Twice at room temperature for 15 minutes 1×SSPE, 0.1% SDS (low stringency wash).
- (2) Once at the hybridization temperature for 15 minutes in 1×SSPE, 0.1% SDS (moderate stringency wash)
In general, salt and/or temperature can be altered to change stringency. With a labeled DNA fragment of greater than about 70 or so bases in length, the following can be used:
Low: 1 or 2×SSPE, room temperature
Low: 1 or 2×SSPE, 42° C.
Moderate: 0.2× or 1×SSPE, 65° C.
High: 0.1×SSPE, 65° C.
Duplex formation and stability depend on substantial complementarity between the two strands of a hybrid, and, as noted above, a certain degree of mismatch can be tolerated. Therefore, polynucleotide sequences of the subject invention include mutations (both single and multiple), deletions, and insertions in the described sequences, and combinations thereof, wherein said mutations, insertions, and deletions permit formation of stable hybrids with a target polynucleotide of interest. Mutations, insertions, and deletions can be produced in a given polynucleotide sequence using standard methods known in the art. Other methods may become known in the future.
The mutational, insertional, and deletional variants of the polynucleotide and amino acid sequences of the invention can be used in the same manner as the exemplified sequences so long as the variants have substantial sequence similarity with the original sequence. As used herein, substantial sequence similarity refers to the extent of nucleotide similarity that is sufficient to enable the variant polynucleotide to function in the same capacity as the original sequence. Preferably, this similarity is greater than 50%; more preferably, this similarity is greater than 75%; and most preferably, this similarity is greater than 90%. The degree of similarity needed for the variant to function in its intended capacity will depend upon the intended use of the sequence. It is well within the skill of a person trained in this art to make mutational, insertional, and deletional mutations that are designed to improve the function of the sequence or otherwise provide a methodological advantage. The identity and/or similarity can also be 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% as compared to a sequence exemplified herein.
The amino acid identity/similarity and/or homology will be highest in critical regions of the protein that account for biological activity and/or are involved in the determination of three-dimensional configuration that ultimately is responsible for the biological activity. In this regard, certain amino acid substitutions are acceptable and can be expected if these substitutions are in regions that are not critical to activity or are conservative amino acid substitutions which do not affect the three-dimensional configuration of the molecule. For example, amino acids may be placed in the following classes: non-polar, uncharged polar, basic, and acidic. Conservative substitutions whereby an amino acid of one class is replaced with another amino acid of the same type fall within the scope of the subject invention so long as the substitution does not materially alter the biological activity of the compound. Table 1 provides a listing of examples of amino acids belonging to each class.
In some instances, non-conservative substitutions can also be made. The critical factor is that these substitutions must not significantly detract from the biological activity of the toxin.
Practicing some embodiments of the subject invention might necessitate the use of expression vectors comprising one or more polynucleotides comprising an exemplified nucleic acid sequences, and capable of expressing the subject peptides, in a suitable host cell. In the vectors of the subject invention, the polynucleotide encoding the peptide is operably linked to suitable transcriptional and/or translational regulatory elements to effect expression of the peptide in a suitable host cell. The regulatory elements may be derived from mammalian, microbial, viral or insect genes and include, for example, promoters, enhancers, transcription and translation initiation sequences, termination sequences, origins of replication, and leader and transport sequences. Suitable regulatory elements are selected for optimal expression in a desired host cell.
Possible regulatory sequences can include, but are not limited to, any promoter already shown to be constitutive for expression, such as those of viral origin (e.g., IEI promoter from Baculoviruses) or so-called “housekeeping” genes (ubiquitin, actin, tubulin) with their corresponding termination/poly A+ sequences. In addition, the gene can be placed under the regulation of inducible promoters and their termination sequences so that gene expression is induced by light (rbcS-3A, cab-1), heat (hsp gene promoters) or wounding (mannopine, HGPGs). Other suitable promoters include the metallothionein promoter, dexamethasone promoter, alcohol dehydrogenase promoter, and the baculovirus promoters, i.e., the early promoter (e.g., IE-1 and et1), the late promoters (e.g., vp39 and p6.9), the very late promoters (e.g., po1 h and p10) and the hybrid promoter (e.g., vp39/po1 h).
It is clear to one skilled in the art that a promoter may be used either in native or truncated form, and may be paired with its own or a heterologous termination/polyA+ sequence. In a preferred embodiment, the subject vectors are regulated by D. melanogaster HSP70 promoter.
Expression vectors can be constructed by well known molecular biological methods as described for example in Sambrook et al. (1989), or any of a myriad of laboratory manuals on recombinant DNA technology that are widely available. Expression vectors into which the polynucleotides of the present invention can be cloned under the control of a suitable promoter are also commercially available. Recombinant viral vectors, including retroviral, baculoviral, parvoviral and densoviral vectors can be used but are not particularly preferred. In host cells containing vectors having an inducible promoter controlling the expression of the nucleic acid encoding CR12-MPED, for example, expression is induced by methods known in the art and suitable for the selected promoter. For example, expression of nucleic acids under the control of the metallothionein promoter is induced by adding cadmium chloride or copper sulfate to the growth media of host cells.
In a specific embodiment, the subject invention includes the pest-control use of a host cell containing a vector comprising nucleotide sequences encoding CR12-MPED under the control of a promoter. The host cell may be procaryotic or eukaryotic, including bacterial, yeast insect and mammalian cells. Insect and mammalian cells are preferred. Particularly preferred host cells include insect cell lines, such as, for example, Spodoptera frugiperda (Sf and Sf21) and Trichoplusia ni (Tn cells), Estigma acrae (Ea4 cells), Drosophila melanogaster (Dm cells), Choristoneura fumiferama (Cf-1 cells), Mamestra brassicae (MaBr-3 cells), Bombyx mori (MnN-4 cells), Helicoverpa zea (Hzlb3 cells), and Lymantria dispar (Ld652Y cells), among others. The host cells may be transformed, transfected or infected with the expression vectors of the present invention by methods well-known to those of ordinary skill in the art. Transfection may be accomplished by known methods, such as liposome-mediated transfection, calcium phosphate mediated transfection, microinjection, and electroporation.
Transgenic cells of the subject invention may be obtained by transfection with a polynucleotide comprising an exemplified (or suggested) nucleic acid sequence. Equipped with the teachings herein, the skilled artisan would be able to transfect cells with the exemplified, as well as future isolated peptide-encoding polynucleotides, to produce cells that make peptides of the subject invention. Progeny cells that retain the peptide-encoding polynucleotide are, of course, within the scope of the subject invention, as are transgenic plants.
The term “transfection” as used herein means an introduction of a foreign DNA or RNA into a cell by mechanical inoculation, electroporation, agroinfection, particle bombardment, microinjection, or by other known methods. The term “transformation” as used herein means a stable incorporation of a foreign DNA or RNA into the cell that results in a permanent, heritable alteration in the cell. Accordingly, the skilled artisan would understand that transfection of a cell may result in the transformation of that cell.
In preferred embodiments, expression of the peptide- and/or toxin-encoding gene results, directly or indirectly, in the intracellular production (and maintenance) of the peptide/protein. Plants can be rendered insect-resistant in this manner. When transgenic/recombinant/transformed/transfected host cells (or contents thereof) are ingested by the pests, the pests will ingest the toxic peptides/proteins. This is one preferred manner in which to cause contact of the pest with the toxin. The result is control (killing or making sick) of the pest. Sucking pests can also be controlled in a similar manner. Alternatively, suitable microbial hosts, e.g., Pseudomonas such as P. fluorescens, can be applied where target pests are present; the microbes can proliferate there, and are ingested by the target pests.
Where the toxin gene(s) is introduced via a suitable vector into a microbial host, and said host is applied to the environment in a living state, certain host microbes should be used. Microorganism hosts are selected which are known to occupy the “phytosphere” (phylloplane, phyllosphere, rhizosphere, and/or rhizoplane) of one or more crops of interest. These microorganisms are selected so as to be capable of successfully competing in the particular environment (crop and other insect habitats) with the wild-type microorganisms, provide for stable maintenance and expression of the gene expressing the polypeptide pesticide, and, desirably, provide for improved protection of the pesticide from environmental degradation and inactivation.
A large number of microorganisms are known to inhabit the phylloplane (the surface of the plant leaves) and/or the rhizosphere (the soil surrounding plant roots) of a wide variety of important crops. These microorganisms include bacteria, algae, and fungi. Of particular interest are microorganisms, such as bacteria, e.g., genera Pseudomonas, Erwinia, Serratia, Klebsiella, Xanthomonas, Streptomyces, Rhizobium, Rhodopseudomonas, Methylophilius, Agrobacterium, Acetobacter, Lactobacillus, Arthrobacter, Azotohacter, Leuconostoc, and Alcaligenes; Fungi, particularly yeast, e.g., genera Saccharomyces, Cryptococcus, Kluyveromyces, Sporobolomyces, Rhodotorula, and Aureobasidium. Of particular interest are such phytosphere bacterial species as Pseudomonas syringae, Pseudomonas fluorescens, Serratia marcescens, Acetobacter xylinum, Agrobacterium tumefaciens, Rhodopseudomonas spheroides, Xanthomonas campestris, Rhizobium melioti, Alcaligenes entrophus, and Azotobacter vinlandii; and phytosphere yeast species such as Rhodotorula rubra, R. glutinis, R. marina, R. aurantiaca, Cryptococcus albidus, C. diffluens, C laurentii, Saccharomyces rosei, S. pretoriensis, S. cerevisiae, Sporobolomyces roseus, S. odorus, Kluyveromyces veronae, and Aureobasidium pollulans. Also of interest are pigmented microorganisms.
One aspect of the subject invention is the transformation/transfection of plants, plant cells, and other host cells with polynucleotides of the subject invention that express proteins of the subject invention. Plants transformed in this manner can be rendered resistant to attack by the target pest(s).
A wide variety of methods are available for introducing a gene encoding a pesticidal protein into the target host under conditions that allow for stable maintenance and expression of the gene. These methods are well known to those skilled in the art and are described, for example, in U.S. Pat. No. 5,135,867.
For example, a large number of cloning vectors comprising a replication system in E. coli/and a marker that permits selection of the transformed cells are available for preparation for the insertion of foreign genes into higher plants. The vectors comprise, for example, pBR322, pUC series, M13 mp series, pACYC184, etc. Accordingly, the sequence encoding the toxin can be inserted into the vector at a suitable restriction site. The resulting plasmid is used for transformation into E. coli. The E. Coli cells are cultivated in a suitable nutrient medium, then harvested and lysed. The plasmid is recovered. Sequence analysis, restriction analysis, electrophoresis, and other biochemical-molecular biological methods are generally carried out as methods of analysis. After each manipulation, the DNA sequence used can be cleaved and joined to the next DNA sequence. Each plasmid sequence can be cloned in the same or other plasmids. Depending on the method of inserting desired genes into the plant, other DNA sequences may be necessary. If, for example, the Ti or Ri plasmid is used for the transformation of the plant cell, then at least the right border, but often the right and the left border of the Ti or Ri plasmid T-DNA, has to be joined as the flanking region of the genes to be inserted. The use of T-DNA for the transformation of plant cells has been intensively researched and described in EP 120 516; Hoekema (1985) In: The Binary Plant Vector System, Offset-durkkerij Kanters B. V., Alblasserdam, Chapter 5; Fraley et al., Crit. Rev. Plant Sci. 4:1-46; and An et al. (1985) EMBO J. 4:277-287.
A large number of techniques are available for inserting DNA into a plant host cell. Those techniques include transformation with T-DNA using Agrobacterium tumefaciens or Agrobacterium rhizogenes as transformation agent, fusion, injection, biolistics (microparticle bombardment), or electroporation as well as other possible methods. If Agrobacteria are used for the transformation, the DNA to be inserted has to be cloned into special plasmids, namely either into an intermediate vector or into a binary vector. The intermediate vectors can be integrated into the Ti or Ri plasmid by homologous recombination owing to sequences that are homologous to sequences in the T-DNA. The Ti or Ri plasmid also comprises the vir region necessary for the transfer of the T-DNA. Intermediate vectors cannot replicate themselves in Agrobacteria. The intermediate vector can be transferred into Agrobacterium tumefaciens by means of a helper plasmid (conjugation). Binary vectors can replicate themselves both in E. coli and in Agrobacteria. They comprise a selection marker gene and a linker or polylinker which are framed by the right and left T-DNA border regions. They can be transformed directly into Agrobacteria (Holsters et al. [1978] Mol. Gen. Genet. 163:181-187). The Agrobacterium used as host cell is to comprise a plasmid carrying a vir region. The vir region is necessary for the transfer of the T-DNA into the plant cell. Additional T-DNA may be contained. The bacterium so transformed is used for the transformation of plant cells. Plant explants can advantageously be cultivated with Agrobacterium tumefaciens or Agrobacterium rhizogenes for the transfer of the DNA into the plant cell. Whole plants can then be regenerated from the infected plant material (for example, pieces of leaf, segments of stalk, roots, but also protoplasts or suspension-cultivated cells) in a suitable medium, which may contain antibiotics or biocides for selection. The plants so obtained can then be tested for the presence of the inserted DNA. No special demands are made of the plasmids in the case of injection and electroporation. It is possible to use ordinary plasmids, such as, for example, pUC derivatives.
The transformed cells grow inside the plants in the usual manner. They can form germ cells and transmit the transformed trait(s) to progeny plants. Such plants can be grown in the normal manner and crossed with plants that have the same transformed hereditary factors or other hereditary factors. The resulting hybrid individuals have the corresponding phenotypic properties.
In some preferred embodiments of the invention, genes encoding the bacterial toxin are expressed from transcriptional units inserted into the plant genome. Preferably, said transcriptional units are recombinant vectors capable of stable integration into the plant genome and enable selection of transformed plant lines expressing mRNA encoding the proteins.
Once the inserted DNA has been integrated in the genome, it is relatively stable there (and does not come out again). It normally contains a selection marker that confers on the transformed plant cells resistance to a biocide or an antibiotic, such as kanamycin, G418, bleomycin, hygromycin, or chloramphenicol, inter alia. The individually employed marker should accordingly permit the selection of transformed cells rather than cells that do not contain the inserted DNA. The gene(s) of interest are preferably expressed either by constitutive or inducible promoters in the plant cell. Once expressed, the mRNA is translated into proteins, thereby incorporating amino acids of interest into protein. The genes encoding a toxin expressed in the plant cells can be under the control of a constitutive promoter, a tissue-specific promoter, or an inducible promoter.
Several techniques exist for introducing foreign recombinant vectors into plant cells, and for obtaining plants that stably maintain and express the introduced gene. Such techniques include the introduction of genetic material coated onto microparticles directly into cells (U.S. Pat. Nos. 4,945,050 to Cornell and 5,141,131 to DowElanco, now Dow AgroSciences, LLC). In addition, plants may be transformed using Agrobacterium technology, see U.S. Pat. No. 5,177,010 to University of Toledo; U.S. Pat. No. 5,104,310 to Texas A&M; European Patent Application 0131624B13; European Patent Applications 120516, 159418B1 and 176,112 to Schilperoot; U.S. Pat. Nos. 5,149,645, 5,469,976, 5,464,763 and 4,940,838 and 4,693,976 to Schilperoot; European Patent Applications 116718, 290799, 320500 all to Max Planck; European Patent Applications 604662 and 627752, and U.S. Pat. No. 5,591,616, to Japan Tobacco; European Patent Applications 0267159 and 0292435, and U.S. Pat. No. 5,231,019, all to Ciba Geigy, now Novartis; U.S. Pat. Nos. 5,463,174 and 4,762,785, both to Calgene; and U.S. Pat. Nos. 5,004,863 and 5,159,135, both to Agracetus. Other transformation technology includes whiskers technology. See U.S. Pat. Nos. 5,302,523 and 5,464,765, both to Zeneca. Electroporation technology has also been used to transform plants. See WO 87/06614 to Boyce Thompson Institute; U.S. Pat. Nos. 5,472,869 and 5,384,253, both to Dekalb; and WO 92/09696 and WO 93/21335, both to Plant Genetic Systems. Furthermore, viral vectors can also be used to produce transgenic plants expressing the protein of interest. For example, monocotyledonous plant can be transformed with a viral vector using the methods described in U.S. Pat. No. 5,569,597 to Mycogen Plant Science and Ciba-Giegy, now Novartis, as well as U.S. Pat. Nos. 5,589,367 and 5,316,931, both to Biosource.
As mentioned previously, the manner in which the DNA construct is introduced into the plant host is not critical to this invention. Any method that provides for efficient transformation may be employed. For example, various methods for plant cell transformation are described herein and include the use of Ti or Ri-plasmids and the like to perform Agrobacterium mediated transformation. In many instances, it will be desirable to have the construct used for transformation bordered on one or both sides by T-DNA borders, more specifically the right border. This is particularly useful when the construct uses Agrobacterium tumefaciens or Agrobacterium rhizogenes as a mode for transformation, although T-DNA borders may find use with other modes of transformation. Where Agrobacterium is used for plant cell transformation, a vector may be used which may be introduced into the host for homologous recombination with T-DNA or the Ti or Ri plasmid present in the host. Introduction of the vector may be performed via electroporation, tri-parental mating and other techniques for transforming gram-negative bacteria, which are known to those skilled in the art. The manner of vector transformation into the Agrobacterium host is not critical to this invention. The Ti or Ri plasmid containing the T-DNA for recombination may be capable or incapable of causing gall formation, and is not critical to said invention so long as the vir genes are present in said host.
In some cases where Agrobacterium is used for transformation, the expression construct being within the T-DNA borders will be inserted into a broad spectrum vector such as pRK2 or derivatives thereof as described in Ditta et al., (PNAS USA (1980) 77:7347-7351 and EPO 0 120 515, which are incorporated herein by reference. Included within the expression construct and the T-DNA will be one or more markers as described herein which allow for selection of transformed Agrobacterium and transformed plant cells. The particular marker employed is not essential to this invention, with the preferred marker depending on the host and construction used.
For transformation of plant cells using Agrobacterium, explants may be combined and incubated with the transformed Agrobacterium for sufficient time to allow transformation thereof. After transformation, the Agrobacteria are killed by selection with the appropriate antibiotic and plant cells are cultured with the appropriate selective medium. Once calli are formed, shoot formation can be encouraged by employing the appropriate plant hormones according to methods well known in the art of plant tissue culturing and plant regeneration. However, a callus intermediate stage is not always necessary. After shoot formation, said plant cells can be transferred to medium which encourages root formation thereby completing plant regeneration. The plants may then be grown to seed and said seed can be used to establish future generations. Regardless of transformation technique, the gene encoding a bacterial toxin is preferably incorporated into a gene transfer vector adapted to express said gene in a plant cell by including in the vector a plant promoter regulatory element, as well as 3′ non-translated transcriptional termination regions such as Nos and the like.
In addition to numerous technologies for transforming plants, the type of tissue that is contacted with the foreign genes may vary as well. Such tissue would include but would not be limited to embryogenic tissue, callus tissue types I, II, and III, hypocotyl, meristem, root tissue, tissues for expression in phloem, and the like. Almost all plant tissues may be transformed during dedifferentiation using appropriate techniques described herein.
A variety of selectable markers can be used, if desired. Preference for a particular marker is at the discretion of the artisan, but any of the following selectable markers may be used along with any other gene not listed herein that could function as a selectable marker.
In addition to a selectable marker, it may be desirous to use a reporter gene. In some instances a reporter gene may be used with or without a selectable marker. Reporter genes are genes that are typically not present in the recipient organism or tissue and typically encode for proteins resulting in some phenotypic change or enzymatic property. An assay for detecting reporter gene expression may then be performed at a suitable time after said gene has been introduced into recipient cells.
The skilled artisan will note that polynucleotides preferred for practicing the subject invention encode proteins (or peptides) capable of expression in cells, localization to cell membrane, and toxin binding. Accordingly, fragments of exemplified sequences as well as functional mutants may equally be used in practicing the subject invention. Such fragments and mutants will be readily obtainable following the teachings herein coupled with the state of the art. For example, using specifically exemplified polynucleotides as probes, useful polynucleotides can be obtained under conditions of appropriate stringency. Standard hybridization conditions include hybridization with nonspecific DNA, such as salmon DNA, at 50° C. and washing at 45° C. To obtain polynucleotides having the lowest detectable homology with the exemplified CR12-MPED (for example), hybridization is conducted under conditions of low standard stringency (30-37° C. and 4-6×SSC). More closely related CR12-MPED like polynucleotides (for example) can be obtained under moderate standard stringency conditions (40-50° C. in 1×SSC).
Having thus described in detail preferred embodiments of the present invention, it is to be understood that the various described embodiments are merely exemplary of the present invention and that many apparent variations thereof are possible without departing from the spirit or scope thereof. Accordingly, one skilled in the art will readily recognize that the present invention is not limited to the specific embodiments described herein.
The description provided in the following examples relates to the preferred method using the available strategy from the published protocols for constructing DNA vectors and the like. Any molecular cloning and recombinant DNA techniques needed would be carried out by standard methods (Sambrook et al., 1995).
All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety to the extent they are not inconsistent with the explicit teachings of this specification.
Following are examples that illustrate procedures for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.
EXAMPLE 1 Summary of Antagonistic Binding and Toxicity Blocking AssaysPreviously, toxin binding regions on Bt-R1 were shown to act as antagonists to Cry1Ab by blocking toxicity (Dorsch et al. 2002; Gomez et al. 2001, Gomez et al. 2003). The CR12-MPED region encoded by the region of Bt-R1a including cad 12 and the MPED was tested using similar experiments. The CR12-MPED region (SEQ ID NO:2, encoded by SEQ ID NO:1) was over-expressed in E. Coli and purified. Peptide was mixed with a LC50 dosage of Cry1Ab and fed to M. sexta larvae. Cry1Ab toxin was obtained by trypsin activation of the protoxin (Accession Number AAA22330). CR12-MPED was expected to block toxicity when mixed with Cry1Ab toxin and fed to larvae. The bioassay results were quite surprising. The CR12-MPED peptide did not suppress Cry1Ab toxicity but very surprisingly increased the mortality of Manduca larvae fed Cry1Ab. Increased concentrations of CR12-MPED mixed with a constant amount of Cry1Ab fed to the larvae killed more larvae. CR12-MPED peptide enhanced Cry1Ab toxicity. This initial result was confirmed upon further testing. CR12-MPED increases the potency of an already highly active Cry toxin against a susceptible insect.
EXAMPLE 2 M. sexta Bioassay Trial 1“group1”—9 ng/cm2 Cry1Ab (toxin:peptide ratio 1:0),
“group2”—9 ng/cm2 Cry1Ab plus 9 ng/cm2 CR12-MPED (ratio 1:1),
“group3”—9 ng/cm2 Cry1Ab plus 90 ng/cm2 CR12-MPED (ratio 1:10),
“group4”—9 ng/cm2 Cry1Ab plus 450 ng/cm2 CR12-MPED (ratio 1:50),
“group5”—9 ng/cm2 Cry1Ab plus 900 ng/cm2 CR12-MPED (ratio 1:100),
“group6”—9 ng/cm2 Cry1Ab plus 4500 ng/cm2 CR12-MPED (ratio 1:500)
“group7”—water only as a control.
Each group had 16 replicates.
After 7 days, many larvae in groups 4 and 5 were dead. This was attributed to the possibility that the Tris-HCl buffer, as the CR12-MPED peptide was in 10 mM Tris-HCl (pH 8.0). Alternatively, the CR12-MPED peptide could have been enhancing the toxicity of Cry1Ab. To determine if the high toxicity of the Cry1Ab/CR12-MPED mixture was reproducible, the bioassay experiment was repeated with additional controls.
EXAMPLE 3 M. sexta Bioassay Trial 2A 1:500 ratio group (i.e., group 6 above) was not included because the 1:50 and 1:100 ratios gave an enhanced effect. Four additional controls were included: 10 mM Tris-HCl (pH 8.0), 9 ng/cm2 CR12-MPED, 90 ng/cm2 CR12-MPED, and 900 ng/cm, CR12-MPED. In two days, almost all of the larvae in highest concentration of CR12-MPED/Cry1Ab were dead, but the larvae fed with the toxin-only were not dead. The CR12-MPED/Cry1Ab treatment groups showed the same trend as obtained in the first trial. Table 2 shows the percentage mortality for the treatments in both M. sexta trials. CR12-MPED enhanced the potency of B.t. Cry1Ab in both trials.
Preliminary data suggested that CR12-MPED synergizes B.t. Cry1Ab toxicity to H. virescens. This is important because H. virescens is the major target of B.t. cotton.
The ability of the CR12-MPED peptide to function synergistically with other combinations of toxin and pest insects can now be tested, in light of the subject disclosure.
EXAMPLE 5 Synergistic Effect of CR12-MPED Peptide on Mortality of Heliothis virescens, Helicoverpa zea, Spodoptera frugiperda, and Plutella xylostella Larvae Fed CR12-MPED Peptide Plus Cry1A ToxinsEggs were hatched and reared on artificial diet on which toxin or/and CR12-MPED peptide were or not added. Bacillus thuringiensis toxin (Cry1Aa, 1Ab and 1Ac) were used in LC50 dosage according to the Bacillus thuringiensis Toxin Specificity Database (see website at glfc.forestry.ca/bacillus). The three toxins as used were obtained by trypsin activation of protoxins (Cry1Aa: DH37 (Accession Number AAA22353); Cry1Ab: NRD12 (Accession Number AAA22330); and Cry1Ac DH73 (Accession AAA22331)). The concentration of each toxin is listed in the following tables. H. virescens and H. zea neonates were transferred to wells in a bioassay tray containing the diet with or without toxin or/and CR12-MPED peptide. Seven days later, mortality and larval body weight were measured. The mortality and body weight were recorded after seven days feeding with toxins or/and CR12-MPED peptide. Each group has sixteen larvae per treatment. The concentration of CR12-MPED peptide was in various mass ratios relative to Cry1A toxin as shown in Tables 3-7 and in
Without being bound by specific theories regarding mechanisms of action, following are possible explanations for the “synergistic” or enhancing effects that peptides of the subject invention have on the insecticidal activity of B.t. proteins. The peptide may bind to the protein (such as a Cry protein) causing a change in conformation of the toxin, thereby allowing cleavage by midgut proteins and facilitating subsequent binding and membrane insertion events. A protein/peptide complex could increase binding to cadherin molecules. In addition, the peptide could increase toxin binding to receptor molecules such as aminopeptidase or other raft-associated proteins sorting in the cell membrane. There is evidence to further support this hypothesis, as cadherin binding increases the affinity of Cry1Ab for aminopeptidase from M. Sexta (Bravo et al. 2004). With the help of a peptide of the subject invention, the toxin could gather or collect on the surface of BBMV and form pores on cell surface. The peptides may function as an adaptor or bridge to connect toxin with cell membrane.
Alternatively or in addition, the peptide may function independently from the Cry toxin, for example. The peptides could exhibit a complete or partial toxic effect elsewhere, separately, or the peptides could function indirectly to enhance the Cry toxin. For example, the peptide could somehow contribute to the stability of the Cry toxin in the insect gut.
The exact mechanism(s) of action, however, are relatively unimportant, as one skilled in the art can now make and use a wide range of embodiments of the subject invention as discussed herein.
EXAMPLE 7 Further Studies7A. Expression and purification of CR12-MPED peptide in E. coli. Two primers were designed with restriction sites of Nco I and Xho I according to BtR1a CR12-MPED sequence. CR12-MPED encoding Bt-R1a (1362Ile-Pro1567) was cloned into pET-30a(+) vector (Novagen). The vector pET-30a(+)/CR12-MPED was transferred into E. coli strain BL21/pRIL. Target protein fused with 6×His-tag at both N- and C-termini was over-expressed by 1 mM IPTG induction when the culture OD600 reached 0.5-0.6. The culture was harvested 4 hours after induction. CR12-MPED purification was according to “Protocol7” in The QIAexpressionist (2nd Edition, summer 1992, QIAGEN) with minor modifications. The resulting peptide was dialyzed against 10 mM Tris-HCl (pH 8.0) and confirmed by 15% SDS-PAGE and western blot with anti-BtR1 serum (1:5000). The CR12-MPED peptide was used in binding competition assays. The PVDF membrane dotted with S2 cells expressing truncated cadherin was incubated with CR12-MPED peptide and 125I-Cry1Ab toxin in a 500:1 mass ratio, respectively. CR12-MPED was also tested with Cry1 toxins in insect bioassays (described below).
7B. Insect bioassays. The LC50 for Cry1Ab against M. sexta neonate larvae is 5 to 10 ng/cm2 (see website: glfc.cfs.nrcan.gc.ca/bacillus Oct. 1, 2003). In a bioassay, we confirmed this LC50 value for Cry1Ab and selected 9 ng/cm2 Cry1Ab for testing the effect of CR12-MPED peptide. Toxin preparations were diluted in deionized water, mixed with varying concentrations of CR12-MPED and then 50 ml applied to the surface of insect diet (Southland Products, Lake Village, Ark.). M. sexta eggs were obtained from Carolina Biologicals. Mortality was scored after 7 days.
H. virescens and Helicoverpa zea eggs were obtained from Benzon Research and bioassays conducted as for M. sexta.
7C. Results. We expressed full length and truncated peptides of BtR1a in S2 cells to investigate their involvement in Cry1Ab binding and toxicity. All truncated cadherin constructs contained the signal leader peptide as well as the transmembrane and cytoplasmic domain for expression on the cell membrane. Truncated cadherin fragment designations included the number of the ectodomain cadherin repeats (CR) they contain and the region included. For example Cad7-12 encodes CR7 and the remainder of Bt-R1a to the carboxy terminus. Transfected S2 cells expressed full length and truncated cadherin fragments, which were recognized by sera against Bt-R1 on immunoblots. As previously reported (Hua et al. 2003), S2 cell-expressed full length Bt-R1 cadherin had a slightly smaller molecular size than Bt-R1 from M. sexta BBMV. Conversely, the Cad7 and Cad7-12 truncated Bt-R, fragments expressed in S2 cells had a molecular size slightly greater than predicted.
Ligand blots of proteins from S2 transfected cells were probed with 125I-labeled Cry1Ab toxin. 125I-Cry1Ab toxin bound to truncated Bt-R1a that contained Cad7-12, 10-12, and 11-12. Expressed truncated proteins that did not contain both CR11 and 12 (i.e. Cad7, Cad 11, Cad12 and Cad-MPED) did not bind 121I-Cry1Ab on blots. These results agreed with previous ligand blot data of truncated Bt-R1 fragments (Dorsch et al. 2002), which showed Cry1Ab binding to a region that included both CR11 and 12. To verify if the space between toxin binding region and cell membrane was important for toxin binding, CR11 was switched with CR12 and cloned into pIZT vector. Both dot-blot and ligand-blot showed Cad12/11 lost binding with Cry1Ab toxin.
Ligand blotting, which involves denaturing conditions, has been reported to yield Cry toxin binding results that are sometimes inconsistent with toxin binding assays done under native conditions (Daniel et al., 2002; Lee and Dean 1996). To investigate the possibility of alteration by ligand blotting of binding epitopes that are functional under native conditions, we performed dot blotting. S2 cells expressing truncated cadherin fragments were dotted on PVDF filters and 125I-Cry1Ab toxin binding tested. In agreement with the ligand blot experiments, proteins containing Bt-R, ectodomains CR11 and 12 (full length cadherin, Cad7-12, Cad10-12, Cad11-12) specifically bound 125I-Cry1Ab. Peptide expressed from Cad12 also bound toxins, which was a surprise since it did not bind toxin on blots. Cad7 and Cad11 did not bind Cry1Ab. Although Cad12-11 contained both CR11 and CR12 domains, it did not bind to labeled Cry1Ab toxin after they were switched each other. These results suggest that the arrangement among CR11, CR12, and MPED is important for toxin binding. Interestingly, the expressed Cad12 peptide, which contained only ectodomain CR12 and MPED, bound Cry1Ab specifically. This result was not observed in ligand blotting and is evidence that native conditions are necessary for Cry1Ab binding to ectodomain CR12, and that ectodomain CR12 is sufficient for Cry1Ab toxin binding. MPED may also be important in maintaining secondary structure of CR12 (a.k.a. EC12) or possibly collaborates with CR12 in toxin binding. These results identify ectodomain CR12 as a critical Cry1Ab binding epitope on Bt-R1a. Interestingly, when radioactivity of the individual dots was counted, the truncated Cad11-12 peptide containing both ectodomain CR11 and 12 bound more Cry1Ab toxin than any other expressed truncated peptide, including full length cadherin (data not shown).
To quantify Cry1Ab binding to expressed Bt-R1a fragments, Cry1Ab binding saturation assays were performed with cell suspensions as previously reported (Hua et al. 2004). In agreement with results from dot blotting, cells expressing full-length cadherin, Cad7-12, Cad11-12 and Cad12 bound Cry1Ab. Toxin binding was specific and saturable in all cases, and cells expressing cad11-12 bound more toxin than any other cell sample. Although all Bt-R1a fragments binding Cry1Ab displayed the same binding affinity (Table 8), the concentration of binding sites was higher for Cad11-12 and Cad12 than for Cad7-12 or full-length cadherin. Furthermore, Cad11-12 had about 3-fold higher concentration of binding sites than Cad12. These results indicate that in full length Bt-R1 conformational limitations may exist that prevent maximal binding of Cry1Ab, and that both CR11 and CR12 contain Cry1Ab binding epitopes.
It was previously reported that Bit-R1a was a functional Cry1A toxin receptor and induced cell death when expressed in S2 cells (Hua et al. 2004). To investigate the role of ectodomains CR11 and 12 in Cry1Ab toxicity, flow cytometry was used to quantitatively measure the percentage of cytotoxic response induced by Cry1Ab in S2 cells expressing different truncated fragments. Co-expression with GFP provided a method to monitor transfection efficiency, and propidium iodide (PI) was used to detect dead cells. Cytotoxicity was quantified using a formula previously reported (Hua et al. 2004) that relates both transfection and cytotoxicity to background cell death in control (mock transfected) cells. Cry1Ab was cytotoxic to cells expressing Cad7-12, Cad10-12, Cad11-12, Cad12 and full length Bt-R1a cadherin. On the other hand, Cry1Ab was not toxic to S2 cells expressing Cad7, Cad11, Cad12-11 and Cad-MPED. There were no significant differences among the toxicities of Cry1Ab on S2 cells expressing Cad7-12, Cad10-12, Cad11-12, Cad12, and full cadherin. These results (summarized in Table 9) are evidence that ectodomain CR12 is the functional receptor epitope for Cry1Ab in Bt-R1a.
To confirm the importance of Cad12-MPED region in toxin binding, Cad12-MPED peptide was used as a competitor in dot-blot assays against 125I-Cry1Ab. Cad12-MPED was expressed in E. coli and purified using immobilized metal affinity chromatography. Cad12-MPED peptide competed Cry1Ab toxin binding to fill-length cadherin, and truncated cadherins 7-12, 10-12, 11-12 and 12. This result was further evidence that cadherin CR12 domain is necessary and sufficient for toxin binding. CR12 contains the key Cry1Ab binding site on Bt-R1a cadherin.
EXAMPLE 8 Summary of Results of Peptide CR12-MPED Enhancing Toxicity of Various Cry1A Proteins Against Various LepidopteransBtR1a was cloned into the insect cell expression vector pIZT-V5-His (Invitrogen). A fragment of BtR1a extending from cadherin repeat (CR) 12 through the membrane proximal extracellular domain (MPED) was cloned into pET30a and expressed in Escherichia coli. The 27-kDa expressed peptide called CR12-MPED was partially purified from inclusion bodies. Surprisingly feeding insect larvae CR12-MPED peptide with Cry1 toxin increased the toxicity of Cry1A toxins to insect larvae.
The CR12-MPED peptide was tested in combination with Cry1A toxins against lepidopteran larvae representing a range of Cry1A toxin susceptibilities. The following insects were tested: Manduca sexta (tobacco hornworm), Heliothis virescens (tobacco budworm), Helicoverpa zea (cotton bollworm, corn earworm), Spodoptera frugiperda (fall armyworm), and Pseudoplusia includens (soybean looper). Cry1Aa, Cry1Ab and Cry1Ac toxins were tested with CR12-MPED using diet-surface treatments, early first instar larvae and a 7 day bioassay period.
EXAMPLE 9 Peptide CR12-MPED Enhances Toxicity of Cry1Ab and Cry1Ac Proteins Against Manduca sextaIn bioassays against M. sexta, CR12-MPED increased mortality from 1.0±1.0% for 2 ng Cry1Ab/cm2 treatments to 26.0±5.5% mortality at a 1:100 Cry1Ab:CR12-MPED mass ratio. As the toxin concentration was increased to 4 ng/cm2 CR12-MPED increased mortality from 4.2±1.1% to 82.3±6.8% (P<0.01). CR12-MPED was inactive alone in all bioassays.
CR12-MPED also enhanced potency of Cry1Ac against M. sexta larvae. For example while 2 ng Cry1Ac/cm2 killed 13.5±6.5% of the larvae, Cry1Ac:CR12-MPED ratios of 1:10 and 1:100 mortality increased morality to 63.5±17.8% (P<0.05) and 93.8±3.1% (P<0.005), respectively.
EXAMPLE 10 Peptide CR12-MPED Enhances Toxicity of Cry1Ac Against Heliothis virescensCR12-MPED enhances Cry1Ac toxicity to H. virescens (tobacco budworm). Neonate larvae were fed Cry1Ac with or without CR12-MPED. At a Cry1Ac concentration of 3 ng/cm2 diet mortality was 8.4±2.1% (toxin only); with inclusion of 300 ng/cm2 of CR12-MPED mortality was increased to 83.4±6.3% (P<0.01). At a Cry1Ac concentration of 6 ng/cm2, CR12-MPED peptide greatly enhanced Cry1Ac toxicity to H. virescens larvae from 46.7±9.9% (toxin only) to 88.5±5.5% (with either 1:10 or 1:100 CR12-MPED ratio) (P<0.05).
EXAMPLE 11 Peptide CR12-MPED Enhances Toxicity of Cry1Ac Proteins Against Helicoverpa zeaH. zea (cotton bollworm, corn earworm, tomato fruitworm) has a wide host range, attacking many vegetables, fruits, and cotton. B.t. transgene crops are not as effective at controlling H. zea as they are other pests. This is because Cry1A toxins are less effective against H. zea than other target pests. H. zea is not as sensitive to Cry1Ac as H. virescens or M. sexta. Therefore, this pest was selected to determine if CR12-MPED peptide could enhance B.t. activity.
In this experiment, 50 ng/cm2, 60 ng/cm2 and 120 ng/cm2 of Cry1Ac were used to test CR12-MPED. Cry1Ac toxin did not kill the larvae efficiently. At 50 ng or 60 ng/cm2 dosages, only 5.2±2.8% of the larvae were killed, compared to 0% (for toxin only). However, the addition of a 1:10 ratio of CR12-MPED increased morality to 56.3±8.3% (P<0.05) and 42.7±3.8% (P<0.01). If the toxin dosage was increased to 120 ng/cm2, it killed 24.0±2.8% of H. zea larvae while an equal proportion of added CR12-MPED increased morality to 47.9±5.5% (P<0.05). A ten-fold amount peptide increased the mortality to 85.4±2.8 (P<0.001).
EXAMPLE 12 Peptide CR12-MPED Enhances Toxicity of Cry1Ab, Cry1Ac, and Cry1C Proteins Against Spodoptera frugiperdaSpodoptera frugiperda is not susceptible to Cry1A toxins (LC50>2000 ng/cm2 dosage; see, e.g., “glfc.forestry.ca/bacillus” website. However, when Cry1Ab or Cry1Ac were combined with CR12-MPED at 1:1 and 1:10 ratios (toxin:CR12-MPED) mortality was increased, and larvae fed combinations of CR12-MPED and Cry1Ab or Cry1Ac were severely stunted in growth S. frugiperda is more susceptible to Cry1Ca (LC50 1144 (813-3227) ng/cm2) compared to Cry1A toxins. Cry1Ca protoxin (GENBANK Accession Number CAA30396), tested at 150 and 300 ng/cm2, killed 6% and 19% of larvae. Addition of CR12-MPED increased morality to 31% and 41%. This is an important observation because there is no published report of Cry1Ca interaction with M. sexta cadherin.
EXAMPLE 13 Summary of CR12-MPED Binding Studies and Conclusions Regarding Toxin EnhancementOverall, CR12-MPED enhances or potentiates the toxicity of Cry1A and Cry1C toxins against susceptible and tolerant insects. In vitro, CR12-MPED binds to toxin forming large-sized protein clusters. These protein clusters still bind specifically to midgut brush border.
EXAMPLE 14 Peptide CR11-MPED Enhances Toxicity of Cry1Ab Against Manduca sextaThe CR11-MPED (SEQ ID NO:4; SEQ ID NO:3 is the DNA) region of BtR1a were cloned into pET30 and expressed in E. coli. The CR11-MPED region consists of CR11 in front of CR12-MPED. Peptide was solubilised from inclusion bodies and tested in bioassays with purified Cry1Ab toxin. Peptide CR11-MPED peptide fed with Cry1Ab toxin to M. sexta larvae was more toxic to larvae than toxin alone (
As discussed in more detail in Example 16, the CR11-MPED peptide also increased Cry1Ac toxicity to soybean loopers (
The peptide CR1-3 (SEQ ID NO:6; SEQ ID NO:5 is the DNA) was constructed as a negative control with the expectation that it would not enhance toxicity based on the lack of a Cry1Ab binding site on the peptide. However, CR1-3 was surprisingly found to be equal to CR12-MPED in the capacity to increase Cry1Ac toxicity to soybean looper (
The CR11-MPED and CR1-3 regions of BtR1a were cloned into pET30 and expressed in E. coli. All peptides were expressed and purified using standard methodology. Purified peptides were run on SDS page using standard methodology. Concentrations of the indicated samples are as follows: CR11-MPED (0.279 mg/ml); CR12-MPED (2.106 mg/ml); CR1-3 (1.809 mg/ml); Ano-Cad (0.50 mg/ml), Ano-PCAP (0.78 mg/ml) and SlyD (0.046 mg/ml). 12.5 ng/cm2 of Cry1Ac was bioassayed with or without different peptides in 1:1, 1:10 and 1:100 ratio. Soybean looper neonates were set in bioassay trays, with each group having 62 larvae. The Ano-Cad, Ano-PCAP, and SlyD peptides are discussed in the following Example.
EXAMPLE 17 Preparation of Peptides Ano-Cad and Ano-PCAP from Mosquito Cadherin Proteins, and Preparation of Peptide SlyDMosquitoes are dipterans, as opposed to lepidopterans as tested above. Because selected mosquito cadherin proteins have low amino acid similarity to BtR1, peptide fragments from mosquito cadherins were expected to be less likely to enhance a toxin's effect in lepidopteran larvae, thereby serving as a negative cadherin control. Additionally, mosquito cadherin fragments could be tested for toxin-enhancing properties in mosquitoes.
Two full-length cDNAs encoding cadherin-type proteins were cloned and sequenced from the mosquito Anopheles gambiae. The cloned cDNA nucleotide sequences correspond to sequences deposited by the Anopheles gambiae genome sequencing project at A. gambiae loci. Fragments similar in size and location to the CR12-MPED region of BtR1a were cloned into pET30 vector and expressed in E. coli. The cDNA fragments, designated, Ano-Cad and Ano-PCAP, cloned in pET are identical to the DNA sequences of A. gambiae loci XM—312086 and XM—321513, respectively.
SEQ ID NO:7 shows the nucleotide sequence of the putative cell adhesion protein of Anopheles gambiae NCBI LOCUS XM—321513). SEQ ID NO:8 shows the corresponding amino acid sequence. SEQ ID NO:9 shows the nucleotide sequence encoding the truncated putative cell-adhesion protein region of the Anopheles gambiae protein. This truncated peptide is referred to herein as PCAP putative cell-adhesion protein) or Ano-PCAP, which has 213 amino acid residues, and is approximately 24,417 Daltons (theoretical pI=4.96). SEQ ID NO:10 shows the truncated PCAP region of the Anopheles gambiae protein. This sequence is for the peptide expressed in E, coli strain BL21/DE3/pRIL having the DNA cloned into the pET-300a vector.
SEQ ID NO:11 shows the full-length Anopheles gambiae cDNA cadherein sequence. BLAST search with the sequence matches the DNA and predicted protein sequence for a partial Anopheles gambiae cDNA (NCBI Locus XM—312086). SEQ ID NO:12 shows the “Ano-Cad”-encoding fragment of SEQ ID NO:11 that was cloned into the pET-30 vector and expressed in E. coli strain BL21/DE3. SEQ ID NO:13 shows the full-length Anopheles gambiae cadherin protein encoded by SEQ ID NO:11. Residues 1358-1569 of SEQ ID NO:13 correspond to the “Ano-Cad” peptide encoded by SEQ ID NO:12.
SlyD is 21-a kDa histidine-rich E. coli protein that frequently co-elutes with other proteins from immobilized metal affinity column (IMAC). Because a similar-sized protein was detected in some eluates, SlyD from E. coli was prepared for testing as well.
EXAMPLE 18 Comparison of the Ability of Ano-PCAP, Ano-Cad, and SlyD Peptides to Enhance Cry1Ac Against Soybean LoopersAs shown in
Cry2Aa protoxin (non-truncated) (GENBANK Accession Number M31738) was fed to soybean looper larvae (neonates) with CR12-MPED, CR1-3, or Ano-PCAP (SEQ ID NO:10). Both CR12-MPED and Ano-PCAP increased Cry2Aa toxicity to the larvae. See
A Cry1Aa protein (GENBANK Accession Number AAA22353), which is a toxin produced in Bacillus thuringiensis (B.t.), was tested as protoxin and trypsin-treated forms to determine its level of anti-rootworm (Diabrotica spp.; coleopterans) activity, if any. The expectation was that this toxin would not be active against this coleopteran, as Cry1 toxins (including Cry1Aa) are known to be “lep active” toxins (toxins with proven activity against caterpillars or lepidopterans). See e.g. Hofte et al. (1989). This protein was surprisingly found to have activity against rootworms. Thus, methods of using Cry1Aa for controlling rootworms are an aspect of the subject invention.
Surprisingly, in the course of this experimentation, it was also found that the CR11-MPED and CR12-MPED peptide have stand-alone activity against rootworms. Other cadherin-like peptides eg. CR1-3 and Ano-Cad were also tested and found to have significant toxicity against rootworms, albeit at lower toxicity (CR11-MPED≈CCR12-MPED>CR1-3≈Ano-Cad). As the testing and data set forth herein are not exhaustive, the subject invention thus includes the use of peptides of the subject invention, alone, for controlling insects. This methodology is yet another aspect of the subject invention. In preferred embodiments of this aspect of the subject invention, “stand-alone” peptides are used to control coleopterans (which include grubs and beetles).
20.A—Preparation of Cry1Aa, CR11-MPED, CR12-MPED, CR1-3, and Ano-Cad and Rootworm Bioassays.
The Cry1Aa construct (cry1Aa gene in pKK223-3 vector) was obtained from Donald H. Dean (The Ohio State University). Toxin was expressed in E. coli and purified by HPLC. The toxin was concentrated and dialyzed against distilled water.
All peptides were over-expressed in E. coli as an inclusion body. Inclusion bodies were extracted from the bacteria and solubilized in 10 mM NaOH. Insoluble materials were removed by centrifugation. The supernatant was applied to Q-sepharose column (30 mM Na2CO3 pH 10.0), and the flow-through fractions containing CR11-MPED were collected because CR11-MPED form large aggregates that fail to bind to the anion exchange column. The fractions were pooled and centrifuged again. The supernatant was concentrated by filtration (Amicon) and dialyzed against distilled water. Rootworm eggs were purchased from Lee French (French Agricultural Research Inc., Minnesota). Southern Corn Rootworm diet was purchased from Bio-Serv.
Bioassays were performed on neonate larvae of Southern Corn Rootworm (Diabrotica undecipunctata). The toxin/peptides was diluted in distilled water and applied on the artificial diet in plastic bioassay trays and air dried. Six larvae were put in each well, and 24 larvae were tested at each toxin dose in Trial 1. In Trial 2, four larvae were put in each well, and 16 larvae were tested at each toxin dose. The bioassays were done at room temperature (23° C.). Mortality was recorded on Day 11 in Trial 1 and Day 10 in Trial 2.
20.8—Toxicity of Cry1Aa CR11-MPED, CR12-MPED, CR1-3, and Ano-Cad on D. undecipunctata.
In Trial 1, 29% mortality was observed at a concentration of 200 μg/cm2 Cry1Aa protoxin and 50% mortality was observed at a concentration of 250 μg/cm2. Higher mortality was recorded for trypsin-treated Cry1Aa. 72% mortality was observed at a concentration of 100 μg/cm2 trypsin-treated Cry1Aa and 67% mortality was observed at a concentration of 150 μg/cm2. In Trial 2, 100% mortality was achieved with Cry1Aa protoxin at a concentration of 300 μg/cm2. Background mortality was between 6 and 8% in both trials. These results (summarized in Table 10) demonstrated that Cry1Aa has insecticidal activity against rootworms.
The toxicity of the peptides (CR11-MPED, CR12-MPED, CR1-3, and Ano-Cad) towards the rootworm larvae was unexpected because initial tests on soybean looper larvae showed no toxic activity when the peptides were applied alone. Also, a concentration of 100 μg/cm2 CR12-MPED did not cause any mortality or growth inhibition to H. zea neonates.
In Trial 1, 25 μg/cm2 CR11-MPED killed 8%, 50 μg/cm2 CR11-MPED killed 8%, 100 μg/cm2 CR11-MPED killed 12%, 150 μg/cm2 CR11-MPED killed 79%, 200 μg/cm2 CR11-MPED killed 83%, and 250 μg/cm2 CR11-MPED killed 92% of the larvae. In the same trial, 25 μg/cm2 CR12-MPED killed 8%, 500 μg/cm2 CR12-MPED killed 21%, 100 μg/cm2 CR12-MPED killed 21%, 150 μg/cm2 CR12-MPED killed 96%, 200 μg/cm2 CR12-MPED killed 92%, and 250 μg/cm2 CR112-MPED killed 83% of the larvae.
In Trial 2, 125 μg/cm2 CR11-MPED killed 87%, 150 μg/cm2 CR11-MPED killed 75%, 200 kg/cm2 CR11-MPED killed 88% of the larvae. In the same trial, 125 μg/cm2 CR1-3 killed 6%, 150 μg/cm2 CR1-3 killed 63%, 200 μg/cm2 CR1-3 killed 44% of the larvae, while 125 μg/cm2 Ano-Cad killed 31%, 150 μg/cm2 Ano-Cad killed 38%, 200 μg/cm2 Ano-Cad killed 50% of the larvae. Background mortality was between 6 and 8% in both trials. These results (summarized in Table 11) demonstrated the stand-alone insecticidal activity of these peptides against rootworms.
The Cry1Aa construct (cry1Aa gene in pKK223-3 vector) was obtained from Donald H. Dean (The Ohio State University). Toxin was expressed in E. coli and purified by HPLC. Table 12 shows the diet overlay bioassay on the soybean looper (Pseudoplusia includens) neonate mortality to Cry1Aa in the forms of either protoxin or trypsin-digested truncated toxin, and with mixtures of CR12-MPED at 1:100 (w/w) ratios. CR12-MPED enhances Cry1Aa toxicity to P. includens. At a Cry1Aa protoxin concentration of 2 ng/cm2 diet mortality was 23% (toxin only); with inclusion of 200 ng/cm2 of CR12-MPED mortality was increased to 50%. At a Cry1Aa protoxin concentration of 5 ng/cm2, 500 ng/cm2 CR12-MPED peptide greatly enhanced Cry1Aa protoxin toxicity to P. includens larvae from 0% (toxin only) to 88% (P<0.001).
Similar results were obtained using trypsin-digested truncated Cry1Aa. At a Cry1Aa trypsin-digested toxin concentration of 2 ng/cm2 diet mortality was 6% (toxin only); with inclusion of 200 ng/cm2 of CR12-MPED mortality was increased to 94% (P<0.001). At a Cry1Aa trypsin-digested toxin concentration of 5 ng/cm2, 500 ng/cm2 CR12-MPED peptide enhanced Cry1Aa protoxin toxicity to P. includens larvae from 38% (toxin only) to 100% (P<0.001). Background mortality was at 0%. These results demonstrated that CR12-MPED peptide was able to enhance the activity of Cry1Aa protoxin (
Click on name to access NCBI entry (if available)
Some of the above toxins could not be given an unambiguous name due to insufficient or uncertain sequence data.
The following Bt proteins have not been assigned a name or entered into the nomenclature for the reasons given.
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Claims
1. A method of inhibiting an insect wherein said method comprises providing a peptide to said insect for ingestion, wherein said peptide enhances toxin activity of a Bacillus thuringiensis Cry protein, wherein said peptide comprises a B.t. Cry binding domain of an ectodomain of an insect cadherin B.t. toxin receptor from an insect midgut epithelial cell, and wherein said peptide is a fragment of said ectodomain.
2. The method of claim 1, wherein said method further comprises providing a Bacillus thuringiensis Cry protein to said insect for ingestion.
3. A method of inhibiting an insect wherein said method comprises providing a peptide to said insect for ingestion, wherein said peptide binds a Bacillus thuringiensis Cry protein and enhances toxin activity of said protein, and wherein said peptide comprises a first B.t. Cry binding domain having at least 85% identity with a second B.t. Cry binding domain of an ectodomain of an insect cadherin B.t. toxin receptor from an insect midgut epithelial cell.
4. The method of claim 3, wherein said peptide is sprayed on to a plant.
5. The method of claim 3, wherein said peptide is produced by and present in a plant.
6. The method of claim 3, wherein said method further comprises providing said Bacillus thuringiensis Cry protein to said insect for ingestion.
7. The method of claim 6, wherein said peptide is sprayed on to a plant that produces said protein.
8. The method of claim 6, wherein said peptide and said protein are sprayed on to a plant.
9. The method of claim 6, wherein said peptide and said protein are produced by and are present in a plant.
10. The method of claim 6, wherein said peptide is fused with said Cry protein.
11. The method of claim 1, wherein said peptide is sprayed on to a plant.
12. The method of claim 1, wherein said peptide is produced by and present in a plant.
13. The method of claim 1, wherein said method further comprises providing said Bacillus thuringiensis Cry protein to said insect for ingestion.
14. The method of claim 13, wherein said peptide is sprayed on to a plant that produces said protein.
15. The method of claim 13, wherein said peptide and said protein are sprayed on to a plant.
16. The method of claim 13, wherein said peptide and said protein are produced by and are present in a plant.
17. The method of claim 3, wherein said first B.t. Cry binding domain has at least 90% identity with said second B.t. Cry binding domain.
18. The method of claim 3, wherein said first B.t. Cry binding domain has at least 95% identity with said second B.t. Cry binding domain.
19. The method of claim 1, wherein said peptide is fused with a protein.
20. A fusion protein comprising a peptide fused to a fused protein, wherein said peptide binds a Bacillus thuringiensis Cry protein and enhances toxin activity of said Bacillus thuringiensis Cry protein, and wherein said peptide comprises a B.t. Cry binding domain having at least 85% identity with a B.t. Cry binding domain of an ectodomain of an insect cadherin B.t. toxin receptor from an insect midgut epithelial cell.
21. The fusion protein of claim 20, wherein said fused protein is said Bacillus thuringiensis Cry protein.
Type: Application
Filed: Jun 27, 2008
Publication Date: Jan 15, 2009
Applicant: University of Georgia Research Foundation, Inc. (Athens, GA)
Inventors: Michael J. Adang (Athens, GA), Gang Hua (Athens, GA), Jian (John) Chen (Athens, GA), Mohd Amir Fursan Abdullah (Zionsville, IN)
Application Number: 12/163,508
International Classification: A01N 61/00 (20060101); C07K 14/325 (20060101); A01P 7/04 (20060101);
