Patent Application
20100242358
The present invention relates to imparting hypersensitive response induced resistance to plants by treatment of seeds.
Living organisms have evolved a complex array of biochemical pathways that enable them to recognize and respond to signals from the environment. These pathways include receptor organs, hormones, second messengers, and enzymatic modifications. At present, little is known about the signal transduction pathways that are activated during a plant's response to attack by a pathogen, although this knowledge is central to an understanding of disease susceptibility and resistance. A common form of plant resistance is the restriction of pathogen proliferation to a small zone surrounding the site of infection. In many cases, this restriction is accompanied by localized death (i.e., necrosis) of host tissues. Together, pathogen restriction and local tissue necrosis characterize the hypersensitive response. In addition to local defense responses, many plants respond to infection by activating defenses in uninfected parts of the plant. As a result, the entire plant is more resistant to a secondary infection. This systemic acquired resistance can persist for several weeks or more (R. E. F. Matthews, Plant Virology (Academic Press, New York, ed. 2, 1981)) and often confers cross-resistance to unrelated pathogens (J. Kuc, in Innovative Approaches to Plant Disease Control, I. Chet, Ed. (Wiley, New York, 1987), pp. 255-274, which is hereby incorporated by reference). See also Kessman, et al., “Induction of Systemic Acquired Disease Resistance in Plants By Chemicals,” Ann. Rev. Phytopathol. 32:439-59 (1994), Ryals, et al., “Systemic Acquired Resistance,” The Plant Cell 8:1809-19 (October 1996), and Neuenschwander, et al., “Systemic Acquired Resistance,” Plant-Microbe Interactions vol. 1, G. Stacey, et al. ed. pp. 81-106 (1996), which are hereby incorporated by reference.
Expression of systemic acquired resistance is associated with the failure of normally virulent pathogens to ingress the immunized tissue (Kuc, J., “Induced Immunity to Plant Disease,” Bioscience, 32:854-856 (1982), which is hereby incorporated by reference). Establishment of systemic acquired resistance is correlated with systemic increases in cell wall hydroxyproline levels and peroxidase activity (Smith, J. A., et al., “Comparative Study of Acidic Peroxidases Associated with Induced Resistance in Cucumber, Muskmelon and Watermelon,” Physiol. Mol. Plant. Pathol. 14:329-338 (1988), which is hereby incorporated by reference) and with the expression of a set of nine families of so-called systemic acquired resistance gene (Ward, E. R., et al., “Coordinate Gene Activity in Response to Agents that Induce Systemic Acquired Resistance,” Plant Cell 3:49-59 (1991), which is hereby incorporated by reference). Five of these defense gene families encode pathogenesis-related proteins whose physiological functions have not been established. However, some of these proteins have antifungal activity in vitro (Bol, J. F., et al., “Plant Pathogenesis-Related Proteins Induced by Virus Infection,” Ann. Rev. Phytopathol. 28:113-38 (1990), which is hereby incorporated by reference) and the constitutive expression of a bean chitinase gene in transgenic tobacco protects against infection by the fungus Rhizoctonia solani (Broglie, K., et al., “Transgenic Plants with Enhanced Resistance to the Fungal Pathogen Rhizoctonia Solani,” Science 254:1194-1197 (1991), which is hereby incorporated by reference), suggesting that these systemic acquired resistance proteins may contribute to the immunized state (Uknes, S., et al., “Acquired Resistance in Arabidopsis,” Plant Cell 4:645-656 (1992), which is hereby incorporated by reference).
Salicylic acid appears to play a signal function in the induction of systemic acquired resistance since endogenous levels increase after immunization (Malamy, J., et al., “Salicylic Acid: A Likely Endogenous Signal in the Resistance Response of Tobacco to Viral Infection,” Science 250:1002-1004 (1990), which is hereby incorporated by reference) and exogenous salicylate induces systemic acquired resistance genes (Yalpani, N., et al., “Salicylic Acid is a Systemic Signal and an Inducer of Pathogenesis-Related Proteins in Virus-Infected Tobacco,” Plant Cell 3:809-818 (1991), which is hereby incorporated by reference), and acquired resistance (Uknes, S., et al., “Acquired Resistance in Arabidopsis,” Plant Cell 4:645-656 (1992), which is hereby incorporated by reference). Moreover, transgenic tobacco plants in which salicylate is destroyed by the action of a bacterial transgene encoding salicylate hydroxylase do not exhibit systemic acquired resistance (Gaffney, T., et al., “Requirement of Salicylic Acid for the Induction of Systemic Acquired Resistance,” Science 261:754-56 (1993), which is hereby incorporated by reference). However, this effect may reflect inhibition of a local rather than a systemic signal function, and detailed kinetic analysis of signal transmission in cucumber suggests that salicylate may not be essential for long-distance signaling (Rasmussen, J. B., et al., “Systemic Induction of Salicylic Acid Accumulation in Cucumber after Inoculation with Pseudomonas Syringae pv. Syringae,” Plant Physiol. 97:1342-1347) (1991), which is hereby incorporated by reference).
Immunization using biotic agents has been extensively studied. Green beans were systemically immunized against disease caused by cultivar-pathogenic races of Colletotrichum lindemuthianum by prior infection with either cultivar-nonpathogenic races (Rahe, J. E., “Induced Resistance in Phaseolus Vulgaris to Bean Anthracnose,” Phytopathology 59:1641-5 (1969); Elliston, J., et al., “Induced Resistance to Anthracnose at a Distance from the Site of the Inducing Interaction,” Phytopathology 61:1110-12 (1971); Skipp, R., et al., “Studies on Cross Protection in the Anthracnose Disease of Bean,” Physiological Plant Pathology 3:299-313 (1973), which are hereby incorporated by reference), cultivar-pathogenic races attenuated by heat in host tissue prior to symptom appearance (Rahe, J. E., et al., “Metabolic Nature of the Infection-Limiting Effect of Heat on Bean Anthracnose,” Phytopathology 60:1005-9 (1970), which is hereby incorporated by reference) or nonpathogens of bean. The anthracnose pathogen of cucumber, Colletotrichum lagenarium, was equally effective as non-pathogenic races as an inducer of systemic protection against all races of bean anthracnose. Protection was induced by C. lagenarium in cultivars resistant to one or more races of C. lindemuthianum as well as in cultivars susceptible to all reported races of the fungus and which accordingly had been referred to as ‘lacking genetic resistance’ to the pathogen (Elliston, J., et al., “Protection of Bean Against Anthracnose by Colletotrichum Species Nonpathogenic on Bean,” Phytopathologische Zeitschrift 86:117-26 (1976); Elliston, J., et al., “A Comparative Study on the Development of Compatible, Incompatible and Induced Incompatible Interactions Between Collectotrichum Species and Phaseolus Vulgaris,” Phytopathologische Zeitschrift 87:289-303 (1976), which are hereby incorporated by reference). These results suggest that the same mechanisms may be induced in cultivars reported as ‘possessing’ or ‘lacking’ resistance genes (Elliston, J., et al., “Relation of Phytoalexin Accumulation to Local and Systemic Protection of Bean Against Anthracnose,” Phytopathologische Zeitschrift 88:114-30 (1977), which is hereby incorporated by reference). It also is apparent that cultivars susceptible to all races of C. lindemuthianum do not lack genes for induction of resistance mechanisms against the pathogen.
Kuc, J., et al., “Protection of Cucumber Against Collectotrichum Lagenarium by Colletotrichum Lagenarium,” Physiological Plant Pathology 7:195-9 (1975), which is hereby incorporated by reference), showed that cucumber plants could be systemically protected against disease caused by Colletotrichum lagenarium by prior inoculation of the cotyledons or the first true leaf with the same fungus. Subsequently, cucumbers have been systemically protected against fungal, bacterial, and viral diseases by prior localized infection with either fungi, bacteria, or viruses (Hammerschmidt, R., et al., “Protection of Cucumbers Against Colletotrichum Lagenarium and Cladosporium Cucumerinum,” Phytopathology 66:790-3 (1976); Jenns, A. E., et al., “Localized Infection with Tobacco Necrosis Virus Protects Cucumber Against Colletotrichum Lagenarium,” Physiological Plant Pathology 11:207-12 (1977); Caruso, F. L., et al. “Induced Resistance of Cucumber to Anthracnose and Angular Leaf Spot by Pseudomonas Lachrymans and Colletotrichum Lagenarium,” Physiological Plant Pathology 14:191-201 (1979); Staub, T., et al., “Systemic Protection of Cucumber Plants Against Disease Caused by Cladosporium Cucumerinum and Colletotrichum Lagenarium by Prior Localized Infection with Either Fungus,” Physiological Plant Pathology, 17:389-93 (1980); Bergstrom, G. C., et al., “Effects of Local Infection of Cucumber by Colletotrichum Lagenarium, Pseudomonas Lachrymans or Tobacco Necrosis Virus on Systemic Resistance to Cucumber Mosaic Virus,” Phytopathology 72:922-6 (1982); Gessler, C., et al., “Induction of Resistance to Fusarium Wilt in Cucumber by Root and Foliar Pathogens,” Phytopathology 72:1439-41 (1982); Basham, B., et al., “Tobacco Necrosis Virus Induces Systemic Resistance in Cucumbers Against Sphaerotheca Fuliginea,” Physiological Plant Pathology 23:137-44 (1983), which are hereby incorporated by reference). Non-specific protection induced by infection with C. lagenarium or tobacco necrosis virus was effective against at least 13 pathogens, including obligatory and facultative parasitic fungi, local lesion and systemic viruses, wilt fungi, and bacteria. Similarly, protection was induced by and was also effective against root pathogens. Other curcurbits, including watermelon and muskmelon have been systemically protected against C. lagenarium (Caruso, F. L., et al., “Protection of Watermelon and Muskmelon Against Colletotrichum Lagenarium by Colletotrichum Lagenarium,” Phytopathology 67:1285-9 (1977), which is hereby incorporated by reference).
Systemic protection in tobacco has also been induced against a wide variety of diseases (Kuc, J., et al., “Immunization for Disease Resistance in Tobacco,” Recent Advances in Tobacco Science 9:179-213 (1983), which is hereby incorporated by reference). Necrotic lesions caused by tobacco mosaic virus enhanced resistance in the upper leaves to disease caused by the virus (Ross, A. F., et al., “Systemic Acquired Resistance Induced by Localized Virus Infections in Plants,” Virology 14:340-58 (1961); Ross, A. F., et al., “Systemic Effects of Local Lesion Formation,” In: Viruses of Plants pp. 127-50 (1966), which are hereby incorporated by reference). Phytophthora parasitica var. nicotianae, P. tabacina and Pseudomonas tabaci and reduced reproduction of the aphid Myzus persicae (McIntyre, J. L., et al., “Induction of Localized and Systemic Protection Against Phytophthora Parasitica var. nicotianae by Tobacco Mosaic Virus Infection of Tobacco Hypersensitive to the Virus,” Physiological Plant Pathology 15:321-30 (1979); McIntyre, J. L., et al., “Effects of Localized Infections of Nicotiana Tabacum by Tobacco Mosaic Virus on Systemic Resistance Against Diverse Pathogens and an Insect,” Phytopathology 71:297-301 (1981), which are hereby incorporated by reference). Infiltration of heat-killed Pseudomonas tabacin (Lovrekovich, L., et al., “Induced Reaction Against Wildfire Disease in Tobacco Leaves Treated with Heat-Killed Bacteria,” Nature 205:823-4 (1965), which is hereby incorporated by reference), and Pseudomonas solanacearum (Sequeira, L, et al., “Interaction of Bacteria and Host Cell Walls: Its Relation to Mechanisms of Induced Resistance,” Physiological Plant Pathology 10:43-50 (1977), which is hereby incorporated by reference), into tobacco leaves induced resistance against the same bacteria used for infiltration. Tobacco plants were also protected by the nematode Pratylenchus penetrans against P. parasitica var. nicotiana (McIntyre, J. L., et al. “Protection of Tobacco Against Phytophthora Parasitica Var. Nicotianae by Cultivar-Nonpathogenic Races, Cell-Free Sonicates and Pratylenchus Penetrans,” Phytopathology 68:235-9 (1978), which is hereby incorporated by reference).
Cruikshank, I. A. M., et al., “The Effect of Stem Infestation of Tobacco with Peronospora Tabacina Adam on Foliage Reaction to Blue Mould,” Journal of the Australian Institute of Agricultural Science 26:369-72 (1960), which is hereby incorporated by reference, were the first to report immunization of tobacco foliage against blue mould (i.e., P. tabacina) by stem injection with the fungus, which also resulted in dwarfing and premature senescence. It was recently discovered that injection external to the xylem not only alleviated stunting but also promoted growth and development. Immunized tobacco plants, in both glasshouse and field experiments, were approximately 40% taller, had a 40% increase in dry weight, a 30% increase in fresh weight, and 4-6 more leaves than control plants (Tuzun, S., et al., “The Effect of Stem Injections with Peronospora Tabacina and Metalaxyl Treatment on Growth of Tobacco and Protection Against Blue Mould in the Field,” Phytopathology 74:804 (1984), which is hereby incorporated by reference). These plants flowered approximately 2-3 weeks earlier than control plants (Tuzun, S., et al., “Movement of a Factor in Tobacco Infected with Peronospora Tabacina Adam which Systemically Protects Against Blue Mould,” Physiological Plant Pathology 26:321-30 (1985), which is hereby incorporated by reference).
Systemic protection does not confer absolute immunity against infection, but reduces the severity of the disease and delays symptom development. Lesion number, lesion size, and extent of sporulation of fungal pathogens are all decreased. The diseased area may be reduced by more than 90%.
When cucumbers were given a ‘booster’ inoculation 3-6 weeks after the initial inoculation, immunization induced by C. lagenarium lasted through flowering and fruiting (Kuc, J., et al., “Aspects of the Protection of Cucumber Against Colletotrichum Lagenarium by Colletotrichum Lagenarium,” Phytopathology 67:533-6 (1977), which is hereby incorporated by reference). Protection could not be induced once plants had set fruit. Tobacco plants were immunized for the growing season by stem injection with sporangia of P. tabacina. However, to prevent systemic blue mould development, this technique was only effective when the plants were above 20 cm in height.
Removal of the inducer leaf from immunized cucumber plants did not reduce the level of immunization of pre-existing expanded leaves. However, leaves which subsequently emerged from the apical bud were progressively less protected than their predecessors (Dean, R. A., et al., “Induced Systemic Protection in Cucumber: Time of Production and Movement of the ‘Signal’,” Phytopathology 76:966-70 (1986), which is hereby incorporated by reference). Similar results were reported by Ross, A. F., “Systemic Effects of Local Lesion Formation,” In: Viruses of Plants pp. 127-50 (1966), which is hereby incorporated by reference, with tobacco (local lesion host) immunized against tobacco mosaic virus by prior infection with tobacco mosaic virus. In contrast, new leaves which emerged from scions excised from tobacco plants immunized by stem-injection with P. tabacina were highly protected (Tuzun, S., et al., “Transfer of Induced Resistance in Tobacco to Blue Mould (Peronospora tabacina Adam.) Via Callus,” Phytopathology 75:1304 (1985), which is hereby incorporated by reference). Plants regenerated via tissue culture from leaves of immunized plants showed a significant reduction in blue mould compared to plants regenerated from leaves of non-immunized parents. Young regenerants only showed reduced sporulation. As plants aged, both lesion development and sporulation were reduced. Other investigators, however, did not reach the same conclusion, although a significant reduction in sporulation in one experiment was reported (Lucas, J. A., et al., “Nontransmissibility to Regenerants from Protected Tobacco Explants of Induced Resistance to Peronospora Hyoscyami,” Phytopathology 75:1222-5 (1985), which is hereby incorporated by reference).
Protection of cucumber and watermelon is effective in the glasshouse and in the field (Caruso, F. L., et al., “Field Protection of Cucumber Against Colletotrichum Lagenarium by C. Lagenarium,” Phytopathology 67:1290-2 (1977), which is hereby incorporated by reference). In one trial, the total lesion area of C. lagenarium on protected cucumber was less than 2% of the lesion areas on unprotected control plants. Similarly, only 1 of 66 protected, challenged plants died, whereas 47 of 69 unprotected, challenged watermelons died. In extensive field trials in Kentucky and Puerto Rico, stem injection of tobacco with sporangia of P. tabacina was at least as effective in controlling blue mould as the best fungicide, metalaxyl. Plants were protected, leading to a yield increase of 10-25% in cured tobacco.
Induced resistance against bacteria and viruses appears to be expressed as suppression of disease symptoms or pathogen multiplication or both (Caruso, F. L., et al., “Induced Resistance of Cucumber to Anthracnose and Angular Leaf Spot by Pseudomonas Lachrymans and Colletotrichum Lagenarium,” Physiological Plant Pathology 14:191-201 (1979); Doss, M., et al., “Systemic Acquired Resistance of Cucumber to Pseudomonas Lachrymans as Expressed in Suppression of Symptoms, but not in Multiplication of Bacteria,” Acta Phytopathologia Academiae Scientiarum Hungaricae 16:(3-4), 269-72 (1981); Jenns, A. E., et al., “Non-Specific Resistance to Pathogens Induced Systemically by Local Infection of Cucumber with Tobacco Necrosis Virus, Colletotrichum Lagenarium or Pseudomonas Lachrymans,” Phytopathologia Mediterranea 18:129-34 (1979), which are hereby incorporated by reference).
As described above, research concerning systemic acquired resistance involves infecting plants with infectious pathogens. Although studies in this area are useful in understanding how systemic acquired resistance works, eliciting such resistance with infectious agents is not commercially useful, because such plant-pathogen contact can weaken or kill plants. The present invention is directed to overcoming this deficiency.
The present invention relates to a method of producing plant seeds which impart pathogen resistance to plants grown from the seeds. This method involves applying a hypersensitive response elicitor polypeptide or protein in a non-infectious form to plant seeds under conditions where the polypeptide or protein contacts cells of the plant seeds.
As an alternative to applying a hypersensitive response elicitor polypeptide or protein to plant seeds in order to impart pathogen resistance to plants grown from the seeds, transgenic seeds can be utilized. This involves providing a transgenic plant seed transformed with a DNA molecule encoding a hypersensitive response elicitor polypeptide or protein and planting that seed in soil. A plant is then propagated from the planted seed under conditions effective to impart pathogen resistance to the plant.
Another aspect of the present invention relates to a pathogen-resistance imparting plant seed to which a non-infectious hypersensitive response elicitor polypeptide or protein has been applied.
The present invention has the potential to: treat plant diseases which were previously untreatable; treat diseases systemically that one would not want to treat separately due to cost; and avoid the use of agents that have an unpredictable effect on the environment and even the plants. The present invention can impart resistance without using agents which are harmful to the environment or pathogenic to the plant seeds being treated or to plants situated near the location that treated seeds are planted. Since the present invention involves use of a natural product that is fully and rapidly biodegradable, the environment would not be contaminated.
The present invention relates to a method of producing plant seeds which impart pathogen resistance to plants grown from the seeds. This method involves applying a hypersensitive response elicitor polypeptide or protein in a non-infectious form to a plant seed under conditions effective to impart disease resistance to a plant grown from the seed.
As an alternative to applying a hypersensitive response elicitor polypeptide or protein to plant seeds in order to impart pathogen resistance to plants grown from the seeds, transgenic seeds can be utilized. This involves providing a transgenic plant seed transformed with a DNA molecule encoding a hypersensitive response elicitor polypeptide or protein and planting that seed in soil. A plant is then propagated from the planted seed under conditions effective to impart pathogen resistance to the plant.
Another aspect of the present invention relates to a pathogen-resistance imparting plant seed to which a non-infectious hypersensitive response elicitor polypeptide or protein has been applied.
The hypersensitive response elicitor polypeptide or protein utilized in the present invention can correspond to hypersensitive response elicitor polypeptides or proteins derived from a wide variety of fungal and bacterial pathogens. Such polypeptides or proteins are able to elicit local necrosis in plant tissue contacted by the elicitor.
Examples of suitable bacterial sources of polypeptide or protein elicitors include Erwinia, Pseudomonas, and Xanthamonas species (e.g., the following bacteria: Erwinia amylovora, Erwinia chrysanthemi, Erwinia stewartii, Erwinia carotovora, Pseudomonas syringae, Pseudomonas solancearum, Xanthomonas campestris, or mixtures thereof).
An example of a fungal source of a hypersensitive response elicitor protein or polypeptide is Phytophthora. Suitable species of such fungal pathogens include Phytophthora parasitica, Phytophthora cryptogea, Phytophthora cinnamomi, Phytophthora capsici, Phytophthora megasperma, and Phytophthora citrophthora.
The embodiment of the present invention where the hypersensitive response elicitor polypeptide or protein is applied to the plant seed can be carried out in a number of ways, including: 1) application of an isolated elicitor polypeptide or protein; 2) application of bacteria which do not cause disease and are transformed with genes encoding a hypersensitive response elicitor polypeptide or protein; and 3) application of bacteria which cause disease in some plant species (but not in those to which they are applied) and naturally contain a gene encoding the hypersensitive response elicitor polypeptide or protein. In addition, seeds in accordance with the present invention can be recovered from plants which have been treated with a hypersensitive response elicitor protein or polypeptide in accordance with the present invention.
In one embodiment of the present invention, the hypersensitive response elicitor polypeptides or proteins to be applied can be isolated from their corresponding organisms and applied to plants. Such isolation procedures are well known, as described in Arlat, M., F. Van Gijsegem, J. C. Huet, J. C. Pemollet, and C. A. Boucher, “PopA1, a Protein which Induces a Hypersensitive-like Response in Specific Petunia Genotypes is Secreted via the Hrp Pathway of Pseudomonas solanacearum,” EMBO J. 13:543-553 (1994); He, S. Y., H. C. Huang, and A. Collmer, “Pseudomonas syringae pv. syringae HarpinPss: a Protein that is Secreted via the Hrp Pathway and Elicits the Hypersensitive Response in Plants,” Cell 73:1255-1266 (1993); and Wei, Z.-M., R. J. Laby, C. H. Zumoff, D. W. Bauer, S.-Y. He, A. Collmer, and S. V. Beer, “Harpin Elicitor of the Hypersensitive Response Produced by the Plant Pathogen Erwinia amylovora, Science 257:85-88 (1992), which are hereby incorporated by reference. See also pending U.S. patent application Ser. Nos. 08/200,024 and 08/062,024, which are hereby incorporated by reference. Preferably, however, the isolated hypersensitive response elicitor polypeptides or proteins of the present invention are produced recombinantly and purified as described below.
In other embodiments of the present invention, the hypersensitive response elicitor polypeptide or protein of the present invention can be applied to plant seeds by applying bacteria containing genes encoding the hypersensitive response elicitor polypeptide or protein. Such bacteria must be capable of secreting or exporting the polypeptide or protein so that the elicitor can contact plant seed cells. In these embodiments, the hypersensitive response elicitor polypeptide or protein is produced by the bacteria after application to the seeds or just prior to introduction of the bacteria to the seeds.
In one embodiment of the bacterial application mode of the present invention, the bacteria to be applied do not cause the disease and have been transformed (e.g., recombinantly) with genes encoding a hypersensitive response elicitor polypeptide or protein. For example, E. coli, which do not elicit a hypersensitive response in plants, can be transformed with genes encoding a hypersensitive response elicitor polypeptide and other related proteins required for production and secretion of the elicitor which is then applied to plant seeds. Expression of this polypeptide or protein can then be caused to occur. Bacterial species (other than E. coli) can also be used in this embodiment of the present invention.
In another embodiment of the bacterial application mode of the present invention, the bacteria do cause disease and naturally contain a gene encoding a hypersensitive response elicitor polypeptide or protein. Examples of such bacteria are noted above. However, in this embodiment these bacteria are applied to plant seeds for plants which are not susceptible to the disease carried by the bacteria. For example, Erwinia amylovora causes disease in apple or pear but not in tomato. However, such bacteria will elicit a hypersensitive response in tomato. Accordingly, in accordance with this embodiment of the present invention, Erwinia amylovora can be applied to tomato seeds to impart pathogen resistance without causing disease in plants of that species.
The hypersensitive response elicitor polypeptide or protein from Erwinia chrysanthemi has an amino acid sequence corresponding to SEQ. ID. No. 1 as follows:
This hypersensitive response elicitor polypeptide or protein has a molecular weight of 34 kDa, is heat stable, has a glycine content of greater than 16%, and contains substantially no cysteine. The Erwinia chrysanthemi hypersensitive response elicitor polypeptide or protein is encoded by a DNA molecule having a nucleotide sequence corresponding to SEQ. ID. No. 2 as follows:
The hypersensitive response elicitor polypeptide or protein derived from Erwinia amylovora has an amino acid sequence corresponding to SEQ. ID. No. 3 as follows:
This hypersensitive response elicitor polypeptide or protein has a molecular weight of about 39 kDa, it has a pI of approximately 4.3, and is heat stable at 100° C. for at least 10 minutes. This hypersensitive response elicitor polypeptide or protein has substantially no cysteine. The hypersensitive response elicitor polypeptide or protein derived from Erwinia amylovora is more fully described in Wei, Z.-M., R. J. Laby, C. H. Zumoff, D. W. Bauer, S.-Y. He, A. Collmer, and S. V. Beer, “Harpin, Elicitor of the Hypersensitive Response Produced by the Plant Pathogen Erwinia amylovora,” Science 257:85-88 (1992), which is hereby incorporated by reference. The DNA molecule encoding this polypeptide or protein has a nucleotide sequence corresponding to SEQ. ID. No. 4 as follows:
The hypersensitive response elicitor polypeptide or protein derived from Pseudomonas syringae has an amino acid sequence corresponding to SEQ. ID. No. 5 as follows:
This hypersensitive response elicitor polypeptide or protein has a molecular weight of 34-35 kDa. It is rich in glycine (about 13.5%) and lacks cysteine and tyrosine. Further information about the hypersensitive response elicitor derived from Pseudomonas syringae is found in He, S. Y., H. C. Huang, and A. Collmer, “Pseudomonas syringae pv. syringae HarpinPss: a Protein that is Secreted via the Hrp Pathway and Elicits the Hypersensitive Response in Plants,” Cell 73:1255-1266 (1993), which is hereby incorporated by reference. The DNA molecule encoding the hypersensitive response elicitor from Pseudomonas syringae has a nucleotide sequence corresponding to SEQ. ID. No. 6 as follows:
The hypersensitive response elicitor polypeptide or protein derived from Pseudomonas solanacearum has an amino acid sequence corresponding to SEQ. ID. No. 7 as follows:
It is encoded by a DNA molecule having a nucleotide sequence corresponding SEQ. ID. No. 8 as follows:
Further information regarding the hypersensitive response elicitor polypeptide or protein derived from Pseudomonas solanacearum is set forth in Arlat, M., F. Van Gijsegem, J. C. Huet, J. C. Pemollet, and C. A. Boucher, “PopA1, a Protein which Induces a Hypersensitive-like Response in Specific Petunia Genotypes, is Secreted via the Hrp Pathway of Pseudomonas solanacearum,” EMBO J. 13:543-533 (1994), which is hereby incorporated by reference.
The hypersensitive response elicitor polypeptide or protein from Xanthomonas campestris pv. glycines has an amino acid sequence corresponding to SEQ. ID. No. 9 as follows:
This sequence is an amino terminal sequence having 26 residues only from the hypersensitive response elicitor polypeptide or protein of Xanthomonas campestris pv. glycines. It matches with fimbrial subunit proteins determined in other Xanthomonas campestris pathovars.
The hypersensitive response elicitor polypeptide or protein from Xanthomonas campestris pelargonii is heat stable, protease sensitive, and has a molecular weight of 20 kDa. It includes an amino acid sequence corresponding to SEQ. ID. No. 10 as follows:
Isolation of Erwinia carotovora hypersensitive response elicitor protein or polypeptide is described in Cai, et al., “The RsmA− Mutants of Erwinia carotovora subsp. carotova Strain Ecc71 Overexpress hrpNEcc and Elicit a Hypersensitive Reaction-Like Response in Tobacco Leaves,” MPMI, 9(7):565-73 (1996), which is hereby incorporated by reference. The hypersensitive response elicitor protein or polypeptide for Erwinia stewartii is disclosed in Ahmad, et al., “Harpin is Not Necessary for the Pathogenicity of Erwinia stewartii on Maize,” 8th Int'l. Cong. Molec. Plant-Microbe Interact, Jul. 14-19, 1996 and Ahmad, et al., “Harpin is Not Necessary for the Pathogenicity of Erwinia stewartii on Maize,” Ann. Mtg. Am. Phytopath. Soc., Jul. 27-31, 1996, which are hereby incorporated by reference.
Hypersensitive response elicitor proteins or polypeptides from Phytophora parasitica, Phytophora cryptogea, Phytophora cinnamoni, Phytophora capsici, Phytophora megasperma, and Phytophora citrophthora are described in Kamoun, et al., “Extracellular Protein Elicitors from Phytophora: Host-Specificity and Induction of Resistance to Bacterial and Fungal Phytopathogens,” Molec. Plant-Microbe Interact., 6(1):15-25 (1993), Ricci, et al., “Structure and Activity of Proteins from Pathogenic Fungi Phytophora Eliciting Necrosis and Acquired Resistance in Tobacco,” Eur. J. Biochem., 183:555-63 (1989), Ricci, et al., “Differential Production of Parasiticein, an Elicitor of Necrosis and Resistance in Tobacco by Isolates of Phytophora paraticica,” Plant Path., 41:298-307 (1992), Baillieul, et al., “A New Elicitor of the Hypersensitive Response in Tobacco: A Fungal Glycoprotein Elicits Cell Death, Expression of Defense Genes, Production of Salicylic Acid, and Induction of Systemic Acquired Resistance,” Plant J., 8(4):551-60 (1995), and Bonnet, et al., “Acquired Resistance Triggered by Elicitins in Tobacco and Other Plants,” Eur. J. Plant Path., 102:181-92 (1996), which are hereby incorporated by reference.
The above elicitors are exemplary. Other elicitors can be identified by growing fungi or bacteria that elicit a hypersensitive response under which genes encoding an elicitor are expressed. Cell-free preparations from culture supernatants can be tested for elicitor activity (i.e. local necrosis) by using them to infiltrate appropriate plant tissues.
It is also possible to use fragments of the above hypersensitive response elicitor polypeptides or proteins as well as fragments of full length elicitors from other pathogens, in the method of the present invention.
Suitable fragments can be produced by several means. In the first, subclones of the gene encoding a known elicitor protein are produced by conventional molecular genetic manipulation by subcloning gene fragments. The subclones then are expressed in vitro or in vivo in bacterial cells to yield a smaller protein or a peptide that can be tested for elicitor activity according to the procedure described below.
As an alternative, fragments of an elicitor protein can be produced by digestion of a full-length elicitor protein with proteolytic enzymes like chymotrypsin or Staphylococcus proteinase A, or trypsin. Different proteolytic enzymes are likely to cleave elicitor proteins at different sites based on the amino acid sequence of the elicitor protein. Some of the fragments that result from proteolysis may be active elicitors of resistance.
In another approach, based on knowledge of the primary structure of the protein, fragments of the elicitor protein gene may be synthesized by using the PCR technique together with specific sets of primers chosen to represent particular portions of the protein. These then would be cloned into an appropriate vector for increased expression of a truncated peptide or protein.
An example of a suitable fragment is the popA1 fragment of the hypersensitive response elicitor polypeptide or protein from Pseudomonas solanacearum. See Arlat, M., F. Van Gijsegem, J. C. Huet, J. C. Pemollet, and C. A. Boucher, “PopA1, a Protein Which Induces a Hypersensitive-like Response in Specific Petunia Genotypes is Secreted via the Hrp Pathway of Pseudomonas solanacearum,” EMBO J. 13:543-53 (1994), which is hereby incorporated by reference. As to Erwinia amylovora, a suitable fragment can be, for example, either or both the polypeptide extending between and including amino acids 1 and 98 of SEQ. ID. NO. 3 and the polypeptide extending between and including amino acids 137 and 204 of SEQ. ID. No. 3.
Variants may be made by, for example, the deletion or addition of amino acids that have minimal influence on the properties, secondary structure and hydropathic nature of the polypeptide. For example, a polypeptide may be conjugated to a signal (or leader) sequence at the N-terminal end of the protein which co-translationally or post-translationally directs transfer of the protein. The polypeptide may also be conjugated to a linker or other sequence for ease of synthesis, purification or identification of the polypeptide.
The protein or polypeptide of the present invention is preferably produced in purified form (preferably at least about 60%, more preferably 80%, pure) by conventional techniques. Typically, the protein or polypeptide of the present invention is produced but not secreted into the growth medium of recombinant E. coli. Alternatively, the protein or polypeptide of the present invention is secreted into the growth medium. In the case of unsecreted protein, to isolate the protein, the E. coli host cell carrying a recombinant plasmid is propagated, homogenized, and the homogenate is centrifuged to remove bacterial debris. The supernatant is then subjected to heat treatment and the hypersensitive response elicitor protein is separated by centrifugation. The supernatant fraction containing the polypeptide or protein of the present invention is subjected to gel filtration in an appropriately sized dextran or polyacrylamide column to separate the proteins. If necessary, the protein fraction may be further purified by ion exchange or HPLC.
Alternatively, the hypersensitive response elicitor protein can be prepared by chemical synthesis using conventional techniques.
The DNA molecule encoding the hypersensitive response elicitor polypeptide or protein can be incorporated in cells using conventional recombinant DNA technology. Generally, this involves inserting the DNA molecule into an expression system to which the DNA molecule is heterologous (i.e. not normally present). The heterologous DNA molecule is inserted into the expression system or vector in proper sense orientation and correct reading frame. The vector contains the necessary elements for the transcription and translation of the inserted protein-coding sequences.
U.S. Pat. No. 4,237,224 to Cohen and Boyer, which is hereby incorporated by reference, describes the production of expression systems in the form of recombinant plasmids using restriction enzyme cleavage and ligation with DNA ligase. These recombinant plasmids are then introduced by means of transformation and replicated in unicellular cultures including procaryotic organisms and eucaryotic cells grown in tissue culture.
Recombinant genes may also be introduced into viruses, such as vaccina virus. Recombinant viruses can be generated by transection of plasmids into cells infected with virus.
Suitable vectors include, but are not limited to, the following viral vectors such as lambda vector system gt11, gt WES.tB, Charon 4, and plasmid vectors such as pBR322, pBR325, pACYC177, pACYC1084, pUC8, pUC9, pUC18, pUC19, pLG339, pR290, pKC37, pKC101, SV 40, pBluescript II SK +/− or KS +/− (see “Stratagene Cloning Systems” Catalog (1993) from Stratagene, La Jolla, Calif., which is hereby incorporated by reference), pQE, pIH821, pGEX, pET series (see F. W. Studier et. al., “Use of T7 RNA Polymerase to Direct Expression of Cloned Genes,” Gene Expression Technology vol. 185 (1990), which is hereby incorporated by reference), and any derivatives thereof. Recombinant molecules can be introduced into cells via transformation, particularly transduction, conjugation, mobilization, or electroporation. The DNA sequences are cloned into the vector using standard cloning procedures in the art, as described by Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Springs Laboratory, Cold Springs Harbor, N.Y. (1989), which is hereby incorporated by reference.
A variety of host-vector systems may be utilized to express the protein-encoding sequence(s). Primarily, the vector system must be compatible with the host cell used. Host-vector systems include but are not limited to the following: bacteria transformed with bacteriophage DNA, plasmid DNA, or cosmid DNA; microorganisms such as yeast containing yeast vectors; mammalian cell systems infected with virus (e.g., vaccinia virus, adenovirus, etc.); insect cell systems infected with virus (e.g., baculovirus); and plant cells infected by bacteria. The expression elements of these vectors vary in their strength and specificities. Depending upon the host-vector system utilized, any one of a number of suitable transcription and translation elements can be used.
Different genetic signals and processing events control many levels of gene expression (e.g., DNA transcription and messenger RNA (mRNA) translation).
Transcription of DNA is dependent upon the presence of a promotor which is a DNA sequence that directs the binding of RNA polymerase and thereby promotes mRNA synthesis. The DNA sequences of eucaryotic promotors differ from those of procaryotic promotors. Furthermore, eucaryotic promotors and accompanying genetic signals may not be recognized in or may not function in a procaryotic system, and, further, procaryotic promotors are not recognized and do not function in eucaryotic cells.
Similarly, translation of mRNA in procaryotes depends upon the presence of the proper procaryotic signals which differ from those of eucaryotes. Efficient translation of mRNA in procaryotes requires a ribosome binding site called the Shine-Dalgarno (“SD”) sequence on the mRNA. This sequence is a short nucleotide sequence of mRNA that is located before the start codon, usually AUG, which encodes the amino-terminal methionine of the protein. The SD sequences are complementary to the 3′-end of the 16S rRNA (ribosomal RNA) and probably promote binding of mRNA to ribosomes by duplexing with the rRNA to allow correct positioning of the ribosome. For a review on maximizing gene expression, see Roberts and Lauer, Methods in Enzymology, 68:473 (1979), which is hereby incorporated by reference.
Promotors vary in their “strength” (i.e. their ability to promote transcription). For the purposes of expressing a cloned gene, it is desirable to use strong promotors in order to obtain a high level of transcription and, hence, expression of the gene. Depending upon the host cell system utilized, any one of a number of suitable promotors may be used. For instance, when cloning in E. coli, its bacteriophages, or plasmids, promotors such as the T7 phage promoter, lac promotor, trp promotor, recA promotor, ribosomal RNA promotor, the PR and PL promotors of coliphage lambda and others, including but not limited, to lacUV 5, ompF, bla, 1 pp, and the like, may be used to direct high levels of transcription of adjacent DNA segments. Additionally, a hybrid trp-lacUV 5 (tac) promotor or other E. coli promotors produced by recombinant DNA or other synthetic DNA techniques may be used to provide for transcription of the inserted gene.
Bacterial host cell strains and expression vectors may be chosen which inhibit the action of the promotor unless specifically induced. In certain operations, the addition of specific inducers is necessary for efficient transcription of the inserted DNA. For example, the lac operon is induced by the addition of lactose or IPTG (isopropylthio-beta-D-galactoside). A variety of other operons, such as trp, pro, etc., are under different controls.
Specific initiation signals are also required for efficient gene transcription and translation in procaryotic cells. These transcription and translation initiation signals may vary in “strength” as measured by the quantity of gene specific messenger RNA and protein synthesized, respectively. The DNA expression vector, which contains a promotor, may also contain any combination of various “strong” transcription and/or translation initiation signals. For instance, efficient translation in E. coli requires a Shine-Dalgarno (SD) sequence about 7-9 bases 5′ to the initiation codon (ATG) to provide a ribosome binding site. Thus, any SD-ATG combination that can be utilized by host cell ribosomes may be employed. Such combinations include but are not limited to the SD-ATG combination from the cro gene or the N gene of coliphage lambda, or from the E. coli tryptophan E, D, C, B or A genes. Additionally, any SD-ATG combination produced by recombinant DNA or other techniques involving incorporation of synthetic nucleotides may be used.
Once the isolated DNA molecule encoding the hypersensitive response elicitor polypeptide or protein has been cloned into an expression system, it is ready to be incorporated into a host cell. Such incorporation can be carried out by the various forms of transformation noted above, depending upon the vector/host cell system. Suitable host cells include, but are not limited to, bacteria, virus, yeast, mammalian cells, insect, plant, and the like.
The method of the present invention can be utilized to treat seeds for a wide variety of plants to impart pathogen resistance to the plants. Suitable seeds are for plants which are dicots and monocots. More particularly, useful crop plants can include: rice, wheat, barley, rye, oats, cotton, sunflower, canola, peanut, corn, potato, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, cauliflower, broccoli, turnip, radish, spinach, onion, garlic, eggplant, pepper, celery, carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, strawberry, grape, raspberry, pineapple, soybean, tobacco, tomato, sorghum, and sugarcane. Examples of suitable ornamental plants are: rose, Saintpaulia, petunia, Pelargonium, poinsettia, chrysanthemum, carnation, and zinnia.
The method of imparting pathogen resistance to plants in accordance with the present invention is useful in imparting resistance to a wide variety of pathogens including viruses, bacteria, and fungi.
Resistance, inter alia, to the following viruses can be achieved by the method of the present invention: Tobacco mosaic virus, cucumber mosaic virus, potato x virus, potato y virus, and tomato mosaic virus.
Resistance, inter alia, to the following bacteria can also be imparted to plants in accordance with the present invention: Pseudomonas solancearum, Pseudomonas syringae pv. tabaci, and Xanthamonas campestris pv. pelargonii.
Plants can be made resistant, inter alia, to the following fungi by use of the method of the present invention: Fusarium oxysporum and Phytophthora infestans.
The embodiment of the present invention involving applying the hypersensitive response elicitor polypeptide or protein to all or part of the plant seeds being treated can be carried out through a variety of procedures. Suitable application methods include high or low pressure spraying, injection, coating, dusting, and immersion. Other suitable application procedures can be envisioned by those skilled in the art. Once treated with the hypersensitive response elicitor of the present invention, the seeds can be planted and cultivated using conventional procedures to produce plants. After plants have been propagated from seeds treated in accordance with the present invention, the plants may be treated with one or more applications of the hypersensitive response elicitor protein or polypeptide to enhance hypersensitive response induced resistance in the plants. See U.S. patent application Ser. No. 08/475,775, which is hereby incorporated by reference. Such propagated plants, which are resistant to disease, may, in turn, be useful in producing seeds or propagules (e.g. cuttings) that produce resistant plants.
The hypersensitive response elicitor polypeptide or protein can be applied to plant seeds in accordance with the present invention alone or in a mixture with other materials.
A composition suitable for treating plant seeds in accordance with the present invention contains a hypersensitive response elicitor polypeptide or protein in a carrier. Suitable carriers include water, aqueous solutions, slurries, or dry powders. In this embodiment, the composition contains greater than 0.5 nM hypersensitive response elicitor polypeptide or protein.
Although not required, this composition may contain additional additives including fertilizer, insecticide, fungicide, nematicide, herbicide, and mixtures thereof. Suitable fertilizers include (NH4)2NO3. An example of a suitable insecticide is Malathion. Useful fungicides include Captan.
Other suitable additives include buffering agents, wetting agents, coating agents, and abrading agents. These materials can be used to facilitate the process of the present invention. In addition, the hypersensitive response elicitor polypeptide or protein can be applied to plant seeds with other conventional seed formulation and treatment materials, including clays and polysaccharides.
In the alternative embodiment of the present invention involving the use of transgenic seeds, a hypersensitive response elicitor polypeptide or protein need not be applied topically to the seeds. Instead, transgenic plants transformed with a DNA molecule encoding a hypersensitive response elicitor polypeptide or protein are produced according to procedures well known in the art, such as biolistics or Agrobacterium mediated transformation. Examples of suitable hypersensitive response elicitor polypeptides or proteins and the nucleic acid sequences for their encoding DNA are disclosed supra. As is conventional in the art, such transgenic plants would contain suitable vectors with various promoters including pathogen-induced promoters, and other components needed for transformation, transcription, and, possibly, translation. Such transgenic plants themselves could be grown under conditions effective to be imparted with pathogen resistance. In any event, once transgenic plants of this type are produced, transgenic seeds are recovered. These seeds can then be planted in the soil and cultivated using conventional procedures to produce plants. The plants are propagated from the planted transgenic seeds under conditions effective to impart pathogen resistance to the plants.
When transgenic plant seeds are used in accordance with the present invention, they additionally can be treated with the same materials (noted above) as are used to treat the seeds to which a hypersensitive response elicitor polypeptide or protein is applied. These other materials, including hypersensitive response elicitors, can be applied to the transgenic plant seeds by high or low pressure spraying, injection, coating, dusting, and immersion. Similarly, transgenic plants additionally may be treated with one or more applications of the hypersensitive response elicitor to enhance hypersensitive response induced resistance in the plants. Such plants may also be treated with conventional plant treatment agents (e.g., insecticides, fertilizers, etc.). The transgenic plants of the present invention are useful in producing seeds or propagules (e.g. cuttings) from which disease resistant plants grow.
Marglobe tomato seeds were submerged in hypersensitive response elicitor protein (ca. 26 μm/ml) from Erwinia amylovora solution or buffer in beakers on day 0 for 24 hours at 28° C. in a growth chamber. After soaking seeds in hypersensitive response elicitor protein from Erwinia amylovora or buffer, they were sown in germination pots with artificial soil on day 1. Seedlings were transplanted to individual pots at the two-true-leaf stage on day 12. After transplanting, some plants that arose from treated seed also were sprayed with hypersensitive response elicitor protein (ca. 13 μm/ml) from Erwinia amylovora (Treatments 3 and 4).
Tomato treated as noted in the preceding paragraph were inoculated with Burkholderia (Pseudomonas) solanacearum K60 strain (See Kelman, “The Relationship of Pathogenicity in Pseudomonas solanacearum to Colony Appearance on a Tetrazolium Medium,” Phytopathology 44:693-95 (1954)) on day 23 by making vertical cuts through the roots and potting medium of tomato plants (on a tangent 2 cm from the stem and 2 times/pot) and putting 10 ml (5×108 cfu/ml) suspension into the soil.
The above procedure involved use of 10 seeds treated with hypersensitive response elicitor protein from Erwinia amylovora per treatment.
Treatments:
The results of these treatments are set forth in Tables 1-4.
The above data shows that the hypersensitive response elicitor protein was more effective than buffer as a seed treatment in reducing disease index and was as effective as spraying leaves of young plants with hypersensitive response elicitor protein.
Marglobe tomato seeds were submerged in hypersensitive response elicitor protein from pCPP2139 or in pCPP50 vector solution (1:50, 1:100 and 1:200) in beakers on day 0 for 24 hours at 28° C. in a growth chamber. After soaking seeds in hypersensitive response elicitor protein or vector, they were sown in germination pots with artificial soil on day 0. Ten uniform appearing plants were chosen randomly from each of the following treatments:
The resulting seedlings were inoculated with Pseudomonas solanacearum K60 by dipping the roots of tomato seedling plants for about 30 seconds in a 40 ml (1×108 cfu/ml) suspension. The seedlings were then transplanted into the pots with artificial soil on day 12.
The results of these treatments are set forth in Tables 5-8.
The above data shows that the hypersensitive response elicitor protein is much more effective than the vector solution in preventing Tomato Southern Bacteria Wilt.
Marglobe tomato seeds were submerged in hypersensitive response elicitor protein from pCPP2139 or in pCPP50 vector solution (1:50, 1:100 and 1:200) in beakers on day 0 for 24 hours at 28° C. in a growth chamber. After soaking seeds in the hypersensitive response elicitor protein or vector, the seeds were sown in germination pots with artificial soil on day 1. Ten uniform appearing plants were chosen randomly from each of the following treatments:
The resulting seedlings were inoculated with Pseudomonas solanacearum K60 by dipping the roots of tomato seedling plants for about 30 seconds in a 40 ml (1×106 cfu/ml) suspension. The seedlings were then transplanted into the pots with artificial soil on day 12.
The results of these treatments are set forth in Tables 9-12.
The above data shows that the hypersensitive response elicitor protein is much more effective in preventing Tomato Southern Bacteria Wilt.
Marglobe tomato seeds were submerged in hypersensitive response elicitor protein from pCPP2139 or in pCPP50 vector solution (1:25, 1:50 and 1:100) in beakers on day 0 for 24 hours at 28° C. in a growth chamber. After soaking seeds in hypersensitive response elicitor protein or vector, they were sown in germination pots with artificial soil on day 1. Ten uniform appearing plants were chosen randomly from each of the following treatments:
The resulting seedlings were inoculated with Pseudomonas solanacearum K60 by dipping the roots of tomato seedling plants for about 30 seconds in a 40 ml (1×108 cfu/ml) suspension. The seedlings were then transplanted into the pots with artificial soil on day 14.
The results of these treatments are set forth in Tables 13-16.
The above data shows that the hypersensitive response elicitor protein is much more effective than the vector solution in preventing Tomato Southern Bacteria Wilt. A hypersensitive response protein concentration of 1:50 is particularly effective in disease control.
Marglobe tomato seeds were submerged in hypersensitive response elicitor protein from pCPP2139 or pCPP50 vector solution (1:25, 1:50 and 1:100) in beakers on day 0 for 24 hours at 28° C. in a growth chamber. After soaking seeds in hypersensitive response elicitor protein or vector, they were sown in germination pots with artificial soil on day 1. Ten uniform appearing plants were chosen randomly from each of the following treatments:
The resulting seedlings were inoculated with Pseudomonas solanacearum K60 by dipping the roots of tomato seedling plants for about 30 seconds in a 40 ml (1×106 cfu/ml) suspension. The seedlings were then transplanted into the pots with artificial soil on day 14.
The results of these treatments are set forth in Tables 17-20.
The above data shows that the hypersensitive response elicitor protein is much more effective than the vector solution in preventing Tomato Southern Bacteria Wilt. A hypersensitive response elicitor protein concentration of 1:50 is more effective in disease control.
Rice seeds (variety, M-202) were submerged in two gallons of hypersensitive response elicitor protein solution at a concentration of 20 μg for 24 hours at room temperature. Rice seeds submerged in the same solution without hypersensitive response elicitor protein were used as a control. After soaking, the seeds were sown in a rice field by air plane spray. There were four replicates for both hypersensitive response elicitor protein and control treatment. The lot size of each replicate is 150 Ft2. The design of each plot was completely randomized, and each plot had substantial level contamination of Sclerotium oryzae. Three months after sowing, stem rot was evaluated according to the following rating scale: Scale 1=no disease, 2=disease present on the exterior of the leaf sheath, 3=disease penetrates leaf sheath completely but is not present on culm, 4=disease is present on culm exterior but does not penetrate to interior of culm, and 5=disease penetrates to interior of culm. 40 plants from each replicate were sampled and assessed for the disease incidence and severity. From Table 21, it is apparent that treating seeds with hypersensitive response elicitor reduced both disease incidence and severity. More particularly, regarding incidence, 67% of the plants were infected by stem rot for the control treatment, however, only 40% plants were infected for the hypersensitive response elicitor protein treatment. As to severity, the disease index* for the hypersensitive response elicitor protein treatment was 34% and 60% for the control. Accordingly, treating rice seed with hypersensitive response elicitor protein resulted in a significant reduction of stem rot disease. The hypersensitive response elicitor protein-induced resistance in rice can last a season long. In addition to disease resistance, it was also observed that hypersensitive response elicitor protein-treated rice had little or no damage by army worm (Spodoptera praefica). In addition, the treated plants were larger and had deeper green color than the control plants.
Onion seed, variety Pennant, (Seed Lot #64387), obtained from the Crookham Co., Caldwell, Id. 83606, treated with hypersensitive response elicitor protein or a control was planted in a natural organic or “muck” soil. Some of the seedlings that grew from the sown seed were healthy, some had lesions characteristic of the Onion Smut disease, and some of the sown seed did not produce seedlings that emerged from the soil. Thus, the effect of treating onion seed with various concentrations of hypersensitive response elicitor protein was determined.
Naturally infested muck soil was obtained from a field in Oswego County, N.Y., where onions had been grown for several years and where the Onion Smut disease commonly had been problematic. Buckets of muck (5-gallon plastic) were stored at 4° C. until used. The soil was mixed, sieved, and put in plastic flats 10 inches wide, 20 inches long, and 2 inches deep for use in the tests described. Based on preliminary experiments, the soil contained many propagules of the Onion Smut fungus, Urocystis cepulae, such that when onion seed was sown in the soil, smut lesions developed on many of the seedlings that emerged from the soil. In addition, the soil harbored other microorganisms, including those that cause the “damping-off” disease. Among the several fungi that cause damping off are Pythium, Fusarium, and Rhizoctonia species.
The hypersensitive response elicitor protein encoded by the hrpN gene of Erwinia amylovora was used to treat seeds. It was produced by fermentation of the cloned gene in a high-expression vector in E. coli. Analysis of the cell-free elicitor preparation by high-pressure liquid chromatography indicated its hypersensitive response elicitor protein content and on that basis appropriate dilutions were prepared in water. Seeds were soaked in a beaker containing hypersensitive response elicitor protein concentrations of 0, 5, 25, and 50 μgm/ml of hypersensitive response elicitor protein for 24 hours. They were removed, dried briefly on paper towels, and sown in the muck soil. Treated seed was arranged by row, 15 seeds in each row for each treatment; each flat contained two replicates, and there were six replicates. Thus, a total of 90 seeds were treated with each concentration of hypersensitive response elicitor protein. The flats containing the seeds were held in a controlled environment chamber operating at 60° F. (15.6° C.), with a 14-hour day/10-hour night. Observations were made on seedling emergence symptoms (smut lesions). The data were recorded 23 days after sowing.
The effect of soaking onion seed in different concentrations of hypersensitive response elicitor protein on emergence of onion seedlings and on the incidence of onion smut is shown in Table 22. Only slight differences in emergence were noted, suggesting that there is no significant effect of treating with hypersensitive response elicitor protein at the concentrations used. Among the seedlings that emerged, substantially more of the seeds that received no hypersensitive response elicitor protein exhibited symptoms of Onion Smut than seedlings that grew from seed that had been treated with hypersensitive response elicitor protein. Treating seed with 25 μgm/ml of hypersensitive response elicitor protein was the most effective concentration tested in reducing Onion Smut. Thus, this example demonstrates that treating onion seed with hypersensitive response elicitor protein reduces the Onion Smut disease.
4.331
1One seedling emerged then died.
Tomato seed, variety New Yorker (Seed lot #2273-2B), obtained from Harris Seeds, Rochester, N.Y., were treated with four concentrations of hypersensitive response elicitor protein (including a no-elicitor protein, water-treated control) and planted in peatlite soil mix. After 12 days and when the seedlings were in the second true-leaf stage, they were inoculated with the Bacterial Speck pathogen. Ten days later, the treated and inoculated plants were evaluated for extent of infection. Thus, the effect of treating tomato seed with various concentrations of hypersensitive response elicitor protein on resistance to Pseudomonas syringae pv. tomato was determined.
The hypersensitive response elicitor protein encoded by the hrpN gene of Erwinia amylovora was used to treat seeds. It was produced by fermentation of the cloned gene in a high-expression vector in E. coli. Analysis of the cell-free elicitor preparation by high-pressure liquid chromatography indicated its hypersensitive response elicitor protein content and, on that basis, appropriate dilutions were prepared in water. Seeds were soaked in a beaker containing hypersensitive response elicitor protein concentrations of 0, 5, 10, and 20 nm/ml of hypersensitive response elicitor protein for 24 hours. They were removed, dried briefly on paper towels, and sown. The soil was a mixture of peat and Pearlite™ in plastic flats 10 inches wide, 20 inches long, and 2 inches deep. Treated seed was arranged by row, 6 seeds in each row for each treatment; each flat contained two replicates, and there were four replicates and thus a total of 24 seeds that were treated with each concentration of hypersensitive response elicitor protein. The flats containing the seeds were held in a controlled environment chamber operating at 75° F. (25° C.), with a 14-hour day/10-hour night.
When twelve-days old, the tomato seedlings were inoculated with 108 colony forming units/ml of the pathogen, applied as a foliar spray. The flats containing the seedlings were covered with a plastic dome for 48 hours after inoculation to maintain high humidity. Observations were made on symptom severity using a rating scale of 0-5. The rating was based on the number of lesions that developed on the leaflets and the cotyledons and on the relative damage caused to the plant parts by necrosis that accompanied the lesions. The cotyledons and (true) leaflets were separately rated for disease severity 11 days after inoculation
The effect of soaking tomato seed in different concentrations of hypersensitive response elicitor protein (i.e. harpin) on the development of Bacterial Speck on leaflets and cotyledons of tomato is shown in Table 23. The seedlings that grew from seed treated with the highest amount of hypersensitive response elicitor protein tested (20 μgm/ml) had fewer diseased leaflets and cotyledons than the treatments. The water-treated control seedlings did not differ substantially from the plants treated with the two lower concentrations of hypersensitive response elicitor protein. Considering the disease ratings, the results were similar. Only plants treated with the highest concentration of hypersensitive response elicitor protein had disease ratings that were less than those of the other treatments. This example demonstrates that treatment of tomato seed with hypersensitive response elicitor protein reduces the incidence and severity of Bacterial Speck of tomato.
Although the invention has been described in detail for the purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention which is defined by the following claims.
This is a continuation of U.S. patent application Ser. No. 09/766,348 filed Jan. 19, 2001, which is a division of U.S. patent application Ser. No. 08/984,207 filed Dec. 3, 1997, now U.S. Pat. No. 6,235,974, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/033,230 filed Dec. 5, 1996.
This invention was made with support from the U.S. Government under USDA NRI Competitive Research Grant No. 91-37303-6430.
| Number | Date | Country | |
|---|---|---|---|
| 60033230 | Dec 1996 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 08984207 | Dec 1997 | US |
| Child | 09766348 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09766348 | Jan 2001 | US |
| Child | 12573869 | US |
