Patent Application
20090104165
The present invention relates to a transgenic Trichoderma spp. having a recombinant nucleic acid molecule encoding a bioactive molecule and methods of using such transgenic Trichoderma spp. for controlling plant disease and delivering bioactive molecules to plants and plant seeds.
Fungi in the genus Trichoderma are being used in increasingly large amounts for control of plant diseases. These fungi recently have been shown to be avirulent plant symbionts. Trichoderma spp. are highly interactive in root, soil, and foliar environments. The most useful of these strains colonize the outer surface of plant roots and produce various signaling molecules. This ability to colonize plant roots and to deliver bioactive plant molecules in vivo makes these fungi highly effective systems for the delivery of bioactive molecules. It has been known for many years that Trichoderma produce a wide range of antibiotic substances (Sivasithamparam et al., “Secondary Metabolism in Trichoderma and Gliocladium,” in Kubicek et al., Trichoderma and Gliocladium, Vol 1, London: Taylor and Francis, pp. 139-191 (1998)) and that they are parasitic on other fungi. They also compete with other microorganisms, for example, for key exudates from seeds that stimulate germination of propagules of plant pathogenic fungi in soil (Howell, C. R., “Cotton Seedling Preemergence Damping-Off Incited by Rhizopus oryzae and Pythium spp. and its Biological Control with Trichoderma spp.,” Phytopathology 92:177-180 (2002)). More generally, they compete with soil microorganisms for nutrients or space (Elad, Y., “Mechanisms Involved in the Biological Control of Botrytis Cinerea Incited Diseases,” Eur J Plant Pathol 102:719-732 (1996)). In addition, they inhibit or degrade pectinases and other enzymes that are essential for plant pathogenic fungi such as Botrytis cinerea to penetrate leaf surfaces (Zimand et al., “Effect of Trichoderma harzianum on Botrytis cinerea Pathogenicity,” Phytopathology 86:1255-1260 (1996)). These direct effects upon other fungi are complex and remarkable and, until very recently, were considered to be the bases for how Trichoderma spp. exert beneficial effects on plant growth and development. The research on these topics has generated a large body of knowledge including isolation and cloning of a range of genes that encode for proteins and metabolites, some of which have antimicrobial activity. There are several recent reviews on these compounds and mechanisms of action (Benitez et al., “Glucanolytic and Other Enzymes and Their Control. In Trichoderma and Gliocladium, in Harman et al., eds., Vol 2, London: Taylor and Francis, pp. 101-127 (1998); Chet et al., “Mycoparasitism and Lytic Enzymes,” in Harman et al., Trichoderma and Gliocladium, Vol 2, London: Taylor and Francis, pp. 153-172 (1998); Howell, C. R., “Mechanisms Employed by Trichoderma Species in the Biological Control of Plant Diseases: The History and Evolution of Current Concepts,” Plant Dis 87:4-10 (2003); Lorito, M., “Chitinolytic Enzymes and Their Genes. In Trichoderma and Gliocladium, Vol 2, pp. 73-99. Edited by G. E. Harnan & C. P. Kubicek. London: Taylor and Francis. (1998)). This research has produced several useful findings including the use of genes encoding fungitoxic cell wall degrading enzymes to produce transgenic plants resistant to diseases (Bolar et al., “Synergistic Activity of Endochitinase and Exochitinase from Trichoderma atroviride (T. harzianum) Against the Pathogenic Fungus (Venturia inaequalis) in Transgenic Apple Plants,” Trans Res 10:533-543 (2001); Lorito et al., “Microbial Genes Expressed in Transgenic Plants to Improve Disease Resistance,” Journal of plant Pathology 81:73-88 (1999)) and the discovery of enzymes useful in bioprocessing of chitin (Donzelli et al., “Enhanced Enzymatic Hydrolysis of Langostino Shell Chitin With Mixtures of Enzymes from Bacterial and Fungal Sources,” Carboh Res 338:1823-1833 (2003)). However, it is becoming increasingly clear that the understanding of the mechanisms of biocontrol has been incomplete. In addition to the ability of Trichoderma spp. to directly attack or inhibit growth of plant pathogens, recent discoveries indicate that they can also induce systemic and localized resistance to a variety of plant pathogens. These new findings are dramatically changing knowledge of the mechanisms of action and uses of these fungi.
Moreover, certain strains of Trichoderma have substantial influence upon plant growth and development. Enhancement of plant growth has been known for many years and can occur in either axenic systems (Lindsey et al., “Effect of Certain Fungi on Dwarf Tomatoes Grown Under Gnotobiotic Conditions,” Phytopathology 57:1262-1263 (1967); Yedidia et al., “Effect of Trichoderma harzianum on Microelement Concentrations and Increased Growth of Cucumber Plants,” Plant Soil 235:235-242 (2001)) or in natural field soils (Chang et al., “Increased Growth of Plants in the Presence of the Biological Control Agent Trichoderma harzianum,” Plant Dis 70:145-148 (1986); Harman, G. E., “Myths and Dogmas of Biocontrol. Changes in Perceptions Derived from Research on Trichoderma harzianum T-22,” Plant Dis 84:377-393 (2000)). The direct effects of these fungi on plant growth and development are critically important for agricultural uses and also for understanding the roles of Trichoderma in natural and managed ecosystems.
Localized and systemic induced resistance occurs in all or most plants in response to attack by pathogenic microbes, physical damage by insects or other factors, treatment with various chemical inducers or the presence of nonpathogenic rhizobacteria (Kuc, J., “Concepts and Direction of Induced Systemic Resistance in Plants and its Application,” Eur J Plant Pathol 107:7-12 (2001); Oostendorp et al., “Induced Resistance in Plants by Chemicals,” Eur J Plant Pathol 107:19-28 (2001)). Much progress has been made in elucidating the pathways of this resistance. In many cases, salicylic acid or jasmonic acid, together with ethylene or nitrous oxide, induce a cascade of events leading to the production of a variety of metabolites and proteins with diverse functions (Hammerschmidt et al., “Inducing Resistance: A Summary of Papers Presented at the First International Symposium on Induced Resistance to Plant Diseases,” Corfu, May 2000, Eur J Plant Pathol 107:1-6 (2001); van Loon et al., “Systemic Resistance Induced by Rhizosphere Bacteria,” Annu Rev Phytopathol 36:453-483 (1998)). Different pathways are induced by different challenges, even though there seems to be cross-talk or competition between the pathways (Bostock et al., “Signal Interactions in Induced Resistance to Pathogens and insect Herbivores,” Eur J Plant Pathol 107:103-111 (2001)).
In recent years, substantial advances have been made in identifying the induced systemic resistance pathway activated by rhizobacteria, which is the closest analog of induced resistance by Trichoderma. The rhizobacteria-induced systemic resistance (RISR) pathway phenotypically resembles systemic acquired resistance (SAR) systems in plants. However, RISR differs in the fact that root colonization by rhizobacteria does not result in the detectable expression of pathogenesis-related proteins, and root colonization by at least some bacterial strains does not induce accumulation of salicylic acid in the plant (Bakker et al., “Understanding the Involvement of Rhizobacteria-Mediated Induction of Systemic Resistance in Involvement of Rhizobacteria-Mediated Induction of Systemic Biocontrol of Plant Diseases,” Can J Plant Pathol 25:5-9 (2003)). Instead, plants are potentiated to react rapidly to pathogen attack. In Arabidopsis, RISR requires functional plant responses to jasmonic acid and ethylene, and may increase sensitivity to them, and is, like SAR, dependent upon the transcription factor NPR1 (Pieterse et al., “Rhizobacteria-Mediated Induced Systemic Resistance: Triggering, Signalling and Expression,” Eur J Plant Pathol 107:51-61 (2001)). The abilities of rhizobacteria to induce systemic resistance have long been known (Kloepper et al., “Plant Growth Promoting Rhizobacteria as Inducers of Systemic Acquired Resistance,” in Lumsden et al., eds., Pest Management: Biologically Based Technologies, Washington, D.C., pp. 10-20 (1993); Pieterse et al., “Rhizobacteria-Mediated Induced Systemic Resistance: Triggering, Signalling and Expression,” Eur J Plant Pathol 107:51-61 (2001)).
Talaromyces flavus has been suggested as a biocontrol agent against the plant pathogens Verticillium dahliae (Marois et al., “Biological Control of Verticillium Wilt of Eggplant in the Field,” In Plant Disease, pp. 1166-1168 (1982)), Sclerotinia sclerotiorum (McLaren et al., “Hyperparasitism of Sclerotinia sclerotiorum by Talaromyces flavus,” J Plant Pathol 8:43-48 (1986)) and Rhizoctonia solani (Boosalis, M. G., “Effect of Soil Temperature and Green-Manure Amendment of Unsterilized Soil on Parasitism of Rhizoctonia solani by Penicillum vermiculatum and Trichoderma sp.,” Phytopathology 46:473-478 (1956)). In vitro experiments performed with culture filtrates of T. flavus grown on glucose suggest that glucose oxidase is responsible for most of the growth inhibition of V. dahliae microsclerotia and hyphae (Murray et al., “Isolation of the Glucose Oxidase Gene from Talaromyces flavus and Characterization of its Role in the Biocontrol of Verticillium dahliae,” Curr Genet. 32:367-375 (1997); Stosz et al., “In vitro Analysis of the Role of Glucose Oxidase from Talaromyces flavus in Biocontrol of the Plant Pathogen Verticillium dahliae,” Appl Environ Microbiol 62:3183-3186 (1996)). A glucose oxidase deficient strain of T. flavus also failed to antagonize Verticillium wilt of eggplant in greenhouse experiments (Brunner et al., “The Nagl N-acetylglucosaminidase of Trichoderma atroviride is Essential for Chitinase Induction by Chitin and of Major Relevance to Biocontrol,” Curr Genet. 43:289-295 (2003)). Glucose oxidase catalyzes the oxygen-dependent oxidation of D-glucose to D-glucono-1,5-lactone and hydrogen peroxide (H2O2). Glucose oxidase, glucose, and gluconate (which is spontaneously formed from D-glucono-1,5-lactone in aqueous solutions) do not inhibit V. dahlia when used individually (Kim et al., “Glucose Oxidase as the Antifungal Principle of Talaron from Talaromyces flavus,” Can J Microbiol 36:760-764 (1993)) but low concentrations of H2O2 significantly inhibit the growth of Pythium ultimum, P. aphanidermatum, R. solani, and V. dahliae. Therefore, the antifungal effect of the glucose oxidase system is due to increased levels of H2O2 (Inglis et al., “Comparative Degradation of Oomycete, Ascomycete, and Basidiomycete Cell Walls by Mycoparasitic Biocontrol Fungi,” Can J Microbiol 48:60-70 (2002)).
Production of hydrogen peroxide and reactive oxygen species is associated with plant response to pathogen attack and involved in the so-called oxidative burst. These compounds are considered to play multiple roles in plant defense, such as triggering of the hypersensitivity reaction (HR), exerting direct antimicrobial activity, diffusing the signal for activation of defense genes, and reinforcing the plant cell wall (Mourgues et al., Strategies to Improve Plant Resistance to Bacterial Diseases Through Genetic Engineering,” Trends Biotechnol 16(5):203-10 (1998)). For this reasons, the production of H2O2 has been considered as a target for genetic improvement of plant pathogen resistance by modifying, for instance, either SOD or catalase activity (Heinen et al., “Increased Resistance to Oxidative Stress in Transgenic Plants That Overexpress Chloroplastic Cu/Zn Superoxidase Dismutase,” Proc Natl Acad Sci USA 90(4):1629-1633 (1993), H. Sanderman, Jr., “Active oxygen Species as Mediators of Plant lnmunity; Three Case Studies,” J. Biol Chem 381:649-653 (2000)). In addition, a fungal glucose-oxidase encoding gene from A. niger was expressed in potato by Wu et al., “Disease Resistance Conferred by Expression of a Gene Encoding H2O2-Generating Glucose Oxidase in Transgenic Potato Plants,” Plant Cell 7(9):1357-68 (1995) to increase the level of H2O2 in transgenic tubers and leaves following bacterial infection. The progeny exhibited an improved resistance to both bacterial (Erwinia amilovora subsp. carotovora) and fungal (Phytophthora infestans) pathogens, while the addition of catalase counteracted the effect of the transgene. This work indicated that microbial enzymes capable of generating active oxygen species may confer resistance to a broad-spectrum of plant pathogens. Several species of Trichoderma are more resistant to the products of glucose oxidase activity than many plant pathogens (Kim et al., “Glucose Oxidase as the Antifungal Principle of Talaron from Talaromyces flavus,” Can J Microbiol 36:760-764 (1993)), even though an orthologue of glucose oxidase has not been found so far in this fungus (Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999)).
Although Trichoderma is clearly an important biocontrol agent, Trichoderma alone does not provide the broad-spectrum of microbial and fungal disease resistance conferred by microbial enzymes capable of generating active oxygen species such as H2O2. It would be highly useful to have the broad-spectrum anti-pathogenic capacity of a bioactive glucose oxidase producing, H2O2-generating bioagent in combination with an agent having the ability of Trichoderma to colonize plant roots and deliver bioactive molecules in vivo.
The present invention is directed to overcoming these and other deficiencies in the art.
The present invention relates to a transgenic Trichoderma spp. having a recombinant nucleic acid molecule encoding a bioactive molecule, where the bioactive molecule is selected from the group consisting of a plant chitinase, a glucanase, a chitosanase, an endochitinase, an osmotin, a ribo some inactivating protein, a trichodiene sintasi, a stilbene sintasi, a killer toxin, a barnase, a ribonuclease, choleric toxin subunit A, a Bacillus thuringiensis toxin, an avirulence factor, a virulence factor, a β-cryptogein, a protonic pump, a pectate lyase, an oligogalacturonide lyase, a tabtoxin resistance protein, an ornitine carbamoyltransferase, a shiva-1, an attacinE, a lysozyme, a lactoferrin, a tachiplesin, resistance protein Xa21, a tionin, and a bacterial opsin.
The present invention also relates to a method of controlling plant disease. This involves applying a transgenic strain of Trichoderma spp. to a plant or plant seed, where the transgenic strain of Trichoderma spp. has a recombinant nucleic acid molecule encoding a bioactive molecule capable of controlling plant disease. The applying is carried out under conditions effective to control plant disease in the plant or a plant grown from the plant seed.
The present invention also relates to a method of delivering a bioactive molecule to a plant or plant seed. The method involves providing a transgenic strain of Trichoderma spp., where the transgenic strain of Trichoderma spp. comprises a recombinant nucleic acid molecule encoding a bioactive molecule, and applying the transgenic strain of Trichoderma spp. to a plant or plant seed. Application is carried out under conditions effective to deliver the bioactive molecule to the plant or plant seed.
The present invention provides a highly effective biocontrol agent and delivery system, having an improved ability to inhibit disease in plants and induce systemic resistance to diseases in plants caused by phytopathogens. Thus, the present invention provides a biologic alternative to the use of chemicals which may be highly attractive to commercial agriculture in instances where the availability of chemical pesticides have been lost to regulatory action or pest resistance, and in which there are no adequate chemical replacements.
The present invention relates to a transgenic Trichoderma spp. having a recombinant nucleic acid molecule encoding a bioactive molecule. The bioactive molecule is selected from the group consisting of a plant chitinase, a glucanase, a chitosanase, an endochitinase, an osmotin, a ribosome inactivating protein, a trichodiene sintasi, a stilbene sintasi, a killer toxin, a barnase, a ribonuclease, choleric toxin subunit A, a Bacillus thuringiensis toxin, an avirulence factor, a virulence factor, a β-cryptogein, a protonic pump, a pectate lyase, an oligogalacturonide lyase, a tabtoxin resistance protein, an ornitine carbamoyltransferase, a shiva-1, an attacinE, a lysozyme, a lactoferrin, a tachiplesin, resistance protein Xa21, a tionin, and a bacterial opsin. Exemplary delivery organisms suitable for this and all other aspects of the present invention are fungi in the genus Trichoderma (U.S. Pat. No. 5,260,213 to Harman et al., which is hereby incorporated by reference in its entirety), including Trichoderma harzianum; the protoplast fusion progeny of Trichoderma harzianum 1295-22, known as “T-22”, (ATCC 20847) (U.S. Pat. No. 5,260,213 to Harman et al.; Harman, G. E., “The Dogmas and Myths of Biocontrol. Changes in Perceptions Based on Research with Trichoderma harzianum T-22,” Plant Dis. 84, 377-393 (2000), which are hereby incorporated by reference in their entirety), and T-22™ (BioWorks, Inc., Geneva, N.Y.); and T. virens, formerly classified as Gliocladium virens (U.S. Pat. No. 5,165,928 to Smith et al., which is hereby incorporated by reference in its entirety). Any natural, mutant, or fused strain of Trichoderma shown to be rhizosphere competent is also suitable for all aspects of the present invention.
Trichoderma are organisms with strong abilities to colonize roots. This ability is known as rhizosphere competence, which is used herein to describe those organisms capable of colonizing the root surface or the surface plus surrounding soil volume (rhizoplane and rhizosphere, respectively), when applied as a seed or other point source at the time of planting in absence of bulk flow of water. Thus, the agents of the present invention have the physiological and genetic ability to proliferate the root as it develops. Rhizosphere competence is not an absolute term, and degrees of this ability may occur among strains (Harman, G. E., “The Development and Benefits of Rhizosphere Competent Fungi for Biological Control of Plant Pathogens,” J Plant Nutrition 15:835-843 (1992); U.S. Pat. Nos. 4,996,157 and 5,165,928 to Smith, which are hereby incorporated by reference in their entirety). Other organisms, including those in the genera Bacillus, Pseudomonas, and Burkholderia also possess good root competence (Brannen et al., “Kodiak: A Successful Biological-Control Product for Suppression of Soil-Borne Plant Pathogens of Cotton,” J. Industr. Microbiol. Biotechnol. 19 (1997) 169-171 (1997); Kloepper et al. “Plant Growth Promoting Rhizobacteria As Inducers of Systemic Acquired Resistance,” In: Lumsden, R. D. and Vaughn, J. L. (ed.): Pest Management: Biologically Based Technologies. Washington, D.C., pp. 10-20 (1993), which are hereby incorporated by reference in their entirety). Procedures for measuring rhizosphere competence are well-known in the art (Harman et al., “Combining Effective Strains of Trichoderma harzianum and Solid Matrix Priming to Improve Biological Seed Treatments,” Plant Dis. 73:631-637 (1989); Harman, G. E., “The Dogmas and Myths of Biocontrol. Changes in Perceptions Based on Research with Trichoderma harzianum T-22,” Plant Dis. 84, 377-393 (2000); Kloepper et al., “A Review of Issues Related to Measuring Colonization of Plant Roots by Bacteria,” Can J. Microbiol. 38, 1219-1232 (1992), which are hereby incorporated by reference in their entirety).
Suitable nucleic acid molecules for use in this aspect and all other aspects of the present invention are any nucleic acid molecules isolated from any source, including, but not limited to, bacteria, fungi, and plants that express bioactive molecules capable of controlling plant disease and conferring systemic disease resistance to plants. In one aspect of the present invention, the nucleic acid molecule is a heterologous nucleic acid molecule (i.e., foreign to Trichoderma spp.). Alternatively, the nucleic acid molecule inserted into the selected expression system may be homologous (i.e., native to Trichoderma spp.). In some aspects of the present invention the bioactive molecule is a glucose oxidase (gox) protein or polypeptide, and the nucleic acid molecule is any nucleic acid molecule encoding glucose oxidase (gox). Suitable gox nucleic acid molecules may be derived from any of the microbial species that contain a gox gene, including, but not limited to, T. flavus (Llwellyn et al., “Isolation of Glucose Oxidase Gene from Talaromyces flavus and Characterisation of it's Role in the Biocontrol of Verticillium dahliae,” Curr Genet. 32(5):367-375 (1997); Fravel et al., “In vitro Analysis of the Role of Glucose Oxidase from Talaromyces flavus in the Biocontrol of Verticillium dahliae,” Appl Environ Microbiol 62(9):3183-86 (1996); Kim et al., “Glucose Oxidase as the Antifungal Principle of Talaron from Talaromyces flavus,” Can J Microbiol 36(11):760-764 (1990), which are hereby incorporated by reference in their entirety) and A. niger (e.g., ATCC. 9029; Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999); Kriechbaum et al., “Cloning and DNA Sequence analysis of the Glucose Oxidase Gene from Aspergillus niger NRRL-3,” FEBS Letters 255(1):63-66 (1989), which are hereby incorporated by reference in their entirety).
A preferred nucleic acid molecule for the present invention is a nucleic acid molecule derived from A. niger, having SEQ ID NO: 1, as follows:
This nucleic acid molecule encodes a gox protein having the amino acid of SEQ ID NO:2, as follows:
Isolation of a nucleic acid molecule encoding gox can be carried out using any of the many methods of DNA isolation or preparation known in the art including, but not limited to, those described in Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Springs Laboratory, Cold Springs Harbor, N.Y. (1989), and Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Applied and Environ. Microbiol. 65(5):1858-1863 (1999), which are hereby incorporated by reference in their entirety.
In another aspect of the present invention, the bioactive molecule is an avirulence protein (avr), and the recombinant nucleic acid molecule is the nucleic acid molecule encoding an avirulence protein (avr). Suitable avr nucleic acid molecules may be derived from any of the microbial or fungal species that contain an avr agene, including, but not limited to, Cladosporium fulvum. For example, a suitable bioactive molecule from C. fulvum is the avr4 protein, which is encoded by the nucleic acid molecule having SEQ ID NO:3, as follows:
Another suitable avirulence protein from C. fulvum is avr9, which is encoded by the nucleic acid molecule having SEQ ID NO:4, as follows:
There are a wide variety of genes that may be delivered to the plant roots by the methods of the present invention and function to decrease the expression of plant disease. These genes encode or result in production of products that act in a variety of ways to decrease plant disease. For the present invention, the genes need to be introduced into a symbiotic, root-colonizing fungus having rhizosphere competence. The gene products expressed by the transgenic fungus need to be secreted into the zone of interaction between the transgenic fungus and the plant. Categories of genes suitable for the present invention include, without limitation: 1) transgenes whose gene products potentiate the defense response of plants to bacteria and fungi by increasing the antimicrobial properties of the plants; 2) genes derived from the pathogen expressed in transgenic plants, which activate the defense response and enhance the ability of the plant to recognize the pathogen; 3) transgenes whose gene products deactivate pathogen toxins or make the plant insensitive to them, and 4) transgenes against bacterial pathogens, which includes the subcategories of a) production of antibacterial proteins of non-plant origin; b) inhibition of the bacterial pathogenicity or of the virulence factors; c) improvement of plant's natural defenses; and d) artificial induction of cell death programmed on the infection site. These categories and examples for each are listed in Tables 1-4, respectively, below. Table 5, below, is a non-limiting list of exemplary genes/proteins suitable for the present invention, with their public database accession numbers. These are provided as non-limiting examples only and others will be obvious to those skilled in the art. However, in general, any gene that, when expressed in a plant or at the plants roots, results in pest or disease reduction, can be used in the present invention.
Serratia
marcescens
Alternaria longipes and R. Solani
Streptomyces sp.
Rhizopus
oligosporus
sclerotiorum and Botrytis cinerea
Trichoderma
harzianum
A. alternata, A. solani, B. cinerea,
R. Solani
nicotianae
Aspergillus niger
carotovora and P. infestans.
Fusarium
sporotrichioides
cinerea
Ustilago maydis
Ustilago. Resistance to U. maydis
Bacillus
amyloliquefaciens
Schizosac
charomyces
pombe
Vibrio cholerae
Pseudomonas syringae pv. tabaci
Bacillus
thuringiensis
Arabidopsis thaliana, etc . . .
C. fulvum
C. fulvum, Phytophthora
infestans
Pseudomonas syringae
Arabidopsis
thaliana
Pseudomonas Syringae Avirulence
P. syringae pv. tomato
P. syringae pv. tomato
A. thaliana
Arabidopsis Induces Hypersensitive
C. fulvum
P. cryptogea
Halobacterium halobium
Erwinia carotovora
Erwinia carotovora,” Physiol Molec
E. carotovora
P. syringae pv. tabaci
P. syringae pv.
phaseolicola
Pseudomonas Syringae pv.
Phaseolicola,” Biotech 10: 905-909
P. syringae
P. syringae
phaseolicola
Syringae pv. Phaseolicola,” Biotechnology 10: 905-909 (1992)
Hyalophora
Ralstonia
cecropia (giant silk
solanacearum
Hyalophora
Pseudomonas
cecropia (giant silk
syringae pv. tabaci
Hyalophora
Erwinia amylovora
cecropia (giant silk
Erwinia carotovora
Pseudomonas
syringae pv. tabaci
Ralstonia
solanacearum
Erwinia carotovora
Pseudomonas
Pseudomonas
syringae pv. tabaci
syringae
Pseudomonas
Pseudomonas
syringae pv.
syringae pv.
phaseolicola
phaseolicola
Erwinia
Erwinia carotovora
carotovora
Xanthomonas oryzae
Aspergillus niger
Erwinia carotovora
Pseudomonas
syringae pv. tabaci
Halobacterium
Pseudomonas
halobium
syringae pv. tabaci
Photorhabdus
luminescens putative
Phytophthora sojae
Pseudomonas syringae
Xanthomonas oryzae pv.
oryzae ATP sulfurylase
Pseudomonas syringae
Pseudomonas syringae
Pseudomonas syringae
Pseudomonas syringae
pathovar phaseolicola
Erwinia amylovora
Erwinia amylovora
Pseudomonas syringae
Pseudomonas syringae
Xanthomonas campestris
Xanthomonas campestris
Xanthomonas oryzae
P. syringae avirulence
Pseudomonas syringae
Pseudomonas syringae
Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana
P. syringae avirulence
Cysteine protease
Peronospora parasitica
Pseudomonas syringae
Pseudomonas syringae
Microbulbifer degradans
lini
lini
lini
Melampsora lini
Melampsora lini
lini
lini
lini
Pseudomonas syringae
syringae (strain DC3000,
Pseudomonas syringae
Pseudomonas syringae
Pseudomonas syringae
oryzae pv. oryzae
Xanthomonas oryzae pv.
oryzae
Pseudomonas syringae
Pseudomonas syringae
syringae pv. phaseolicola
campestris
In all aspects of the present invention, the desired nucleic acid molecule encoding a recombinant nucleic acid molecule capable of controlling plant disease is introduced into Trichoderma spp. using conventional recombinant technology. Generally, this involves inserting the nucleic acid molecule into an expression system to which the molecule is heterologous (i.e., not normally present). The introduction of a particular foreign or native gene into a host is facilitated by first introducing the gene sequence into a suitable nucleic acid vector. “Vector” is used herein to mean any genetic element, such as a plasmid, phage, transposon, cosmid, chromosome, virus, virion, etc., which is capable of replication when associated with the proper control elements and which is capable of transferring gene sequences between cells. Thus, the term includes cloning and expression vectors, as well as viral vectors.
U.S. Pat. No. 4,237,224 to Cohen and Boyer, which is hereby incorporated by reference in its entirety, 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 prokaryotic organisms and eukaryotic cells grown in tissue culture.
Recombinant genes may also be introduced into viruses, including vaccinia virus, adenovirus, and retroviruses, including lentivirus. Recombinant viruses can be generated by transfection 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, pACYC184, 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 in its entirety), pQE, pIH821, pGEX, pET series (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 in its entirety), and any derivatives thereof. Recombinant molecules can be introduced into cells via transformation, particularly transduction, conjugation, mobilization, or electroporation. The nucleic acid 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 in its entirety.
A variety of host-vector systems may be utilized to express the protein-encoding sequence of the present invention. 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).
Depending on the vector system and host utilized, any number of suitable transcription and/or translation elements, including constitutive, inducible, and repressible promoters, as well as minimal 5′ promoter elements may be used. Promoters 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 promoters 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 promoters may be used. For instance, when cloning in E. coli, its bacteriophages, or plasmids, promoters such as the T7 phage promoter, lac promoter, trp promoter, recA promoter, ribosomal RNA promoter, the PR and PL promoters of coliphage lambda and others, including but not limited, to lacUV5, ompF, bla, lpp, and the like, may be used to direct high levels of transcription of adjacent DNA segments. Additionally, a hybrid trp-lacUV5 (tac) promoter or other E. coli promoters produced by recombinant DNA or other synthetic nucleic acid molecule techniques may be used to provide for transcription of the inserted gene. Particularly suitable for the present invention is the use of an inducible promoter that expresses the heterologous or homologous nucleic acid molecule harbored by the transgenic Trichoderma when it is advantageous for the biocontrol molecule to be presented to the plant system, including to the roots and seeds. An exemplary promoter for the construct of the present invention is the promoter region from the T. atroviride gene encoding N-acetylhexosaminidase (nag1). The pnag promoter is not constitutive, therefore, no, or only low, levels of expression are expected from genes driven by this promoter when it is grown on glucose or other repressive substrates. However, the genes driven by the nag1 promoter are expected to be highly expressed in the absence of high levels of glucose and in the presence of fungal cell walls, chitin, target fungi, or any combination thereof (Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999), which is hereby incorporated by reference in its entirety). For a review on maximizing gene expression see Roberts and Lauer, Methods in Enzymology, 68:473 (1979), which is hereby incorporated by reference in its entirety. Expression vectors may be chosen which inhibit the action of the promoter unless specifically induced. In certain operons, 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.
The nucleic acid molecule(s) of the present invention, a 5′ nucleotide regulatory region of choice, a suitable 3′ regulatory region, and if desired, a reporter gene, are incorporated into a vector-expression system of choice to prepare the nucleic acid construct of present invention using standard cloning procedures known in the art, such as described by Sambrook et al., Molecular Cloning: A Laboratory Manual, Third Edition, Cold Spring Harbor: Cold Spring Harbor Laboratory Press, New York (2001), which is hereby incorporated by reference in its entirety.
In one aspect of the present invention, a nucleic acid molecule encoding a protein of choice is inserted into a vector in the sense (i.e., 5′→3′) direction, such that the open reading frame is properly oriented for the expression of the encoded protein under the control of a promoter of choice. Single or multiple nucleic acids may be ligated into an appropriate vector in this way, under the control of a suitable promoter, to prepare a nucleic acid construct of the present invention. In all aspects of the present invention, a highly suitable nucleic acid construct includes multiple nucleic acid molecules, each encoding a bioactive molecule, all of which are in sense orientation and linked, 5′-3′ to one another, and all of which are under the control of one or more operably linked 5′ and 3′ regulatory regions for overexpression of the bioactive molecules under the appropriate conditions.
Once the isolated nucleic acid molecule encoding the desired biocontrol molecule of the present invention has been cloned into an expression vector, it is ready to be incorporated into a host. The selected molecules can be introduced into a chosen host via transformation, particularly transduction, conjugation, lipofection, protoplast fusion, mobilization, particle bombardment, or electroporation. The DNA sequences are cloned into the desired host using standard cloning procedures known in the art, as described by Sambrook et al., Molecular Cloning: a Laboratory Manual, Second Edition, Cold Springs Laboratory, Cold Springs Harbor, N.Y. (1989), which is hereby incorporated by reference in its entirety.
Transient expression in protoplasts allows quantitative studies of gene expression since the population of cells is very high (on the order of 106). To deliver DNA inside protoplasts, several methodologies have been proposed, but the most common are electroporation (Neumann et al., “Gene Transfer into Mouse Lyoma Cells by Electroporation in High Electric Fields,” EMBO J. 1: 841-45 (1982); Wong et al., “Electric Field Mediated Gene Transfer,” Biochem Biophys Res Commun 30; 107(2):584-7 (1982); Potter et al., “Enhancer-Dependent Expression of Human Kappa Immunoglobulin Genes Introduced into Mouse pre-B Lymphocytes by Electroporation,” Proc. Natl. Acad. Sci. USA 81: 7161-65 (1984), which are hereby incorporated by reference in their entirety) and polyethylene glycol (PEG) mediated DNA uptake, Sambrook et al., Molecular Cloning: A Laboratory Manual, Chap. 16, Second Edition, Cold Springs Laboratory, Cold Springs Harbor, N.Y. (1989), which is hereby incorporated by reference in its entirety). During electroporation, the DNA is introduced into the cell by means of a reversible change in the permeability of the cell membrane due to exposure to an electric field. PEG transformation introduces the DNA by changing the elasticity of the membranes. Unlike electroporation, PEG transformation does not require any special equipment and transformation efficiencies can be equally high. Another appropriate method of introducing the gene construct of the present invention into a host cell is fusion of protoplasts with other entities, either minicells, cells, lysosomes, or other fusible lipid-surfaced bodies that contain the chimeric gene (Fraley et al., “Entrapment of a Bacterial Plasmid in Phospholipid Vesicles: Potential for Gene Transfer,” Proc Natl Acad Sci USA 76(7):3348-52 (1979); Fraley et al., “Introduction of Liposome-Encapsulated SV40 DNA into Cells,” J Biol Chem 255(21):10431-10435 (1980), which are hereby incorporated by reference in the entirety).
Stable transformants are preferable for the methods of the present invention, which can be achieved by using variations of the methods above as describe in Sambrook et al., Molecular Cloning: A Laboratory Manual, Chap. 16, Second Edition, Cold Springs Laboratory, Cold Springs Harbor, N.Y. (1989), which is hereby incorporated by reference in its entirety.
Typically, an antibiotic or other compound useful for selective growth of the transformed cells only is added as a supplement to the media. The compound to be used will be dictated by the selectable marker element present in the plasmid with which the host cell was transformed. Suitable genes are those which confer resistance to gentamycin, G418, hygromycin, streptomycin, spectinomycin, tetracycline, chloramphenicol, and the like. Similarly, “reporter genes,” which encode enzymes providing for production of an identifiable compound, or other markers which indicate relevant information regarding the outcome of gene delivery, are suitable. For example, various luminescent or phosphorescent reporter genes are also appropriate, such that the presence of the transgene may be ascertained visually. The selection marker employed will depend on the target species and/or host or packaging cell lines compatible with a chosen vector.
After the transgenic host cells are identified, they are grown to a desired density in cell culture media appropriate for the cell type, under conditions suitable for the maintenance and, if desired, expansion of the cell population prior to the application of the cells in accordance with the methods of the present invention.
The present invention also relates to a method of controlling plant disease. This involves applying a transgenic strain of Trichoderma spp., prepared as described herein above, to a plant or plant seed, where the transgenic strain of Trichoderma spp. includes a recombinant nucleic acid molecule encoding a bioactive molecule capable of controlling plant disease. The applying is carried out under conditions effective to control plant disease in the plant or a plant grown from the plant seed.
The transgenic Trichoderma of the present invention harboring one or more nucleic acid molecule(s) encoding one or more biocontrol molecules can be introduced to a plant, plants roots, or plant seed in a number of ways. In one aspect of the present invention, the transgenic Trichoderma is applied to the roots of a plant to control disease when the transgene encoding a bioactive molecule is expressed by the Trichoderma in the root environs. This application can be directly to the roots, or to the soil in which a plant or plant seed is growing or is to be planted. Several methods for application are known in the art, including, but not limited, to the following described below.
The transgenic Trichoderma of the present invention may be formulated or mixed to prepare granules, dusts or liquid suspensions. These can be incorporate directly into soils or planting mixes. The preparations are then mixed into the soil or planting mix volume for greenhouse applications or into the upper volume of field soil (Harman, G. E., “The Dogmas and Myths of Biocontrol. Changes in Perceptions Based on Research with Trichoderma harzianum T-22,” Plant Dis. 84, 377-393 (2000), which is hereby incorporated by reference in its entirety). Equipment and procedures for such applications are well known and used in various agricultural industries. Typical rates are 0.1 to 50 kg of product containing 107 to 109 colony forming units (cfu) per cubic meter of planting mix or soil. The amount of formulated product can be adjusted proportionally to higher or lower levels of colony forming units. There are approximately 1011 conidia per gram (Jin et al., “Development of Media and Automated Liquid Fermentation Methods to Produce Desiccation-Tolerant Propagules of Trichoderma harzianum,” Biol Contr 7:267-274 (1996), which is hereby incorporated by reference in its entirety). A cfu level of between about 106 and 1011 is commercially useful.
Alternatively, liquid suspensions (drenches) of the transgenic Trichoderma of the present invention can be prepared by mixing dry powder formulations into water or other aqueous carrier, including fertilizer solutions, or by diluting a liquid formulation containing the microbe in water or other aqueous solutions, including those containing fertilizers. Such solutions can then be used to water planting mixes either prior to planting or else when plants are actively growing.
Dry powders containing the transgenic Trichoderma of the present invention can be applied as a dust to roots, bulbs or seeds. Generally fine powders (usually 250 μm or smaller) are dusted onto seeds, bulbs or roots to the maximum carrying powder (i.e., until no more powder will adhere to the treated surface). Such powders typically contain 106 to 1011 cfu/g.
Liquid suspensions of products may be prepared as described above for preparing drenches suitable for in-furrow application. Such materials may be added to the furrow into which seeds are planted or small plants are transplanted. Equipment for such applications is widely used in the agricultural industry. Typical rates of application are 0.1 to 200 kg of product (106 to 1011 cfu/g) per hectare of field.
Granules, as described above, can be broadcast onto soil surfaces that contain growing plants, to soil at the time of planting, or onto soils into which seeds or plants will be planted. Typical rate ranges for broadcast application are from 0.1 to 1000 kg of product (106 to 1011 cfu/g) per hectare of field. Alternatively, spray solutions can be prepared as described above, and applied to give similar rates (Harman, G. E., “The Dogmas and Myths of Biocontrol. Changes in Perceptions Based on Research with Trichoderma harzianum T-22,” Plant Dis. 84, 377-393 (2000); Lo et al., “Biological Control of Turfgrass Diseases With a Rhizosphere Competent Strain of Trichoderma harzianum,” Plant Dis. 80, 736-741 (1996); Lo et al., “Improved Biocontrol Efficacy of Trichoderma harzianum 1295-22 For Foliar Phases of Turf Diseases By Use of Spray Applications,” Plant Dis. 81: 1132-1138 (1997), which are hereby incorporated by reference in their entirety).
In this aspect of the present invention, the transgenic strain of Trichoderma is applied directly to a seed, using any method of seed treatment known in the art. For example, seeds are commonly treated using slurry, film-coating or pelleting by processes well known in the trade (Harman et al., “Factors Affecting Trichoderma hamatum Applied to Seeds As a Biocontrol Agent,” Phytopathology 71: 569-572 (1981); Taylor et al., “Concepts and Technologies of Selected Seed Treatments,” Ann. Rev. Phytopathol. 28: 321-339 (1990), which is hereby incorporated by reference in its entirety). The beneficial microbial agents of the present invention can effectively be added to any such treatment, providing that the formulations do not contain materials injurious to the beneficial organism. Depending on the microbe in question, this may include chemical fungicides. Typically, powder or liquid formulations (106 to 1011 cfi/g) of ithe organism are suspended in aqueous suspensions to give a bioactive level of the microbe. The liquid typically contains adhesives and other materials to provide a good level of coverage of the seeds and may also improve its shape for planting or its cosmetic appeal.
For the purposes of the present invention, all treatments are designed to accomplish the same purpose, i.e., to provide a means of application that will result in effective colonization of the root by the beneficial microbe (Harman and Björkman, “Potential and Existing Uses of Trichoderma and Gliocladium For Plant Disease Control and Plant Growth Enhancement,” In: Harman, G. E. and Kubicek, C. P. (ed.): Trichoderma and Gliocladium, Vol. 2. Taylor and Francis, London, pp. 229-265 (1998), which is hereby incorporated by reference in its entirety).
On one aspect of the present invention “controlling plant disease” involves conferring systemic (as opposed to localized) disease resistance to a plant. The method involves applying a transgenic strain of Trichoderma spp. to a plant or plant seed, where the transgenic strain of Trichoderma spp. has a recombinant nucleic acid molecule encoding a bioactive molecule capable of conferring systemic disease resistance to the plant or a plant grown from the plant seed. Application of the transgenic strain of Trichoderma spp. is carried out under conditions effective to confer systemic disease resistance to the plant or a plant grown from the plant seed. Suitable in this aspect of the present invention are the Trichoderma strains, heterologous or homologous nucleic acid molecules encoding a bioactive molecule, and the method of making the transgenic Trichoderma spp. of the present invention as described herein above.
The present invention also relates to a method of delivering a bioactive molecule to a plant or plant seed. The method involves providing a transgenic strain of Trichoderma spp., where the transgenic strain of Trichoderma spp. comprises a recombinant nucleic acid molecule encoding a bioactive molecule, and applying the transgenic strain of Trichoderma spp. to a plant or plant seed. Application is carried out under conditions effective to deliver the bioactive molecule to the plant or plant seed. Suitable in this aspect of the present invention are the Trichoderma strains, heterologous or homologous nucleic acid molecules encoding a bioactive molecule, and methods of making the transgenic Trichoderma as described herein above. Application of the transgenic Trichoderma to effect delivery of the bioactive molecule can be to plant roots, soil or plant seed, also as described in detail above, or as known in the art.
The methods and the delivery system of the present invention can be practiced with a wide variety of plants and their seeds. For all aspects of the present invention described herein above, or in the Examples below, suitable plants to which the transgenic Trichoderma spp. of the present invention can be applied include all varieties of dicots and monocots, including crop plants and ornamental plants. More particularly, useful crop plants include, without limitation: alfalfa, rice, wheat, barley, rye, cotton, sunflower, peanut, corn, potato, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, brussel sprout, beet, parsnip, turnip, cauliflower, broccoli, radish, spinach, onion, garlic, eggplant, pepper, celery, carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, citrus, strawberry, grape, raspberry, pineapple, soybean, tobacco, tomato, sorghum, and sugarcane. Examples of suitable ornamental plants are, without limitation, Arabidopsis thaliana, Saintpaulia, petunia, pelargonium, poinsettia, chrysanthemum, carnation, zinnia, and turfgrasses.
A transgenic form (SJ3 4) of strain P1 (ATCC 74058) of T. atroviride (formerly T. harzianum) was prepared as previously described (Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999), which is hereby incorporated by reference in its entirety), except that the transgenic Trichoderma of the present invention contains 12-14 copies of a glucose oxidase A (gox) gene obtained (although not identical to) from A. niger, ATCC 9029, having the nucleic acid sequence of SEQ ID NO:1, shown above. This nucleotide sequence encodes a protein having the amino acid sequence of SEQ ID NO:2, shown above.
The construct used for transformation contains the promoter region from the T. atroviride gene encoding N-acetylhexosaminidase (nag1) fused to the nucleic acid molecule encoding gox. This construct is referred to hereafter as pnag:gox. The pnag promoter is not constitutive, therefore, no, or only low, levels of expression are expected from genes driven by this promoter when it is grown on glucose or other repressive substrates. However, the genes driven by the nag1 promoter are expected to be highly expressed in the absence of high levels of glucose and in the presence of fungal cell walls, chitin, target fungi, or any combination thereof.
Culture filtrates from the parental or transgenic strains were obtained as follows: The strain was precultivated in shake flasks (250 rpm) in PDB (potato dextrose broth; Merck, Whitehouse Station, N.J.) for 48 hrs at 25° C., harvested by filtration through Miracloth (Calbiochem, La Jolla, Calif.), washed with sterile tap water, and transferred to SM media ((in g/l): KH2PO4, 2; (NH4)2SO4, 1.4; CaCl2.2H2O, 0.3; MgSO4.7H2O, 0.3; urea, 0.6; (mg/l): FeSO4.7H2O, 10; ZnSO4.2H2O, 2.8; CoCl2.6H2O, 3.2 (pH 5.4), and either 1.5% (w/v) glucose or colloidal chitin as carbon source). After 3 days culture filtrates were obtained by filtration through a 0.22 μm filter. The culture filtrate was dialyzed against 20 volumes of distilled water for 24 hrs at 4° C. Thereafter, concentration of culture filtrates was carried out by covering the dialysis bags with polyethylene glycol 8000, (Fluka Biochemika, Buchs, Switzerland) and leaving them for 10 hours at 4° C. leading to a 20-fold concentrated solution. The filtrates were stored at −20° C. with 20% (v/v) glycerol final concentration until use.
The transgenic strains were similar or identical to the parental strain in growth rate and sporulation ability.
It was previously demonstrated that the parental strain P1 of T. atroviride P1 has no glucose oxidase activity (Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999), which is hereby incorporated by reference in its entirety). Strain SJ3 4 produced 4 [±1] and 300 [±19] mU/ml of glucose oxidase activity on media containing glucose or colloidal chitin, respectively. These results are consistent with previous observations that nag expression is induced by chitin, as well as by pathogen cell walls (Lorito et al., “Mycoparasitic Interaction Relieves Binding of the Crel Carbon Catabolite Repressor Protein to Promoter Sequences of the ech42 (Endochitinase-Encoding) Gene in Trichoderma harzianum,” Proc Natl Acad Sci USA 93:14868-14872 (1996); Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” App/Environ Microbiol 65:1858-1863 (1999), which are hereby incorporated by reference in their entirety).
To demonstrate that glucose oxidase expression was induced by direct contact with a potential host (plant pathogen), plate confrontation assays were conducted with B. cinerea. A red halo indicative of glucose oxidase activity was observed around Trichoderma strain SJ3 4 one to two hours after it contacted the host (Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999), which is hereby incorporated by reference in its entirety). Neither the wild type nor strains transformed only with the hygromycin B resistance-conferring vector pHATα (Goldman et al., “Transformation of Trichoderma harzianum by High Voltage Electric Pulse,” Current Gen 17:169-174 (1990), which is hereby incorporated by reference in its entirety) exhibited such a fast pH shift. A general acidification leading to the occurrence of red halos was observed with all strains during later stages of biocontrol (18 to 24 hours after contact). These findings indicate that induction of nah (naphthalene dioxygenase) gene expression caused by contact with the pathogenic host and glucose oxidase production are correlated in T. atroviride strain SJ3 4, and therefore the nag1 promoter is driving the expression of the transgene as expected (Mach et al., “Expression of Two Major Chitinase Genes of Trichoderma atroviride (T. harzianum P1) is Triggered by Different Regulatory Signals,” Appl Environ Microbiol 65:1858-1863 (1999), which is hereby incorporated by reference in its entirety).
Chitinolytic activity was not detected in filtrates from either Trichoderma strain growing on glucose or glycerol. However, there was clearly detectable chitinolytic enzyme activity in filtrates from both strains following transfer to a medium containing colloidal chitin as the sole carbon source. Under these conditions, SJ3 4 showed 55% and 70% of the N-acetyl-β-glucosaminidase and endochitinase activities produced by the wild type, but an unmodified level of chitobiosidase activity. Therefore, transformation with several copies of the transgene in SJ3 4 produced no apparent changes in viability, but reduced expression of two biocontrol-related chitinase genes.
In vitro B. cinerea spore germination inhibition was tested in ELISA plates essentially as previously described. A suspension of 3×103 Botrytis spores and 50 μl PDB with 5 mM potassium phosphate buffer, pH 6.7, were placed in a well of an ELISA plate and 10 μl of the 20-fold concentrated culture supernatants of strain P1 or SJ3 4 grown on colloidal chitin were added. The addition of 100 mM H2O2 instead of culture filtrates was used as a control. The number of germinated spores was counted after 8 hours of incubation, averaged, and related to the germination percentage of a control treatment containing sterile water instead of culture filtrate, taken as 100 percent gennination.
These results demonstrate that in the presence of chitin, where the pnag:gox constructs were expressed, the ability of the filtrates from SJ3 4 to inhibit germination of conidia of the plant pathogen B. cinerea were substantially greater than any other treatment.
For plate confrontation assays, which measure the direct parasitism of Trichoderma strains on target fungi, 5-mm disks of T. atroviride (either P1 wild-type or SJ3 4), and either R. solani or P. ultimum were placed on potato dextrose agar (PDA) at a distance from each other of 4 cm. The plates shown in
Tests were conducted to compare the ability of SJ3 4 and P1 to protect bean cultivars (Phaseolus vulgaris cv. Borlotto) against two different plant pathogens. For these tests, the bean seeds were coated with a 10% (w/v) suspension of Pelgel (Liphatech, Milwaukee, Wis.) in 20 mM potassium phosphate buffer containing 20 mM glucose. One ml of a 1×108 conidia/ml suspension of Trichoderma was used for coating 10 g of seeds. As a control, the same suspension without Trichoderma was used. Pathogen-infested soil was prepared by inoculating 500 ml of PDB with R. solani mycelium from a 4-day old 8-cm PDA plate. Two g wet weight of the resulting biomass was used to inoculate 1 L of sterile soil. For P. ultimum, 1 liter of sterile soil was infested with four 3 d old 8 cm plates of the pathogen homogenized in a blender for 30 s. After 2 days the infested soil was diluted 1:4 with sterile soil and used for biocontrol assays as described above. The coated seeds were planted 4 cm deep into infested soil and their germination was monitored for 2 weeks.
In soil tests with low amounts of pathogen (R. solani 1 g biomass, P. ultimum 4 homogenized plates per liter of soil), the glucose oxidase producing strain provided approximately the same level of protection against R. solani and P. ultimum as the wild type strain. Both the number of germinated seeds and the plant height were comparable to the results previously published by Woo et al., “Disruption of the ech42 (Endochitinase-Encoding) Gene Affects Biocontrol Activity in Trichoderma harzianum P1,” Molec Plant-Microbe Interact 12:419-429 (1999), which is hereby incorporated by reference in its entirety. Increase of the disease pressure by doubling the inoculum caused a complete rot of nearly all uncoated seeds and seeds coated with conidia of the wild type, as shown in Table 6, below. Instead, almost all beans treated with the glucose oxidase-producing strain could be germinated in soil infested with high amounts of either one of the two pathogens and produced plants of a size similar to the control without pathogen.
Rhizoctonia
Pythium
adpc (disease pressure control) indicates germination of seeds not protected by Trichoderma.
These results demonstrate clearly that strain SJ3 4 is more effective in protecting seeds and seedlings against R. solani than the wild type strain.
Previous research has clearly demonstrated that Trichoderma strains added to roots and localized on roots can protect plants against foliar diseases. This is a consequence of significant changes induced by the biocontrol agents that results in systemic protection of the plant against pathogens that are located at sites that are temporally or spatially distant from the point of application, and spatially distant from the location of the Trichoderma strain (Harman et al., “Trichoderma Species—Opportunistic, Avirulent Plant Symbionts,” Nature Microbiol Rev 2:43-56 (2004), which is hereby incorporated by reference in its entirety). Bean seeds were coated with a 10% (w/v) aqueous suspension of Pelgel containing 1×108 spores/ml of T. atroviride strains wild type P1 or transgenic strain SJ3 4 plus an untreated control without Trichoderma, then left in an open Petri dish to air dry overnight in a laminar flow hood. Seven seeds were planted into 14 cm vases of sterile soil (one hr at 122° C.), at a depth of 4 cm, incubated at 25° C. with light, and maintained at high relative humidity. Leaves were inoculated at two points and four leaves per plant, using 10 plants per treatment and two replicates for each experiment. The experiments were repeated at two different times. The lesion size was calculated on the basis of: Area=π×(measured diameter A/2)×(measured diameter B/2), where “diameter” was the treatment mean for each experiment. Statistical analyses included an analysis of variance (ANOVA) of treatment means and unpaired t-tests were conducted among the Trichoderma seed coat treatments for each experiment.
Clearly, the transgenic strain has a much greater ability to reduce foliar disease and, therefore, induces a higher level of induced resistance than the wild type strain.
The present invention is not limited only to the gox gene or to bean plants. The ability of symbiotic Trichoderma spp. to exchange molecules and affect plant metabolism has been conclusively demonstrated. The model system was the expression of resistance and hypersensitive reactions in tomato. T. atroviride strain P1 was transformed with the avirulence gene, avr4, from C. fulvum, under control of a strong constitutive promoter. Avr4 causes a strong hypersensitive reaction in tomatoes carrying the Cf4 gene for resistance to the pathogen, but not in tomatoes carrying the Cf5 gene. This provided a very useful marker for introduction of the protein into the plant that was verified experimentally. When the transformed strain of P1 was applied to roots of young plants with the Cf4 gene, the plants died from the hypersensitive reaction, while in older plants a strong hypersensitive reaction was seen. No such reaction occurred when the transformed strain was applied to plants with the Cf5 gene, conclusively demonstrating that inoculation of plant roots resulted in transfer of the Avr4 gene to tomato, as demonstrated by the hypersensitive reaction shown in
The present findings indicate that Avr and other similar signalling molecules from Trichoderma and other symbiotic root colonizing microbes may be different in function and nature from those of pathogenic fungi. The reasons for this are as follows:
1. There are numerous Avr like proteins, and genes encoding them, in Trichoderma spp.
2. These different proteins probably act in concert.
3. The Avr proteins from pathogens such as C. fulvum interact very specifically with particular genotypes of plants. However, the interactions, resulting in localized and systemic resistance, and increased plant growth and yield, are not very specific and, in fact, occur across a wide range of plants (e.g., see Table 6, above).
Thus, the symbiotic plant microbes and their biochemical elicitors of improved plant phenotype are highly useful and novel new findings.
The present invention is not restricted to any specific type of plant, particular transgene, or strain of Trichoderma. A wide range of Trichoderma strains and species are symbiotic with plants and any of them are highly suitable for the present invention. Similarly, a wide range of plant species are hosts to Trichoderma strains. Many strains and plants have been described in (Harman et al., “Trichoderma Species—Opportunistic, Avirulent Plant Symbionts,” Nature Microbiol Rev 2:43-56 (2004), which is hereby incorporated by reference in its entirety). In fact, a preferred embodiment of the present invention is the use of highly rhizosphere competent strains such as T. harzianum strain T22 and T. virens strain 41. These strains effectively colonize entire root systems for the life of at least annual crops providing long-term effective and beneficial plant interactions. These have been summarized in Harman, G. E., “Myths and Dogmas of Biocontrol. Changes in Perceptions Derived from Research on Trichoderma harzianum T-22,” Plant Dis 84:377-393 (2000); (Harman et al., “Trichoderma Species—Opportunistic, Avirulent Plant Symbionts,” Nature Microbiol Rev 2:43-56 (2004), which are hereby incorporated by reference in their entirety.
Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 60/612,028, filed Sep. 22, 2004, which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US05/33762 | 9/21/2005 | WO | 00 | 3/10/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60612028 | Sep 2004 | US |
