Numerous Trichoderma spp. are mycoparasites and commercially applied as biological control agents against a large number of plant pathogenic fungi. The mycoparasitic interaction is host-specific and several research s...Numerous Trichoderma spp. are mycoparasites and commercially applied as biological control agents against a large number of plant pathogenic fungi. The mycoparasitic interaction is host-specific and several research strategies have been applied to identify the main genes and compounds involved in the antagonist-plant-pathogen three-way interaction. During mycoparasitism, signals from the host fungus are recognised by Trichoderma, stimulating antifungal activities that are accompanied by morphological changes and the secretion of hydrolytic enzymes and antibiotics. Interestingly some morphological changes appeared highly conserved in the strategy of pathogenicity within the fungal world, i.e. the formation of appressoria as well as the secretion of hydrolytic enzymes seem to be general mechanisms of attack both for plant pathogens and mycoparasitic antagonists. This knowledge is being used to identify receptors and key components of signalling pathways involved in fungus-fungus interaction. For this purpose we have cloned the first genes (tmk1, tga1, tga3) from T. atroviride showing a high similarity to MAP kinase and G protein subunits (see abstract by Zeilinger et al.), which have been found to have an important role in pathogenicity by Magnaporthe grisea. To identify the function and involvement of these factors in mycoparasitism by T. atroviride, tmk1, tga1, tga3 disruptant strains were produced. The knock-out mutants were tested by in vivo biocontrol assays for their ability to inhibit soil and foliar plant pathogens such as Rhizoctonia solani, Pythium ultimum and Botrytis cinerea . Disruption of these genes corresponded to a complete loss of biocontrol ability, suggesting a significant role in mycoparasitism. In particular, it has been suggested that tga3 regulates the expression of chitinase-encoding genes, the secretion of the corresponding enzymes and the process of conidiation. Comparative proteome analysis of wild type and disruptants supported this hypothesis, and indicated many changes in the protein profiles of T. atroviride in different interaction conditions with plants and pathogenic hosts.展开更多
Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subseque...Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subsequent penetration and killing of the host. Investigations on the underlying events revealed that Trichoderma responds to multiple signals from the host (e.g. lectins or other ligands such as low molecular weight components released from the host’s cell wall) and host attack is accompanied by morphological changes and the secretion of hydrolytic enzymes and antibiotics. Degradation of the cell wall of the host fungus is-besides glucanases and proteases-mainly achieved by chitinases. In vivo studies showed that the ech42 gene (encoding endochitinase 42) is expressed before physical contact of Trichoderma with its host, probably representing one of the earliest events in mycoparasitism, whereas Nag1 (N-acetylglucosaminidase) plays a key role in the general induction of the chitinolytic enzyme system of T. atroviride . Investigations on the responsible signal transduction pathways of T. atroviride led to the isolation of several genes encoding key components of the cAMP and MAP kinase signaling pathways, as alpha and β subunits of heterotrimeric G proteins, the regulatory subunit of cAMP-dependent protein kinase, adenylate cyclase, and three MAP kinases. Analysis of knockout mutants, generated by Agrobacterium-mediated transformation, revealed that at least two alpha-subunits of heterotrimeric G proteins are participating in mycoparasitism-related signal transduction. The Tga1 G alpha subunit was shown to be involved in mycoparasitism-related processes such as chitinase expression and overproduction of toxic secondary metabolites, whereas Tga3 was found to be completely avirulent showing defects in chitinase formation and host recognition.展开更多
文摘Numerous Trichoderma spp. are mycoparasites and commercially applied as biological control agents against a large number of plant pathogenic fungi. The mycoparasitic interaction is host-specific and several research strategies have been applied to identify the main genes and compounds involved in the antagonist-plant-pathogen three-way interaction. During mycoparasitism, signals from the host fungus are recognised by Trichoderma, stimulating antifungal activities that are accompanied by morphological changes and the secretion of hydrolytic enzymes and antibiotics. Interestingly some morphological changes appeared highly conserved in the strategy of pathogenicity within the fungal world, i.e. the formation of appressoria as well as the secretion of hydrolytic enzymes seem to be general mechanisms of attack both for plant pathogens and mycoparasitic antagonists. This knowledge is being used to identify receptors and key components of signalling pathways involved in fungus-fungus interaction. For this purpose we have cloned the first genes (tmk1, tga1, tga3) from T. atroviride showing a high similarity to MAP kinase and G protein subunits (see abstract by Zeilinger et al.), which have been found to have an important role in pathogenicity by Magnaporthe grisea. To identify the function and involvement of these factors in mycoparasitism by T. atroviride, tmk1, tga1, tga3 disruptant strains were produced. The knock-out mutants were tested by in vivo biocontrol assays for their ability to inhibit soil and foliar plant pathogens such as Rhizoctonia solani, Pythium ultimum and Botrytis cinerea . Disruption of these genes corresponded to a complete loss of biocontrol ability, suggesting a significant role in mycoparasitism. In particular, it has been suggested that tga3 regulates the expression of chitinase-encoding genes, the secretion of the corresponding enzymes and the process of conidiation. Comparative proteome analysis of wild type and disruptants supported this hypothesis, and indicated many changes in the protein profiles of T. atroviride in different interaction conditions with plants and pathogenic hosts.
文摘Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subsequent penetration and killing of the host. Investigations on the underlying events revealed that Trichoderma responds to multiple signals from the host (e.g. lectins or other ligands such as low molecular weight components released from the host’s cell wall) and host attack is accompanied by morphological changes and the secretion of hydrolytic enzymes and antibiotics. Degradation of the cell wall of the host fungus is-besides glucanases and proteases-mainly achieved by chitinases. In vivo studies showed that the ech42 gene (encoding endochitinase 42) is expressed before physical contact of Trichoderma with its host, probably representing one of the earliest events in mycoparasitism, whereas Nag1 (N-acetylglucosaminidase) plays a key role in the general induction of the chitinolytic enzyme system of T. atroviride . Investigations on the responsible signal transduction pathways of T. atroviride led to the isolation of several genes encoding key components of the cAMP and MAP kinase signaling pathways, as alpha and β subunits of heterotrimeric G proteins, the regulatory subunit of cAMP-dependent protein kinase, adenylate cyclase, and three MAP kinases. Analysis of knockout mutants, generated by Agrobacterium-mediated transformation, revealed that at least two alpha-subunits of heterotrimeric G proteins are participating in mycoparasitism-related signal transduction. The Tga1 G alpha subunit was shown to be involved in mycoparasitism-related processes such as chitinase expression and overproduction of toxic secondary metabolites, whereas Tga3 was found to be completely avirulent showing defects in chitinase formation and host recognition.
