Trichoderma viride

Abstract: Chitinase and β-1,3-glucanase purified from pea pods acted synergistically in the degradation of fungal cell walls. The antifungal potential of the two enzymes was studied directly by adding protein preparations to paper discs placed on agar plates containing germinated fungal spores. Protein extracts from pea pods infected with Fusarium solani f.sp. phaseoli, which contained high activities of chitinase and β-1,3-glucanase, inhibited growth of 15 out of 18 fungi tested. Protein extracts from uninfected pea pods, which contained low activities of chitinase and β-1,3-glucanase, did not inhibit fungal growth. Purified chitinase and β-1,3-glucanase, tested individually, did not inhibit growth of most of the test fungi. Only Trichoderma viride was inhibited by chitinase alone, and only Fusarium solani f.sp. pisi was inhibited by β-1,3-glucanase alone. However, combinations of purified chitinase and β-1,3-glucanase inhibited all fungi tested as effectively as crude protein extracts containing the same enzyme activities. The pea pathogen, Fusarium solani f.sp. pisi, and the nonpathogen of peas, Fusarium solani f.sp. phaseoli, were similarly strongly inhibited by chitinase and β-1,3-glucanase, indicating that the differential pathogenicity of the two fungi is not due to differential sensitivity to the pea enzymes. Inhibition of fungal growth was caused by the lysis of the hyphal tips.

Abstract: The antimicrobial arsenal of plants is thought to consist mainly of secondary metabolites, among which the phytoalexins are the best-studied1–3. But plants may also possess antimicrobial proteins4,5: it has been reported that wheat-germ agglutinin, a chitin-binding lectin from wheat embryos, inhibits growth of the fungus Trichoderma viride4. This has led to the notion that plant lectins, with their intriguing biochemical similarity to animal antibodies, have an antibody-like antimicrobial function4,6,7. We report here that the main proteinaceous inhibitor of fungal growth in bean leaves is chitinase, an enzyme that can be induced by the plant hormone ethylene, or by pathogen attack. Among commercial preparations of purified chitin-binding lectins (from wheat germ, tomato, potato, pokeweed and gorse), only those containing contaminating chitinase activity inhibit fungal growth. Our data indicate that plant chitinases, but not chitin-binding lectins, are important antifungal proteins in plants.

Abstract: Cellulase is an adaptive enzyme in most fungi (Reese and Levinson, 1952), although it is constitutive in cellulolytic bacteria (Hammerstrom et al., 1955). Many polysaccharases are adaptive in fungi, including: pentosanase (Simpson, 1954), polygalacturonase (Phaff, 1947), chitinase (Reynolds, 1954), dextranase (Hultin and Nordstr6m, 1949), and xylanase and mannanase (S0rensen, 1952). Since many of these substrates are insoluble, the question arises as to how an insoluble substrate can induce the formation of an extracellular enzyme. Products of polysaceharide hydrolysis can often induce their respective polysaccharases: galacturonic acid for polygalacturonase in Penicilliurn chrysogenum (Phaff, 1947); xylose for pentosanase in several molds (Simpson, 1954); maltose for amylase in Aspergillus niger (Tanabe and Tonomura, 1953); N-acetylglucosamine for chitinase in Aspergillus fumigatus and Myrothecium verrucaria (Reese, unpublished data). The use of the product as an inducer often leads to lower enzyme yields than are obtained with the substrate. In most cellulolytic fungi tested, however, neither glucose nor cellobiose acted as inducers of cellulase (Reese and Levinson, 1952). Further studies relating to this problem showed that, under certain conditions, some sugars can induce cellulase formation in Trichoderma viride. The present study is a reinvestigation of the induction of cellulase. For comparative purposes, some data on amylase production are also included.

Abstract: Resistance against the leaf mold fungus Cladosporium fulvum is mediated by the tomato Cf proteins which belong to the class of receptor-like proteins and indirectly recognize extracellular avirulence proteins (Avrs) of the fungus. Apart from triggering disease resistance, Avrs are believed to play a role in pathogenicity or virulence of C. fulvum. Here, we report on the avirulence protein Avr4, which is a chitin-binding lectin containing an invertebrate chitin-binding domain (CBM14). This domain is found in many eukaryotes, but has not yet been described in fungal or plant genomes. We found that interaction of Avr4 with chitin is specific, because it does not interact with other cell wall polysaccharides. Avr4 binds to chitin oligomers with a minimal length of three N-acetyl glucosamine residues. In vitro, Avr4 protects chitin against hydrolysis by plant chitinases. Avr4 also binds to chitin in cell walls of the fungi Trichoderma viride and Fusarium solani f. sp. phaseoli and protects these fungi against normally deleterious concentrations of plant chitinases. In situ fluorescence studies showed that Avr4 also binds to cell walls of C. fulvum during infection of tomato, where it most likely protects the fungus against tomato chitinases, suggesting that Avr4 is a counter-defensive virulence factor.