Regulation of three genes encoding cell-wall-degrading enzymes of Trichoderma aggressivum during interaction with Agaricus bisporus

Members of the genus Trichoderma are very effective competitors of a variety of fungi. Cell-wall-degrading enzymes, including proteinases, glucanases, and chitinases, are commonly secreted as part of the competitive process. Trichoderma aggressivum is the causative agent of green mould disease of the button mushroom, Agaricus bisporus. The structures of 3 T. aggressivum genes, prb1 encoding a proteinase, ech42 encoding an endochitinase, and a beta-glucanase gene, were determined. Promoter elements in the prb1 and ech42 genes suggested that transcription is regulated by carbon and nitrogen levels and by stress. Both genes had mycoparasitism-related elements indicating potential roles for the protein products in competition. The promoter of the beta-glucanase gene contained CreA and AreA binding sites indicative of catabolite regulation but contained no mycoparasitism elements. Transcription of the 3 genes was measured in mixed cultures of T. aggressivum and A. bisporus. Two A. bisporus strains, U1, which is sensitive to green mould disease, and SB65, which shows some resistance, were used in co-cultivation tests to assess possible roles of the genes in disease production and severity. prb1 and ech42 were coordinately upregulated after 5 days, whereas beta-glucanase transcription was upregulated from day 0 with both Agaricus strains. Upregulation was much less pronounced in mixed cultures of T. aggressivum with the resistant strain, SB65, than with the sensitive strain, U1. These observations suggested that the proteins encoded by these genes have roles in both nutrition and in severity of green mould disease.