Tracking the cellulose to cellulase signalling cascade in Hypocrea jecorina

Species of the fungal genus Trichoderma are saprophytes, and their respective teleomorphs lignicolous and necrotrophic ascomycetes of the genus Hypocrea. It is believed that evolution drove these fungi from mere parasitism on wood-degrading basidiomycetes to adaptation to the partially destroyed wood (Rossman 1996). Hence, in nature they encounter a wide variety of polysaccharides among which cellulose makes up about a significant part of the total amount. Trichoderma spp. also play a significant role in cellulose degradation in soil. Hypocrea jecorina (the pantropical teleomorph of the imperfect fungus Trichoderma reesei), is probably the most prominent cellulose degrader within the genus Trichoderma. Originally isolated in the South Pacific (Solomon Islands) during the second world-war, where it was observed to degrade cotton fabric, tents and belts, it was first recognized as a potential industrial producer of cellulases in the late sixties. It uses at least three different types of enzymes for cellulose degradation, i.e. exoglucanases (i.e. cellobiohydrolases EC 3.2.1.91), endoglucanases (EC 3.2.1.4) and ß-glucosidase (EC 3.2.1.21), which occur in various isozymic forms . The industrial potential of this enzyme mixture led to a detailed investigation of the biochemical properties, three-dimensional protein structures and mechanism of action of several of these proteins. Apart from studies on the enzymology of cellulose degradation, there has also been a continuing interest in understanding how the synthesis of these enzymes is regulated. Such knowledge is warranted to understand the physiology of the organism, to provide strategies for improving enzyme production through nutritional or recombinant means, and for using cellulase promoters for the overproduction of heterologous proteins in Trichoderma. In the present project application, we will study the mechanism by which the insoluble molecule cellulose signals its presence to the fungus. Preliminary evidence in our lab indicates the involvement of a G-protein/cyclic-AMP- dependent pathway, that shall be investigated in detail. Furthermore a PAS-domain protein and a CAAX-domain containing protein have been shown to influence cellulase gene transcription. Therefore the respective genes shall be characterized and the relative order of involvement of the various components and localization of key proteins within the fungal cell will be determined. A knowledge of this signalling cascade will not only help to improve the biotechnological exploitation of this fungus but also aid to the development of agents against wood rotting and plant pathogenic fungi.

Species of the fungal genus Trichoderma are saprophytes, and their respective teleomorphs lignicolous and necrotrophic ascomycetes of the genus Hypocrea. It is believed that evolution drove these fungi from mere parasitism on wood-degrading basidiomycetes to adaptation to the partially destroyed wood (Rossman 1996). Hence, in nature they encounter a wide variety of polysaccharides among which cellulose makes up about a significant part of the total amount. Trichoderma spp. also play a significant role in cellulose degradation in soil. Hypocrea jecorina (the pantropical teleomorph of the imperfect fungus Trichoderma reesei), is probably the most prominent cellulose degrader within the genus Trichoderma. Originally isolated in the South Pacific (Solomon Islands) during the second world-war, where it was observed to degrade cotton fabric, tents and belts, it was first recognized as a potential industrial producer of cellulases in the late sixties. It uses at least three different types of enzymes for cellulose degradation, i.e. exoglucanases (i.e. cellobiohydrolases EC 3.2.1.91), endoglucanases (EC 3.2.1.4) and ß-glucosidase (EC 3.2.1.21), which occur in various isozymic forms . The industrial potential of this enzyme mixture led to a detailed investigation of the biochemical properties, three-dimensional protein structures and mechanism of action of several of these proteins. Apart from studies on the enzymology of cellulose degradation, there has also been a continuing interest in understanding how the synthesis of these enzymes is regulated. Such knowledge is warranted to understand the physiology of the organism, to provide strategies for improving enzyme production through nutritional or recombinant means, and for using cellulase promoters for the overproduction of heterologous proteins in Trichoderma. In the present project application, we will study the mechanism by which the insoluble molecule cellulose signals its presence to the fungus. Preliminary evidence in our lab indicates the involvement of a G-protein/cyclic-AMP- dependent pathway, that shall be investigated in detail. Furthermore a PAS-domain protein and a CAAX-domain containing protein have been shown to influence cellulase gene transcription. Therefore the respective genes shall be characterized and the relative order of involvement of the various components and localization of key proteins within the fungal cell will be determined. A knowledge of this signalling cascade will not only help to improve the biotechnological exploitation of this fungus but also aid to the development of agents against wood rotting and plant pathogenic fungi.