Interaction of ammonium, glucose, and chitin regulates the expression of cell wall-degrading enzymes in Trichoderma atroviride strain P1

Chitinolytic and glucanolytic fungal cell wall-degrading enzymes have been suggested to be primary determinants of biocontrol by Trichoderma spp. We e xamined the effects of ammonium, glucose, chitin, and chito-oligomers on tr anscription of specific genes and secretion of fungal cell wall-degrading e nzymes. The genes ech42, nag1, and gluc78 were examined, as were the enzyme s they encode (endochitinase CHIT42, N-acetylhexosaminidase CHIT73, and glu can exo-1,3-beta -glucanase GLUC78, respectively). gluc78 could be induced by nitrogen starvation alone, while both ech42 and nag] required nitrogen s tarvation and the presence of chitin for induction. Starvation for both amm onium and glucose resulted in very early expression and secretion of all ce ll wall-degrading enzymes examined. In the presence of low levels of ammoni um (10 mM), both chito-oligomers and chitin triggered CHIT42 and CHIT40 (ch itobiosidase) production. CHIT73 secretion occurred in the presence of N-ac etylglucosamine and chito-oligomers, while chitin was less effective. The p resence of different chito-oligomers resulted in secretion of specific N-ac etylhexosaminidases, of which CHIT73 is one. Our results indicate that the expression and secretion of cell wall-degrading enzymes is nitrogen repress ed, that effects of carbon and nitrogen nutrition are interactive, and that especially for chitinolytic enzymes, the inductive effect of chitin is alt ered by the level of ammonium or glucose in the medium.