ROLE OF 4 MAJOR CELLULASES IN TRIGGERING OF CELLULASE GENE-EXPRESSIONBY CELLULOSE IN TRICHODERMA-REESEI

The relative contributions of four major cellulases of Trichoderma ree sei (1,4-beta-D-glucan cellobiohydrolase I [CEH I], CBH II, endo-1,4-b eta-D-glucanase I [EG I], and EG II) to the generation of the cellulas e inducer from cellulose were studied with isogenic strains in which t he corresponding genes (cbh1, cbh2, egl1, and egl2) had been deleted b y insertion of the Aspergillus nidulans aindS marker gene. During grow th on lactose (a soluble carbon source provoking cellulase gene expres sion), these strains showed no significant alterations in their abilit y to express the respective other cellulase genes, with the exception of: the strain containing Delta cbh1, which exhibited an increased ste ady-state level of cbk2 mRNA. On crystalline cellulose as the only car bon source, however, significant differences were apparent: strains in which cbh2 and egl2, respectively, had been deleted showed no express ion of the other cellulase genes, whereas strains carrying the cbh1 or egl1 deletion showed these transcripts. The Delta cbh1-containing str ain also showed enhanced cbh2 mRNA levels under these conditions. A st rain in which both cbh1 and cbh2 had been deleted, however, was unable to initiate growth on cellulose. Addition of 2 mM sophorose, a putati ve inducer of cellulase gene expression, to such cultures induced the transcription of egl1 and egl2 and restored the ability to grow on cel lulose. We conclude that CBH ii and EG II are of major importance for the efficient formation of the inducer from cellulose in T. reesei and that removal of both cellobiohydrolases renders T. reesei unable to a ttack crystalline cellulose.