ACEI is a repressor of cellulase and xylanase genes in Trichoderma reesei

T. reesei is an efficient producer of cellulolytic and xylanolytic enzymes. In general, cellulose and its derivatives and different xylans induce cellulase and xylanase expression while glucose represses cellulase and xylanase genes. The production of these enzymes is regulated at the transcriptional level at least by the glucose repressor CREI and the activator ACEII. We have isolated a third factor, ACEI, that binds to and activates the main cellulase promoter cbh1in vivo in yeast. ACEI is a Cys2-His2 type of a transcription factor that binds in vitro to eight sites scattered along the cbh1 promoter containing the core 5'AGGCA sequence. Although originally isolated as a protein capable of activating thecbh1 promoter of T. reesei in S. cerevisiae, further studies oface1 deletion strain indicated that ACEI is a repressor of cellulase and xylanase genes. The deletion of the ace1 gene led up to 10 times higher expression of cellulase genes, cbh1, cbh2, egl1, and egl2 after the transfer of glycerol grown mycelia to cellulose media or when the cellulase genes were induced by the addition of a disaccharide sophorose into glycerol media. Similarly, the expression of xyn1 and xyn2 was increased by ace1 deletion. Deletion of the ace2 gene, encoding the ACEII activator, in a strain deleted for ace1 did not affect the high level of cellulase expression seen in the ace1 deletion strain indicating, that there is at least one additional cellulase and xylanase activator present in T. reesei.