A new Zn(II)(2)Cys(6)-type transcription factor BglR regulates β-glucosidase expression in Trichoderma reesei

BglR (PI: 52368, beta-glucosidaseregulator) was identified as a new transcription factor that up-regulates expression of specific genes encoding β-glucosidases. Based on a comparative genomic analysis to verify SNPs between Trichoderma reesei mutant PC-3-7 and its parent KDG-12, 19 were confirmed. One of the SNPs was found to cause a missense mutation close to the end of the DNA-binding region of BglR that turned out to be a Zn(II)(2)Cys(6)-type fungal-specific transcription factor. BglR was found to share little homologous to amyR of Aspergillus oryzae that is commonly considered a key regulator of starch degradation. A mutant lacking the bglr gene as well as the PC-3-7 mutant exhibited elevated cellulase production during growth on cellobiose. Reversion of the SNP missence mutation within bglr to the wild-type allele resulted in reduced cellulase production. Expression of specific β-glucosidase genes in a bglr gene disruptant was repressed with the mutant exhibiting little ability to hydrolyze cellobiose during early log phase even when induced. Thus, one of the functions of BglR is to up-regulate specific β-glucosidase genes (with the exception of bgl1, which is seemingly under the direct control of Xyr1). The glucose produced then triggers carbon catabolite repression in cellobiose culture.