Genomic identification and coordinated analysis of transcription factors regulating cellulolytic genes in Penicillium oxalicum

Cellulolytic fungi have evolved sophisticated systems for adaptation to their natural habitat. The transcriptional-regulatory network that governs expression of cellulolytic genes remains poorly understood. A single-gene disruptant mutant library for 470 transcriptional regulators was constructed in Penicillium oxalicum. Twelve transcription factors that play a pivotal role in the activation or repression of cellulase synthesis were identified, most of which are not characterized in P. oxalicum and any other fungi before. Of these transcription factors, CreA and a new Zn(II)₂Cys₆-type regulator play opposing roles in cellulolytic gene expression. Overexpression of the Zn(II)₂Cys₆-type transcriptional activator is sufficient to increase cellulase activity while its deletion abrogates cellulase gene expression and reduces cellulolytic activity on crystalline cellulose (Avicel). Surprisingly, we also discovered that the absence of both CreA and the Zn(II)₂Cys₆-type transcriptional activator resulted in obvious increase in cellulolytic activity compared with the wild-type strain on Avicel. Finally, we found strong evidence that additive effect on cellulose degradation by several transcription factors combinatorial regulation were observed in mutation and overexpression experiments during Avicel induction. These data refined our understanding of transcriptional-regulatory network as a “seesaw model”, in which coordinated regulation of cellulolytic genes is established using activators and repressors counteracting under inducing condition.