Transcription Factors ClrB and XlnR and Their Effect on the Transcription of Cellulase Genes in the Filamentous Fungus Penicillium verruculosum

The filamentous fungus <i>Penicillium verruculosum</i> (anamorph <i>Talaromyces verruculosus</i>) has been shown to be an efficient producer of secreted cellulases, used in biorefinery processes. Understanding the mechanisms of regulation of cellulase gene expression in the fungus <i>P. verruculosum</i> is a current task in industrial biotechnology, since it allows for targeted changes in the composition of the complex secreted by the fungus. Expression of cellulase genes in fungi is regulated mainly at the level of transcription via pathway-specific transcription factors (TF), the majority of which belong to the Zn(II)2Cys6 family of zinc binuclear cluster proteins. Transcriptional regulation of cellulase genes may have a species-specific pattern and involves several transcription factors. In this study, we used a qPCR method and transcriptome analysis to investigate the effect of knockouts and constitutive expression of genes encoding homologues of the regulatory factors XlnR and ClrB from <i>P. verruculosum</i> on the transcription of <i>cbh1</i>, <i>egl2</i>, and <i>bgl1</i> genes, encoding three key cellulases, cellobiohydrolase, endoglucanase, and β-glucosidase, in the presence of various inducers. We have shown that the transcription factor XlnR of the filamentous fungus <i>P. verruculosum</i> is strictly responsible for the transcription of the main cellulolytic genes (<i>cbh1</i>, <i>egl2</i>, and <i>bgl1</i>) in the presence of xylose and xylobiose, but not in the presence of cellobiose. ClrB/Clr-2, a homologue from <i>P. verruculosum</i>, does not represent the main transcription factor regulating transcription of cellulolytic genes in the presence of selected inducers, unlike in the cases of <i>Aspergillus nidulans</i>, <i>Aspergillus niger</i>, and <i>Penicillium oxalicum;</i> apparently, it has a different function in fungi from the genus <i>Talaromyces</i>. We have also shown that constitutive expression of the transcription factor XlnR resulted in 3.5- and 2-fold increases in the activity of xylanase and β-glucosidase in a B1-XlnR enzyme preparation, respectively. In a practical sense, the obtained result can be used for the production of enzyme preparations based on the <i>P. verruculosum</i> B1-XlnR strain used for the bioconversion of renewable cellulose-containing raw materials into technical sugars.