PoxCbh, a novel CENPB‐type HTH domain protein, regulates cellulase and xylanase gene expression in Penicillium oxalicum

The essential transcription factor PoxCxrA is required for cellulase and xylanase gene expression in the filamentous fungus Penicillium oxalicum that is potentially applied in biotechnological industry as a result of the existence of the integrated cellulolytic and xylolytic system. However, the regulatory mechanism of cellulase and xylanase gene expression specifically associated with PoxCxrA regulation in fungi is poorly understood. In this study, the novel regulator PoxCbh (POX06865), containing a centromere protein B‐type helix‐turn‐helix domain, was identified through screening for the PoxCxrA regulon under Avicel induction and genetic analysis. The mutant ∆PoxCbh showed significant reduction in cellulase and xylanase production, ranging from 28.4% to 59.8%. Furthermore, PoxCbh was found to directly regulate the expression of important cellulase and xylanase genes, as well as the known regulatory genes PoxNsdD and POX02484, and its expression was directly controlled by PoxCxrA. The PoxCbh‐binding DNA sequence in the promoter region of the cellobiohydrolase 1 gene cbh1 was identified. These results expand our understanding of the diverse roles of centromere protein B‐like protein, the regulatory network of cellulase and xylanase gene expression, and regulatory mechanisms in fungi. This work identified the novel regulator PoxCbh, which controls the expression of major cellulase and xylanase genes, and the known regulatory genes POX02484 and PoxNsdD in P. oxalicum. PoxCbh acts downstream of the key TF PoxCxrA. PoxCbh is a CENPB‐homologous protein.