Regulatory function of the novel transcription factor CxrC in Penicillium oxalicum

Numerous transcription factors (TFs) in ascomycete fungi play crucial roles in cellular processes; however, how most of them function is poorly understood. Here, we identified and characterized a novel TF, CxrC (POX01387), acting downstream of the key TF CxrA, which is essential for plant‐biomass‐degrading‐enzyme (PBDE) production in Penicillium oxalicum. Deletion of cxrC in P. oxalicum significantly affected the production of PBDEs, as well as mycelial growth and conidiospore production. CxrA directly repressed the expression of cxrC after about 12 hr following switch to Avicel culture. CxrC bound the promoters of major PBDE genes and genes involved in conidiospore development. CxrC was found to bind the TSSGTYR core sequence (S: C and G; Y: T and C; R: G and A) of the important cellulase genes cbh1 and eg1. Both N‐ and C‐terminal peptides of CxrC and the CxrC phosphorylation were found to mediate its homodimerization. The conserved motif LPSVRSLLTP (65–74) in CxrC was found to be required for regulating cellulase production. This study reveals novel mechanisms of TF‐mediated regulation of the expression of PBDE genes and genes involved in cellular processes in an ascomycete fungus. This work identified the novel regulator CxrC, which mainly represses the expression of major cellulase and xylanase genes, and the known regulatory genes such as cxrB, creA, and nsdD in Penicillium oxalicum. CxrC acts downstream of the key TF CxrA. CxrC is a Zn2Cys6 zinc finger protein that forms homodimers and is modified by phosphorylation.