The transcription factor MtHAC-1 plays a dual role in regulating the production of cellulase and xylanase in Myceliophthora thermophila
Background: Filamentous fungi produce large quantities of extracellular enzymes, such as cellulase and xylanase, to degrade polysaccharides derived from plant biomass. This process is controlled by a complex network of transcription factors (TFs). However, the regulatory mechanisms of cellulase and xylanase gene expression are poorly understood. Results: In this study, we reveal that the bZIP transcription factor Mthac-1 exerts dual regulatory effects on the production of cellulase and xylanase in the filamentous fungus Myceliophthora thermophila. The absence of Mthac-1 caused a reduction in cellulase and xylanase activities, as well as decreased protein secretion during the early phase of cultivation in Avicel medium, compared with the wild-type (WT) strain. However, in the middle and late stages, enzyme activities and protein secretion were noticeably enhanced by the deletion of Mthac-1. Additionally, the loss of Mthac-1 led to severe growth defects on sloid media containing various carbon sources, characterized by few hyphae branching and reduced conidiation. Real-time quantitative reverse transcription PCR (RT-qPCR) analysis showed that Mthac-1 dynamically regulates the expression of major cellulase genes. Furthermore, electrophoretic mobility shift assays (EMSAs) demonstrated that Mthac-1 directly binds to the promoter regions of the ß-glucosidase gene bgl1 (MYCTH_66804), cellobiohydrolase gene cbh1 (MYCTH_109566), endoglucanase gene egl2 (MYCTH_86753), xylanase gene xyn1 (MYCTH_112050), and the crucial regulatory gene xyr1 (MYCTH_2310145), exhibiting higher binding affinity for xyn1 and xyr1. Notably, comparative transcriptomic analysis indicated that Mthac-1 also plays an important role in the expression of 26S proteasome-encoding genes under cellulolytic conditions. Conclusions: Mthac-1 functions as a dual regulator of cellulase and xylanase production by regulating the expression of major cellulase and xylanase genes, as well as the key transactivator gene Mtxyr1, via direct promoter binding. Our work provides new insights into the regulatory mechanisms underlying cellulase and xylanase gene expression and has potential applications in fungal strain engineering in biorefinery industries. Overall design: The transcription factor MtHac-1 regulates cellulase and xylanase production in M. thermophila. To comprehensively clarify the regulation of MtHac-1, we conducted transcriptional profiling analysis of the WT and ?Mthac-1 strains cultured on Avicel for 48 h after transferring from glucose.