A GTPase activating protein Polrg1 regulates the development and cellulase expression of Penicillium oxalicum

Penicillium oxalicum, a filamentous fungus renowned for its robust cellulase production, regulates the inducible expression of cellulases through complex signaling pathways, with signal transduction playing a pivotal role in effective cellulase induction and expression. In this study, we identified the signaling protein Polrg1 within the Ras signaling pathway of P. oxalicum. Knockout of the Polrg1 gene led to a significant decrease in cellulase activity. The global cellulase, endoglucanase, cellobiohydrolase and β-glucosidase activities of the ΔPolrg1 mutant strain were 48%, 60%, 73% and 60% of those of the wild-type strain, respectively. Moreover, the transcription levels of cellulase genes cbh1, eg1 and bgl1 and positive regulators of cellulase transcription ClrB and XlnR were decreased. Furthermore, the deletion of Polrg1 profoundly impacted fungal growth and development. The ΔPolrg1 mutant exhibited a dramatic decline in conidiation capacity, with expression levels of the transcription factors FlbC and StuA, which are essential for conidial formation reduced by 52% and 69%, respectively. These results demonstrate that Polrg1 is essential for regulating cellulase expression, hyphal growth, development, and conidium formation in P. oxalicum. The findings of this study contribute to elucidating the mechanisms by which the Ras signaling pathway governs cellulase expression and developmental processes in filamentous fungi.