The ERAD Pathway Participates in Fungal Growth and Cellulase Secretion in .

is a powerful fungal cell factory for the production of cellulolytic enzymes due to its outstanding protein secretion capacity. Endoplasmic reticulum-associated degradation (ERAD) plays an integral role in protein secretion that responds to secretion pressure and removes misfolded proteins. However, the role of ERAD in fungal growth and endogenous protein secretion, particularly cellulase secretion, remains poorly understood in . Here, we investigated the ability of to grow under different stresses and to secrete cellulases by disrupting three major genes (, and ) involved in the critical parts of the ERAD pathway. Under the ER stress induced by high concentrations of DTT, knockout of , and resulted in severely impaired growth, and the mutants Δ and Δ exhibited high sensitivity to the cell wall-disturbing agents, CFW and CR. In addition, the absence of either or led to the decreased heat tolerance of this fungus. These mutants showed significant differences in the secretion of cellulases compared to the parental strain QM9414. During fermentation, the secretion of endoglucanase in the mutants was essentially consistent with that of the parental strain, while cellobiohydrolase and β-glucosidase were declined. It was further discovered that the transcription levels of the endoglucanase-encoding genes ( and ) and the cellobiohydrolase-encoding gene () were not remarkedly changed. However, the β-glucosidase-encoding gene () was significantly downregulated in the ERAD-deficient mutants, which was presumably due to the activation of a proposed feedback mechanism, repression under secretion stress (RESS). Taken together, our results indicate that a defective ERAD pathway negatively affects fungal growth and cellulase secretion, which provides a novel insight into the cellulase secretion mechanism in .