Deciphering the regulatory role of SREBP pathway in protein secretion in Neurospora crassa

In nature, Filamentous fungi have developed a highly efficient ability to secrete enzymes to degrade the plant cell wall, with this property it has been subsequently applied in industry for lignocellulase production. Most currently used industrial strains with outstanding yield, such as Trichodema reesei and Aspergillus spp. were generated by random mutagenesis. However, for further rationally performing strain engineering, a clear genetic mechanism to understand the requirements for efficient protein secretion need to be elucidated. In this study, we used the model laboratory lignocellulolytic filamentous fungus Neurospora crassa to study the underlying mechanism associated with lignocellulases secretion. Firstly, we systematically screened the gene knockout mutant which contains gene potentially associated with protein secretion based on the secreted protein level and lignocellulases activity. From the 586 deletion mutants screened in N. crassa, we observed that strains carrying the deletion of tul-1 (NCU07340) and dsc-2 (NCU03459), which are possible orthologs of dsc1 and dsc2 in Schizosaccharomyces pombe, showed significantly increased levels of secreted protein and cellulolytic enzyme activity (endoglucanase and xylanase) when cultured on Avicel as compared to the wild-type parental strain. Since the DSC complex in S. pombe and Aspergillus fumigatus is involved in the activation of SREBP pathway, we further investigated the effect of SREBP pathway on the protein secretion and the involved mechanism using transcriptomic analysis combined with genetic screens. The discoveries of this work will contribute to the strain engineering to improve the lignocellulase and biomass-based chemical production.