Disruption of SREBP pathway results in hyper-secretion of cellulases in Filamentous fungi

Filamentous fungi are the main source of enzymes used to degrade lignocellulose to fermentable sugars for the production of biofuels. To further improve the the production of ligonocellulases by rationally genetic engineering,  a model laboratory organism Neurospora crassa was used to search for uncharacterized factors associated with the regulation of plant cell wall deconstruction and utilization. A set of 586 single gene deletion strains were screened by measurement of secreted protein and cellulase activity. 8 hyper-secretion and 18 hypo-secretion strains in which the mutant genes are involved in transcription, protein synthesis and intracellular trafficking were identified. Two of the identified mutants implicated the loss of the SREBP pathway and showed a hyper-secreted phenotype.  To establish the connection between SREBP pathway and hyper-secretion phenotype, the secreted protein level of strains carrying deletions in additional components of SREBP pathway were also evaluated and the results showed these mutants demonstrated a similar hyper-secretion phenotype, suggesting that the disruption of SREBP pathway could improve cellulases production in N.crassa. To determine whether this new discovery observed in model strain N. crassa was conserved among other lignocellulolytic  filamentous fungi, The cellulases production levels of  Trichoderma reesei strains carrying the deletion of genes associated SREBP pathway were evaluated. As expectedly, T. reesei mutants with defect of SREBP pathway demonstrated hyper-secretion phenotype, indicating that this function is highly conserved among fungi capable of degrading plant biomass.