Single Mutation in Transcriptional Activator Xyr1 Enhances Cellulase and Xylanase Production in Trichoderma reesei on Glucose

To achieve cost-effective production of lignocellulolytic enzymes for biorefinery processes, engineering transcription factors represents a powerful strategy to boost cellulase and xylanase in Trichoderma reesei. In this study, a novel mutation (R434L) in xylanase regulator 1 (Xyr1) was identified based on the yeast one-hybrid screening system. The point mutation was located in the middle homology region of Xyr1 with unclear functions, indicating a significant role for this domain in tuning Xyr1 transactivation. When constitutively expressed in T. reesei Δxyr1 (OEX_R434L), Xyr1_R434L led to highly improved production of both cellulases and xylanases on glucose compared with a strain similarly expressing Xyr1 (OEX). The respective 0.8- and 0.7-fold increases in extracellular pNPCase and xylanolytic activity were further verified to result from the greatly elevated transcription of major cellulase and xylanase genes in OEX_R434L. Moreover, the saccharification efficiency of corn stover with OEX_R434L enzyme cocktails was enhanced by 21% compared with that of OEX.