Tailoring the expression of Xyr1 leads to efficient production of lignocellulolytic enzymes in Trichoderma reesei for improved saccharification of corncob residues.

BACKGROUND: The filamentous fungus Trichoderma reesei is extensively used for the industrial-scale cellulase production. It has been well known that the transcription factor Xyr1 plays an important role in the regulatory network controlling cellulase gene expression. However, the role of Xyr1 in the regulation of cellulase expression has not been comprehensively elucidated, which hinders further improvement of lignocellulolytic enzyme production. RESULTS: Here, the expression dosage of xyr1 was tailored in T. reesei by differentially overexpressing the xyr1 gene under the control of three strong promoters (Pegl2, Pcbh1, and Pcdna1), and the transcript abundance of xyr1 was elevated 5.8-, 12.6-, and 47.2-fold, respectively. We found expression of cellulase genes was significantly increased in the Pegl2-driven xyr1 overexpression strain QE2X, whereas relatively low in the Pcbh1- and Pcdna1-driven overexpression strains. We also found that the Pegl2-driven overexpression of xyr1 caused a more significant opening of chromatin in the core promoter region of the prominent cellulase genes. Furthermore, the cellulase activity showed a 3.2-fold increase in the strain QE2X, while insignificant improvement in the Pcbh1- and Pcdna1-driven strains. Finally, the saccharification efficiency toward acid-pretreated corncob residues containing high-content lignin by the crude enzyme from QE2X was increased by 57.2% compared to that from the parental strain. Moreover, LC-MS/MS and RT-qPCR analysis revealed that expression of accessory proteins (Cip1, Cip2, Swo1, and LPMOs) was greatly improved in QE2X, which partly explained the promoting effect of the Pegl2-driven overexpression on enzymatic hydrolysis of lignocellulose biomass. CONCLUSIONS: Our results underpin that the precise tailoring expression of xyr1 is essential for highly efficient cellulase synthesis, which provide new insights into the role of Xyr1 in regulating cellulase expression in T. reesei. Moreover, these results also provides a prospective strategy for strain improvement to enhance the lignocellulolytic enzyme production for use in biorefinery applications.