Transcriptomic profiling and genetic analyses reveal novel key regulators of cellulase and xylanase gene expression in .

BACKGROUND

The transition to a more environmentally friendly economy has prompted studies of modern biorefineries, including the utilization of low-value lignocellulose. The major challenge facing the widespread application of biorefineries is the high cost of enzymes that can efficiently hydrolyze recalcitrant cellulose to sugars. produces large amounts of plant-cell-wall-degrading enzymes, but their production is tightly controlled by complex regulatory networks, resulting in low yields of the native enzymes. Regulatory genes have been the targets of genetic engineering to improve enzyme production in microorganisms. In this study, we used transcriptomic profiling and genetic analyses to screen for and identify novel key regulators of cellulase and xylanase gene expression in .

RESULTS

A comparative analysis of the transcriptomes of . HP7-1 on different carbon sources, including glucose, wheat bran, and wheat bran plus Avicel, identified 40 candidate genes regulating the expression of cellulolytic enzyme genes. Deletion mutants of 31 candidate genes were constructed in . ∆ and 11 resultant mutants showed significant changes in their filter-paper cellulase production compared with the parental strain ∆. Among these 11 mutants, Δ, Δ, and Δ showed the most significant reduction in the enzyme production (96.8, 75.9, and 58.5%, respectively). Ten of these 11 genes are here reported to be involved in cellulase production for the first time. Further tests revealed that Δ, Δ, and Δ displayed significantly reduced xylanase production, whereas Δ produced negligible xylanase. Interestingly, Δ and Δ showed significantly increased β-glucosidase production. Real-time quantitative reverse transcription-PCR and an electrophoretic mobility shift assay (EMSA) showed that , , and regulate the expression of one another, but the mode of regulation changes dynamically during the growth of fungal cells in the presence of cellulose. EMSA showed that PoxCxrA, PoxCxrB, and PoxNsdD directly bind the putative promoters of major cellulase and xylanase genes.

CONCLUSIONS

We have detected and identified three key new regulatory genes, , , and , that directly and indirectly regulate the expression of cellulase and xylanase genes in . . This study provides novel insights into the regulatory mechanisms of fungal cellulase and xylanase gene expression.