Trichoderma reesei ACE4, a Novel Transcriptional Activator Involved in the Regulation of Cellulase Genes during Growth on Cellulose

Abstract

The filamentous fungus Trichoderma reesei is a model strain for cellulase production. Cellulase gene expression in T. reesei is controlled by multiple transcription factors. Here, we identified by comparative genomic screening a novel transcriptional activator ACE4 ( A ctivator of c ellulase e xpression 4) that positively regulates cellulase gene expression on cellulose in T. reesei . Disruption of the ace4 gene significantly decreased expression of four main cellulase genes, and the essential cellulase transcription factor encoding gene ace3 . Overexpression of ace4 increased cellulase production by approximately 22% compared to that in the parental strain. Further investigations using electrophoretic mobility shift assays, DNase I footprinting assays, and chromatin immunoprecipitation assays indicated that ACE4 directly binds to the promoter of cellulase genes by recognizing the two adjacent 5′-GGCC-3′ sequences. Additionally, ACE4 directly binds to the promoter of ace3 and, in turn, regulates the expression of ACE3 to facilitate cellulase production. Collectively, these results demonstrate an important role for ACE4 in regulating cellulase gene expression, which will contribute to understanding the mechanism underlying cellulase expression in T. reesei . IMPORTANCE T. reesei is commonly utilized in industry to produce cellulases, enzymes that degrade lignocellulosic biomass for the production of bioethanol and bio-based products. T. reesei is capable of rapidly initiating the biosynthesis of cellulases in the presence of cellulose, which has made it useful as a model fungus for studying gene expression in eukaryotes. Cellulase gene expression is controlled through multiple transcription factors at the transcriptional level. However, the molecular mechanisms by which transcription is controlled remain unclear. In the present study, we identified a novel transcription factor, ACE4, which regulates cellulase expression on cellulose by binding to the promoters of cellulase genes and the cellulase activator ace3 . Our study not only expands the general functional understanding of the novel transcription factor ACE4 but also provides evidence for the regulatory mechanism mediating gene expression in T. reesei .

Inducer-free cellulase production system based on the constitutive expression of mutated XYR1 and ACE3 in the industrial fungus Trichoderma reesei

“…2 ), suggesting that it is necessary to enhance the expression of ACE3 beyond the upregulation by mutated XYR1 V821F . It was previously reported that ACE4 directly binds to the ace3 promoter and regulates ACE3 expression to promote cellulase production 56 . Possibly ACE3 is regulated not only by XYR1 but also by other factors, including ACE4, which suggests that enhanced expression of ACE3 by factors other than XYR1 may be the key to the cellulase expression.…”

Development of an auto-inducible expression system by nitrogen sources switching based on the nitrogen catabolite repression regulation

“…Compared with other filamentous fungi, A. nidulans is rarely used in the scaled-up production of industrial enzymes because of their low expression capacity. Trichoderma reesei is the main strain for cellulase production because of its excellent secretory ability [ 43 , 44 ]. However, the fermentation process of T. reesei usually takes up to a week.…”

Transcription factor FfMYB15 regulates the expression of cellulase gene FfCEL6B during mycelial growth of Flammulina filiformis

“…In previous studies, cellulase genes were regulated by different transcription factors. For example, in T. reesei , Xyr1 and ACEI can regulate the expression of the cellulase cbh1 gene, and ACE4 can regulate the expression of the cellulase gene by binding to the promoter of cellulase gene [ 52 , 53 ]. In this study, we also found that FfMYB15 could regulate the expression of cellulase gene, which indicated that MYB can also participate in the cellulose degradation mechanism, however, the mechanism of cellulose degradation has not been thoroughly studied.…”