A truncated form of the Carbon catabolite repressor 1 increases cellulase production in Trichoderma reesei

Abstract

Background: Rut-C30 is a cellulase-hyperproducing Trichoderma reesei strain and, consequently, became the ancestor of most industry strains used in the production of plant cell wall-degrading enzymes, in particular cellulases. Due to three rounds of undirected mutagenesis its genetic background differs from the wild-type QM6a in many ways, of which two are the lack of a 83 kb large sequence in scaffold 15 and the partial lack of the gene encoding the Carbon catabolite repressor 1 (CREI). However, it is still unclear, what exactly enhances cellulase production in Rut-C30. Results: The investigation of the expression of two genes encoding cellulases (cbh1 and cbh2) and the gene encoding their main transactivator (xyr1) revealed that the presence of the truncated form of CREI (CREI-96) contributes more to the Rut-C30 phenotype than a general loss of CREI-mediated carbon catabolite repression (cre1 deletion strain) or the deletion of 29 genes encoded in the scaffold 15 (83 kb deletion strain). We found that the remaining cre1 in Rut-C30 (cre1-96) is transcribed into mRNA, that its putative gene product (Cre1-96) is still able to bind DNA, and that the CREI-binding sites in the upstream regulatory regions of the chosen CREI-target genes are still protected in Rut-C30. As it was previously reported that CREI acts on the nucleosome positioning, we also analyzed chromatin accessibility of the core promoters of CREI-target genes and found them open even on D-glucose in the presence of CREI-96.

Trichoderma reesei XYR1 recruits SWI/SNF to facilitate cellulase gene expression

“…Although several transcriptional factors have been identified to be involved in regulating the expression of cellulase genes, only limited data are available on the role of chromatin in regulating transcription from cellulase gene promoters in T. reesei. Nonetheless, nucleosome repositioning or loss of nucleosomes upon cellulose induction has been shown to occur on cbh1 and cbh2 promoters (Zeilinger et al, 1998;Zeilinger et al, 2003;Mello-de-Sousa et al, 2014). Moreover, changes in the chromatin status of the regulatory regions of cellulase genes have been demonstrated both in context to the applied conditions (repressing/inducing) and to the presence of XYR1 (Mello- de-Sousa et al, 2015).…”

“…Chromatin status changes have been recently shown to occur in T. reesei for cellulase genes in context to the applied conditions (repressing/inducing), which are probably mediated by specific transcription factors including XYR1 and the catabolite repressor CRE1 (Portnoy et al, 2011;Mello-de-Sousa et al, 2014;Mello-de-Sousa et al, 2015). Whereas changes in nucleosome positioning flanking a CAE (cbh2 activating element) region of the cbh2 promoter have been observed in response to applied conditions (Zeilinger et al, 1998), chromatin opening was found to occur in two prominent cellulase-encoding genes, cbh1 and cbh2, during cellulase induction compared to repression (Mello-de-Sousa et al, 2015).…”

The DNA‐methyltransferase inhibitor 5‐aza‐2‐deoxycytidine affects Humicola grisea enzyme activities and the glucose‐mediated gene repression

“…reesei strain, in which the cre 1 CCR gene is truncated. Mello‐de Sousa et al have demonstrated that the remaining cre 1 gene ( cre 1‐96) is transcribed and that the corresponding gene product still binds to DNA; the authors presented evidences suggesting that this truncated protein is related to chromatin opening and consequently increased expression of the cbh 1 and cbh 2 cellulase genes, as well as of the xyr 1 transactivator gene. In a following study , it was shown that, in T .…”

“…Relevant information has arisen from studies on the Rut-C30 cellulase-hyperproducing T. reesei strain, in which the cre1 CCR gene is truncated. Mello-de Sousa et al [48] have demonstrated that the remaining cre1 gene (cre1-96) is transcribed and that the corresponding gene product still binds to DNA; the authors presented evidences suggesting that this truncated protein is related to chromatin opening and consequently increased expression of the cbh1 and cbh2 cellulase genes, as well as of the xyr1 transactivator gene. In a following study [19], it was shown that, in T. reesei, Xyr1 (the main transactivator of cellulase and xylanase expression) is related to an open chromatin status associated with the Dsophorose-induced cbh1, cbh2, xyn1, and xyn2 genes expression.…”

Precision engineering of the transcription factor Cre1 in Hypocrea jecorina (Trichoderma reesei) for efficient cellulase production in the presence of glucose

“…Notably, the presence of monosaccharides, like D-glucose, during cellulolytic enzyme production triggers CCR, which is regulated mainly by the cellulase transcriptional repressor Cre1 and activators Xyr1, Clr1, Clr2, etc., and significantly downregulates the transcription of cellulolytic enzymes in T. reesei (Wang et al, 2019). Endogenous Cre1, which belongs to the group of C2H2-type zinc finger proteins, binds to the promoters of target genes, such as cel7a, and inhibits the transcription of encoded cellulase genes (Mello-de-Sousa et al, 2014).…”