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

Abstract

BackgroundRut-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.ResultsThe 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.ConclusionsThe lack of the full version of CREI in Rut-C30 corresponds with a partial release from carbon catabolite repression but is not completely explained by the lack of CREI. In contrast, the truncated CREI-96 of Rut-C30 exerts a positive regulatory influence on the expression of target genes. Mechanistically this might be explained at least partially by a CREI-96-mediated opening of chromatin.

Engineering of Trichoderma reesei for enhanced degradation of lignocellulosic biomass by truncation of the cellulase activator ACE3

“…In T. reesei Rut-C30, three mutations have been well studied: one is a truncation in the cre1 gene, which renders this strain carbon catabolite depressed [23]; another mutation leads to a frameshift mutation in the glycoprotein processing β-glucosidase II encoding gene [27]; the last mutation lacks a 83-kb (29 gene-encoding in the scaffold 15) region [28]. Interestingly, Rut-C30 and PC-3-7 strains, which originate from two mutation branches, possess the mutated CRE1 [6,22].…”

“…It is suggested that the mutation in CRE1 is common in such high cellulasesecreting mutants and corresponds with a partial release from carbon catabolite repression. Mello-de-Sousa et al [23] indicated that the truncated CRE1 contributes more to the Rut-C30 phenotype than the deletion of 29 genes encoded in the scaffold 15. But lack of the full version of CRE1 in Rut-C30 does not completely explain its hyperproduction of cellulase [26].…”

“…Several particular mutations located in these TFs cause cellulase hyper-production in classical mutants. The CRE1 mutations in T. reesei Rut-C30 and PC-3-7, which allow the transcription of cellulase genes in glucose-containing media, resulted in higher cellulase and hemicellulase activities [7,22,23].…”

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

“…Genes were selected by direct searching for SNF2, ISW1, ISW2, INO80, CDH1, RSC8 (the most prominent chromatin remodelling-related proteins characterized in yeast) in the T. reesei genome database [39]. Additional candidate genes were obtained by using BLASTp (basic local alignment search tool) search in the NCBI database employing respective S. cerevisiae sequences as baits to identify similar sequences in filamentous fungi.…”

CRZ1 regulator and calcium cooperatively modulate holocellulases gene expression in Trichoderma reesei QM6a

“…Despite the evidence that CRZ1 and Ca 2+ may improve holocellulases expression, these results were obtained when the industrial strain of T. reesei RUT-C30 was evaluated in different environmental conditions. Yet, this strain harbors a deletion of approximately 85 kilobases (kb) from T. reesei’s genome which includes the cre1 locus, resulting in phenotypes that are independent on CRE1-mediated influence [34,35]. Regarding, the role of CRZ1 and Ca 2+ have not been investigated in wild type strain of T. reesei (QM6a), which harbors the full set of regulatory components into its genome.…”