Transcriptional Regulation of xyr1 , Encoding the Main Regulator of the Xylanolytic and Cellulolytic Enzyme System in Hypocrea jecorina

Abstract

In Hypocrea jecorina, Xyr1 (xylanase regulator 1) is the main transcription activator of hydrolase-encoding genes, such as xyn1, xyn2, bxl1, cbh1, cbh2, egl1, and bgl1. Even though Xyr1 mediates the induction signal for all these genes derived from various inducing carbon sources and compounds, xyr1 transcription itself is not inducible by any of these substances. However, cultivation on glucose as the carbon source provokes carbon catabolite repression of xyr1 transcription mediated by Cre1. In addition, xyr1 transcription is repressed by the specific transcription factor Ace1. Moreover, Xyr1 is permanently available in the cell, and no de novo synthesis of this factor is needed for a first induction of xyn1 transcription. The constitutive expression of xyr1 leads to a significant elevation/deregulation of the xyn1, xyn2, and bxl1 transcription compared to what is seen for the parental strain. Overall, the corresponding xylanolytic enzyme activities are clearly elevated in a constitutively xyr1-expressing strain, emphasizing this factor as an auspicious target for genetically engineered strain improvement.

L -Arabitol Is the Actual Inducer of Xylanase Expression in Hypocrea jecorina (Trichoderma reesei)

“…Furthermore, these results are in accordance with the finding that XlnR, the corresponding A. niger Xyr1 orthologue (23) (12). This is in accordance with our previous finding that, although the presence of Xyr1 is indispensable for xyn1 expression (20), no de novo synthesis of Xyr1 is needed for initial xyn1 induction in H. jecorina (8).…”

“…We have previously reported that transcription of xyr1, the central activator of hydrolase expression in H. jecorina, does not respond to induction by a specific carbon source (8). In this study, we confirmed our observation by demonstrating similar xyr1 transcription levels under all conditions and strains tested.…”

Enhanced glycosyl hydrolase production in Aspergillus nidulans using transcription factor engineering approaches

“…Xylanase production in xylan cultures of a T. reesei strain constitutively expressing the xylanolytic activator Xyr1 was also shown to be greater than that of the wild type at relatively early culture stages (about four times after 48 hours), though the maximum levels of activity achieved by both strains were similar after 72 hours [36]. Characteristics specific to each fungal species (for example protein folding, secretory ability and protease activity), differences in XlnR/Xyr1 expression levels, different requirements for XlnR/Xyr1 of the xylanolytic gene promoters and/or differences in the culture conditions (such as the use of distinct inducers) might account for the differences in improvements reported in each study.…”

Xylanase Gene Transcription in Trichoderma reesei Is Triggered by Different Inducers Representing Different Hemicellulosic Pentose Polymers

“…xyn1 and xyn2 were previously reported to be subject to regulation by the C 2 H 2 carbon catabolite repressor CRE1 via a doublelock mechanism (19,38) that controls xylanase transcription at two different levels, by direct repression through CRE1, and indirectly through the CRE1-mediated repression of the transcriptional activator XYR1 (39). Binding sites for the carbon catabolite repressor CRE1 are present in all xylanase genes ( Fig.…”