Abstract
The filamentous fungus Trichoderma reesei secretes large quantities of cellulases and hemicellulases that have found wide applications in industry. Compared with extensive studies on the mechanism controlling cellulase gene expression, less is known about the regulatory mechanism behind xylanase gene expression. Herein, several putative sugar transporter encoding genes that showed significant upregulation on xylan were identified in T. reesei. Deletion of one such gene, gat1, resulted in increased xylanase production but hardly affected cellulase induction. Further analyses demonstrated that deletion of gat1 markedly increased XYNI production at the transcriptional level and only exerted a minor effect on XYNII synthesis. In contrast, overexpressing gat1 caused a continuous decrease in xyn1 expression. Deletion of gat1 also affected the expression of xyn1 and pectinase genes when T. reesei was cultivated with galacturonic acid as the sole carbon source. Transcriptome analyses of Δgat1 and its parental strain identified 255 differentially expressed genes that are enriched in categories of glycoside hydrolases, lipid metabolism, transporters, and transcriptional factors. The results thus implicate a repressive role of the sugar transporter GAT1 in xyn1 expression and reveal that distinct regulatory mechanisms may exist in controlling the expression of different xylanase genes in T. reesei.
Highlights
Lignocellulose including cellulose, hemicellulose, and pectin is the most abundant renewable carbon resource in nature (Rubin, 2008)
Whereas T. reesei produces a much lower amount of xylanases compared to cellulases, these enzyme components play an indispensable role in increasing the accessibility of cellulases to cellulose that is embedded in hemicellulose matrix mainly composed of xylan, and enhancing the overall efficiency of lignocellulose hydrolysis (Gupta et al, 2016)
We found that GAT1 is involved in the regulation of both pectinase and xylanase gene expression when T. reesei was cultivated with galacturonic acid as carbon source
Summary
Lignocellulose including cellulose, hemicellulose, and pectin is the most abundant renewable carbon resource in nature (Rubin, 2008). A number of microorganisms are capable of efficiently degrading lignocellulose by secreting a large quantity of lignocellulolytic enzymes. The filamentous fungus Trichoderma reesei is one of the most prolific producers of cellulases and hemicellulases (mainly xylanases), which have found applications in many industrial fields for a long history (Bischof et al, 2016; Liu and Qu, 2021). Whereas T. reesei produces a much lower amount of xylanases compared to cellulases, these enzyme components play an indispensable role in increasing the accessibility of cellulases to cellulose that is embedded in hemicellulose matrix mainly composed of xylan, and enhancing the overall efficiency of lignocellulose hydrolysis (Gupta et al, 2016).
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