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Abstract
Enhancing cellulase production in Trichoderma reesei is of great interest for an economical biorefinery. Artificial transcription factors are a potentially powerful molecular strategy for improving cellulase production in T. reesei. In this study, enhanced transcriptional activators XYR1VP, ACE2VP, and ACE1VP were constructed by linking the C terminus of XYR1, ACE2, or ACE1 with an activation domain of herpes simplex virus protein VP16. T. reesei transformants TXYR1VP, TACE2VP, and TACE1VP showed improved cellulase and/or xylanase production. TXYR1VP has a cellulase-free phenotype but with significantly elevated xylanase production. Xylanase I and xylanase II activities [U/(mg biomass)] increased by 51% and 80%, respectively, in TXYR1VP in comparison with parental strain RUT C30. The filter paper activity of TACE2VP in the Avicel-based medium increased by 52% compared to that of RUT C30. In the Avicel-based medium, TACE1VP manifested an 80% increase in FPase activity and a 50% increase in xylanase activity as compared to those of RUT C30. Additionally, when pretreated corn stover was hydrolyzed, crude enzymes produced from TACE1VP yielded a greater glucose release than did the enzymes produced by parental strain RUT C30.
Highlights
Production of environment-friendly biofuels and chemicals from lignocellulosic biomass, which forms the skeleton of all plant cells, has received extensive attention (Hahn-Hagerdal et al 2006)
We hypothesized that cellulase production would be increased by fusing the strong transcriptional activation domain of VP16 to the C terminus of a natural transcription factor (TF) to enhance its transcriptional activation
Three enhanced transcriptional activator (ETA) including XYR1VP, ACE2VP, and ACE1VP were designed by fusing the VP16 domain to the C terminus of XYR1, ACE2, and ACE1, respectively (Fig. 1)
Summary
Production of environment-friendly biofuels and chemicals from lignocellulosic biomass, which forms the skeleton of all plant cells, has received extensive attention (Hahn-Hagerdal et al 2006). The enhancement of cellulase production greatly reduces the cost of a biorefinery of lignocellulosic biomass (Vicari et al 2012; Biddy et al 2016). T. reesei produces three types of cellulases: cellobiohydrolases (CBH1 and CBH2), endoglucanases (mainly include EGL1 and EGL2), and β-glucosidase (mainly BGL1). Cellobiohydrolases and Cellulase production in T. reesei RUT C30 is transcriptionally coregulated by a set of transcription factors (TFs), including XYR1, ACE3, ACE2, and ACE1 (Mach-Aigner et al 2008; Häkkinen et al 2014; Bischof et al 2016). XYR1 and ACE3 are key transcriptional activators, and deletion of xyr or ace abrogates cellulase production (Stricker et al 2006; Akel et al 2009; Häkkinen et al 2014; Castro Santos et al 2016). ACE2 serves as a transcriptional activator of cellulase production, and deletion of ace decreases mRNA levels of cellulase-encoding genes, Zhang et al Bioresour. ACE1 is recognized as a transcriptional repressor of cellulase production, and deletion of ace increased the production of all main cellulase and xylanase in sophorose- and cellulose-induced cultures (Saloheimo et al 2000; Aro et al 2003; Portnoy et al 2011)
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