Abstract
The ascomycete Trichoderma reesei is one of the main fungal producers of cellulases and xylanases based on its high production capacity. Its enzymes are applied in food, feed, and textile industry or in lignocellulose hydrolysis in biofuel and biorefinery industry. Over the last years, the demand to expand the molecular toolbox for T. reesei to facilitate genetic engineering and improve the production of heterologous proteins grew. An important instrument to modify the expression of key genes are promoters to initiate and control their transcription. To date, the most commonly used promoter for T. reesei is the strong inducible promoter of the main cellobiohydrolase cel7a. Beside this one, there is a number of alternative inducible promoters derived from other cellulase- and xylanase encoding genes and a few constitutive promoters. With the advances in genomics and transcriptomics the identification of new constitutive and tunable promoters with different expression strength was simplified. In this review, we will discuss new developments in the field of promoters and compare their advantages and disadvantages. Synthetic expression systems constitute a new option to control gene expression and build up complex gene circuits. Therefore, we will address common structural features of promoters and describe options for promoter engineering and synthetic design of promoters. The availability of well-characterized gene expression control tools is essential for the analysis of gene function, detection of bottlenecks in gene networks and yield increase for biotechnology applications.
Highlights
Trichoderma reesei is a model organism for plant biomass degradation and a production platform for proteins and enzymes (Bischof et al, 2016)
As detailed in the previous chapters, there is an adequate selection of promoters available for recombinant protein expression derived from cellulase or xylanase genes, respectively a few constitutive promoters with medium strength
Addition of L-methionine to the medium does not interfere with T. reesei biomass formation or native cellulase production making this amino acid a suitable substance to repress gene expression (Gremel et al, 2008; Bischof et al, 2015)
Summary
Trichoderma reesei is a model organism for plant biomass degradation and a production platform for proteins and enzymes (Bischof et al, 2016). As a production host for cellulases and xylanases, the promoters of genes of the main secreted enzymes are attractive targets for use in overexpression cassettes. As detailed in the previous chapters, there is an adequate selection of promoters available for recombinant protein expression derived from cellulase or xylanase genes, respectively a few constitutive promoters with medium strength.
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