Abstract
Cellulase production in the model cellulolytic fungus Trichoderma reesei is subject to a variety of environmental and physiological conditions involving an intricate regulatory network with multiple transcription factors. Here, we identified the mating type locus protein MAT1-2-1 as an interacting partner for the key transcriptional activator Xyr1 of T. reesei cellulase genes. Yeast two-hybrid and GST pulldown analyses revealed that MAT1-2-1 directly interacted with the putative transcription activation domain (AD, 767~940 aa) and the middle homology region (MHR2, 314~632 aa) of Xyr1. Disruption of the mat1-2-1 gene compromised the induced expression of cellulase genes with Avicel in response to light or with lactose. Chromatin immunoprecipitation (ChIP) demonstrated that MAT1-2-1 was recruited to the cbh1 (cellobiohydrolase 1-encoding) gene promoter in a Xyr1-dependent manner. These results strongly support an important role of MAT1-2-1 as a physiological cofactor of Xyr1, and suggest that MAT1-2-1 represents another regulatory node that integrates the light response with carbon source signaling to fine tune cellulase gene transcription.
Highlights
The ascomycete Trichoderma reesei, a saprophytic filamentous fungus, represents an important workhorse for industrial production of cellulases as well as other proteins
With the C-terminal putative activation domain (AD) of Xyr[1] (767~940 aa) as a bait, a T. reesei cDNA expression library prepared under cellulase-inducing conditions was transformed into the reporter strain and transformants were selected on the quadruple dropout medium (QDO, SD/–Ade/–His/–Leu/–Trp) containing 100 ng/ml AbA
In accordance with the results of Y2H, His-tagged MAT1-2-1 was efficiently retained by recombinant GST-Xyr1AD and -Xyr1MHR2, whereas none of them could be detected in the GST only coupled beads (Fig. 1B)
Summary
The ascomycete Trichoderma reesei (teleomorph Hypocrea jecorna), a saprophytic filamentous fungus, represents an important workhorse for industrial production of cellulases as well as other proteins. Regulation of Xyr[1] expression and/or activity has been considered to be crucial for the production of various hydrolytic enzymes in T. reesei though the exact mechanism remains largely elusive[4,5,6]. It has been found that neither pheromone precursor genes nor pheromone receptor genes of T. reesei are transcribed in a strictly mating type dependent manner enhanced expression levels have been observed in www.nature.com/scientificreports/. Potential signaling pathways transmitting these light signals in controlling development have been extensively investigated[11,16,17] Both the PAS domain protein ENVOY (ENV1) and the light-dependent regulator VEL1 have been found to be important for balanced regulation of pheromone precursor genes and receptor genes largely in a mating type dependent manner, and crucial for successful mating[16,17]. MAT1-2-1 may represent another regulatory node that integrates the light response with carbon source signaling to fine tune cellulase gene transcription
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