Impact of xylanase expression-inducing compounds on DNA accessibility in Trichoderma reesei

The ascomycete Trichoderma reesei produces industrially applied plant cell wall-degrading enzymes. The two major xylanases XYNI (encoded by xyn1) and XYNII (encoded by xyn2) are amongst those enzymes. The transactivator Xyr1, the repressor Cre1, and gene-specific transcription factors regulate the expression of both xylanases. The inducing compounds D-xylose and sophorose trigger the expression of the xylanases, however, to different extents. D-glucose causes carbon catabolite repression (CCR) mediated by Cre1, which leads to a down-regulation of expression of both. Apart from transcription factors, DNA packaging adds an important layer to the regulation of the production of xylanolytic enzymes. In this study the chromatin status in two upstream regulatory regions (URRs) of the xyn1 and xyn2 genes and the transcript levels were investigated in the wild-type strain QM6a and the hypercellulolytic mutant Rut-C30. This analysis demonstrated more open chromatin and higher transcript levels in both strains and genes under at least one of the two inducing conditions. Additionally, a generally more open chromatin could be observed in Rut-C30 independent of the carbon source that was accompanied by elevated transcript levels. In vivo footprinting analyses demonstrated that protein-DNA interactions differ between D-xylose compared to D-glucose in both strains. In addition, different DNA occupancies were observed in the URR of xyn2 in dependency of the applied inducer. Obviously, the usage of a certain inducer influences the final promoter architecture.