Prepared for the possible: xylanase gene transcription in Trichoderma reesei

23 The ascomycete Trichoderma reesei is a paradigm for the regulation and production of plant 24 cell wall degrading enzymes including xylanases. Four xylanases including XYN1 and XYN2 of 25 the glycosyl hydrolase family 11, the GH10 XYN3 and the GH30 XYN4 were already 26 described. By genome mining we identified a fifth xylanase XYN5 belonging to GH11. 27 Transcriptional analysis reveals that the expression of all xylanases but xyn3 is induced by D28 xylose, dependent on the cellulaseand xylanase-regulator XYR1 and negatively regulated by 29 the carbon catabolite repressor CRE1. Impairment of D-xylose catabolism at the D-xylose 30 reductase and xylitol dehydrogenase step strongly enhanced induction by D-xylose. Knock 31 out of the L-xylulose reductase encoding gene lxr3, which connects the D-xylose and L32 arabinose catabolic pathway had no effect on xylanase induction. Beside the induction by D33 xylose, the T. reesei xylanases were also induced by L-arabinose, and this induction was also 34 enhanced in knock out mutants in L-arabinose reductase (xyl1), L-arabitol dehydrogenase 35 (lad1) and L-xylulose reductase (lxr3). Induction by L-arabinose was also XYR1 dependent. 36 Analysis of intracellular polyols revealed accumulation of xylitol in all strains only during 37 incubation with D-xylose, and accumulation of L-arabitol only during incubation with L38 arabinose. Induction by L-arabinose could be further stimulated by addition of D-xylose. We 39 conclude that the expression of the T. reesei xylanases can be induced by both D-xylose and 40 L-arabinose, but independently of each other, and by using different inducing metabolites. 41 42