Xpp1 regulates the expression of xylanases, but not of cellulases in Trichoderma reesei

Abstract

BackgroundThe ascomycete Trichoderma reesei is industrially used for the production of cellulases. During the production process xylanases are co-secreted, which uses energy and nutrients. Cellulases and xylanases share the same main regulators, which makes a knowledge-based strain design difficult. However, previously a cis-element in the promoter of the main xylanase-encoding gene was identified as binding site for a putative repressor. Subsequently, three candidate repressors were identified in a pull-down approach. The expression of the most promising candidate, Xpp1 (Xylanase promoter-binding protein 1), was reported to be up-regulated on the repressing carbon source d-glucose and to bind the cis-element in vitro.ResultsIn this study, Xpp1 was deleted and over-expressed in T. reesei. An in vivo DNA-footprint assay indicated that Xpp1 binds a palindromic sequence in the xyn2 promoter. Comparison of the deletion, the over-expression, and the parent strain demonstrated that Xpp1 regulates gene expression of xylanolytic enzymes at later cultivation stages. Xpp1 expression was found to be up-regulated, additionally to d-glucose, by high d-xylose availability. These findings together with the observed xyn2 transcript levels during growth on xylan suggest that Xpp1 is the mediator of a feedback mechanism. Notably, Xpp1 has neither influence on the d-xylose metabolism nor on the expression of cellulases.ConclusionsXpp1 as regulator acting on the expression of xylanases, but not cellulases, is a highly promising candidate for knowledge-based strain design to improve the cellulases-to-xylanases ratio during industrial cellulase production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0298-8) contains supplementary material, which is available to authorized users.

Transcription factor Xpp1 is a switch between primary and secondary fungal metabolism

“…Previously, the expression of Xpp1 itself was shown to depend on growth rate (33). Taken together, we propose that the general role of Xpp1 is to direct the flow of material and energy toward the accumulation of biomass.…”

“…The pigment is a mixture of different sorbicillin derivatives, of which biosynthesis results from a gene cluster that is present in a range of not closely related ascomycetes (38,39). However, in a previous study, we cultivated an xpp1 deletion strain and its parent strain on carboxymethylcellulose (CMC) to determine the expression levels of cellulases (33). Throughout growth, we observed that cultures of the xpp1 deletion strain turned yellow earlier and that coloring was more pronounced compared with the parent strain.…”

“…As mentioned in the Introduction, Xpp1 was originally identified and described as a repressor of xylanase expression (32,33). Therein, Xpp1 was reported to regulate the expression of xylanolytic enzymes at late time points during cultivation on xylan.…”

“…To gain insight into how Xpp1 influences the fungal transcriptome, we performed RNA-Seq analysis. For this purpose, the xpp1 deletion and parent strains were grown for 48 h on CMC, on which the two strains grow similarly (33). The processing of individual samples (Fig.…”

“…In this study, we describe the identification of a transcription factor that acts as a switch between primary and secondary metabolism. The deletion of the previously described xylanase repressor Xylanase promoter binding protein 1 (Xpp1) (32,33) results in a decline of the primary metabolism and the up-regulation of secondary metabolism in terms of compound diversity and quantity in the saprotrophic ascomycete Trichoderma reesei [teleomorph; Hypocrea jecorina (34)]. To study the extent of the Xpp1 regulon in detail, we performed RNAsequencing (RNA-Seq) analysis.…”