title: Xpp1 regulates the expression of xylanases, but not of cellulases in Trichoderma reesei.
abstract: BACKGROUND
  The 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.
  
  
  RESULTS
  In 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.
  
  
  CONCLUSIONS
  Xpp1 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.
authors.affiliation: Department for Biotechnology and Microbiology, Institute of Chemical Engineering, TU Wien, Gumpendorfer Str. 1a, 1060 Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Derntl
authors.affiliation: Department for Biotechnology and Microbiology, Institute of Chemical Engineering, TU Wien, Gumpendorfer Str. 1a, 1060 Vienna, Austria.
authors.forename: Alice
authors.initials: A
authors.lastname: Rassinger
authors.affiliation: Department of Biochemical Engineering, Institute of Chemical Engineering, TU Wien, Gumpendorfer Str. 1a, 1060 Vienna, Austria.
authors.forename: Ewald
authors.initials: E
authors.lastname: Srebotnik
authors.affiliation: Department for Biotechnology and Microbiology, Institute of Chemical Engineering, TU Wien, Gumpendorfer Str. 1a, 1060 Vienna, Austria.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Mach
authors.affiliation: Department for Biotechnology and Microbiology, Institute of Chemical Engineering, TU Wien, Gumpendorfer Str. 1a, 1060 Vienna, Austria.
authors.forename: Astrid R
authors.initials: AR
authors.lastname: Mach-Aigner
keywords: Cellulases; Cellulosic ethanol; Gene regulation; Transcription factor; Trichoderma reesei; Xylanases