Xyr1 receives the lactose induction signal and regulates lactose metabolism in Hypocrea jecorina

Abstract

This study reports the vital regulatory influence of Xyr1 (xylanase regulator 1) on the transcription of hydrolytic enzyme-encoding genes and hydrolase formation on lactose in Hypocrea jecorina. While the transcription of the xyr1 gene itself is achieved by release of carbon catabolite repression, the transcript formation of xyn1 (xylanase 1) is regulated by an additional induction mechanism mediated by lactose. Xyr1 has an important impact on lactose metabolism by directly activating xyl1 (xylose reductase 1) transcription and indirectly influencing transcription of bga1 (b-galactosidase 1). The latter is achieved by regulating the conversion of D D-galactose to the inducing carbon source galactitol.

Differential Regulation of the Cellulase Transcription Factors XYR1, ACE2, and ACE1 in Trichoderma reesei Strains Producing High and Low Levels of Cellulase

“…Stricker et al have recently postulated that xyr1 is not regulated by induction but solely by carbon catabolite (de)repression (37). In order to rule out the possibility that the enhanced expression of xyr1 on lactose is due to relief of carbon catabolite repression on this carbon source, we used a ⌬cre1 strain of T. reesei QM 9414, cultivating it under the same conditions as those described above for QM 9414.…”

“…Many of them, therefore, are further induced by the conditions for which they are needed and are degraded once they are no longer needed (40). In contrast, xyr1 expression has been reported to be regulated solely by CRE1-dependent CCR and by repression by the specific transcription factor ACE1, not by induction (19,37). Such a mechanism, if correct, would tightly link xyr1 expression to the flux through carbohydrate catabolism but would preclude the possibility of responding to the presence of a potential inducer.…”

Regulation of transcription of cellulases- and hemicellulases-encoding genes in Aspergillus niger and Hypocrea jecorina (Trichoderma reesei)

“…Regulation of the respective genes via Xyr1 is not affected by the substances mediating the induction (degradation and transglycosylation products, such as D-xylose, xylobiose, sophorose as well as the inducer molecule lactose) and is indispensable for all modes of gene expression (Stricker et al 2007a;Stricker et al 2006). Id est, neither the Cre1 (carbon catabolite repressor protein 1)-dependent de-repressed or induced transcriptional level of xyn1 nor the basal or induced transcriptional level of xyn2 could be observed in a Δxyr1 strain.…”

Identification of Major Facilitator Transporters Involved in Cellulase Production during Lactose Culture ofTrichoderma reeseiPC-3-7

“…Several studies have analyzed cellulase and hemicellulase gene expression using RUT C30 as a model strain. [12][13][14][15] Early reports have indicated that RUT C30 harbors the following genetic modifications: (i) a truncation in cre1, which relieves catabolite repression, 16) (ii) a frame-shift in the glucosidase II alpha subunit gene gls2, which increases protein expression, 17) and (iii) an 85-kb deletion in chromosome 2, which deletes a total of 29 genes and is responsible for the truncation of cre1. 18) More recently, LeCrom et al (2009) 19) sequenced the genome of RUT C30 and reported 223 SNPs, but to date, no mutation other than those in cre1 and gls2 has been linked to the hyper-cellulolytic phenotype of RUT C30.…”