The D-xylose reductase of Hypocrea jecorina is the major aldose reductase in pentose and D-galactose catabolism and necessary for beta-galactosidase and cellulase induction by lactose.
The Hypocrea jecorina D-xylose reductase encoding gene xyl1 shows low basal transcript levels, and is induced by D-xylose, L-arabinose and L-arabinitol and, to a lesser extent, by lactose, D-galactose, galactitol and xylitol. The recombinantly expressed XYL1 catalyzes the NADPH-dependent reduction of the pentoses D-xylose and L-arabinose and the hexose D-galactose. Deletion of xyl1 slightly reduces growth on all carbon sources, but a significant decrease is found on D-xylose, L-arabinose and D-galactose. Similar to pentose degradation, XYL1 reduces D-galactose to galactitol in a recently identified second D-galactose pathway. Strains impaired in both D-galactose pathways are almost unable to grow on D-galactose. Deltaxyl1 strains show reduced growth on lactose and are impaired in beta-galactosidase expression and induction of the major cellobiohydrolase gene cbh1. A strain deleted in the cellulase regulator XYR1 is even more severely impaired in growth and beta-galactosidase expression on lactose, and does not produce any cbh1 transcript at all. In this strain, only a low basal level of xyl1 transcription is found on lactose. Galactitol, but not D-galactose is able to induce xyl1 transcription in a XYR1-independent manner. Our results show that the role of the H. jecorina XYL1 is not restricted to D-xylose catabolism and demonstrates its importance for induction of cellulases and beta-galactosidases.
Seiboth
Bernhard
B
Research Area Gene Technology and Applied Biochemistry, Institute of Chemical Engineering, Vienna University of Technology, Austria. bseiboth@mail.zserv.tuwien.ac.at
Gamauf
Christian
C
Pail
Manuela
M
Hartl
Lukas
L
Kubicek
Christian P
CP
D000449:Aldehyde Reductase / Q000235:genetics / Q000378:metabolism*; D002480:Cellulase / Q000096:biosynthesis*; D004790:Enzyme Induction; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D035901:Hypocrea / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D008969:Molecular Sequence Data; D010429:Pentoses / Q000378:metabolism; D017422:Sequence Analysis, DNA; D001616:beta-Galactosidase / Q000096:biosynthesis*
D005656:Fungal Proteins; D010429:Pentoses; D000449:Aldehyde Reductase; D001616:beta-Galactosidase; D002480:Cellulase; D007785:Lactose; D005690:Galactose