Expression patterns of ten hemicellulase genes of the filamentous fungus Trichoderma reesei on various carbon sources

Abstract

The filamentous fungus Trichoderma reesei produces a multitude of cellulolytic and hemicellulolytic enzymes. The expression of ten hemicellulase-encoding genes was studied by Northern analyses in various culture conditions including polymeric and di- and monomeric sugars. The study included genes encoding two β-xylanases ( xyn1 and xyn2) and a β-mannanase ( man1) which hydrolyze the main chain of hemicellulose polymers by endo fashion, and the acetyl xylan esterase ( axe1), the αr-glucuronidase ( glr1), the α- l-arabinofuranosidase ( abf1), and three α-galactosidases ( agi1, agl2 and agl3), which attack the side groups of hemicellulosic substrates. The genes encoding the oligosaccharide-hydrolysing enzymes β-glucosidase ( bgl1) and β-xylosidase ( bxl1) were also studied and as a reference the cellulase encoding gene cbh1. A general picture of their relative expression patterns and relative expression levels in particular conditions was obtained. Growth in the presence of cellulose, sophorose, xylobiose, xylan and l-arabitol gave rise to abundant expression of most genes studied, α-galactosidase I and II, β-xylosidase and α- l-arabinofuranosidase encoding genes were the ones most frequently expressed in the conditions studied, whereas expression of the mannanase and α-galactosidase III was rarely seen. Expression of the genes was not detected in the presence of glucose in the strain QM9414 but derepressed expression of most of them occurred after glucose depletion. Expression of at least xyn1, bxl1, agi1, agl2, agl3 and axe1 is under control of the glucose represser cre 1 as studied in the cre1-l mutant Rut-C30 and Rut-C30 transformed with the wild type cre 1 allele.