The arabinolytic pathway in Trichoderma reesei

One of the most widespread pentose sugars found in plant biomass is L-arabinose, a constituent of plant cell-wall polysaccharides L-arabinan, arabinogalactans and arabinoxylans. The pentose catabolic pathways are relevant for micro-organisms living on decaying plant material but also in biotechnology when cheap raw materials such as plant hydrolysates are used as a carbon source. Genes coding for both extracellular and intracellular enzymes of the arabinolytic pathway have been cloned from the industrially important fungusTrichoderma reesei. The fungal intracellular L-arabinose pathway consists of five enzymes, aldose reductase, L-arabinitol 4-dehydrogenase, L-xylulose reductase, xylitol dehydrogenase and xylulokinase. All the genes coding for the enzymes of this pathway have been cloned in our laboratory. These genes have been utilized to construct an arabinose-utilizing S. cerevisiae strain. We have investigated the expression of the extracellular arabinofuranosidase that cleaves arabinose form arabinoxylans and intracellular arabinolytic genes in T. reesei cells grown on various carbon sources and the regulation of these genes with respect to the carbon catabolite repressor CREI.