Molecular analysis of the (hemi)cellulose metabolism of the fungus Hypocrea jecorina (anamorph: Trichoderma reesei) in the light of developmental changes

Abstract

The saprobic ascomycete Hypocrea jecorina (anamorph Trichoderma reesei) is one of the most widely applied and also best studied plant cell wall degrading fungi. This thesis focused on the genes involved in the catabolism of the hemicelluloses constituent L-arabinose. I could show that a recently identified L-xylulose reductase (encoded by lxr1) is not involved in L-arabinose metabolism in vivo but encodes a D-mannitol dehydrogenase whose main expression was observed during the developmental steps of conidiation, executing the utilization of D-mannitol pool while germination of spores. To identify the true L-xylulose reductase, a bioinformatic research of the genome of T.<br />reesei combined with expression analysis under hemicelluloses degrading conditions revealed three candidate lxr genes. Gene deletion and in vitro protein overexpression experiments led to the result that T.<br />reesei posses at least one further L-xylulose reductase (LXR3) encoding gene which has the major impact on L-arabinose metabolism in vivo.<br />The upregulation of lxr1 during spore formation enabled me to use it as marker gene in a genome wide investigation of the conidiation process by using microarray analysis. Interestingly, I found that cellulase and hemicellulase formation is a major event during sporulation of T.<br />reesei. This upregulation was XYR1 dependent, but sporulation was normal in a delta-xyr1 background. Further, the upregulation of transcripts during sporulation occurred in genomic clusters, suggesting an epigenetic regulation.<br />This thesis has therefore identified a missing link in the catabolism of L-arabinose during hemicelluloses assimilation in T. reesei. The data also support the importance of cellulases and hemicellulases for the ability of the dormant spores of T. reesei to compete with and sensing of its environment for exploitable plant biomass.<br />