Transcriptome during shift of Trichoderma reesei from mycelial growth to asexual sporulation

The asexual spore or conidium plays a critical role in the life cycle of many filamentous fungi, being the primary means for dispersion in the environment. To investigate the transcriptional changes taking place during the sporulation phase in T. reesei, which culminates with the production of the conidiospores, microarray experiments were performed. Among the 1,994 distinct genes displaying >90 % confidence , a total of 900 were classified as differentially expressed, relative to time zero of sporulation, at at least one of the time points analyzed. The main functional categories (FunCat) overrepresented among upregulated genes were those involving solute transport, metabolism, transcriptional regulation, secondary metabolite synthesis, lipases, proteases and particularly cellulases and hemicellulases. Categories overrepresented among downregulated genes were especially those associated with ribosomal and mitochondrial functions. The upregulation of cellulase and hemicellulase genes was depending on the function of the positive transcriptional regulator XYR1, but the latter exerted no influence on sporulation itself. At least 20 % of the significantly regulated genes occured non-randomly distributed within the T. reesei genome suggesting an epigenetic component in the regulation of conidiation. The significant upregulation of cellulases and hemicellulases during conidiation, and thus cellulase and hemicelulase content in the spores of T. reesei lend to hypothesize that the ability to hydrolyse plant biomass is a major trait of this fungus to break dormancy and reinitiate vegetative growth after a period of facing unfavorable conditions One control and three sample points, checked by a marker enzyme for sporulation and by microscopy, were done in two biologicvao replicas