Cellular responses to protein production in the filamentous fungus Trichoderma reesei

The filamentous fungus Trichoderma reesei is known as an efficient producer of a variety of extracellular enzymes, the major products being cellulases and hemicellulases e.g. cellobiohydrolases, endoglucanases, Beta-glucosidases, xylanases, and hemicellulose side-chain cleaving enzymes. Altogether, analysis of the genome sequence has revealed over 200 genes classified in glycoside hydrolase gene families. T. reesei has potential to produce extracellular proteins in very large quantities, and it has been used as an industrial host organism for production of both the fungal enzymes as well as for heterologous proteins. Production of secreted proteins in large quantities or production of the heterologous proteins originating from distantly related organisms challenge the capability of the cells to fold and transport the proteins, and are known to provoke stress responses in the cell. Impaired protein folding in the endoplasmic reticulum (ER) activates the unfolded protein response pathway (UPR) which result in induction of a number of genes involved e.g. in folding, glycosylation and transport. The fungal cells have also a feed-back mechanism to reduce the load in the secretory pathway by negative transcriptional regulation of genes encoding the major secreted proteins. The availability of the genome sequence information has made it possible to apply genome-wide approaches in studies of the cellular responses to protein production under different conditions. Specifically, we have compared the effects of production of two different heterologous proteins, human tPA and Melanocarpus albomyces laccase, in T. reesei using proteome and transcriptome data. The analysis showed a clear difference between the responses induced by the proteins, the main difference being in the induction of the UPR pathway. Furthermore, in order to obtain information on protein production at different physiological conditions we have carried out transcriptome and proteome analysis of carbon-limited chemostat cultures of T. reesei under different conditions, e.g. at different specific growth rates and cell density