Proteome and transcriptome analysis of the cellular responses to production of the heterologous protein, Melanocarpus albomyces laccase, in the filamentous fungus Trichoderma reesei

Trichoderma reesei Rut-C30 and its transformant producing Melanocarpus
albomyces laccase were cultivated in lactose-containing minimal medium in chemostats and subjected to proteome and transcriptome analysis to identify differentially expressed genes under these conditions. The cultures were carried out using a dilution rate (0.03/h) previously shown to be optimal for production of endogenous extracellular proteins under these conditions. The TRAC method for multiplexed transcriptional analysis was first applied to analyse the expression levels of a selected set of genes and to monitor the steady state in the chemostat cultures. The results indicated that UPR (unfolded protein response) pathway was not activated as a response to laccase production. On the contrary, the expression levels of e.g. the foldase and chaperone genes pdi1 and bip1 were expressed at a slightly higher level in the host. Also the expression levels of the genes encoding the endogenous secreted cellulases, egl1 and cbh1, were slightly higher in the host strain. Both proteome and genome wide transcriptional analysis using oligonucleotide microarrays revealed only a modest number of cellular responses to laccase production. Altogether 32
genes were differentially expressed between the strains, only five of the genes being upregulated in the laccase producing strain, and the rest having a higher expression level in the host strain and including many genes encoding extracellular enzymes. Proteome analysis using 2D gel electrophoresis with DIGE showed increased expression of a group of proteins including e.g. heat shock proteins as well ubiquitin associated proteins and proteins involved in ERassociated protein degradation. The result indicates that although laccase expression does not induce apparent UPR, other type stress responses are induced e.g. activated protein degradation. The results were also compared to those obtained in previous studies on the production human tissue plasminogen activator (tPA) in T. reesei.