Functional studies of the secretory pathway of filamentous fungi: The effect of unfolded protein response on protein production: Dissertation

This study describes the cloning and characterisation of three genes from the filamentous fungus Trichoderma reesei. Snc1 encoding a putative v-SNARE was shown to be the functional homologue of Saccharomyces cerevisiae SNC1 and SNC2 genes that encode proteins shown to function in exo- and endocytosis. Two components of the unfolded protein response (UPR) pathway have also been identified. Ire1 encodes a serine /threonine kinase that has been shown to be involved the sensing of the protein folding status in the ER and transferring the signal to the nucleus. Ptc2 on the other hand, encodes a putative negative regulator of UPR. Both genes were isolated from T. reesei and shown to be the functional homologues of S. cerevisiae genes. The effects of UPR activation on gene expression and protein production in S. cerevisiae and two filamentous fungi, T. reesei and Aspergillus niger var. awamori are also presented. The data shows that the UPR induction, either by HacA or Ire1 overexpression in A. niger var awamori and T. reesei, respectively, induces the expression of an ER-resident foldase and an ER-resident chaperone. Moreover, the UPR induction induces the expression of genes encoding functions at different steps of the secretory pathway in both fungi. This is in correlation with results obtained in other organisms. The UPR induction was in this study shown to induce production of secreted proteins both in S. cerevisiae and A. niger var. awamori. In yeast the UPR induction by constitutive over-expression of activated yeast HAC1 and T. reesei hac1 resulted in induction of both native and foreign protein production. On the other hand, deletion of HAC1 resulted in decrease in protein production. In A. niger var. awamori only the production of foreign proteins was induced in HacA over-expressing transformants. The production of native proteins was lower in these transformants compared to the controls. The over-expression of Ire1 in T. reesei had no effect on foreign protein production.