Unfolded protein response (UPR) is an intracellular signaling pathway for adaptation to endoplasmic reticulum (ER) stress. In yeast UPR, Ire1 cleaves the unconventional intron of HAC1 pre-mRNA, and the functional Hac1 protein translated from the spliced HAC1 mRNA induces the expression of ER chaperone genes and ER-associated degradation genes for the refolding or degradation of unfolded proteins. To examine the role of UPR under conditions inducing secretory protein production in Aspergillus oryzae, we attempted to construct a disruption mutant of IRE1 ortholog (ireA). However, no homokaryotic ireA disruption mutant could be obtained. Hence, we constructed an ireA conditionally expressing strain, and examined the contribution of UPR to ER stress adaptation under physiological conditions. Repression of ireA completely blocked A. oryzae growth under conditions inducing the production of amylases. This growth defect was restored by the introduction of unconventional intronless hacA. Furthermore, UPR was observed to be induced by amylolytic gene expression, and the disruption of the transcriptional activator (AmyR) for amylolytic genes resulted in partial growth restoration of the ireA-repressing strain. In addition, a homokaryotic ireA disruption mutant was successfully generated using the strain harboring unconventional intronless hacA as a parental host. These results indicated that UPR is required for A. oryzae growth to alleviate ER stress induced by excessive production of hydrolytic enzymes.
Full conference title:
- Asperfest 14 (2017)