Atg8 and Ire1 in combination regulate the autophagy-related endoplasmic reticulum stress response in Candida albicans

The unfolded protein response (UPR) is an important pathway to prevent endoplasmic reticulum (ER) stress in eukaryotic cells. In Saccharomyces cerevisiae, Ire1 is a key regulatory factor required for HAC1 gene splicing for further production of functional Hac1 and activation of UPR gene expression. Autophagy is another mechanism involved in the attenuation of ER stress by ER-phagy, and Atg8 is a core protein in autophagy. Both autophagy and UPR are critical for ER stress response, but whether they act individually or in combination in Candida albicans is unknown. In this study, we explored the interaction between Ire1 and the autophagy protein Atg8 for the ER stress response by constructing the atg8Δ/Δire1Δ/Δ double mutant in the pathogenic fungus C. albicans. Compared to the single mutants atg8Δ/Δ or ire1Δ/Δ, atg8Δ/Δire1Δ/Δ exhibited much higher sensitivity to various ER stress-inducing agents and more severe attenuation of UPR gene expression under ER stress. Further investigations showed that the double mutant had a defect in ER-phagy, which was associated with attenuated vacuolar fusion under ER stress. This study revealed that Ire1 and Atg8 in combination function in the activation of the UPR and ER-phagy to maintain ER homeostasis under ER stress in C. albicans.