The endoplasmic reticulum-associated degradation machinery selectively degrades stress-induced TIN1 during stress recovery

The unfolded protein response (UPR) signaling pathway is activated by accumulation of misfolded proteins in the endoplasmic reticulum (ER) and stimulates production of ER chaperones to restore ER proteostasis. However, how UPR-induced proteins return to their pre-stress levels upon removal of ER stress remains unknown. TUNICAMYCIN-INDUCED1 (TIN1) is an Arabidopsis (Arabidopsis thaliana) protein that is normally expressed in pollen but is rapidly induced by ER stresses in vegetative tissues. Here we show that the ER stress-induced TIN1 is rapidly degraded in the UPR recovery phase. We found that TIN1 degradation depends on its asparagine-linked glycans and requires both EMS-mutagenized bri1 suppressor 5 (EBS5) and EBS6 for its recruitment to the ER-associated degradation (ERAD) complex. Loss-of-function mutations in the core component of this Arabidopsis ERAD complex greatly stabilize TIN1. Interestingly, two other UPR-induced proteins that are coexpressed with TIN1 remained stable upon ER stress removal, suggesting that rapid degradation during the stress-recovery phase likely applies to a subset of UPR-induced proteins. Further investigation is needed to uncover the mechanisms by which the ERAD machinery selectively degrades UPR-induced ER proteins.