Sec24C mediates a Golgi-independent trafficking pathway that is required for tonoplast localization of ABCC1 and ABCC2

Abstract

Protein sorting is an essential biological process in all organisms. Trafficking membrane proteins generally relies on the sorting machinery of the Golgi apparatus. However, many proteins have been found to be delivered to target locations via Golgi-independent pathways, but the mechanisms underlying this delivery system remain unknown. Here, we report that Sec24C, a component of coat protein complex II (COPII) vesicles, mediates the direct secretory trafficking of the phytochelatin transporters ABCC1 and ABCC2 from the endoplasmic reticulum (ER) to prevacuolar compartments (PVCs). After performing a genetic screening, we found that Sec24C loss-of-function mutants are hypersensitive to cadmium (Cd) and arsenic (As) treatments due to mislocalization of ABCC1 and ABCC2, which results in defects in the vacuole compartmentalization of the toxic metals. Further studies showed that Sec24C recognizes ABCC1 and ABCC2 through direct interactions to mediate their exit from the ER to PVCs in a Golgi-independent manner. These findings expand our understanding of Golgi-independent trafficking as well as COPII vesicles.