RABC1, an Arabidopsis RAB18 regulates binding and subsequent detachment of autophagosomes from the ER in autophagy

Macroautophagy/autophagy is a strategy cells use to cope with detrimental conditions, e.g. nutrient deficiency. Phagophores, the precursors to autophagosomes, are initiated and expanded on the endoplasmic reticulum (ER). However, how phagophores and completed autophagosomes are linked to the ER remains incompletely understood. We recently unveiled a RAB GTPase-based linkage between the two structures. RABC1 is a plant member of RABC/RAB18 GTPases. Our biochemical and microscopy data indicated that RABC1 promotes autophagy in response to nutrient starvation, but not under ER stress. Under nutrient-starvation conditions, active RABC1 interacts with ATG18a on the ER, controlling the association of ATG18a to the ER. Subsequently, active RABC1 is turned off allowing expanded phagophores or autophagosomes to detach from the ER. Our work identifies a RAB GTPase-mediated autophagy process in plant cells, opening a door for improving crop productivity in the changing environment.