SINAT proteins modulate autophagic vesicle degradation by regulating V-ATPase subunit proteolysis in Arabidopsis

Macroautophagy/autophagy is a process conserved across eukaryotes that maintains cellular homeostasis by delivering cellular components to the vacuole or lysosome for further breakdown and recycling. Although the molecular mechanisms regulating autophagosome formation have been extensively studied, those underlying the modulation of autophagic body degradation in plant cells remain unclear. Here, we determined that VAB1 (V-ATPase catalytic subunit B1), a direct target of SINAT (SEVEN IN ABSENTIA OF ARABIDOPSIS THALIANA), is involved in the modulation of autophagic body degradation in plants. SINAT physically associated with VAB1 in vitro and in vivo to regulate its ubiquitination and degradation in planta. Compared with the wild-type (WT), the vab1 mutants showed decreased tolerance to nutrient starvation and premature leaf senescence. Moreover, deletion of vab1 led to impaired starvation-induced autophagic vesicle degradation by disrupting V-ATPase activity mediated vacuolar acidification. Consistently, lysines K34 and K221 of VAB1 protein contributed to SINAT1-mediated ubiquitination, destabilization, and suppression of autophagy-associated nutrient starvation tolerance. Thus, our findings demonstrate that SINAT proteins are involved in autophagy regulation by modulating VAB1-mediated autophagic degradation in Arabidopsis.