Arabidopsis MACP2 contributes to autophagy induction by modulating starvation-induced reactive oxygen species homeostasis.

In plants, autophagy is a conserved recycling system essential for development and stress responses by targeting cellular components for massive degradation in the vacuole. Our previous work suggested that autophagy contributes to Arabidopsis (Arabidopsis thaliana) stress responses by modulating NADPH-oxidase-mediated reactive oxygen species (ROS) homeostasis; however, the molecular link between extracellular ROS and autophagy remains unknown. We performed a yeast two-hybrid screen to identify components involved in autophagy, using the central autophagy component ATG8e as a bait. We identified MEMBRANE ATTACK COMPLEX/PERFORIN-LIKE 2 (MACP2) as an interactor of ATG8e via its the ATG8-interacting motif and confirmed this interaction by co-immunoprecipitation and bimolecular fluorescence complementation assays. MACP2-overexpressing lines showed enhanced sensitivity to nutritional starvation, accelerated leaf senescence, and increased hydrogen peroxide (HO) levels, resembling the phenotypes of atg mutants defective in autophagy. Conversely, macp2 knockouts exhibited diminished starvation-induced HO accumulation and attenuated autophagosome formation and fully suppressed the starvation-hypersensitive phenotypes of the atg5-1 mutant. In particular, MACP2 was degraded through the autophagy machinery during prolonged starvation, suggesting a feedback regulatory mechanism for maintaining MACP2 homeostasis. Our findings suggest that MACP2 acts as a key regulator in autophagy induction by controlling influx of extracellular HO in Arabidopsis.