Rab3GAPL toggles between activities to optimize autophagy and defense-related secretion by hindering Rab8a-mediated vesicle trafficking through promoting the GTP hydrolysis of Rab8a. Rab3GAPL suppresses autophagy by binding to ATG8, the core autophagy adaptor, using its ATG8-interacting motif (AIM) and deactivating Rab8a using its GTPase-activating protein (GAP) domain. Beyond autophagy regulation, Rab3GAPL modulates Rab8a-mediated defense-related secretion toward the cell surface/pathogen interface. This immune modulation is independent of its AIM, but dependent on its GAP domain. Consequently, Rab3GAPL functions as a molecular rheostat, dynamically balancing autophagy and immune responses to maintain cellular homeostasis. This model highlights the molecular interplay between a RabGAP-Rab pair and ATG8, providing new insights into the complex membrane transport mechanisms that underpin plant autophagy and immunity.
