摘要Delivery of proteins to the plasma membrane occurs via secretion,which requires tethering,docking,prim-ing,and fusion of vesicles.In yeast and mammalian cells,an evolutionarily conserved RAB GTPase activa-tion cascade functions together with the exocyst and SNARE proteins to coordinate vesicle transport with fusion at the plasma membrane.However,it is unclear whether this is the case in plants.In this study,we show that the small GTPase RABA2a recruits and interacts with the VAMP721/722-SYP121-SNAP33 SNARE ternary complex for membrane fusion.Through immunoprecipitation coupled with mass spectrometry analysis followed by the validatation with a series of biochemical assays,we identified the SNARE proteins VAMP721 and SYP121 as the interactors and downstream effectors of RABA2a.Further expreiments showed that RABA2a interacts with all members of the SNARE complex in its GTP-bound form and modu-lates the assembly of the VAMP721/722-SYP121-SNAP33 SNARE ternary complex.Intriguingly,we did not observe the interaction of the exocyst subunits with either RABA2a or theSNARE proteins in several different experiments.Neither RABA2a inactivation affects the subcellular localization or assembly of the exocystnorthe exocyst subunit mutant exo84b shows the disrupted RABA2a-SNARE association or SNARE assembly,suggesting that the RABA2a-SNARE-and exocyst-mediated secretory pathways are largely in-dependent.Consistently,our live imaging experiments reveal that the two sets of proteins follow non-overlapping trafficking routes,and genetic and cell biologyanalyses indicate that the two pathways select different cargos.Finally,we demonstrate that the plant-specific RABA2a-SNARE pathway is essential for the maintenance of potassium homeostasis in Arabisopsis seedlings.Collectively,our findings imply that higher plants might have generated different endomembrane sorting pathways during evolution and may enable the highly conserved endomembrane proteins to participate in plant-specific trafficking mech-anisms for adaptation to the changing environment.