627 / 2019-04-25 20:19:05

RabA2A GTPase Regulates the Secretory Pathway in Parallel to the Exocyst Complex in Arabidopsis

RabA2A GTPase; Exocyst complex; Exocytosis; Vesicle trafficking

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Classic studies from yeast and mammalian cells have showed that membrane tethering between exocytic vesicles and plasma membrane (PM) occurs via the octameric exocyst complex. The exocyst assembles at the sites of exocytosis by directly binding to Ypt31/Rab11 and interacts with the SNARE complex to start the membrane fusion process. The subclass RabA2 GTPases in Arabidopsis are the closest paralogs of the yeast Ypt31/32 and the mammalian Rab11 proteins. Previous work from our lab revealed that RabA2A GTPase regulates polar secretion of auxin transporter PIN2 to the apical PM. As the follow-up work to explore the mechanism of RabA2A mediated apical trafficking, we performed the immunoprecipitation and mass spectrometry analysis. The SNARE proteins VAMP721 and SYP121 were among the top hits whereas no exocyst subunits were found in the interatom. Multiple biochemical experiments have verified the interaction between RabA2A and the VAMP721-SYS121 SNARE complex. Moreover, constitutive-active RabA2A enhanced the membrane localization of the SNARE complex while dominant-negative RabA2A impeded the interaction. However, neither RabA2A nor SNARE proteins interacted with the exocyst subunits. Genetic experiments implied that the RabA2A-SNARE and the exocyst pathway are mutually exclusive with different cargo selections. Based on these findings, we proposed that two parallel pathways may exist to regulate the exocytosis and membrane fusion processes with different cargo selections.