A SNARE Complex Unique to Seed Plants Is Required for Protein Storage Vacuole Biogenesis and Seed Development of Arabidopsis thaliana

The SNARE complex is a key regulator of vesicular traffic, executing membrane fusion between transport vesicles or organelles and target membranes. A functional SNARE complex consists of four coiled-coil helical bundles, three of which are supplied by Q-SNAREs and another from an R-SNARE. Arabidopsis thaliana VAMP727 is an R-SNARE, with homologs only in seed plants. We have found that VAMP727 colocalizes with SYP22/VAM3, a Q- SNARE, on a subpopulation of prevacuolar compartments/endosomes closely associated with the vacuolar membrane. Genetic and biochemical analyses, including examination of a synergistic interaction of vamp727 and syp22 mutations, histological examination of protein localization, and coimmunoprecipitation from Arabidopsis lysates indicate that VAMP727 forms a complex with SYP22, VTI11, and SYP51 and that this complex plays a crucial role in vacuolar transport, seed maturation, and vacuole biogenesis. We suggest that the VAMP727 complex mediates the membrane fusion between the prevacuolar compartment and the vacuole and that this process has evolved as an essential step for seed development.