Involved in the trafficking of soluble cargo proteins from the prevacuolar compartment to the central vacuole (PubMed:12724533, PubMed:21899678). Involved in vacuolar transport of storage proteins with EREX as effector. Regulates membrane trafficking to protein storage vacuoles (PSVs). Interacts with VPS9A (PubMed:18055610). Interacts with EREX (via PX domain) (PubMed:27288222). Binds to VPS3 (PubMed:29463724). High in stem, root, and inflorescence. Expressed during pollen germination and pollen tube growth. Activated by VPS9A. Belongs to the small GTPase superfamily. Rab family.