Plays an important role in intracellular trafficking of seed storage proteins to the protein storage vacuoles (PSVs) (PubMed:21105928). Participates in the transport of the proglutelins from the Golgi apparatus to the PSVs in endosperm (PubMed:21825104). Functions cooperatively with VPS9A to regulate post-Golgi dense vesicle-mediated transport of storage proteins to the type II protein bodies (PBII) protein storage vacuoles in developing endosperm (PubMed:23723154). Involved in the maintenance of the general structural organization of the endomembrane system in developing endosperm (PubMed:21105928, PubMed:21825104). Binds GTP in vitro (PubMed:21105928, PubMed:21825104, PubMed:23723154). Forms a quaternary complex with the two glutelin zipcode RNA-binding proteins RBP-L and RBP-P, and the membrane trafficking factor NSF (PubMed:32471860). This quaternay complex carries glutelin mRNAs for active transport on endosomes to the cortical endoplasmic reticulum membrane, and enables endosome-mediated glutelin mRNA transport in endosperm cells (PubMed:32471860). Interacts with VPS9A (PubMed:23723154, PubMed:24488962). Interacts with NSF and RBP-L (PubMed:32471860). Highly expressed in roots (Ref.1). Expressed at low levels in shoots, flowers and grains (Ref.1). Expression in developing seeds is low from 6 to 12 days after flowering (DAF), peaks at 12 DAF and is barely detected at 15 DAF. Induced by nitrogen and phosphorus starvation in roots. Accumulation of proglutelins in seed endosperm (PubMed:21105928, PubMed:21825104). Mistargeting of dense vesicles (DVs) to the type II protein bodies (PBII) protein storage vacuoles and reduction of PBII size in endosperm. Formation of paramural bodies (PMBs) secretory vesicle-like structures charged with DVs in endosperm (PubMed:21105928, PubMed:21825104). Belongs to the small GTPase superfamily. Rab family.