Involved in auxin-mediated response. May be involved in vesicle trafficking of components involved in polar auxin transport. Binds GTP and GDP and possesses intrinsic GTPase activity. Located in the plasma membrane and endocytic vesicles derived from the plasma membrane. By auxin. Slight increase of primary root elongation and lateral root branching and hypersensitivity of root growth in response to exogenous auxin. Plants overexpressing RABA1A show reduced growth of roots and shoots and smaller leaf sizes. Belongs to the small GTPase superfamily. Rab family.