Activates the ARF proteins by exchanging bound GDP for free GTP. Plays a role in vesicular protein sorting. Acts as the major regulator of endosomal vesicle trafficking but is also involved in the endocytosis process. Could function redundantly with GNL1 in the retrograde Golgi to endoplasmic reticulum trafficking. Regulates vesicle trafficking required for the coordinated polar localization of auxin efflux carriers which in turn determines the direction of auxin flow. Mediates the sorting of PIN1 from endosomal compartments to the basal plasma membrane and the polarization of PIN3 to the bottom side of hypocotyl endodermal cells. Involved in the specification of apical-basal pattern formation in the early embryo and during root formation. Required for correct cell wall organization leading to normal cell adhesion during seedling development. Also plays an essential role in hydrotropism of seedling roots. Inhibited by brefeldin A (BFA). Homodimer. Interacts with CYP19-4/CYP5 in vitro. Soluble and partially membrane-bound. Stems, leaves, flowers, siliques, floral inflorescence and roots. Expressed in the whole plant (at the protein level). Continually expressed in both embryogenesis and postembryonic organ development. Strongly expressed in actively dividing or elongating cells but only weakly or not at all in differentiated tissues other than the vasculature. The DCB domain is required for both homodimerization and interaction with CYP protein. Heterotypic interaction of DCB domain with the N-terminal part of the SEC7 domain is required for membrane association and catalytic activity of the protein. Lack of morphological features of apical-basal polarity resulting of no root, no true hypocotyl and abnormal shoot apical meristem. Cell wall alterations. Defects in cell adhesion. Aberrant leaf venation. Truncated N-terminus.