Activates the ARF proteins by exchanging bound GDP for free GTP. Plays a role in vesicular protein sorting. Acts as the major regulator of early endosomal vesicle trafficking, particularly at the trans-Golgi-network/early endosome (TGN/EE), but is also involved in the endocytosis process (PubMed:23737757). Together with VPS45/BEN2 required for polar PIN-FORMED (PIN) proteins localization, for their dynamic repolarization, and consequently for auxin activity gradient formation and auxin-related developmental processes (e.g. embryonic patterning, organogenesis and vasculature venation patterning) (PubMed:23737757). Target of hopM1, a conserved Pseudomonas syringae virulence protein that directs the protein to its own proteasome-mediated degradation. Plays a broad role in PAMP-triggered immunity (PTI), effector-triggered immunity (ETI), and salicylic acid (SA)-regulated immunity. Inhibited by brefeldin A. Homodimer (By similarity). Interacts with hopM1 (PubMed:16840699). Interacts with HLB1 (PubMed:26941089). Soluble and partially membrane-bound. A number of isoforms are produced. According to EST sequences. By the pathogen elicitor flagellin 22 and by benzothiadiazole (BTH), a synthetic activator of the salicylic acid (SA)-dependent immunity (at protein level). Ubiquitinated. Inhibited trafficking at the trans-Golgi-network/early endosome (TGN/EE) leading to an increased accumulation of PIN2 in agglomerated intracellular compartments leading to an altered auxin gradient and subsequent growth defects (e.g. disrupted roots architecture and shoot growth) (PubMed:23737757). Increased susceptibility to Pseudomonas syringae infection (PubMed:16840699). Displays growth and polarity defects (PubMed:19230664).