Possesses E3 ubiquitin-protein ligase activity in vitro. Mediates mainly 'Lys-48'-linked polyubiquitination. Promotes abscisic acid (ABA)-induced stomatal closure, reactive oxygen species (ROS) production and drought tolerance (PubMed:26508764). Involved in the regulation of stomatal aperture (PubMed:25002225). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with SRK2D/2SNRK2.2, SRK2I/SNRK2.3 and SRK2E/SNRK2.6. Expressed in roots, leaves, and anthers and stigma of open flowers. Induced during sucrose starvation. Repressed by sucrose (PubMed:17217462). Induced by cold, drought and salt stresses, and abscisic acid (ABA) (PubMed:26508764). Phosphorylated at Ser-173, Thr-178 and Ser-208 by SRK2E/SNRK2.6 in response to abscisic acid (ABA). Phosphorylation activates its E3 ubiquitin-protein ligase activity. Decreased relative stomata aperture under normal growth conditions (PubMed:25002225). No visible phenotype under normal growth conditions, but mutant plants display decreased sensitivity to abscisic acid (ABA) during seed germination (PubMed:26508764). Truncated N-terminus.