Functions as an E3 ubiquitin-protein ligase. Prevents premature senescence probably by targeting proteins involved in this process for degradation. Promotes the degradation of AAO3 and thus represses abscisic acid (ABA) biosynthesis. 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 AAO3. Binds to SD129. Expressed in leaves, root vasculature and guard cells. Premature senescence under low light conditions accompanied by enhanced ABA biosynthesis, accumulation of AAO3, and reduced photosynthetic capacity. May be due to a competing acceptor splice site.