E3 ubiquitin-protein ligase that promotes the ubiquitination and proteasomal degradation of aquaporin PIP2-1. Forms a ubiquitin ligase complex in cooperation with the E2 enzymes UCB8/UCB10. 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. Ubiquitous. Highly expressed in roots. The RING-type zinc finger domain is required for E3 ligase activity. The C-terminal transmembrane is dispensable for the ubiquitin ligase activity in vitro, but is critical for correct subcellular localization and substrate recognition in vivo. No visible phenotype and no effect on drought stress response, probably due to the redundancy with RMA2 and RMA3.