Probable E3 ubiquitin-protein ligase involved in female gametophyte development. Required for fusion of polar nuclei in the embryo sac. 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. Embryo sac development arrest. Unfused polar nuclei.