E3 ubiquitin-protein ligase which accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates. Modulates amyloplast dynamics and sedimentation in statocytes during inflorescence, hypocotyl and root gravitropism, probably by regulating amyloplast interaction with actin filaments (AFs) in endodermal cells. 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. Localized at amyloplasts within gravity-sensing cells. Expressed in seedlings, hypocotyls, roots and stems. Present especially in hypocotyl and inflorescence endodermis, as well as in root cap columella, tissues that act as statocytes. Auto-ubiquitinated as part of the enzymatic reaction. Reduced gravitropism, altered amyloplasts sedimentation but increased amyloplasts saltatory movement. Abnormal interactions between amyloplasts and actin filaments (AFs) in endodermal cells. Truncated N-terminus.