Probable E3 ubiquitin-protein ligase involved in the regulation of root growth. Acts as positive regulator of root gravitropism. 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. Expressed in root tips, cotyledons, leaf primordia and hypocotyls.