E3 ubiquitin ligase that may function as positive regulator of brassinosteroid (BR) signaling. Possesses E3 ubiquitin ligase in vitro (PubMed:24299927, PubMed:23526892). Acts together with the heterotrimeric G alpha subunit GPA1 at the plasma membrane to mediate a BR signaling pathway that affects plant growth and development. Does not seem to be involved in gibberellin or cytokinin responses (PubMed:23526892). 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 GPA1. Expressed highly in panicles at flowering time, at moderate levels in vegetative shoot apices, leaf sheaths, leaf blades, and elongating internodes, and at low levels in roots. Slightly down-regulated by brassinolide. Dwarf phenotype with erect leaves and short grains (PubMed:24299927, PubMed:23526892). Dwarf phenotype is mainly due to decreased cell proliferation and disorganized cell files in aerial organs (PubMed:23526892).