PUB/U-box E3 ligase functions (plasma-membrane localization, regulation of brassinosteroid mediated signaling pathway) propagated across the PANTHER PTN004573631 phylogenetic group are consistent with the rice TUD1 experimental data.

SwissProt keyword-derived (SPKW) annotation present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.

For TUD1, the keyword "Brassinosteroid signaling pathway" maps to a genuinely correct pathway-membership term (GO:0009742); TUD1 is a true BR signaling-pathway component (epistatic to and physically bound to the Galpha subunit D1), so this is a legitimate-keep case rather than an over-annotation. The more specific regulatory term GO:1900457 is retained in current GOA, so removal did not leave the gene without a BR-process annotation.

The UniProt "Cell membrane" subcellular location (SL-0039) maps to GO plasma membrane; confirmed experimentally by TUD1::sGFP imaging.

InterPro/ARBA/EC-based IEA methods assign ubiquitin-protein transferase / ubiquitin protein ligase activity and protein ubiquitination from the U-box and PUB-family domains; confirmed experimentally by in vitro E3 ligase assays.

TUD1 (Os03g0232600, intronless ORF encoding a 459-aa U-box protein) is a functional E3 ubiquitin ligase; purified GST-TUD1 shows in vitro ubiquitination activity, abolished in tud1-1/tud1-3/tud1-4 mutant proteins.

TUD1::sGFP localizes predominantly to the plasma membrane in rice protoplasts.

TUD1 physically interacts with the rice Galpha subunit D1 (BiFC, yeast two-hybrid, GST pull-down); binds both GDP- and GTPgammaS-bound D1.

tud1 is epistatic to d1 and additive with d61 (OsBRI1), placing TUD1 downstream of D1 in a Galpha-mediated BR signaling pathway parallel to / partly overlapping the canonical OsBRI1 pathway.

tud1 mutants are BR-insensitive (reduced lamina-joint bending and seminal-root inhibition) but have normal GA and cytokinin responses; dwarfism is due mainly to decreased cell proliferation and disorganized cell files in aerial organs.

ELF1 (= TUD1) encodes a protein with a U-box domain and ARMADILLO (ARM) repeats and possesses E3 ubiquitin ligase activity in vitro; the entire ARM-repeat region is indispensable for activity.

The spontaneous elf1-1 mutant is a BR-insensitive dwarf with erect leaves and short grains; ELF1 functions as a positive regulator of brassinosteroid signaling in rice.

ELF1 is proposed to ubiquitinate target proteins through an ARM-repeat-mediated interaction; ELF1 itself does not appear to be polyubiquitinated.

Synthesizes the rice TUD1/ELF1/OsPUB75 literature, concluding TUD1 is a plant U-box (PUB) E3 ubiquitin ligase that positively regulates BR-mediated growth and architecture; it shows in vitro E3 activity, predominant plasma-membrane localization, direct interaction with the Galpha subunit D1/RGA1, and genetic placement downstream of D1 in a BR-related signaling branch overlapping the OsBRI1 pathway.

Reports a later mechanistic model (Liu et al. 2025, Plant Communications) in which TUD1 promotes BR-induced degradation of the GSK3/SHAGGY-like kinase GSK2, a central negative regulator of BR signaling, providing a candidate in vivo substrate.

Notes tud1/elf1 loss-of-function mutants are BR-insensitive dwarfs with erect leaves and short grains (grain length reduced ~30-44%); phenotypes attributed mainly to reduced cell proliferation.