ARR5 notes (Q9SB04, At3g48100, IBC6/ATRR2)

2026-10-05 review session (cytokinin two-component signaling module)

• Identity checked: UniProt Q9SB04 ARR5_ARATH, At3g48100, 184 aa, receiver domain only (type-A).
• Deep research tooling failed; review from cached publications.
• Rapid primary cytokinin induction [PMID:9634588 "this induction did not require de novo protein synthesis"; PMID:11115887].
• Receiver phosphorylation (Asp87) required for function; cytokinin stabilizes ARR5 PMID:18065689.
• Negative regulator, redundant with other type-A ARRs PMID:14973166; AXR1-dependent proteolysis PMID:23279608.
• Circadian: period phenotype maps to ARR3/ARR4, not ARR5 PMID:16326927 -> GO:0007623 over-annotated.
• IBA DNA-binding TF and sequence-specific DNA binding from PTN008123536 (seeded by type-B ARRs) removed: ARR5 lacks the B-motif output domain.
• Proposed NEW: GO:0080037 negative regulation of cytokinin-activated signaling pathway (IMP, PMID:14973166).