AHK2 notes (Q9C5U2, At5g35750)

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

• Identity checked: UniProt Q9C5U2 AHK2_ARATH, At5g35750, 1176 aa CHASE-domain hybrid histidine kinase.
• Deep research (just deep-research-perplexity-lite) failed in this environment ("All providers failed"); no deep-research file was produced. Review is based on cached publications.
• One of three cytokinin receptors PMID:14503005.
• Positive regulator of cytokinin signaling, redundant with AHK3/AHK4 PMID:15155880; triple mutant is fully cytokinin-insensitive PMID:15166290.
• Kinase-favouring receptor: PMID:16753566 -> supports the NOT phosphoprotein phosphatase annotation.
• Location: mainly ER PMID:21709172; plasma membrane kept as non-core.
• Physiology (non-core): secondary growth/procambium PMID:19622803, flower development via CUC2/CUC3 PMID:19913077, cold/ABA PMID:20463025, drought/salt negative regulation PMID:18077346, seed germination & chlorophyll retention PMID:16361392.
• Flags:
• GO:0009636 (PMID:17216481): abstract describes the cre1 (AHK4) mutant, not ahk2 -> UNDECIDED.
• GO:0046686 (PMID:40858022): "AtHK2" in a glycolysis/autophagy context may be HEXOKINASE2 -> UNDECIDED.
• GO:0034757 (PMID:18397377): abstract names AHK3 and CRE1 only -> UNDECIDED.
• Protein-binding rows (Y2H): AHK-AHK -> MODIFY to GO:0043424; AHK-AHP and screen partners -> REMOVE (phosphotransfer captured by GO:0000155).
• Proposed NEW: GO:0009885 transmembrane histidine kinase cytokinin receptor activity (AHK4 already carries it by IDA).

2026-10-06 follow-up: resolving UNDECIDED rows

• Tried full text for PMID:17216481, PMID:18397377, PMID:40858022: none has a PMC/Europe PMC copy (Europe PMC: no pmcid, not open access); publisher pages (Springer, Wiley, ScienceDirect) blocked (403/login redirect). Web search snippets repeat the abstracts only.
• PMID:17216481 (GO:0009636) and PMID:18397377 (GO:0034757 IMP + ARBA IEA): cannot see whether ahk2 was assayed; deferred to curator as KEEP_AS_NON_CORE (plausible for a redundant cytokinin receptor, indirect output).
• PMID:40858022 (GO:0046686): "AtHK2" appears with AtGAPDH/AtENO2 in a glycolysis/energy context, most consistent with HEXOKINASE2; marked MARK_AS_OVER_ANNOTATED with a reference_review noting the suspected gene mis-mapping (unverified without full text).