InterPro-to-GO mappings (IPR016164 FAD-linked oxidase-like C-terminal; IPR015345 Cytokinin_DH_FAD/cytokin-bd; IPR016166 FAD-bd_PCMH; IPR006094) assign catalytic activity, cytokinin metabolic process, FAD binding and FAD-binding to OsCKX2.

UniProt subcellular-location mapping (SL-0112) assigns extracellular region; OsCKX2 has an N-terminal signal peptide and is annotated as Secreted, extracellular space (by similarity).

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 OsCKX2 the keyword "Cytokinin signaling pathway" mapped to "cytokinin-activated signaling pathway" (GO:0009736); this is an over-annotation because OsCKX2 is a cytokinin-DEGRADING enzyme, not a signal-transduction component. Its removal lost no correct biology.

Combined IEA methods (ARBA/InterPro/RHEA:13625/EC:1.5.99.12) assign the specific molecular function cytokinin dehydrogenase activity, matching the curated EC 1.5.99.12 reaction.

The grain-number QTL Gn1a is OsCKX2, a gene for cytokinin oxidase/dehydrogenase (EC 1.5.99.12), an enzyme that degrades the phytohormone cytokinin.

Reduced expression of OsCKX2 causes cytokinin accumulation in inflorescence meristems and increases the number of reproductive organs, enhancing grain yield; OsCKX2 expression correlates inversely with grain number.

OsCKX2 activity was demonstrated by expressing alleles in yeast and showing cleavage of the isopentenyl (iP) side chain; QTL pyramiding of Gn1a with plant-height loci generated lines with beneficial yield traits.

OsCKX2 is preferentially expressed in leaves, culms, inflorescence meristems and flowers, especially vascular tissues; the disruption phenotype is enhanced grain production with higher cytokinin in inflorescence meristems.

Cytokinin oxidases catalyse irreversible degradation of cytokinins and hence modulate cellular cytokinin levels; OsCKX2 is an inflorescence meristem-specific rice cytokinin oxidase (a catabolic enzyme, not a signaling component). This is the second experimental FUNCTION reference cited by UniProt.

RNAi knockdown of OsCKX2 caused a significant increase in cytokinins in the inflorescence meristem (measured by UPLC), confirming the enzyme's role in lowering the bioactive cytokinin pool.

There is a negative correlation between OsCKX2 expression and plant productivity (panicle branching, filled grains per plant, harvest index) under both control and salinity-stress conditions; OsCKX2 regulates floral primordial activity via controlling cytokinin levels, supporting its negative-regulator role in inflorescence/grain development.

Synthesizes Ashikari et al. 2005 (Science) with RNAi (Joshi et al. 2018; Yeh et al. 2015), CRISPR (Rashid et al. 2024) and review (Thiruppathi et al. 2024) literature, concluding OsCKX2 is an FAD-linked cytokinin oxidase/dehydrogenase that irreversibly inactivates cytokinins by N6-isoprenoid side-chain cleavage and controls cytokinin homeostasis in inflorescence meristems, acting as a major negative regulator of grain number/yield.

CKX enzymes catalyse irreversible cytokinin degradation, removing the N6-substituted isoprene chain of cytokinins and their ribonucleosides to produce adenosine/adenine and corresponding aldehydes; CKX enzymes are FAD-linked oxidoreductases with FAD-binding and cytokinin-binding domains.

Cytokinin levels are controlled by biosynthesis/activation, transport, signaling and irreversible degradation; OsCKX2 acts on the degradation arm, lowering the bioactive cytokinin pool rather than transducing the cytokinin signal.

No direct experimental subcellular-localization assay for OsCKX2 itself is reported; a precise compartment (apoplast vs ER vs vacuole) cannot be assigned from the retrieved evidence, though apoplastic cytokinin metabolism occurs in rice.

Reduced OsCKX2 (RNAi/CRISPR) increases tiller and/or grain number, delays senescence and improves salinity/drought-stress yield maintenance, confirming the negative-regulator role; OsCKX2 expression is stage-dependent and inflorescence-meristem enriched.

Reference framework for assessing computational GO/EC predictions and over-annotation error types; relevant background for evaluating the IEA/keyword-derived annotations reviewed here (not gene-specific to OsCKX2).