KAO1 (ent-kaurenoic acid oxidase, CYP88A3; At1g05160) is an endoplasmic reticulum membrane-anchored cytochrome P450 that catalyses three successive oxidations of ent-kaurenoic acid (ent-7alpha-hydroxylation, then formation of GA12-aldehyde with B-ring contraction, then oxidation to the C-7 carboxylic acid) to produce GA12, the first gibberellin and common precursor of all bioactive GAs. KAO1 and its paralog KAO2 are expressed mainly in germinating seeds and young developing organs and act redundantly: single mutants are wild-type, whereas the kao1 kao2 double mutant is a non-germinating, severely GA-deficient dwarf resembling ga1-3.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004497 monooxygenase activity | IEA GO_REF:0000002 | MODIFY | Summary: Monooxygenase activity from InterPro P450 domains. Reason: Correct parent; the specific activity (ent-kaurenoic acid oxidase, EC 1.14.14.107) is experimentally established. Proposed replacements: ent-kaurenoic acid monooxygenase activity Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0005506 iron ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Iron ion binding from InterPro P450 signatures; reflects the heme iron. Reason: The P450 coordinates the heme iron through its proximal cysteine thiolate, so iron binding is not wrong. GO:0020037 heme binding is not a descendant of GO:0005506, so the two terms are not redundant. Iron is a catalytic cofactor rather than the core function (consistent with other ARATH P450 reviews and with magnesium ion binding on the GA1/GA2 terpene cyclases); retained as non-core. Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: ER localization inherited within the CYP88A clade. Reason: Consistent with GFP targeting. Supporting Evidence: PMID:11722763 The leader sequences of the two ent-kaurenoic acid oxidases (AtKAO1 and AtKAO2) from Arabidopsis direct GFP to the endoplasmic reticulum. |
| GO:0005783 endoplasmic reticulum | IDA PMID:11722763 A plastid envelope location of Arabidopsis ent-kaurene oxida... | ACCEPT | Summary: The KAO1 leader sequence directs GFP to the ER. Reason: Direct experimental evidence. Supporting Evidence: PMID:11722763 The leader sequences of the two ent-kaurenoic acid oxidases (AtKAO1 and AtKAO2) from Arabidopsis direct GFP to the endoplasmic reticulum. |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA ER localization. Reason: Consistent with experimental data. Supporting Evidence: PMID:11722763 The leader sequences of the two ent-kaurenoic acid oxidases (AtKAO1 and AtKAO2) from Arabidopsis direct GFP to the endoplasmic reticulum. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: ER membrane (UniProt subcellular location; N-terminal membrane anchor typical of microsomal P450s). Reason: Most specific supported location; used as core-function location. Supporting Evidence: PMID:11722763 The leader sequences of the two ent-kaurenoic acid oxidases (AtKAO1 and AtKAO2) from Arabidopsis direct GFP to the endoplasmic reticulum. |
| GO:0009686 gibberellin biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: KAO converts ent-kaurenoic acid to GA12, the precursor of all GAs. Reason: Consistent with experimental data. Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0009686 gibberellin biosynthetic process | TAS PMID:15923331 The involvement of gibberellin 20-oxidase genes in phytochro... | ACCEPT | Summary: Author statement in a GA20ox expression study listing KAO among GA biosynthetic genes. Reason: Correct; directly supported by enzyme assays and kao1 kao2 double mutant phenotype. Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). PMID:25146977 the kao1 kao2 double mutant exhibits typical non-germinating GA-dwarf phenotypes, similar to those observed in the severely GA-deficient ga1-3 mutant |
| GO:0016705 oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen | IEA GO_REF:0000002 | MODIFY | Summary: Generic P450 oxidoreductase activity. Reason: Correct parent; use the specific activity. Proposed replacements: ent-kaurenoic acid monooxygenase activity Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0020037 heme binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Heme binding (P450 cofactor). Reason: Correct cofactor binding; non-core. Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0048868 pollen tube development | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Pollen tube development, propagated from rice KAO/RPE1 (REDUCED POLLEN ELONGATION 1). Reason: GA is required for pollen tube elongation and the rice KAO mutant shows a pollen-tube defect, so the inference is biologically plausible for Arabidopsis KAOs, but it is a downstream consequence of GA supply rather than a distinct molecular role; in Arabidopsis the redundant KAO1/KAO2 pair has only been shown to be required for GA production throughout development. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN001209423 SUPPORTS TRANSFER CYP88A KAO clade node; transfer within orthologous KAO enzymes is phylogenetically sound. UniProtKB:Q5VRM7 SUPPORTS TRANSFER Rice KAO/RPE1, whose mutant has reduced pollen tube elongation; the phenotype reflects GA deficiency in pollen. Supporting Evidence: PMID:25146977 the kao1 kao2 double mutant exhibits typical non-germinating GA-dwarf phenotypes, similar to those observed in the severely GA-deficient ga1-3 mutant |
| GO:0051777 ent-kaurenoic acid monooxygenase activity | IBA GO_REF:0000033 | ACCEPT | Summary: ent-Kaurenoic acid oxidase activity conserved in the CYP88A clade. Reason: Experimentally supported on the target itself. Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0051777 ent-kaurenoic acid monooxygenase activity | IDA PMID:11172076 The CYP88A cytochrome P450, ent-kaurenoic acid oxidase, cata... | ACCEPT | Summary: Yeast expressing KAO1 converts ent-kaurenoic acid to GA12 in three steps. Reason: Core activity (RHEA:33219). Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
| GO:0051777 ent-kaurenoic acid monooxygenase activity | IEA GO_REF:0000120 | ACCEPT | Summary: EC/Rhea mapping. Reason: Matches experimental evidence. Supporting Evidence: PMID:11172076 Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA(12). |
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Download this section (compressed HTML)Q: Do KAO1 and KAO2 differ in substrate kinetics, ER subdomain or cell-type expression in a way that explains why both paralogs are retained?
Experiment: Compare recombinant KAO1 and KAO2 kinetics in a common microsomal system and map promoter activities at cellular resolution in germinating seeds and inflorescences.
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