GA20OX1 (GA5, AtGA20ox1; At4g25420) encodes a gibberellin 20-oxidase, a soluble 2-oxoglutarate- and Fe(II)-dependent dioxygenase that catalyses the successive oxidation of C-20 of GA12 and GA53 (via the alcohol and aldehyde) and its removal to form the C19-gibberellins GA9 and GA20, the immediate precursors of bioactive GA4 and GA1. It is one of five Arabidopsis GA20ox genes and, with GA20ox2, is the main paralog in vegetative and early reproductive development; the two act partially redundantly to promote hypocotyl and internode elongation, flowering, anther filament and silique growth. ga5 mutants are semi-dwarfs. GA20OX1 transcription is a major control point of GA levels: it is repressed by bioactive GA through DELLA-dependent feedback, induced by long days and far-red-rich light, and subject to circadian and auxin regulation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | ISM GO_REF:0000122 | ACCEPT | Summary: Predicted cytoplasmic localization. Reason: GA 20-oxidases are soluble 2-oxoglutarate-dependent dioxygenases without targeting signals; the late steps of GA biosynthesis are cytosolic. Supporting Evidence: PMID:22533671 In higher plants, GAs are synthesized by the action of terpene cyclases, cytochrome P450 mono-oxygenases and 2-oxoglutarate-dependent dioxygenases localized, respectively, in plastids, the endomembrane system and the cytosol. |
| GO:0005737 cytoplasm | TAS PMID:10330476 Feedback regulation of GA5 expression and metabolic engineer... | ACCEPT | Summary: Author statement that GA20ox is cytoplasmic. Reason: Consistent with the cytosolic location of GA dioxygenases. Supporting Evidence: PMID:22533671 In higher plants, GAs are synthesized by the action of terpene cyclases, cytochrome P450 mono-oxygenases and 2-oxoglutarate-dependent dioxygenases localized, respectively, in plastids, the endomembrane system and the cytosol. |
| GO:0009416 response to light stimulus | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Response to light stimulus propagated in the GA20ox clade. Reason: GA20ox1 transcript levels respond to photoperiod and far-red light, and the gene contributes to light-regulated petiole elongation in short days; this is regulation of the enzyme rather than its core function. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN001612387 SUPPORTS TRANSFER GA20ox clade node seeded by Arabidopsis GA20ox1/GA20ox2, whose expression is light/photoperiod regulated. AGI_LocusCode:AT5G51810 SUPPORTS TRANSFER GA20ox2, the most far-red-responsive GA20ox gene. Supporting Evidence: PMID:7604047 Expression of the GA5 gene in Ara-bidopsis leaves was enhanced after plants were transferred from short to long days; it was reduced by GA4 treatment, suggesting end-product repression in the GA biosynthetic pathway. PMID:15923331 AtGA20ox1 also responded but to a lesser extent. PMID:15923331 it was only in SD that a T-DNA insertional mutant of AtGA20ox1 (ga5-3) showed reduced response |
| GO:0009686 gibberellin biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: GA20ox1 oxidizes C-20 of GA12/GA53 through to the C19-GAs GA9/GA20, the immediate precursors of bioactive GA4/GA1. Reason: Conserved role of the GA20ox clade. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0009686 gibberellin biosynthetic process | IDA PMID:7630935 Isolation and expression of three gibberellin 20-oxidase cDN... | ACCEPT | Summary: GA20ox1 oxidizes C-20 of GA12/GA53 through to the C19-GAs GA9/GA20, the immediate precursors of bioactive GA4/GA1. Reason: Recombinant enzyme converts GA12 to GA9. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0009686 gibberellin biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: GA20ox1 oxidizes C-20 of GA12/GA53 through to the C19-GAs GA9/GA20, the immediate precursors of bioactive GA4/GA1. Reason: Consistent with experimental evidence. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0009686 gibberellin biosynthetic process | TAS PMID:15923331 The involvement of gibberellin 20-oxidase genes in phytochro... | ACCEPT | Summary: GA20ox1 oxidizes C-20 of GA12/GA53 through to the C19-GAs GA9/GA20, the immediate precursors of bioactive GA4/GA1. Reason: Consistent with experimental evidence. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0009739 response to gibberellin | IEP PMID:7604047 The GA5 locus of Arabidopsis thaliana encodes a multifunctio... | KEEP AS NON CORE | Summary: GA20ox1 (GA5) transcript is down-regulated by bioactive GA (negative feedback). Reason: Genuine transcriptional response forming part of GA homeostasis, but a regulatory property rather than the enzyme's function. Supporting Evidence: PMID:7604047 Expression of the GA5 gene in Ara-bidopsis leaves was enhanced after plants were transferred from short to long days; it was reduced by GA4 treatment, suggesting end-product repression in the GA biosynthetic pathway. PMID:10330476 Negative feedback regulation of GA5 expression was demonstrated in stems of Arabidopsis by bioactive GAs but not by inactive GA. |
| GO:0009740 gibberellic acid mediated signaling pathway | TAS PMID:10330476 Feedback regulation of GA5 expression and metabolic engineer... | MARK AS OVER ANNOTATED | Summary: GA20ox1 makes GA precursors; it is not a component of GA signal transduction. Reason: Feedback regulation of GA5 by GA signaling makes GA20ox1 a target, not a component, of the pathway; the process role is GA biosynthesis. Supporting Evidence: PMID:10330476 Negative feedback regulation of GA5 expression was demonstrated in stems of Arabidopsis by bioactive GAs but not by inactive GA. |
| GO:0045544 gibberellin 20-oxidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: GA 20-oxidase activity conserved in the GA20ox clade. Reason: Experimentally supported on the target. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0045544 gibberellin 20-oxidase activity | IDA PMID:7604047 The GA5 locus of Arabidopsis thaliana encodes a multifunctio... | ACCEPT | Summary: Recombinant GA5 protein converts GA53 to GA44 and GA19 to GA20; ga5 carries a nonsense mutation. Reason: Direct enzyme assay. Supporting Evidence: PMID:7604047 the identity of the cDNA clone was confirmed by analyzing the capability of the fusion protein expressed in Escherichia coli to convert GA53 to GA44 and GA19 to GA20 PMID:7604047 The ga5 semidwarf mutant contains a G-->A point mutation that inserts a translational stop codon in the protein-coding sequence, thus confirming that the GA5 locus encodes GA 20-oxidase. |
| GO:0045544 gibberellin 20-oxidase activity | IDA PMID:7630935 Isolation and expression of three gibberellin 20-oxidase cDN... | ACCEPT | Summary: Recombinant At2301 (GA20ox1) oxidizes GA12 to GA15, GA24 and GA9. Reason: Core activity (RHEA:60772). Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0045544 gibberellin 20-oxidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Rhea/ARBA mapping. Reason: Matches experimental evidence. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0045544 gibberellin 20-oxidase activity | TAS PMID:10330476 Feedback regulation of GA5 expression and metabolic engineer... | ACCEPT | Summary: Author statement on GA5 20-oxidase function. Reason: Consistent with direct enzyme assays. Supporting Evidence: PMID:10330476 The gibberellin (GA) 20-oxidase encoded by the GA5 gene of Arabidopsis directs GA biosynthesis to active GAs |
| GO:0045544 gibberellin 20-oxidase activity | TAS PMID:15923331 The involvement of gibberellin 20-oxidase genes in phytochro... | ACCEPT | Summary: Author statement on GA20ox function. Reason: Consistent with direct enzyme assays. Supporting Evidence: PMID:7630935 each of which oxidized GA12 at C-20 to GA15, GA24, and the C19 compound GA9, a precursor of bioactive GAs |
| GO:0048366 leaf development | IMP PMID:20460583 Increased leaf size: different means to an end. | KEEP AS NON CORE | Summary: GA20OX1 overexpression increases leaf size, mainly through increased cell number. Reason: Overexpression shows that GA supply can promote leaf growth; a downstream developmental consequence of GA biosynthesis, and loss-of-function ga20ox1 ga20ox2 plants show little leaf-expansion defect, so this is non-core. Supporting Evidence: PMID:20460583 we selected five genes belonging to different functional classes that all positively affect leaf size when overexpressed: AVP1, GRF5, JAW, BRI1, and GA20OX1. |
| GO:0048575 short-day photoperiodism, flowering | IEP PMID:7604047 The GA5 locus of Arabidopsis thaliana encodes a multifunctio... | KEEP AS NON CORE | Summary: GA5 expression increases on transfer from short to long days; GA20ox1 contributes redundantly to flowering time. Reason: The supporting observation is transcript-level (GA5 induction on short-to-long-day transfer), which does not by itself place GA20ox1 in either short-day or long-day photoperiodic flowering. The curator's short-day term is consistent with the classical finding that GA is required for Arabidopsis flowering specifically under short days (GA-deficient ga1 mutants fail to flower in short days but flower in long days; Wilson, Heckman and Somerville 1992, Plant Physiol, not in the local publication cache), and GA20ox1/GA20ox2 act redundantly to promote flowering time (PMID:18069939, photoperiod not stated in the cached abstract). The short-day-specific ga5-3 phenotype in PMID:15923331 concerns end-of-day far-red petiole elongation, not flowering, so it does not adjudicate this term. Retained as non-core because GA20ox1 supplies GA precursors and the flowering role is a downstream consequence of GA biosynthesis. Supporting Evidence: PMID:7604047 Expression of the GA5 gene in Ara-bidopsis leaves was enhanced after plants were transferred from short to long days; it was reduced by GA4 treatment, suggesting end-product repression in the GA biosynthetic pathway. PMID:18069939 AtGA20ox1 and AtGA20ox2 act redundantly to promote hypocotyl and internode elongation, flowering time, elongation of anther filaments, the number of seeds that develop per silique and elongation of siliques |
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Experiment: Quantify GA12/GA53-derived intermediates by isotope-dilution LC-MS in ga20ox1 single and ga20ox1 ga20ox2 double mutant organs to assign the in vivo contribution of GA20ox1 to each branch.
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