Key oxidase enzyme in the biosynthesis of gibberellin that catalyzes the conversion of GA53 to GA20 via a three-step oxidation at C-20 of the GA skeleton (PubMed:12077303, PubMed:11961544, PubMed:30002253). Catalyzes the conversion of GA12 to GA9 via a three-step oxidation at C-20 of the GA skeleton (PubMed:30002253). Contributes to the promotion of internode elongation in response to submergence via ethylene and gibberellin signalings (PubMed:30002253). 2 2-oxoglutarate + gibberellin A12 + H(+) + 3 O2 = 3 CO2 + gibberellin A9 + 2 H2O + 2 succinate 2 2-oxoglutarate + gibberellin A53 + H(+) + 3 O2 = 3 CO2 + gibberellin A20 + 2 H2O + 2 succinate Strongly expressed in leaf blades, stems and unopened flowers. Lower expression in leaf sheath, rachis, shoot apex and roots. Expressed within 48 hours after sowing, as well as in 10-day-old plants and flowering panicles. Induced by ethylene. Sd-1 is the major semidwarfing allele extensively used in modern rice cultivars. This gene, also known as the 'green revolution gene' has been introduced by conventional breeding procedures into several cultivars. It provides rice cultivars with short, thick culms, raises the harvest index, improves lodging resistance and responsiveness to nitrogen fertilizer, resulting high yields without affecting panicle and grain quality. A second gene, 20ox1, is preferentially expressed in the reproductive organs and enables the flowers in sd1 plants to develop and be fertilized normally. Belongs to the iron/ascorbate-dependent oxidoreductase family. GA20OX subfamily.