Key oxidase enzyme in the biosynthesis of gibberellin (Ref.1, PubMed:15604710). Catalyzes the conversion of GA12 and GA53 to GA9 and GA20 respectively, via a three-step oxidation at C-20 of the GA skeleton (Ref.1). 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 Binds 1 Fe(2+) ion per subunit. Preferentially expressed in reproductive organs (PubMed:11961544). Expressed in the epithelium of embryos and the tapetum of anthers. Expressed at low levels in the shoot apical meristem (PubMed:12834406). Negatively controlled by the level of physiologically active gibberellin. Plants over-expressing GA20OX1 have high levels of bioactive gibberellins, and exhibit an overgrowth phenotype with increased internode elongation and leaf sheath length (PubMed:15604710). Plant silencing GA20OX1 exhibit a semi-dwarf phenotype (PubMed:15604710). Belongs to the iron/ascorbate-dependent oxidoreductase family. GA20OX subfamily. Truncated N-terminus.