Converts the inactive gibberellin (GA) precursors GA9 and GA20 in the bioactives gibberellins GA4 and GA1 (PubMed:9836749). Involved in the production of bioactive GA for vegetative growth and development (PubMed:16460513). 2-oxoglutarate + gibberellin A20 + O2 = CO2 + gibberellin A1 + succinate Binds 1 Fe(2+) ion per subunit. Plant hormone biosynthesis; gibberellin biosynthesis. Highly expressed in seedlings but also expressed in roots, leaves, stems, flowers, siliques and seeds. Detected predominantly in the hypocotyl and roots of young seedlings and in the petioles and vasculature of leaves. Not expressed in the shoot apical meristem, but found in the elongation zone, the quiescent center cells and the columella cells of the root tips. Found in the cortex and the endodermis of the embryo axis in germinating seeds. Expressed in germinating seeds and in very young seedlings. Declines to low levels during later stages of development. Not under feedback regulation. Regulated by phytochrome. Induced by red light pulse and reaches its maximum level after 12 hours. Transcriptionally regulated by LEAFY COTYLEDON2 and FUSCA3. Not regulated by cold treatment or auxin. Up-regulated by paclobutrazol. No visible phenotype; probably due to redundancy with GA3OX1. Ga3ox1 and ga3ox2 double mutant has a severe defect in seed germination and root growth, and a dwarf phenotype. Belongs to the iron/ascorbate-dependent oxidoreductase family. GA3OX subfamily.