GA3ox

GA3ox, short for gibberellin 3-oxidase, refers to a group of plant enzymes that catalyze a key late step in gibberellin biosynthesis. These enzymes perform a 3β-hydroxylation on inactive gibberellin precursors to generate bioactive gibberellins, such as converting GA9 to GA4 and producing other active 3-oxidized GA forms. Through this reaction, GA3ox controls the pool of active gibberellins that regulate growth and development in plants.

GA3ox enzymes belong to the 2-oxoglutarate-dependent dioxygenase (2-ODD) family and require Fe2+ and 2-oxoglutarate as cofactors. They are typically localized in the cytosol and share the characteristic iron-binding motif common to 2-ODD enzymes, enabling them to catalyze oxygen insertion into their substrates.

Gene family and expression patterns vary across plant species. In Arabidopsis thaliana, several GA3ox genes exist (for example, AtGA3ox1, AtGA3ox2, AtGA3ox3), and crops such as rice also possess multiple GA3ox members. Expression of GA3ox genes is developmentally regulated and responsive to environmental cues, contributing to tissue-specific and stage-specific GA activity. GA3ox operates downstream of GA biosynthetic steps catalyzed by GA20ox, and together these enzymes shape the levels of bioactive gibberellins that promote processes such as stem elongation, seed germination, and flowering. Loss-of-function mutations in GA3ox can result in dwarfism or delayed development, underscoring its central role in GA signaling and plant morphology.

GA3ox is often discussed alongside other gibberellin oxidases, such as GA20ox and GA2ox, which contribute to GA biosynthesis and deactivation, respectively.