GA3oxidases

GA3oxidases, or GA3ox, are a family of plant enzymes that catalyze the final 3β-hydroxylation step in the biosynthesis of bioactive gibberellins. They convert the inactive GA precursors GA20 and GA9 into the active gibberellins GA1 and GA4, respectively, by adding a hydroxyl group at carbon-3. Through this step, GA3ox activity controls the main flux toward the biologically active GA pool and thereby influences growth-related processes such as seed germination, stem elongation, flowering time, and leaf expansion.

Biochemical properties: GA3ox enzymes belong to the 2-oxoglutarate-dependent dioxygenase (2-ODD) superfamily. They require Fe2+ and 2-oxoglutarate as cofactors and share characteristic motifs such as the HxD…H catalytic triad. The GA3ox gene family is present in many land plants, often with multiple paralogs (for example Arabidopsis thaliana GA3ox1–GA3ox4 and rice GA3ox1–GA3ox4).

Regulation and function: GA3ox expression is developmentally regulated and subject to feedback by GA levels and environmental cues such as light. Loss-of-function mutations in GA3ox genes typically reduce levels of active GA and cause dwarfism or delayed germination, while overexpression can lead to taller plants and altered flowering time, depending on the genetic background and environment.

Evolution and significance: Because they act downstream of GA20-oxidases in the biosynthetic pathway, GA3ox enzymes are key control points for active GA production. They have been studied in crop species to manipulate plant height and yield, and their activity contributes to species-specific GA responses.