GA Associated Dwarf 5 encodes an ent-kaurenoic acid oxidase required for maize gibberellin biosynthesis and morphogenesis

Gibberellin(GA) functions in plant growth and development. However, genes involved in the biosynthesis and regulation of GA in crop plants are poorly understood. We isolated the mutant gad5-1(GAAssociated Dwarf 5), characterized by dwarfing, short internodes, and dark green and short leaves.Map-based gene cloning and allelic verification confirmed that Zm GAD5 encodes ent-kaurenoic acid oxidase(KAO), which catalyzes KA(ent-kaurenoic acid) to GA12 conversion during GA biosynthesis in maize.Zm GAD5 is localized to the endoplasmic reticulum and is present in multiple maize organs. In gad5-1, the expression of Zm GAD5 is severely reduced, and the levels of the direct substrate of KAO, KA, is increased,leading to a reduction in GA content. The abnormal phenotype of gad5-1 was restored by exogenous application of GA3. The biomass, plant height, and levels of GA12and GA3in transgenic Arabidopsis overexpressing Zm GAD5 were increased in comparison with the corresponding controls Col-0. These findings deepen our understanding of genes involved in GA biosynthesis, and could lead to the development of maize lines with improved architecture and higher planting-density tolerance.