Maize ZmMYB59 inhibits post‐germinative shoot and root elongation through ZmGA2ox3 /10‐mediated gibberellin catabolism

Summary Gibberellin (GA) promotes seed germination, but sustained or excessive GA signaling after germination can lead to aberrant root and shoot elongation. How GA homeostasis is transcriptionally restrained during post‐germinative seedling development remains unclear. Using overexpression and gene‐edited maize materials, we demonstrate that ZmMYB59 inhibits root and shoot elongation during post‐germinative growth. Integrated RNA‐Seq and CUT&Tag analyses identified the GA catabolism genes ZmGA2ox3 and ZmGA2ox10 as candidate direct targets of ZmMYB59. Hormone profiling analysis showed elevated bioactive GA 1 and GA 4 levels in the scutellum and aleurone layer cells of zmmyb59 mutants. Dual‐luciferase assays, electrophoretic mobility shift assays, and ChIP‐qPCR further confirmed that ZmMYB59 directly binds AC8 cis ‐elements in the ZmGA2ox3/10 promoters and activates their transcription. The zmga2ox3/10 double mutant, but neither single mutant, exhibited enhanced root and shoot elongation, accompanied by GA 4 accumulation. This phenotype was suppressed by exogenous application of the GA biosynthesis inhibitor uniconazole. Transcriptomic and biochemical analyses further revealed enhanced starch degradation, reduced starch content, and increased soluble sugar accumulation in the double mutant. Taken together, these findings reveal that the ZmMYB59‐ZmGA2ox3/10 module restrains GA accumulation and starch mobilization after germination, thereby coordinating reserve utilization with post‐germinative root and shoot growth in maize.