GA is an important phytohormone that regulates numerous developmental processes throughout the plant life-cycle, however, it remains unclear how GA regulates the development of leaf margins. Wen et al. (see pp. 321-333) investigated the critical role of GA levels in leaf margin formation by identifying a loss of function mutant ga3-oxidase 1 (mtga3ox1) in the model legume Medicago truncatula. MtGA3ox1 was found to be under the feedback-dependent control of the MtDELLA1/2/3-MtGAF1 complexes, while MtARF3 was shown to behave as a competitive inhibitor of the MtDELLA2/3-MtGAF1 complexes to repress the expression of MtGA3ox1 indirectly. These findings suggest that GA feedback regulatory circuits play a fundamental role in leaf margin formation.