Dual role of <i>Glossy15</i> in regulating flowering by modulating gibberellins and floral organ gene expression in maize

Flowering time is determined by two developmental transitions (vegetative phase change and floral transition), and is a key determinant of maize adaptation and yield potential. Glossy15 (Gl15) encodes an APETALA2 (AP2)-like transcription factor that negatively regulates maize vegetative phase change. However, the underlying explicit molecular mechanism of Gl15 remains unclear. In this study, we report that Gl15 is a candidate quantitative trait locus (QTL) for vegetative phase change and a selective target during modern maize breeding, and demonstrate that the Hap1 allele of Gl15 likely represents a favorable haplotype under selection for early flowering. We show that Gl15 directly downregulates the expression of a gibberellin (GA) biosynthesis gene (DWARF1, D1), but upregulates the expression of a GA catabolism gene (ZmGA2ox3) in both the leaf and shoot apices, leading to reduced bioactive GA levels and delayed flowering. We also find that Gl15 directly inhibits the expression of the floral activator ZMM4 in the shoot apex to delay floral transition. Our findings suggest a dual role of Gl15 in regulating flowering by modulating gibberellins and floral organ gene expression in maize, and provide new genetic targets for improving flowering time in maize cultivars.