FT5a interferes with the Dt1-AP1 feedback loop to control flowering time and shoot determinacy in soybean

Flowering time and stem growth habit determine inflorescence architecture in soybean, which in turn influences seed yield. Dt1, a homolog of Arabidopsis TERMINAL FLOWER 1 (TFL1), is a major controller of stem growth habit, but its underlying molecular mechanisms remain unclear. Here, we demonstrate that Dt1 affects node number and plant height, as well as flowering time, in soybean under long-day conditions. The bZIP transcription factor FDc1 physically interacts with Dt1, and the FDc1-Dt1 complex directly represses the expression of APETALA1 (AP1). We propose that FT5a inhibits Dt1 activity via a competitive interaction with FDc1 and directly upregulates AP1. Moreover, AP1 represses Dt1 expression by directly binding to the Dt1 promoter, suggesting that AP1 and Dt1 form a suppressive regulatory feedback loop to determine the fate of the shoot apical meristem. These findings provide novel insights into the roles of Dt1 and FT5a in controlling the stem growth habit and flowering time in soybean, which determine the adaptability and grain yield of this important crop.