Rewiring the SVP-AGL24 module into a flowering-promoting cascade via legume-specific E1 repressors in soybean

Photoperiodic flowering is a critical determinant of soybean regional adaptation and yield, and is predominantly governed by the legume-specific E1 repressor family. How evolutionarily conserved MADS-box transcription regulators such as AGAMOUS-LIKE 24 (AGL24) and SHORT VEGETATIVE PHASE (SVP) integrate into the E1 module remains unclear. Here, we show that soybean GmSVP1 and GmSVP2 promote flowering under long-day conditions. GmSVP1/2 directly bind to and repress the E1 family genes, and genetic analyses demonstrate that this repression accounts for the flowering-promoting activity of endogenous GmSVP1/2. Although GmSVP1/2 can also directly repress the florigen gene GmFT2a, their net endogenous function is to advance floral transition via the E1 pathway. We further identify GmAGL24 as an upstream regulator of GmSVP1/2. Collectively, these results establish a GmAGL24-GmSVP-E1-GmFT regulatory cascade that controls photoperiodic flowering in soybean. This work provides mechanistic insight into the functional diversification of conserved flowering regulators in legumes and identifies promising genetic targets for breeding broadly adapted soybean cultivars.