Phytochrome B modulates high-temperature-induced flowering in soybean by promoting degradation of PSEUDO-RESPONSE REGULATOR 5 proteins

High ambient temperature accelerates soybean (Glycine max) flowering to escape stress and accomplish reproduction, but the underlying molecular mechanism remains unclear. Here, we report that phytochrome B1 (phyB1) and phyB2 and the core circadian-clock components PRR5a and PRR5b regulate high-temperature-mediated early flowering. PRR5a and PRR5b repress FLOWERING LOCUS T (FT)2a and FT5a expression by directly binding to their promoters. Under high temperature, enhanced phyB and PRR5 interaction promotes PRR5 degradation, facilitating FT induction and precocious flowering. prr5a prr5b and phyB1 phyB2 double mutants showed temperature-insensitive flowering at 25°C and 30°C. PRR5a and PRR5b are epistatic to phyB1 and phyB2, and this circuit bypasses the E1 photoperiod module to promote flowering. Taken together, this study uncovers a phyB-PRR5-FT module controlling high-temperature-mediated early flowering, broadening our understanding of plants' adaptation strategies for maximizing reproductive success under environmental stress.