Two soybean homologues of TERMINAL FLOWER 1 control flowering time under long day conditions

Flowering time is a key agronomic trait that directly affect the adaptation and yield of soybean. After whole genome duplications, about 75% of genes being represented by multiple copies in soybean. There are four TERMINAL FLOWER 1 (TFL1) genes in soybean, and the TFL1b (Dt1) has been characterized as the determinant of stem growth habit. The function of other TFL1 homologs in soybean is still unclear. Here, we generated knockout mutants by CRISPR/Cas9 genome editing technology and found that the tfl1c/tfl1d double mutants flowered significantly earlier than wild-type plants. We investigated that TFL1c and TFL1d could physically interact with the bZIP transcription factor FDc1 and bind to the promoter of APETALA1a (AP1a). RNA-seq and qRT-PCR analyses indicated that TFL1c and TFL1d repressed the expressions of the four AP1 homologs and delayed the flowering time in soybean. The two genes play important roles in the regulation of flowering time in soybean and mainly act as the flowering inhibitors under long-day conditions. Our results identify novel components in the flowering-time regulation network of soybean and will be invaluable for molecular breeding of improved soybean yield.