SiFTL and SiHd3a are positive regulators of flowering time in sesame (Sesamum indicum L.)

Flowering time, a critical trait for crop adaptation, is regulated by plants' ability to sense light signals, which influences gene expression and the transition from vegetative to reproductive growth. In this study, five populations of sesame (<i>Sesamum indicum</i>) were developed by crossing 'Yuzhi 4' with 'BS377' (late-flowering variety). Linkage mapping analysis revealed that a ~400 kb region on chromosome 11 had the most significant and stable effect on flowering time. <i>FLOWERING LOCUS T-like</i> (<i>FTL</i>) and <i>HEADING DATE 3A</i> (<i>Hd3a</i>), located within the candidate region, are associated with flowering time as revealed by RNA-seq and qRT-PCR analyses. Integrated analyses of <i>SiFTL</i> gene structure and transcript level revealed that the absence of <i>SiFTL</i> expression leads to the late-flowering phenotype in BS377. Moreover, <i>SiFTL</i> and <i>SiHd3a</i>, which are highly homologous to <i>Arabidopsis FT</i> and <i>TWIN SISTER OF FT</i> (<i>TSF</i>), are associated with earlier flowering. Furthermore, the Yuzhi 4 haplotypes of <i>SiFTL</i> and <i>SiHd3a</i> locus co-segregated with the early-flowering trait in a recombinant inbred line (RIL) population. In addition, heterologous expression of the Yuzhi 4 haplotypes of <i>SiFTL</i> and <i>SiHd3a</i> significantly accelerated flowering in <i>Arabidopsis</i> Col-0 and the <i>ft-10</i> mutant under both long-day (LD) and short-day (SD) conditions. These haplotypes may function as universal floral activators downstream of flowering pathways. These findings not only enhance our understanding of the molecular mechanisms controlling flowering time in sesame but also offer valuable genetic resources for breeding early-maturing varieties.