Characterization of FLOWERING LOCUS T-related genes and their putative gene regulatory network in semi-winter Brassica napus cultivar Zhongshaung11

In many species, FLOWERING LOCUS T (FT)-like genes promote the floral transition by integrating environmental signals, in particular photoperiod, and internal cues. Here we show that Brassica napus contains six FT-like genes and two pseudogenes belonging to three orthogroups. All B. napus FT-like genes induce early flowering when expressed at the shoot apical meristems of Arabidopsis thaliana ft mutants; however, BnaFT.C6 and non-orthologous FT-like genes do not encode fully functional mobile florigens. In the case of BnFT.C6, the functional change is associated with a T to C amino acid change that is restricted to semi-winter accessions. Expression of orthologs of FT is photoperiod-dependent, and two distal enhancers are conserved; however, the homeologs BnaFT.A7 and BnaFT.C6 show rearrangements of DNA motifs binding NF-Y/CO and NF-Y transcriptional activator complexes between the promoter and downstream enhancers. Motif rearrangements correlate with differences in tissue-specific expression. Furthermore, homeologs with rearranged motifs could not be transactivated by B. napus CO in transient assays, although they show LD photoperiod-dependent expression. We propose that differential diurnal expression of NF-Y genes contributes to the photoperiod-dependent regulation of B. napus FT genes.