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 6 FT-like genes and 2 pseudogenes belonging to 3 orthogroups. All B. napus FT-like genes induce early flowering when expressed at the shoot apical meristems of Arabidopsis thaliana ft mutants, but 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 trans-activated by B. napus CO in transient assays although they genes 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. Significance statementB. napus FT-like genes are a case study for gene retention and retraction after multiple rounds of polyploidisation. Retained B. napus FT-like genes show preferred expression in different developmental stages and amino-acid changes that affect florigen function.