Characterisation of FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) Homologs: Functional and Evolutionary Insights

Flowering in angiosperms is an outcome of complex regulatory network involving multiple genes wherein FT and SOC1 are defined as pathway integrators. Herein, we characterize Brassica homologs of FT and SOC1 to provide evolutionary perspectives on fate of duplicate genes in polyploids. Twenty-eight and 27 transcripts; 7 and 8 genomic copies of FT and SOC1, respectively, were isolated from Indian cultivars of Brassicas. Sequence analysis permitted identification of signature sequences within FT and SOC1. Coexistence of interrupted and intronless SOC1 gene copies was identified. Phylogenetic analysis unambiguously established ancestry of SOC1 sequences and revealed sub-genomic organisation in uncharacterised Brassica genomes. Analysis of cumulative expression pattern of FT homologs revealed increasing levels correlating with attainment of physiological maturity; highest levels were detected in older leaves implying conservation in expression domains vis-à-vis Arabidopsis. Expression analysis of sub-genome-specific SOC1 homeologs of B. juncea revealed near identical expression pattern with evidence for regulatory diversification. Representative FT and SOC1 variants were characterized using gain-of-function mutants in Brassica and Arabidopsis. Transgenic plants exhibited earliness in flowering and crop maturity correlating to enhanced transgene levels relative to control. Brassica transgenics over-expressing FT displayed increased seed yield/plant, number of pods/plant due to increased number of lateral shoots vis-à-vis control. In contrast, knockdown mutants in B. juncea expressing artificial miRNA targeting FT and SOC1 displayed delayed flowering, decreased seed yield/plant and lateral shoots concomitant to presence of cleaved target transcripts. Overall, homologs of FT and SOC1 exhibit functional conservation highlighting criticality in floral induction with homeologs undergoing regulatory evolution.