Evolution of the FLOWERING LOCUS T-like genes in angiosperms: a core-Lamiales-specific diversification

Plant life-history is determined by two transitions, the germination and the flowering times, in which the phosphatidylethanolamine-binding proteins (PEBP) FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) play key regulatory roles. Compared to the highly conserved TFL1-likes, FT-like genes vary in copy numbers significantly in gymnosperms and monocots of the angiosperms, while sporadic duplications can be observed in eudicots. Here, via a systematic analysis of the PEBPs in angiosperms with a special focus on twelve representative species featuring high-quality genomes in the Lamiales order, we identified a successive lineage-specific but systematic expansion of FT-like genes in the families of core Lamiales. The first expansion event generated FT1-likes mainly via a core-Lamiales-specific whole-genome-duplication (cL-WGD), while on the other hand, a likely random duplication produced the FT2-likes in the lineages containing Scrophulariaceae and rest of the core Lamiales. Both FT1- and FT2-like genes were further amplified tandemly in some families. These expanded FT-likes featured highly diverged expression patterns and structural variation, indicating functional diversification. Intriguingly, some core Lamiales contained the relict MOTHER OF FT AND TFL1 like 2 (MFT2) that likely expanded in the common ancestor of angiosperms. Our data showcase the highly dynamic lineage-specific expansion of the FT-like genes, thus provide important and fresh evolutionary insights into the gene-regulatory-network underpinning flowering time diversity in Lamiales, and more generally, in angiosperms.