Molecular Evolution Study of PdeFTL1, a FT/TFL1-Like Gene from Pinus densiflora, for Flowering Control

In flowering plants, FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1), members of the phosphatidylethanolamine-binding protein (PEBP) family, are key players in flowering control with antagonistic functions: FT promotes flowering, while TFL1 represses it. Here, we report the functional characterization of FT/TFL1-like ( FTL ) genes from Pinus densiflora ( PdeFTL1 and PdeFTL2 ). Sequence analysis showed that both PdeFTL1 and PdeFTL2 had a conserved PEBP domain with several specific amino acid residues characteristic of TFL1 function, including Serine (S) at position 137, which is Tryptophan (W) in FT function. We generated a chimeric gene of PdeFTL1_S137W and tested its floral regulatory function by heterologous expression in tobacco and Arabidopsis. Our results showed that tobacco plants transiently expressing PdeFTL1_S137W significantly accelerate flowering time. Likewise, transgenic Arabidopsis overexpressing PdeFTL1_S137W produced flower buds at a very immature stage with only 3–5 true leaves, similar to 35S::AtFT plants. However, 35S::PdeFTL1 plants showed a mild delay in flowering compared to the control. Collectively, our molecular evolution study successfully demonstrated that substituting only one amino acid of the PdeFTL1 protein could completely change the biochemical activity of this protein to a floral activator. Therefore, this strategy can be utilized as a basis to modulate flowering time in conifers.