Functional characterization of MiFTs implicated in early flowering and stress resistances of mango

Phosphatidylethanolamine binding protein (PEBP) family plays important roles in multiple developmental processes in plants. In this study, a total of 11 PEBP gene family members were identified from the mango (Mangifera indica L.) genome, and these proteins were divided into three subfamilies based on their phylogenetic relationships: TERMINAL FLOWER 1 (TFL1)-like, MOTHER OF FT AND TFL (MFT)-like, and FLOWERING LOCUS T (FT)-like. Expression analysis revealed that MiFT1a, MiFT1b and MiFT2 were expressed mainly in leaves, whereas MiFT3 and MiFT4 were expressed mainly in embryos. The overexpression of MiFTs significantly promoted early flowering under both long- and short-day conditions. Interestingly, it still significantly promoted early flowering at 16 °C and 28 °C, with MiFT1a exhibiting the most significant, followed by MiFT1b and MiFT2. Additionally, the expression level of MiFT3 is related to the embryonic development of mango. Further studies revealed that overexpression of MiFT3 inhibited seed germination in transgenic Arabidopsis lines. In addition, the MiFT1a and MiFT1b transgenic lines did not respond to abiotic stress, while MiFT2, MiFT3 and MiFT4 enhanced resistance to salt or drought stress in Arabidopsis. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays revealed that MiFTs can interact with flower related and multiple stress proteins, such as bZIP protein (MiFD), 14-3-3 protein, zinc finger protein (MiZFP4), RING zinc-finger protein (MiRZFP34), and phosphatase 2C (MiPP2C25A and MiPP2C25B). These results indicate that FT subfamily not only regulates flowering but also participates in stress response, but there are differences in the function among these genes.