Genome-wide identification of the 14–3-3 gene family and its participation in floral transition by interacting with TFL1/FT in apple

Background Apple ( Malus domestica Borkh.) is a popular cultivated fruit crop with high economic value in China. Apple floral transition is an important process but liable to be affected by various environmental factors. The 14–3-3 proteins are involved in regulating diverse biological processes in plants, and some 14–3-3 members play vital roles in flowering. However, little information was available about the 14–3-3 members in apple. Results In the current study, we identified eighteen 14–3-3 gene family members from the apple genome database, designated MdGF14a to MdGF14r . The isoforms possess a conserved core region comprising nine antiparallel α-helices and divergent N and C termini. According to their structural and phylogenetic features, Md14–3-3 proteins could be classified into two major evolutionary branches, the epsilon (ɛ) group and the non-epsilon (non-ɛ) group. Moreover, expression profiles derived from transcriptome data and quantitative real-time reverse transcription PCR analysis showed diverse expression patterns of Md14–3-3 genes in various tissues and in response to different sugars and hormone treatments during the floral transition phase. Four Md14–3-3 isoforms ( MdGF14a , MdGF14d , MdGF14i , and MdGF14j ) exhibiting prominent transcriptional responses to sugars and hormones were selected for further investigation. Furthermore, yeast two-hybrid and bimolecular fluorescence complementation experiments showed that the four Md14–3-3 proteins interact with key floral integrators, MdTFL1 (TERMINAL FLOWER1) and MdFT (FLOWERING LOCUS T). Subcellular localization of four selected Md14–3-3 proteins demonstrated their localization in both the cytoplasm and nucleus. Conclusion We identified the Md14–3-3 s family in apple comprehensively. Certain Md14–3-3 genes are expressed predominantly during the apple floral transition stage, and may participate in the regulation of flowering through association with flower control genes. Our results provide a preliminary framework for further investigation into the roles of Md14–3-3 s in floral transition.