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

Background: Apple ( Malus domestica Borkh.) is one of the most popular cultivated fruit crops 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 have been identified to 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 apple genome database, designated MdGF14a to MdGF14r , 17 of them are transcribed. The isoforms possess a conserved core region composed of nine antiparallel α-helices and divergent N and C termini. According to their structural and phylogenetic features, Md14-3-3s 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 reverse-transcription PCR (qRT-PCR) analysis exhibited diverse expression patterns of Md14-3-3 genes in various tissues and in response to different sugars and hormones treatments during 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. Subcellular localization of four selected Md14-3-3 proteins demonstrated their localization in both the cytoplasm and nucleus. Furthermore, yeast two-hybrid and bimolecular fluorescence complementation (BiFC) experiments showed that the four Md14-3-3 proteins interact with key floral integrators, MdTFL1 (TERMINAL FLOWER1) and MdFT (FLOWERING LOCUS T). Conclusion: We comprehensively identified Md14-3-3s family in apple. Some Md14-3-3 genes are predominantly expressed during apple flowering transition stage, and may participate in regulation of flowering through association with flower control genes. Our results provide a preliminary framework for further investigation into the roles of Md14-3-3s for flower transition.