Ectopic expression of the apple Md-miR172e gene alters flowering time and floral organ identity in Arabidopsis

The miRNA miR172 is involved in the regulation of flowering time and floral organ development by specifically restricting the transcripts of target gene APETELA2 (AP2) transcription factors. In our study, Md-miR172e and its target genes, MdAP2 and MdAP2-1 to MdAP2-7, were isolated from the apple cultivar Royal Gala (Malus x domestica). Phylogenetic tree analysis revealed that eight MdAP2 genes were similar to the AtAP2 subfamily and were putative targets of miR172. qRT-PCR and western blotting analyses indicated Md-miR172e regulation of the expression of the target gene MdAP2 at the translation level. Next, an over-expression construct 35S::Md-miR172e was generated and transformed into Arabidopsis. qRT-PCR showed that Md-miR72e expression and mature miR172e accumulation increased, and transgenic plants exhibited early flowering (20-30 days early in flowering) under long days and floral defects compared with wild-type. Taken together, these results suggest that miR172 and its target AP2-like genes are involved in flower developmental processes, particularly with regards to flowering time and floral organ development, and miR172 mediates a conserved regulatory pathway in apple and Arabidopsis.