MdTFL1, a TFL1-like gene of apple, retards the transition from the vegetative to reproductive phase in transgenic Arabidopsis

Unlike herbaceous plants, fruit trees such as the apple (Malus × domestica Borkh.) flower and set fruit only after an extended juvenile phase lasting several years. While studying juvenility in apple trees, we cloned Malus domestica TFL1 (MdTFL1), a gene homologous to TERMINAL FLOWER 1 (TFL1) that suppresses the floral meristem identity genes LEAFY (LFY) and APETALA1 (AP1) and maintains the inflorescence meristem in Arabidopsis. MdTFL1 mRNA was expressed preferentially in apple vegetative tissues such as apical buds, stems and roots of seedlings, and expression peaked in early July in apical buds, about two weeks prior to floral bud differentiation. Transgenic Arabidopsis expressing MdTFL1 flowered noticeably later than wild-type plants and exhibited a phenotype similar to that of transgenic Arabidopsis overexpressing TFL1. These results suggest that MdTFL1 is involved in the maintenance of the vegetative phase in apple and that it functions analogously to TFL1.