Functional characterization of two antagonistic acting flowering genes in apple Malus x domestica Borkh.

Apple Malus × domestica Borkh. has a long period of juvenility during which plants are unable to produce flowers and fruits. Flowering is only possible on trees which have passed the transition from juvenility to the adult stage. Several genes have been identified which control this switch and promote or delay flowering in different plant species. FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1) are two flowering genes of Arabidopsis which are similar, but act antagonistically. FT and TFL1 homologous genes are present in the apple genome, but little is known about their function. Therefore we produced transgenic apple lines which over-expressed the MdFT2 gene under the control of the constitutive CaMV 35S promoter. Transgenic shoots expressing the MdFT2 gene driven by the CaMV 35S promoter flowered in vitro. To study the function of MdTFL1 we silenced the gene by expressing an MdTFL1 specific hairpin under the control of the CaMV 35S promoter. Transgenic plants of different apple cultivars flowered in vitro and later in the greenhouse. Transgenic flowers were evaluated for phenotypic differences and tested on their usability for crossbred breeding programs.