Transcription profiling on transgenic apple plants after over-expression of genes, which are involved in the flower development

The breeding of new apple cultivars is time-consuming due to the long generation time of apple. Shortened juvenility and precocious flowering are, therefore, important breeding goals. To break the juvenile stage two different flowering genes, the BpMADS4 gene of birch Betula pendula L., which is similar to FRUITFULL (FUL), and the LEAFY (LFY) gene of Arabidopsis thaliana L. driven by the constitutive CaMV 35S promoter were over-expressed in transgenic plants of the apple cv. 'Pinova'. No precocious flowering was observed in LFY transgenic plants. These plants produced more internodes and the internode length was reduced compared to the wild type. Several BpMADS4 transgenic lines produced their first flowers on in vitro shoots. Most of these flowers appeared morphologically normal. Five lines of each transgene were selected and investigated on mRNA levels of the native flowering genes AFL1 (apple FLORICAULA/LFY), AFL2 (apple FLORICAULA/LFY), MdMADS5 (Malus domestica MADS5), MdTFL1-1 (M. domestica TERMINAL FLOWER 1-1) and MdFT (M. domestica FLOWERING LOCUS 7). Sequences of each gene were isolated from genomic DNA of 'Pinova' and sequence specific primers were designed. These primers were used to establish the Real-Time PCR on apple. On LFY transgenic lines no effect on the expression of native flowering genes was observed. In BpMADS4 transgenic lines the mRNA levels of AFL2 and MdFT were increased. However, the level of MdTFL1-1 was lower than in the wild type. No effect was found for AFL1 and MdMADS5. The results obtained indicate that AFL2 is likely to be more involved in meristem transition than AFL1. Furthermore, it was shown that the biological function of BpMADS4 in apple is similar but not identical to FUL in Arabidopsis.