Abstract: The key gene MdMADS50 of SHORT VEGETATIVE PHASE（SVP）was cloned by homologous recombination method using short shoot buds of‘Nagafu 2’apple. The open reading frame （ORF）of MdMADS50 was 675 bp，that encoded 224 amino acids. Protein sequence analysis revealed that this gene contains conserved MADS-box and K-box domains belonging to MIKC-type MADS-box genes. Phylogenetic analysis indicated that the MdMADS50 protein has high homology with MdSVP. By quantitative real-time PCR（qRT-PCR）tissue-specificity expression of MdMADS50 was identified，that displayed that MdMADS50 has higher expression in shoots and leaves. In addition，exogenous GA3 treatment promoted the expression of MdMADS50，and the expression level of cultivar ‘Nagafu 2’in the initial stage of flower induction was significantly higher compared to other cultivars. Furthermore，the GUS activity assay showed that the MdMADS50 promoter had promoter activity and was enhanced by exogenous GA3. In conclusion，our study showed that MdMADS50 may significantly inhibit the flower induction of apple in response to GA3 treatment，mediating the regulation of gibberellin signaling in apple flower buds.

Key words: Malus, flowering induction, SVP, GA, gene clone, gene expression, GUS