Abstract: The shoot tips of columnar apple‘Lujia 5’were used as experimental materials for cloning MdGAI gene encoding DELLA protein and researching its expression characterization via rapid amplification of cDNA ends（RACE）and real time PCR methods. The full length sequence of MdGAI was 2 491 bp，encoding 635 amino acids. The nucleic acid sequence was highly homologous with those of other Malus plants. Sequence analysis of the product of the MdGAI indicated that they shared a highly conserved N terminus that contained two recognizable domains DELLA and VHYNP，and a highly conserved C terminus that contained two recognizable domains VHVID and SAW. The real-time quantitative PCR analysis showed that MdGAI gene were always expressed in shoot apices of columnar and standard apple trees during the spring，summer and autumn growing season. In the same season，the MdGAI of columnar apples were expressed at higher level than that of standard apples. It is perhaps that the growing habit of columnar apple is related to MdGAI gene with high levels expression. The MdGAI gene were expressed in seeds，leaf buds，shoot tips，internodes，floral buds，flowers and young fruits of columnar apple ‘Lujia 5’. However，the amounts of the expression were obviously different. In the early development of young fruit，the relative expression level of MdGAI gene was up to the maximum value. This means that GAI gene may play a crucial role during the fruit developing of columnar apple.

Key words: apple, DELLA protein, MdGAI gene, Real-time PCR