Abstract: An E3 ubiquitin ligase gene（Gene ID：MDP0000199588）was cloned from‘Royal Gala’ apple（Malus × domestica Borkh.）. Sequence analysis showed that the length of MdPUB24 gene was 1 212 bp，which encoded 404 amino acids. A phylogenetic tree analysis indicated that our cloned apple E3 ubiquitin ligase exhibited the highest sequence similarity to Arabidopsis AtPUB24，so named MdPUB24. In silico analysis suggested that the promoter sequence of MdPUB24 contained several typical cis-acting elements，including abscisic acid-，light-，MeJA- and drought-responsive elements using PlantCare Databases. qPCR analysis showed that MdPUB24 widely expressed in different tissues of‘Royal Gala’ apple，and highly expressed in apple leaves. The expression of MdPUB24 was significantly inhibited by exogenous ABA and NaCl and low temperature. The growing potential of MdPUB24-expressing apple calli of‘Orin’cultivar and Arabidopsis were much weaker than that of control under salt stress condition，suggesting that MdPUB24 negatively regulated salt tolerance. In contrast，the growing potential of MdPUB24-expressing apple calli of‘Orin’and Arabidopsis were much stronger than that of control in the presence of exogenous ABA，suggesting that MdPUB24 was insensitive to exogenous ABA.

Key words: apple, E3 ubiquitin ligase, MdPUB24, salt stress, abscisic acid stress