Abstract: Calcineurin B-like protein（CBLs），as a plant calcium sensor，plays critical role in the regulation of plant growth and stress response process. However，CBL2 gene sequence feature，expression  characteristic and physiological function in birch-leaf pear（Pyrus betulaefolia Bunge）are largely unknown. In this study，we isolated the cDNA，genomic DNA and its responding promoter sequences of PbCBL2 gene from birch-leaf pear seedlings by EST database mining，rapid amplification of cDNA ends（RACE）and genome walking approaches. The results have showed that PbCBL2 cDNA sequence contained a 681 bp open reading frame which encoded 226 amino acid residues. The length of genomic DNA sequence was 1 927 bp which consists of 8 exons and 7 introns. The promoter region of PbCBL2 harbored some specific regulatory elements or motifs，such as light responsive element，cis-acting regulatory element essential for the anaerobic induction，gibberellin-responsive element and cis-acting element involved in salicylic acid responsiveness. The deduced PbCBL2 polypeptide had four EF-hand structure domains（58–71，95–106，132–143 and 176–187 amino acids）which was necessary for calcium-binding and one calcineurin A subunit binding sites（156–171 amino acids）. Semi-quantitative RT-PCR and prokaryotic expression analyses validated that the mRNA abundance of PbCBL2 is responsive to different abiotic stresses. However，PbCBL2 expression was barely detected in roots and leafs of birch-leaf pear seedling without abiotic stresses treatment. The inhibition effects on BL21（DE3）growth causing by NaCl，mannitol or PEG6000 were significantly alleviated after PbCBL2 gene transformation. Our studies have suggested that PbCBL2 gene has the inherent characteristics of the CBLs gene family in plants，which transcription level is respond to salt，drought，osmotic stresses and ABA treatment. E. coli BL21（DE3）tolerance to salt stress and osmotic stress was enhanced by transferred PbCBL2.

Key words: Pyrus betulaefolia Bunge, calcineurin B-like protein, gene cloning, gene expression characteristics, prokaryotic expression；environment stress