Abstract: A cysteine protease gene，CsCysP（KJ093387），was cloned from the fruit abscission zone of sweet orange[Citrus sinensis（L.）‘Olinda’] using RT-PCR and RACE. The 1 485 bp full-length cDNA of CsCysP contains a 1 083 bp open reading frame（ORF）encoding a protein of 360 amino acid residues. Comparison between cDNA and genomic DNA sequences showed that the gene contains three introns. The phylogenetic analysis placed the gene into papain-like（C1A）group. BLASTp analysis showed that CsCysP protein shared 73%–83% amino acid identities with CPRs from Arabidoposis thaliana，soybean，tobacco，Populus trichocapa and other species. Transient expression of a 35S-CsCysP-GFP fusion gene in onion epidermal cells revealed that CsCysP protein was localized in cell wall. Quantitative Real-time PCR results showed that the expression of CsCysP was higher in senescent leaves，fruit abscission zone cells and flowers than in leaves，stems and roots of young seedlings. CsCysP was induced by salt，PEG6000 and ABA but repressed by low temperature，ethylene（ET），brassinolide（BR），methyl jasmonic acid（MeJA）and salicylic acid（SA）. Five transgenic citrus lines overexpressing CsCysP were also obtained in this study and will be further characterized.

Key words: citrus, cysteine protease, stress, gene expression