Abstract: The AP2 family of Citrus sinensis will be annotated and analyzed while the citrus canker related transcription factor CsAP2-09 will be cloned and analyzed in this study. It is also aimed to confirm the subcellular localization and the expression profiles induced by exogenous hormones，Xanthomonas citri subsp. citri（Xcc）and mechanical wounding. Twelve AP2 genes are extracted and annotated from the public genomic databases of C. sinensis. These 12 AP2s can be divided into 4 categories based on the phylogeny and the motifs. Amino acid sequence and structure analysis indicates that the full-length of CsAP2-09 is 4 159 bp with a 1 467 bp open reading frame which codes a protein containing 488 amino acids. CsAP2-09 contains classic AP2 domains and some specific motifs which give essential and special functions. Subcellular localization results confirm the prediction of the protein localization in nucleus. The promoter contains multiple cis-acting elements involved in plant adversity or hormone responses，such as BOX-W1，CGTCA-motif，TCA-element，WUN-motif and so on. Based on the qPCR data，the CsAP2-09 responds to the exogenous salicylic acid，jasmonic acid methyl ester，mechanical damage and ethylene. Xcc attack can significantly increase the expression of CsAP2-09 in Calamondin but no significant change in Newhall navel orange. All the experiments show CsAP2-09 would be an important transcription factor which is closely associated with the resistance of citrus canker. This gene should be a potential candidate in the molecular breeding to improve the canker resistance of citrus. We have over expressed CsAP2-09 in C. sinensis and obtain 8 transgenic seedlings. Then the evaluation of the resistance will be performed to determine the value of molecular breeding.

Key words: Citrus, citrus canker disease, AP2, transcription factors, subcellular localization, gene expression