Abstract: To explore the key genes of citrus canker resistance，the MAPK gene family were annotated，and the functional domain of these genes was analyzed in citrus. The expressing tissue specificity of CsMPK1，CsMPK3，CsMPK4，CsMPK6 and CsMPK19 and their expression in the resistant ‘Jindan’（Fortunella japonica Swingle）and the susceptible‘Wanjincheng’orange（Citrus sinensis Osbeck）induced by Xanthomonas citri subsp. citri（Xcc）were determined. The CsMPK19 was further analyzed by bioinformatics. A total of 12 MAPK gene family members containing Pkinase domain were annotated from the citrus genome，which were divided into 3 subclasses according to the phylogenetic tree. The expression levels of CsMPK1，CsMPK3，CsMPK4-1 and CsMPK6 were relatively high in fruits，while the expression level of CsMPK19 was relatively high in leaves. The expression of CsMPK1 was strongly induced by Xcc in both resistant and susceptible varieties，and the upregulated amplitude was higher in the susceptible variety than in the resistant one. CsMPK3 and CsMPK6 showed strong response only in the early stage of pathogen treatment in susceptible cultivar. The expression of CsMPK4-1 and CsMPK4-2 were up-regulated after Xcc treatment in the susceptible cultivar，but decreased in the resistant cultivar，compared with the water treatment. The expression of CsMPK19 was also strongly induced by Xcc in both resistant and susceptible varieties，while the upregulation was higher in the resistant cultivar. A 1 824 bp coding sequence of CsMPK19 was cloned which encodes a 69 174.36 D protein of 607 amino acids. Bioinformatics analysis indicated that CsMPK19 is a non-secretory protein and the 25–316 aa is a typical Pkinase domain. There are significant differences in the cis-acting elements of the MPK19 promoters between the Wanjincheng orange and the Jindan. These results suggest that MAPK genes strongly respond to Xcc infection，and the CsMPK19 had potential application value in regulation of resistance to citrus canker.

Key words: citrus, canker, MAPK, gene cloning, expression level, promoter