Over-expression of the citrus gene CtNH1 confers resistance to bacterial canker disease

• Citrus canker disease is caused by Xanthomonas axonopodis pv. citri (Xac).
• An NPR1 homolog, Citrus NPR1 homolog 1 (CtNH1), was isolated from citrus.
• Overexpression of CtNH1 leads to resistance to Xac.
• A novel strategy was used to predict NPR1 orthologs in other plant species.

Citrus canker is a devastating disease, caused by Xanthomonas axonopodis pv. citri (Xac). It is well established that the NPR1 gene plays a pivotal role in systemic acquired resistance (SAR) in Arabidopsis. In this study, we report the isolation and characterization of an NPR1 homolog from citrus, namely Citrus NPR1 homolog 1 (CtNH1). Sequence alignment and phylogenetic analysis indicate that CtNH1 is closely-related to the Arabidopsis NPR1 gene and its orthologs from rice, grapevine, and cacao. When over-expressed in citrus, CtNH1 confers resistance to Xac and leads to constitutive expression of the pathogenesis-related (PR) gene chitinase 1 (Chi1), suggesting that CtNH1 is orthologous to NPR1.