Bacterial resistance in AtNPR1 transgenic sweet orange is mediated by priming and involves EDS1 and PR2

In sweet orange, varietal resistance is crucial to avoid citrus canker, a disease caused by Xanthomonas citri subsp. citri (Xcc) that is a significant problem for some of the world\'s leading producers. In the present study, transgenic sweet orange plants (Hamlin) overexpressing the A. thaliana Npr1 (non-expressor of pathogenesis-related [PR] genes) gene were produced and assessed for Xcc resistance and for the levels of expression of disease resistance genes. The leaves of these transgenic plants exhibited fewer lesions and reduced bacterial concentrations compared to non-transformed control. Both in vitro and screenhouse experiments on the transgenic plants yielded similar results, which makes in vitro screening an interesting prospect for the initial identification of citrus canker resistance. The stronger expression of EDS1 and PR2 after pathogen inoculation correlated with a higher tolerance response suggesting a possible priming effect. The use of AtNPR1 is an alternative against citrus canker since it led to higher tolerance in a pathogen-dependent response.