CONICET | Buscador de Institutos y Recursos Humanos

Background: Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker is maintained as an epiphyte oncitrus leaves until entering the plant tissue. During epiphytic survival, bacteria may encounter low wateravailability that challenges the infection process. Proteomics analyses of Xcc under saline stress, mimicking theconditions found during epiphytic survival, showed increased abundance of a putative NAD(P)H dehydrogenaseencoded by XAC2229.Methods: Expression levels of XAC2229 and a Xcc mutant in XAC2229 were analyzed in salt and oxidative stressand during plant-pathogen interaction. An Escherichia coli expressing XAC2229 was obtained, and the role of thisprotein in oxidative stress resistance and in reactive oxygen species production was studied. Finally, Xac2229protein was purified, spectrophotometric and cofactor analyses were done and enzymatic activities determined.Results: XAC2229 was expressed under salt stress and during plant-pathogen interaction. ΔXAC2229 mutantshowed less number of cankers and impaired epiphytic survival than the wild type strain. ΔXAC2229 survivedless in the presence of H2O2 and produced more reactive oxygen species and thiobarbituric acid-reactive substancesthan the wild type strain. Similar results were observed for E. coli expressing XAC2229. Xac2229 is a FADcontaining flavoprotein, displays diaphorase activity with an optimum at pH 6.0 and has quinone reductaseactivity using NADPH as an electron donor.Conclusions: A FAD containing flavoprotein from Xcc is a new NADPH quinone reductase required for bacterialvirulence, particularly in Xcc epiphytic survival on citrus leaves.General significance: A novel protein involved in the worldwide disease citrus canker was characterized.