A novel Xanthomonas citri subsp. citri NADPH quinone reductase involved in salt stress response and virulence

BARCAROLO, MV; GARAVAGLIA, BS; GOTTIG, N; CECCARELLI, EA; CATALANO-DUPUY DANIELA L*; OTTADO, J*

BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2020 vol. 1864

0304-4165

Background: Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker ismaintained as an epiphyte on citrus leaves until entering the plant tissue. Duringepiphytic survival, bacteria may encounter low water availability that challenges theinfection process. Proteomics analyses of Xcc under saline stress, mimicking theconditions found during epiphytic survival, showed increased abundance of a putativeNAD(P)H dehydrogenase encoded by XAC2229.Methods: Expression levels of XAC2229 and a Xcc mutant in XAC2229 were analyzedin salt and oxidative stress and during plant-pathogen interaction. An Escherichia coliexpressing XAC2229 was obtained, and the role of this protein in oxidative stressresistance and in reactive oxygen species production was studied. Finally, Xac2229protein was purified, spectrophotometric and cofactor analyses were done andenzymatic activities determined.Results: XAC2229 was expressed under salt stress and during plant-pathogeninteraction. XAC2229 mutant showed less number of cankers and impaired epiphyticsurvival than the wild type strain. XAC2229 survived less in the presence of H2O2 andproduced more reactive oxygen species and thiobarbituric acid-reactive substances thanthe wild type strain. Similar results were observed for E. coli expressing XAC2229.Xac2229 is a FAD containing flavoprotein, displays diaphorase activity with anoptimum at pH 6 and has quinone reductase activity using NADPH as an electrondonor.Conclusions: A FAD containing flavoprotein from Xcc is a new NADPH quinonereductase required for bacterial virulence, particularly in Xcc epiphytic survival oncitrus leaves.