Xanthomonas axonopodis pv. citri causes citrus canker, provoking defoliation and premature fruit drop with the concomitant economical damage. In plant pathogenic bacteria, lipopolysaccharides are important virulence factors and they are being increasingly recognized as major pathogen associated molecular patterns for plants. In general three domains are recognized in a lipopolysaccharide: the hydrophobic lipid A, the hydrophilic O-antigen polysaccharide and the core oligosaccharide, connecting lipid A and O-antigen. In this work we have determined the structure of purified lipopolysaccharides obtained from Xanthomonas axonopodis pv. citri wild type and a mutant of the O-antigen ABC transporter encoded by wzt gene. High pH anion exchange chromatography and matrix assisted laser desorption/ionization mass spectra analysis were performed enabling determination of the structure not only of the released oligosaccharides and lipid A moieties but also the intact lipopolysaccharides. The results demonstrate that Xac wild type and Xacwzt LPSs are composed mainly of a penta or tetra-acylated di-glucosamine backbone attached to either two pyrophosphoryl ethanolamine groups or one pyro and one phosphorylethanolamine groups. The core region consists of a branched oligosaccharide formed by Kdo(2)Hexose(6)GalA(3)Fuc3NAcRha(4) and two phosphate groups. As expected, the presence of a rhamnose homo-oligosaccharide as O-antigen was determined only in the Xac wild type lipopolysaccharide. In addition, we have examined how lipopolysaccharides from Xac function in the pathogenesis process. We analyzed the response of the different lipopolysaccharides during the stomata aperture-closure cycle, the callose deposition, the expression of defense-related genes and ROS production in citrus leaves suggesting a functional role of the O-antigen from Xac lipopolysaccharides in the basal response.
Lipopolysaccharide, ABC transporter, virulence factor, Xanthomonas axonopodis pv. citri
NCBI PubMed ID: 21596742Journal NLM ID: 2985121RPublisher: Baltimore, MD: American Society for Biochemistry and Molecular Biology
Correspondence: orellano@ibr.gov.ar; acouto@qo.fcen.uba.ar
Institutions: Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Te´cnicas (IBR-CONICET-UNR), Facultad de Ciencias Bioquímicas y Farmace´uticas, Suipacha 531 (S2002LRK), Rosario, Argentina
Methods: PCR, GC-MS, sugar analysis, DNA techniques, TLC, MALDI-TOF MS, composition analysis, genetic methods, UV-MALDI-TOF MS
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