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Examining the role of an EF-Hand Protein in regulating virulence in Xanthomonas

Shaheen Bibi: Department of Plant Pathology, University of Florida

<div>Bacterial spot is a major disease of tomato and pepper. Four species of <em>Xanthomonas</em> are causal agents of this disease: <em>Xanthomonas euvesicatoria</em>, <em>X. vesicatoria</em>, <em>X. perforans</em> and <em>X. gardneri</em>. A gene was identified in <em>X. fuscans </em>subsp. <em>aurantifolii </em>that when expressed in <em>X. perforans</em>, elicited an HR in tomato. Based on analysis of the gene using bioinformatics tools, the protein is predicted to contain a region of unknown function at the amino-terminus, a single putative transmembrane helix and two EF-Hand calcium-binding domains at the carboxy-terminus. Genomic searches have revealed that the gene is also present in <em>X. perforans </em>and <em>X. euvesicatoria. </em>Interestingly, in <em>X. euvesicatoria </em>strains isolated from pepper, this gene is intact, whereas in strains isolated from tomato, there is a stop codon immediately upstream of the EF-hand domains. <em>X. perforans </em>strains that are associated with tomato contain a stop codon preceding the EF-Hand domain sequences. Expression of the full-length form of the gene in strains of <em>X. perforans</em> isolated from peppers resulted in reduced ability to grow in tomato leaflets compared to the wild-type strain. The preliminary data of population and electrolyte leakage of these mutants indicate possible role in virulence. Our aim is to look into the possible role of the transmembrane region and EF-hands in the regulation of pathogenicity of these strains. The next step is to use this knowledge to identify the function of this protein in <em>Xanthomonas</em> and try to understand its role in the calcium environment by generating various mutants.</div>