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POSTERS: Molecular plant-microbe interactions

Functional analysis and subcellular localization of EF-hand protein in Xanthomonas
Shaheen Bibi - University of Florida. Sujan Timilsina- University of Florida, Jason C. Hulbert- Department of Chemistry, Physics and Geology, Winthrop University, Juliana Pereira-Martin- University of Florida, Jeffrey Jones- University of Florida, Gerald Minsavage- University of Florida

Bacterial spot of tomato and pepper is caused by Xanthomonas euvesicatoria (Xe), X. vesicatoria, X. perforans (Xp) and X. gardneri. A gene, putatively named as Efh-Xfa was identified in X. fuscans subsp. aurantifolii (Xfa) that has a possible role in elicitation of HR when inoculated in tomato. Bioinformatic analysis predicts the presence of two EF-hand motifs and a single transmembrane domain in Efh-Xfa. Sequence analysis indicated that Efh-Xfa homologs are present in Xp and Xe. Efh-Xfa and its homolog in Xe strains from pepper shares a core region of 138 amino acids. Xe and Xp strains pathogenic to tomato are mutated in this gene such that the protein is truncated upstream of the EF-hand motifs. The Efh-Xfa gene contains additional amino acids at the N terminus. Xp expressing the Efh-Xfa was unable to grow to high populations in tomato while Xp expressing the Xe homolog, designated Efh-Xe grew to slightly higher populations but lower than Xp alone. Furthermore, Xp expressing Efh-Xe did not elicit an HR in tomato. We mutated the N terminus of the Efh-Xe by moving the translational start upstream to match that of Efh-Xfa gene. Infiltration of Xp expressing the mutated Efh-Xe resulted in rapid confluent necrosis, although bacterial growth in tomato leaves was similar to Xp expressing Efh-Xe gene. Our preliminary data indicate the importance of the N-terminus of the Efh-Xfa gene and its possible role in rapid confluent necrosis. Subcellular localization using an Efh-Xfa-phoA fusion based assay suggests that Efh-Xfa protein is localized to periplasm