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A Global Outlook on the Evolution of Type Three Effectors in Xanthomonads causing Bacterial Spot on Tomato and Pepper

Mustafa Jibrin: Ahmadu Bello University

<div><em>Xanthomonas euvesicatoria (Xe), X. vesicatoria (Xv), X. perforans (Xp) </em>and <em>X. gardneri (Xg) </em>are generally regarded as the bacteria species causing bacterial spot of tomato and pepper. <em>Xe </em>and <em>Xp </em>are closely related and may be regarded as a single species. Resistance breeding efforts have often targeted type three effector proteins found in these species. While unique effector profiles have been associated with each species, there is a need to understand the distribution and evolution of effectors on a global scale due to apparent international movement of these pathogens. In this study, we sequenced more than one hundred genomes, representing populations from more than fifteen countries covering Africa, North America, South America, Europe, Asia and Australia. We also included previously sequenced strains representing additional populations from the NCBI database. We utilized comparative genomics and phylogenetic approaches to evaluate the evolution of these effectors across and within species and geographies. Our findings suggest diverse dynamics of effectors, not only between or within species but across geographies. For example, the TAL effector, AvrHah1, originally found in <em>Xg</em>, is present in <em>Xp </em>strains from Nigeria, Mauritius, South Africa and Italy but absent in strains from Florida, USA. This comprehensive global study looking at populations of bacterial spot xanthomonads from different countries in six continents has several implications for disease management.</div>