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Population genomic insights into the evolution of pathogenicity and host range expansion of Xanthomonas perforans to pepper

Eric Newberry: Department of Entomology and Plant Pathology, Auburn University

<div><em>Xanthomonas perforans </em>is among four species within the genus <em>Xanthomonas</em> responsible for bacterial leaf spot of tomato and pepper. While the host range of other bacterial leaf spot xanthomonads such as <em>X. euvesicatoria, X. vesicatoria, </em>and <em>X. gardneri </em>encompass a variety of solanaceous plant species, <em>X. perforans </em>is generally considered to be restricted to tomato. Recently, a novel <em>X. perforans </em>lineage isolated from diseased peppers grown in Florida was described, thus suggesting a recent host range expansion of this pathogen. The objective of the present study was to assess the genetic diversity of <em>X. perforans </em>strains that are pathogenic on pepper, and to identify genes that are significantly correlated with this pathogenicity phenotype. We screened a collection of strains that were isolated from diseased tomato and pepper plants grown in Alabama, South Carolina, and Indiana for pathogenicity, and conducted whole genome sequencing. A core genome phylogeny revealed the presence of three distinct lineages within <em>X. perforans </em>that were capable of infecting pepper. Genome-wide association identified several genes related to carbohydrate and amino acid metabolism to be significantly correlated with pathogenicity on this host. These findings provide novel gene candidates potentially modulating the host range of <em>X. perforans</em>, and are in contrast to previous studies that have emphasized the contribution of effector genes towards host-specificity.</div>