title: Whole-Genome Sequences ofXanthomonas euvesicatoriaStrains Clarify Taxonomy and Reveal a Stepwise Erosion of Type 3 Effectors.
abstract: Multiple species ofXanthomonascause bacterial spot of tomato (BST) and pepper. We sequenced fiveXanthomonas euvesicatoriastrains isolated from three continents (Africa, Asia, and South America) to provide a set of representative genomes with temporal and geographic diversity. LMG strains 667, 905, 909, and 933 were pathogenic on tomato and pepper, except LMG 918 elicited a hypersensitive reaction (HR) on tomato. Furthermore, LMG 667, 909, and 918 elicited a HR on Early Cal Wonder 30R containingBs3. We examined pectolytic activity and starch hydrolysis, two tests which are useful in differentiatingX. euvesicatoriafromX. perforans, both causal agents of BST. LMG strains 905, 909, 918, and 933 were nonpectolytic while only LMG 918 was amylolytic. These results suggest that LMG 918 is atypical ofX. euvesicatoria. Sequence analysis of all the publicly availableX. euvesicatoriaandX. perforansstrains comparing seven housekeeping genes identified seven haplotypes with few polymorphisms. Whole genome comparison by average nucleotide identity (ANI) resulted in values of >99% among the LMG strains 667, 905, 909, 918, and 933 andX. euvesicatoriastrains and >99.6% among the LMG strains and a subset ofX. perforansstrains. These results suggest thatX. euvesicatoriaandX. perforansshould be considered a single species. ANI values between strains ofX. euvesicatoria, X. perforans, X. allii, X. alfalfasubsp. citrumelonis,X. dieffenbachiae, and a recently described pathogen of rose were >97.8% suggesting these pathogens should be a single species and recognized asX. euvesicatoria. Analysis of the newly sequencedX. euvesicatoriastrains revealed interesting findings among the type 3 (T3) effectors, relatively ancient stepwise erosion of some T3 effectors, additionalX. euvesicatoria-specific T3 effectors among the causal agents of BST, orthologs ofavrBs3andavrBs4, and T3 effectors shared among xanthomonads pathogenic against various hosts. The results from this study supports the finding that T3 effector repertoire and host range are fundamental for the study of host-microbe interaction but of little relevance to bacterial speciation.
authors.affiliation: UMR Interactions - Plantes - Microorganismes - Environnement, IRD-Cirad-Université MontpellierMontpellier, France; Department of Plant Pathology, University of WisconsinMadison, WI, USA.
authors.forename: Jeri D
authors.initials: JD
authors.lastname: Barak
authors.affiliation: UMR Interactions - Plantes - Microorganismes - Environnement, IRD-Cirad-Université MontpellierMontpellier, France; Faculty of Biology, Sofia University St. Kliment OhridskiSofia, Bulgaria.
authors.forename: Taca
authors.initials: T
authors.lastname: Vancheva
authors.affiliation: Pôle de Protection des Plantes, UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical, Cirad-Université de la Réunion Saint-Pierre, Ile de la Réunion, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Lefeuvre
authors.affiliation: Department of Plant Pathology, University of Florida Gainsville, FL, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Jones
authors.affiliation: Department of Plant Pathology, University of Florida Gainsville, FL, USA.
authors.forename: Sujan
authors.initials: S
authors.lastname: Timilsina
authors.affiliation: Department of Plant Pathology, University of Florida Gainsville, FL, USA.
authors.forename: Gerald V
authors.initials: GV
authors.lastname: Minsavage
authors.affiliation: Gulf Coast Research and Education Center, University of Florida Wimauma, FL, USA.
authors.forename: Gary E
authors.initials: GE
authors.lastname: Vallad
authors.affiliation: UMR Interactions - Plantes - Microorganismes - Environnement, IRD-Cirad-Université Montpellier Montpellier, France.
authors.forename: Ralf
authors.initials: R
authors.lastname: Koebnik
keywords: HrpX regulon; PIP box; Xanthomonas euvesicatoria; Xanthomonas perforans; cell wall degrading enzymes; comparative genomics; taxonomy; type III effectors