title: Comparative genomics of host adaptive traits in Xanthomonas translucens pv. graminis.
abstract: Xanthomonas translucens pathovars differ in their individual host ranges among Poaceae. As the causal agent of bacterial wilt in Italian ryegrass (Lolium multiflorum Lam.), X. translucens pv. graminis (Xtg) is one of the most important bacterial pathogens in temperate grassland regions. The genomes of six Xtg strains from Switzerland, Norway, and New Zealand were sequenced in order to gain insight into conserved genomic traits from organisms covering a wide geographical range. Subsequent comparative analysis with previously published genome data of seven non-graminis X. translucens strains including the pathovars arrhenatheri, poae, phlei, cerealis, undulosa, and translucens was conducted to identify candidate genes linked to the host adaptation of Xtg to Italian ryegrass.
  
  
  
  Phylogenetic analysis revealed a tight clustering of Xtg strains, which were found to share a large core genome. Conserved genomic traits included a non-canonical type III secretion system (T3SS) and a type IV pilus (T4P), which both revealed distinct primary structures of the pilins when compared to the non-graminis X. translucens strains. Xtg-specific traits that had no homologues in the other X. translucens strains were further found to comprise several hypothetical proteins, a TonB-dependent receptor, transporters, and effector proteins as well as toxin-antitoxin systems and DNA methyltransferases. While a nearly complete flagellar gene cluster was identified in one of the sequenced Xtg strains, phenotypic analysis pointed to swimming-deficiency as a common trait of the pathovar graminis.
  
  
  
  Our study suggests that host adaptation of X. translucens pv. graminis may be conferred by a combination of pathovar-specific effector proteins, regulatory mechanisms, and adapted nutrient acquisition. Sequence deviations of pathogen-associated molecular patterns (PAMPs), as observed for the pilins of the T4P and T3SS, are moreover likely to impede perception by the plant defense machinery and thus facilitate successful host colonization of Italian ryegrass.
authors.affiliation: Molecular Ecology, Agroscope, 8046, Zurich, Switzerland.
authors.forename: Lena
authors.initials: L
authors.lastname: Hersemann
authors.affiliation: Center for Biotechnology, Bielefeld University, 33615, Bielefeld, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wibberg
authors.affiliation: Bioinformatics and Systems Biology, Justus Liebig University Giessen, 35392, Giessen, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Blom
authors.affiliation: Bioinformatics and Systems Biology, Justus Liebig University Giessen, 35392, Giessen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Goesmann
authors.affiliation: Molecular Ecology, Agroscope, 8046, Zurich, Switzerland.
authors.forename: Franco
authors.initials: F
authors.lastname: Widmer
authors.affiliation: Center for Biotechnology, Bielefeld University, 33615, Bielefeld, Germany.|MVZ Dr. Eberhard & Partner Dortmund, 44137, Dortmund, Germany.
authors.forename: Frank-Jörg
authors.initials: FJ
authors.lastname: Vorhölter
authors.affiliation: Molecular Ecology, Agroscope, 8046, Zurich, Switzerland. roland.koelliker@usys.ethz.ch.
authors.forename: Roland
authors.identifier: 0000-0003-1959-0402
authors.initials: R
authors.lastname: Kölliker
mesh_terms: D059646:Genome Size; D016680:Genome, Bacterial; D023281:Genomics / Q000379:methods; D059014:High-Throughput Nucleotide Sequencing; D054884:Host-Pathogen Interactions; D005810:Multigene Family; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D006109:Poaceae / Q000382:microbiology; D019655:Quantitative Trait, Heritable; D000069376:Type VI Secretion Systems / Q000235:genetics; D014774:Virulence / Q000235:genetics; D014974:Xanthomonas / Q000235:genetics* / Q000472:pathogenicity
chemical_list: D000069376:Type VI Secretion Systems
keywords: HrpE; Inter-pathovar comparison; LPS O-antigen; PilA; Type VI secretion system