title: Type three effector gene distribution and sequence analysis provide new insights into the pathogenicity of plant-pathogenic Xanthomonas arboricola.
abstract: Xanthomonas arboricola is a complex bacterial species which mainly attacks fruit trees and is responsible for emerging diseases in Europe. It comprises seven pathovars (X. arboricola pv. pruni, X. arboricola pv. corylina, X. arboricola pv. juglandis, X. arboricola pv. populi, X. arboricola pv. poinsettiicola, X. arboricola pv. celebensis, and X. arboricola pv. fragariae), each exhibiting characteristic disease symptoms and distinct host specificities. To better understand the factors underlying this ecological trait, we first assessed the phylogenetic relationships among a worldwide collection of X. arboricola strains by sequencing the housekeeping gene rpoD. This analysis revealed that strains of X. arboricola pathovar populi are divergent from the main X. arboricola cluster formed by all other strains. Then, we investigated the distribution of 53 type III effector (T3E) genes in a collection of 57 X. arboricola strains that are representative of the main X. arboricola cluster. Our results showed that T3E repertoires vary greatly between X. arboricola pathovars in terms of size. Indeed, X. arboricola pathovars pruni, corylina, and juglandis, which are responsible for economically important stone fruit and nut diseases in Europe, harbored the largest T3E repertoires, whereas pathovars poinsettiicola, celebensis, and fragariae harbored the smallest. We also identified several differences in T3E gene content between X. arboricola pathovars pruni, corylina, and juglandis which may account for their differing host specificities. Further, we examined the allelic diversity of eight T3E genes from X. arboricola pathovars. This analysis revealed very limited allelic variations at the different loci. Altogether, the data presented here provide new insights into the evolution of pathogenicity and host range of X. arboricola and are discussed in terms of emergence of new diseases within this bacterial species.
authors.affiliation: INRA, UMR 077 PaVé, Beaucouzé, France.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Hajri
authors.forename: Joël F
authors.initials: JF
authors.lastname: Pothier
authors.forename: Marion
authors.initials: M
authors.lastname: Fischer-Le Saux
authors.forename: Sophie
authors.initials: S
authors.lastname: Bonneau
authors.forename: Stéphane
authors.initials: S
authors.lastname: Poussier
authors.forename: Tristan
authors.initials: T
authors.lastname: Boureau
authors.forename: Brion
authors.initials: B
authors.lastname: Duffy
authors.forename: Charles
authors.initials: C
authors.lastname: Manceau
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D005060:Europe; D014644:Genetic Variation; D058507:Host Specificity; D008969:Molecular Sequence Data; D010802:Phylogeny; D010944:Plants / Q000382:microbiology; D017422:Sequence Analysis, DNA; D037521:Virulence Factors / Q000235:genetics*; D014974:Xanthomonas / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D037521:Virulence Factors; D012321:DNA-Directed RNA Polymerases
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