Publications (19) View all
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Article: Variations in type III effector repertoires, pathological phenotypes and host range of Xanthomonas citri pv. citri pathotypes
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ABSTRACT: The mechanisms determining the host range of Xanthomonas are still undeciphered, despite much interest in their potential roles in the evolution and emergence of plant pathogenic bacteria. Xan-thomonas citri pv. citri (Xci) is an interesting model of host spe-cialization because of its pathogenic variants: pathotype A strains infect a wide range of Rutaceous species, whereas pathotype A*/A W strains have a host range restricted to Mexican lime (Citrus aurantifolia) and alemow (Citrus macrophylla). Based on a collec-tion of 55 strains representative of Xci worldwide diversity assessed by amplified fragment length polymorphism (AFLP), we investigated the distribution of type III effectors (T3Es) in relation to host range. We examined the presence of 66 T3Es from xan-thomonads in Xci and identified a repertoire of 28 effectors, 26 of which were shared by all Xci strains, whereas two (xopAG and xopC1) were present only in some A*/A W strains. We found that xopAG (=avrGf1) was present in all A W strains, but also in three A* strains genetically distant from A W , and that all xopAG-containing strains induced the hypersensitive response (HR) on grapefruit and sweet orange. The analysis of xopAD and xopAG suggested hori-zontal transfer between X. citri pv. bilvae, another citrus patho-gen, and some Xci strains. A strains were genetically less diverse, induced identical phenotypic responses and possessed indistin-guishable T3E repertoires. Conversely, A*/A W strains exhibited a wider genetic diversity in which clades correlated with geographi-cal origin and T3E repertoire, but not with pathogenicity, according to T3E deletion experiments. Our data outline the importance of taking into account the heterogeneity of Xci A*/A W strains when analysing the mechanisms of host specialization.Molecular Plant Pathology 02/2013; · 3.90 Impact Factor -
Article: Evolutionary History of the Plant Pathogenic Bacterium Xanthomonas axonopodis.
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ABSTRACT: Deciphering mechanisms shaping bacterial diversity should help to build tools to predict the emergence of infectious diseases. Xanthomonads are plant pathogenic bacteria found worldwide. Xanthomonas axonopodis is a genetically heterogeneous species clustering, into six groups, strains that are collectively pathogenic on a large number of plants. However, each strain displays a narrow host range. We address the question of the nature of the evolutionary processes - geographical and ecological speciation - that shaped this diversity. We assembled a large collection of X. axonopodis strains that were isolated over a long period, over continents, and from various hosts. Based on the sequence analysis of seven housekeeping genes, we found that recombination occurred as frequently as point mutation in the evolutionary history of X. axonopodis. However, the impact of recombination was about three times greater than the impact of mutation on the diversity observed in the whole dataset. We then reconstructed the clonal genealogy of the strains using coalescent and genealogy approaches and we studied the diversification of the pathogen using a model of divergence with migration. The suggested scenario involves a first step of generalist diversification that spanned over the last 25 000 years. A second step of ecology-driven specialization occurred during the past two centuries. Eventually, secondary contacts between host-specialized strains probably occurred as a result of agricultural development and intensification, allowing genetic exchanges of virulence-associated genes. These transfers may have favored the emergence of novel pathotypes. Finally, we argue that the largest ecological entity within X. axonopodis is the pathovar.PLoS ONE 01/2013; 8(3):e58474. · 4.09 Impact Factor -
Article: Genomic insights into strategies used by Xanthomonas albilineans with its reduced artillery to spread within sugarcane xylem vessels.
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ABSTRACT: BACKGROUND: Xanthomonas albilineans causes leaf scald, a lethal disease of sugarcane. X. albilineans exhibits distinctive pathogenic mechanisms, ecology and taxonomy compared to other species of Xanthomonas. For example, this species produces a potent DNA gyrase inhibitor called albicidin that is largely responsible for inducing disease symptoms; its habitat is limited to xylem; and the species exhibits large variability. A first manuscript on the complete genome sequence of the highly pathogenic X. albilineans strain GPE PC73 focused exclusively on distinctive genomic features shared with Xylella fastidiosa---another xylem-limited Xanthomonadaceae. The present manuscript on the same genome sequence aims to describe all other pathogenicity-related genomic features of X. albilineans, and to compare, using suppression subtractive hybridization (SSH), genomic features of two strains differing in pathogenicity. RESULTS: Comparative genomic analyses showed that most of the known pathogenicity factors from other Xanthomonas species are conserved in X. albilineans, with the notable absence of two major determinants of the "artillery" of other plant pathogenic species of Xanthomonas: the xanthan gum biosynthesis gene cluster, and the type III secretion system Hrp (hypersensitive response and pathogenicity). Genomic features specific to X. albilineans that may contribute to specific adaptation of this pathogen to sugarcane xylem vessels were also revealed. SSH experiments led to the identification of 20 genes common to three highly pathogenic strains but missing in a less pathogenic strain. These 20 genes, which include four ABC transporter genes, a methyl-accepting chemotaxis protein gene and an oxidoreductase gene, could play a key role in pathogenicity. With the exception of hypothetical proteins revealed by our comparative genomic analyses and SSH experiments, none genes potentially involved in any offensive or counter-defensive mechanism specific to X. albilineans were identified, supposing that X. albilineans has a reduced artillery compared to other pathogenic Xanthomonas species. Particular attention has therefore been given to genomic features specific to X. albilineans making it more capable of evading sugarcane surveillance systems or resisting sugarcane defense systems. CONCLUSIONS: This study confirms that X. albilineans is a highly distinctive species within the genus Xanthomonas, and opens new perpectives towards a greater understanding of the pathogenicity of this destructive sugarcane pathogen.BMC Genomics 11/2012; 13(1):658. · 4.07 Impact Factor -
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Article: Type three effector gene distribution and sequence analysis provide new insights into the pathogenicity of plant-pathogenic Xanthomonas arboricola.
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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.Applied and environmental microbiology 11/2011; 78(2):371-84. · 3.69 Impact Factor
