29 research outputs found

    Contribution de l'effectome et de l'effecteur de type 3 XopAC de Xanthomonas campestris pv. campestris à l'agressivité sur A. thaliana

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    Xanthomonas campestris pv. campestris (Xcc) est un pathogène vasculaire bactérien responsable de la nervation noire des Brassicacées. Afin de coloniser ses plantes hôtes, Xcc utilise un système de sécrétion de type 3 permettant d'injecter des protéines de virulence bactériennes appelées effecteurs de type 3 (ET3) directement à l'intérieur des cellules hôtes. Les ET3 manipulent alors le métabolisme de la cellule hôte et suppriment les défenses végétales pour favoriser la multiplication de la bactérie. Dans le but d'identifier des ET3 associés à un changement d'agressivité sur deux écotypes d'Arabidopsis thaliana (Kashmire et Columbia-0), une étude de génétique d'association (GWA) a été mise au point en utilisant les ET3 variables de Xcc. L'étude de GWA et la mutagénèse des ET3 de la souche 8004 ont permis d'identifier 9 ET3 associés à un changement différentiel d'agressivité de Xcc entre les deux écotypes d'A. thaliana. Parmi eux, xopAC a été identifié comme un gène majeur d'avirulence sur l'écotype Col-0 tandis que xopAM est un gène mineur d'avirulence sur cette même plante. L'analyse fonctionnelle de xopAC montre que les deux domaines de la protéine (LRR et Fic) sont nécessaires à sa fonction d'avirulence sur l'écotype Col-0 ainsi qu'à l'induction de nécrose chez des plantes non hôtes. Le domaine LRR est également requis pour la localisation membranaire de XopAC in planta. Enfin, la recherche des protéines végétales cibles de XopAC a permis d'identifier deux Receptor-Like Cytoplasmic Kinases, RIPK et PBL2, requis pour la reconnaissance de la souche 8004 de Xcc chez Col-0. Ce travail pose les bases génétiques de la dissection de l'immunité des Brassicacées à Xcc.Xanthomonas campestris pv. campestris (Xcc) is a vascular bacterial pathogen and the causal agent of black rot disease of Brassicaceae. To colonize its host plants, Xcc translocates virulence proteins called type 3 effectors (T3E) directly into the host cell thanks to its type 3 secretion system. Inside the host cell, T3E manipulates the cell metabolism to dampen the plant defenses and allow efficient multiplication of the pathogen. In order to identify T3E associated with a modification of the aggressiveness of Xcc on two ecotypes of Arabidopsis thaliana (Kashmir and Columbia-0), a Genome-Wide Association (GWA) study was performed using the variable T3E of Xcc. The GWA study and the deletion of the T3E in the strain 8004 allowed the identification of nine T3E controlling aggressiveness of Xcc. Among them, xopAC was identified as the major avirulence gene of Xcc on Col-0 ecotype whereas xopAM is a minor avirulence gene on the same plant. Functional analyses of xopAC show that the two domains of XopAC (LRR and Fic) are required to its avirulence function on the Col-0 ecotype and for xopAC-induced necrosis on nonhost plants. The LRR domain is also necessary to localize XopAC in planta to the plasma membrane. Moreover, search for plant targets of XopAC identified two Receptor-Like Cytoplasmic Kinase, RIPK and PBL2 which are required for the recognition of the strain 8004 by Col-0. This work gives the genetic bases to unravel the immunity of Brassicaceae to Xcc

    Fast Evolution and Lineage-Specific Gene Family Expansions of Aphid Salivary Effectors Driven by Interactions with Host-Plants

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    Effector proteins play crucial roles in plant-parasite interactions by suppressing plant defenses and hijacking plant physiological responses to facilitate parasite invasion and propagation. Although effector proteins have been characterized in many microbial plant pathogens, their nature and role in adaptation to host plants are largely unknown in insect herbivores. Aphids rely on salivary effector proteins injected into the host plants to promote phloem sap uptake. Therefore, gaining insight into the repertoire and evolution of aphid effectors is key to unveiling the mechanisms responsible for aphid virulence and host plant specialization. With this aim in mind, we assembled catalogues of putative effectors in the legume specialist aphid, Acyrthosiphon pisum, using transcriptomics and proteomics approaches. We identified 3,603 candidate effector genes predicted to be expressed in A. pisum salivary glands (SGs), and 740 of which displayed up-regulated expression in SGs in comparison to the alimentary tract. A search for orthologs in 17 arthropod genomes revealed that SG-up-regulated effector candidates of A. pisum are enriched in aphid-specific genes and tend to evolve faster compared with the whole gene set. We also found that a large fraction of proteins detected in the A. pisum saliva belonged to three gene families, of which certain members show evidence consistent with positive selection. Overall, this comprehensive analysis suggests that the large repertoire of effector candidates in A. pisum constitutes a source of novelties promoting plant adaptation to legumes

    Genome sequencing of Xanthomonas axonopodis pv. phaseoli CFBP4834-R reveals that flagellar motility is not a general feature of xanthomonads.

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    Xanthomonads are plant-associated bacteria that establish neutral, commensal or pathogenic relationships with plants. The list of common characteristics shared by all members of the genus Xanthomonas is now well established based on the entire genome sequences that are currently available and that represent various species, numerous pathovars of X. axonopodis (sensu Vauterin et al., 2000), X. oryzae and X. campestris, and many strains within some pathovars. These ?-proteobacteria are motile by a single polar flagellum. Motility is an important feature involved in biofilm formation, plant colonization and hence considered as a pathogenicity factor. X. axonopodis pv. phaseoli var. fuscans (Xapf) is one of the causal agents of common bacterial blight of bean and 4834-R is a highly aggressive strain of this pathogen that was isolated from a seed-borne epidemic in France in 1998. We obtained a high quality assembled sequence of the genome of this strain with 454-Solexa and 2X Sanger sequencing. Housekeeping functions are conserved in this genome that shares core characteristics with genomes of other xanthomonads: the six secretion systems which have been described so far in Gram negative bacteria are all present, as well as their ubiquitous substrates or effectors and a rather usual number of mobile elements. Elements devoted to the adaptation to the environment constitute an important part of the genome with a chemotaxis island and dispersed MCPs, numerous two-component systems, and numerous TonB dependent transporters. Furthermore, numerous multidrug efflux systems and functions dedicated to biofilm formation that confer resistance to stresses are also present. An intriguing feature revealed by genome analysis is a long deletion of 35 genes (33 kbp) involved in flagellar biosynthesis. This deletion is replaced by an insertion sequence called ISXapf2. Genes such as flgB to flgL and fliC to fleQ which are involved in the flagellar structure (rod, P- and L-ring, hook, cap and filament) are absent in the genome of strain 4834-R that is not motile. Primers were designed to detect this deletion by PCR in a collection of more than 300 strains representing different species and pathovars of Xanthomonas, and less than 5% of the tested xanthomonads strains were found nonmotile because of a deletion in the flagellum gene cluster. We observed that half of the Xapf strains isolated from the same epidemic than strain 4834-R was non-motile and that this ratio was conserved in the strains colonizing the next bean seed generation. Isolation of such variants in a natural epidemic reveals that either flagellar motility is not a key function for fitness or that some complementation occurs within the bacterial population. (Résumé d'auteur

    Genome sequence of Xanthomonas fuscans subsp. fuscans strain 4834-R reveals that flagellar motility is not a general feature of xanthomonads

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    Abstract\ud \ud \ud \ud Background\ud Xanthomonads are plant-associated bacteria responsible for diseases on economically important crops. Xanthomonas fuscans subsp. fuscans (Xff) is one of the causal agents of common bacterial blight of bean. In this study, the complete genome sequence of strain Xff 4834-R was determined and compared to other Xanthomonas genome sequences.\ud \ud \ud \ud Results\ud Comparative genomics analyses revealed core characteristics shared between Xff 4834-R and other xanthomonads including chemotaxis elements, two-component systems, TonB-dependent transporters, secretion systems (from T1SS to T6SS) and multiple effectors. For instance a repertoire of 29 Type 3 Effectors (T3Es) with two Transcription Activator-Like Effectors was predicted. Mobile elements were associated with major modifications in the genome structure and gene content in comparison to other Xanthomonas genomes. Notably, a deletion of 33 kbp affects flagellum biosynthesis in Xff 4834-R. The presence of a complete flagellar cluster was assessed in a collection of more than 300 strains representing different species and pathovars of Xanthomonas. Five percent of the tested strains presented a deletion in the flagellar cluster and were non-motile. Moreover, half of the Xff strains isolated from the same epidemic than 4834-R was non-motile and this ratio was conserved in the strains colonizing the next bean seed generations.\ud \ud \ud \ud Conclusions\ud This work describes the first genome of a Xanthomonas strain pathogenic on bean and reports the existence of non-motile xanthomonads belonging to different species and pathovars. Isolation of such Xff variants from a natural epidemic may suggest that flagellar motility is not a key function for in planta fitness.AI is funded by a PhD grant from INRA-SPE and region Pays de la Loire, France. EG was funded by a PhD grant from the French Ministry of National Education and Research and French Guyana. SC, EG, MA, EL and LDN are funded by the LABEX TULIP (ANR-10-LABX-41), LSG is funded by ANR-2010-GENM-013 Xanthomix

    Genome Sequence of Xanthomonas campestris pv. campestris Strain Xca5.

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    International audienceAn annotated high-quality draft genome sequence for Xanthomonas campestris pv. campestris race 1 strain Xca5 (originally described as X. campestris pv. armoraciae), the causal agent of black rot on Brassicaceae plants, has been determined. This genome sequence is a valuable resource for comparative genomics within the campestris pathovar
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