Plant pathogens of the genera Phytophthora and Pythium, together with some obligate parasites (downy mildews and white rusts) cause highly destructive diseases on many dicots, thereby having major ecological and economic consequences worldwide. Pathogenic oomycetes are eukaryotic and filamentous microrganisms infecting various hosts (plants, insects, vertebrates, and other microorganisms). They constitute an adaptation both for survival, by protecting species from fluctuating conditions, and for molecular dialogs favored by promiscuity between species. To address these issues, mixed-species biofilms formed by pathogens and resident microbiota in the host vicinity are good models. Then the question of pathogenicity is not restricted at the single genotype or species level, but is extended at level of microbiota that represent a pathogenic entity. Such results contribute to evaluate the updating of our view of pathogenic processes taking into account a broader vision of pathogenesis. For example, interactions between microbes may promote pathogenicity by production of bacterial toxins that are essential for fungal virulence or by co-infection events that enhance effector gene expression. Studies suggest that fitness results of ability to suppress host defenses and acquire nutrients from host tissues, and also of features that minimize or maximize events associated with undesirable or beneficial co-infections. For plant pathogens, the incidence of microbe-microbe interactions on virulence is investigated. This includes stimulation of seed germination and plant growth, promotion of resistance to abiotic stresses, as well as elicitation of plant systemic defense, and antibiosis functions against pathogens. For plants, microbiota encompass various functional contexts. Microbiota associated either with hosts or/and pathogens regulate the course of infection. It contributes to the habitat extension of Pseudomonas species mediated through a physical association between the oomycete and the bacteria. parasitica in the tomato rhizosphere leads to a shift in the rhizospheric microbiota composition. The presence of the pathogenic oomycete P. Bacteria preferentially colonize the surface of the biofilm rather than the roots, so that they can infect plant cells without any apparent infection of P. establishes commensal interactions with the oomycete. parasitica effectors to Pseudomonas suggested that the increase in plant susceptibility was not associated with an increase in virulence. The lack of significant gene expression response of P. One Pseudomonas phylotype was found to exacerbate disease symptoms in tomato plants. parasitica extract-based medium (ii), exhibit in vitro probiotic or antibiotic activity towards the oomycete (iii), have an impact on the oomycete infection cycle in a tripartite interaction S. parasitica-associated microbiota interfering with biology and oomycete infection was carried out by screening for bacteria able to (i) grow on a P. Colonization of the host root surface by the oomycete was associated with a shift in microbial community involving a Bacteroidetes/Proteobacteria transition and Flavobacteriaceae as the most abundant family. ResultsĬomposition of the rhizospheric microbiota of Solanum lycopersicum was characterized using deep re-sequencing of 16S rRNA gene to analyze tomato roots either free of or partly covered with P. The nature of these interactions was explored for the polyphagous and telluric species Phytophthora parasitica. Interactions between pathogenic oomycetes and microbiota residing on the surface of the host plant root are unknown, despite being critical to inoculum constitution.
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