Letteratura scientifica selezionata sul tema "Bactéries phytopathogènes – Adaptation"
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Tesi sul tema "Bactéries phytopathogènes – Adaptation":
Mhedbi-Hajri, Nadia. "Approches cumulées de phylogénie et d'écologie pour déterminer les bases génétiques de la spécificité d'hôte des bactéries phytopathogènes, cas des Xanthomonas spp". Angers, 2010. http://www.theses.fr/2010ANGE0057.
Host specificity combines distinct successive phases of interaction between bacteria and host plant: attraction, ability to multiply on or inside the host and transmission to new hosts. We hypothesized that determinants responsible for bacterial host specificity are expressed starting from chemotactic attraction by host tissues and adhesion. We established the distribution of 70 genes involved in chemotactic attraction, chemical environment sensing and adhesion in a large collection of xanthomonad strains. These 173 strains belong to different pathovars of Xanthomonas spp and display different host ranges. Most pathovars (28/34) were characterized by unique repertoires of candidate genes highlighting a correspondence between pathovar clustering and repertoires of sensors and adhesins. In contrast, six pathovars may display the same repertoire. This may reflect common ecological behaviors. To further challenge our hypothesis, we tested for molecular signatures of selective pressures on genes encoding chemotactic sensors and adhesins of xanthomonad strains. We identified strong evidence of adaptive divergence acting on most candidate genes. Within X. Axonopodis, candidate genes were identified to be under purifying selection or positive selection. Most of sites under positive selection were located in conserved domains within proteins. These finding suggest that purifying selection may act on genes involved in recognition of common structures of plant tissues and positive selection may act on genes coding for sensors and adhesins used for colonization of specific niches. These findings provide new insights in the evolutionary importance of chemotactic attraction and adhesion in the host specificity of plant pathogenic bacteria. Thus, events leading to host specificity may occur as early as chemotactic attraction by host and adhesion to tissues for plant pathogenic xanthomonads. Phylogenetical and genealogical analyses conducted on X. Axonopodis strains strongly supported clustering of these strains into 6 subgroups corresponding to known subgroups within this species and indicated that the divergence between some subgroups is very ancient. Furthermore, recombination events due to genetic exchanges have been found to occur recently in X. Axonopodis strains and some were associated to transfers of virulence-associated genes. All these data support the importance of perception of the environment and adhesion in the plant-microbe interactions
Mhedbi, Nadia. "Approches cumulées de phylogénie et d'écologie pour déterminer les bases génétiques de la spécificité d'hôte des bactéries phytopathogènes, cas des Xanthomonas spp". Phd thesis, Université d'Angers, 2010. http://tel.archives-ouvertes.fr/tel-00648729.
Gopalan, Nair Rekha. "Déterminants moléculaires de l'adaptation à l'hôte chez la bactérie phytopathogène Ralstonia solanacearum". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30207.
The Ralstonia solanacearum species complex (RSSC) is a destructive plant pathogen that infects more than 250-plant species including tomato, potato, pelargonium, ginger and banana. In addition, this multihost pathogen is known for rapid adaptation to new plant species and new environments. In order to overcome this pathogen, it is important to understand the molecular mechanisms that govern host adaptation. The objectives of this thesis were (1) to decipher the genetic bases of adaptation of a RSSC strain to a resistant cultivar, (2) to investigate the potential role of epigenetic modifications in host adaptation and (3) to analyze to impact of the plant species on genetic, transcriptomic and epigenetic modifications in RSSC adapted clones. This study was conducted on clones generated by experimental evolution of GMI1000 RSSC strain after 300 generation of serial passages on the resistant tomato ‘Hawaii 7996’ plant, the susceptible eggplant ‘Zebrina’ and the tolerant plant Bean ‘Blanc precoce’. Competitive experiments with the GMI1000 ancestral clone demonstrated that 95% of the clones evolved on Hawaii 7996 were better adapted to the growth into this tomato plant than the ancestral clone. Genomic sequence analysis of these adapted clones found between 0 and 2 mutations per clone and we demonstrated that they were adaptive mutations. Transcriptome analysis of the Hawaii, Zebrina and Bean evolved clones revealed a convergence towards a global rewiring of the virulence regulatory network as evidenced by largely overlapping gene expression profiles. Two transcription regulators, HrpB, the activator of the type 3 secretion system regulon and EfpR, a global regulator of virulence and metabolic functions, emerged as key nodes of this regulatory network that were frequently targeted by either genetic or potential epigenetic modification affecting their expression. Significant transcriptomic variations were also detected in evolved clones showing no mutation, suggesting a potential role of epigenetic modifications in adaptation. Comparison of the DNA methylation profiles between the evolved clones and the ancestral clone revealed between 13 and 35 differentially methylated regions (DMRs). No impact of the host plant on the list of DMRs appeared. Some of these DMRs targeted genes that were identified to be differentially expressed between the evolved clones and the ancestral clone. This result supported the hypothesis that epigenetic modifications regulate gene expression and could play a major role in RSSC adaptation to new host plants
Caby, Marine. "Rôle du phosphorelais EnvZ/OmpR chez la bactérie phytopathogène Dickeya dadantii". Thesis, Lille 1, 2020. http://www.theses.fr/2020LIL1S108.
During their lifetime, pathogenic bacteria are confronted with numerous environmental variations often referred to stress, particularly during infection. In order to survive and successfully colonize its host, the bacterium must perceive this new and dangerous environment to adapt quickly. This is the main role assigned to phosphorelays. These systems are composed of a sensor and a cognate regulator. Under the action of a stimulus, the sensor autophosphorylates and transmits the phosphate group to its regulator, which in turn modulates the activity of a set of target genes allowing adaptation to the new environment. Our experimental model Dickeya dadantii is a necrotrophic plant pathogen bacterium responsible for soft rot disease in a wide range of plant species. The variation of pH and osmolarity are two stresses often faced and fought by pathogenic bacteria. EnvZ/OmpR and RcsCDB phosphorelays are two major systems known to respond to these stresses. The laboratory had previously demonstrated that the level of activation of the RcsCDB system was dependent on the concentration of periplasmic osmoregulated glucans (OPG). Their concentration in the periplasm increases as the medium osmolarity decreases, making OPGs a major intermediate in the perception of osmolarity. This prompted us to decipher the relationship between EnvZ/OmpR and OPGs. I showed that, unlike for the activation of the RcsCDB system, the activation of EnvZ/OmpR doesn’t depend on the concentration of OPGs, but still requires its presence for proper activation of the phosphorelay. To go deeper into the EnvZ/OmpR system, activities of this system have been studied in vivo and in planta. While the EnvZ/OmpR system is activated in a medium with an acidic pH and a high osmolarity in E. coli, my work shows that only pH variation activates this phosphorelay in D. dadantii. In addition, only one major porin (versus two in E. coli) was previously detected in D. dadantii. My studies revealed the existence of a second porin expressed at acidic pH in vivo and in planta. These two OmpF-like porins are regulated by the pH via OmpR. After adaptation for a few hours in planta, the pattern of these two porines remains the same over the rest of the infection. However, the level of OmpR activation during the same period fluctuates indicating that at least one other environmental parameter modulates the activation of EnvZ/OmpR in planta. The steady state level of the porines in the envelope during this same period suggests that another regulatory system, perhaps RcsCDB may maintain their expression level
Blin, Pauline. "Dynamique des interactions entre Dickeya dianthicola, Dickeya solani et leur hôte Solanum tuberosum". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS267/document.
In potato plant (Solanum tuberosum), blackleg and soft rot are diseases caused by bacterial populations associating one or more species of the genus Pectobacterium and Dickeya. For several decades in Europe, the involvement of the genus Dickeya has increased, notably with the recent emergence of D. solani in the 2000s. No effective control exists against these plant pathogens; only prophylactic approaches are set up by the production industry. In this work, analysis of the structure of pathogenic populations in potato fields of northern France shows that D. dianthicola and D. solani dominate populations of Pectobacterium in relative abundance, while D. dianthicola dominates D. solani when both populations coexist. In a second part, artificial populations of D. dianthicola and D. solani isolates have allowed to assessed their aggressiveness and competitiveness in a greenhouse experiment. While the D. dianthicola population confirms its strongest aggressiveness and competitiveness when whole plants of S. tuberosum are infected, D. solani population is more aggressive and competitive when infecting Hyacinthus orientalis, as well as in rich and minimal liquid mediums. The individual analysis of the isolates of the artificial populations of D. dianthicola and D. solani shows that different aggressiveness in the host S. tuberosum is a distinctive trait of these pathogenic species; which reinforces the hypothesis of a recent host transfer (bulb plants to potato plants) of D. solani. Remarkably, in infected tissues of S. tuberosum (stem and tubers), the virulence genes pelD and pelE are highly expressed and more heterogeneously among D. solani isolates than those of D. dianthicola. A comparative transcriptomic analysis confirms the variability of the expression of virulence functions between 3 isolates of D. solani. All this work reveals that D. solani is still in adaptation phase to the host S. tuberosum, with less competitiveness against D. dianthicola during co-infection but an expression of the virulence functions in maceration condition greater that D. dianthicola. Thus, under the condition of selection of favorable genetic variations to its establishment on S. tuberosum host plant and the improvement of its competitiveness against D. dianthicola, D. solani represents a medium-term major risk for potato cultivation
Cochard, Clémence. "Régulation fine du système EnvZ/OmpR chez Dickeya dadantii : clef d'une infection réussie". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILS109.
Throughout their life, the bacteria must confront numerous environmental variations. They must adapt rapidly and effectively to ensure their survival. To accomplish this, they possess phosphorelays, or two-component systems, which are the major molecular tools enabling perception and adaptation to the environment in bacteria. These phosphorelays consist of a sensor and an associated regulator. Following the perception of a stimulus, the sensor autophosphorylates and transmits the phosphate group to the regulator, which then modulates the expression of the entire target gene set, known as a regulon. During the infection process, pathogenic bacteria must deal with multiple stresses. A significant number of these systems are found in various pathogenic bacteria, such as our study model Dickeya dadantii. Responsible for soft rot disease, D. dadantii is a wide-host-range phytopathogenic enterobacterium. It possesses a battery of 32 phosphorelays to deal with host defenses and the general stresses of nutritional deficiencies or physicochemical variations in the environment.First this study focuses on one of them, the EnvZ/OmpR system. My work initially shows that the pH in the plant remains acidic during infection. However, despite activation of the system by acidic pH, it is not activated during this process. To understand the reason for this inconsistency, the system's regulon was studied. It was then discovered that during the emergence of the Dickeya genus, the ompF gene, encoding the porin of the same name, was duplicated. Interestingly, the expression of ompF is constitutive, whereas that of ompF2, the duplicated gene, which is dependent on OmpR phosphorylation levels. The expression of this second porin is also detrimental to infection. Thus, during infection, the activation of EnvZ/OmpR is counteracted by the perception of host defense molecules to prevent the expression of ompF2 and enable proper virulence progression.In a second phase, a comprehensive study of the importance of each phosphorelay in D. dadantii's virulence was conducted in my work. The initial results show that only 6 systems are involved in virulence. The number and complexity of stresses encountered by pathogenic bacteria do not seem to align with this low number. Reducing the quantity of inoculated bacteria allowed for a more precise detection of the systems contributing to virulence, which now totals 12. Overall, these results indicate the significance of finely regulating the activity of a phosphorelay, as EnvZ/OmpR must be activated for infection, but this activation must be strongly controlled to avoid detrimental effects on virulence
Richard, Damien. "Microévolution et adaptation à une pression de sélection anthropique chez Xanthomonas citri pv. citri, une bactérie pathogène des agrumes : dynamique du compartiment plasmidique". Thesis, La Réunion, 2019. http://www.theses.fr/2019LARE0001.
Copper, frequently used in agriculture to control bacterial diseases, is commonly used against Xanthomonas citri pv. citri (Xcc), the bacterial agent of Asiatic citrus canker. The recent detection of a copper-resistant phenotype in two French overseas regions motivated a genomic study which revealed, in copper-resistant (CuR) strains, a conjugative plasmid encoding an adaptive transposon of the Tn3 family. Its conservation in several Xanthomonas species suggested the role of horizontal gene transfer (HGT) in Xcc adaptation. We therefore analyzed the evolutionary history of susceptible and CuR Xcc strains in the Indian Ocean using both SNP and gene content variations. The dating of the obtained phylogeny allowed us to hypothesize the history of Xcc introduction into the region. The phylogeny showed a strong geographic structure among islands of the Indian Ocean region, which faded at the Réunion scale and disappeared at the grove scale. Among the groves, admixture is a factor favoring HGT between genetically distinct strains. This form of evolution is however largely uncharacterized in the Xanthomonas genus. To fill this gap, we searched genetic homology between the whole known plasmid gene content of the Xanthomonadaceae family and the complete set of genomes hosted in NCBI databases. We highlighted both the ubiquity of plasmid genes in the Xanthomonadaceae family and the taxonomical barrier of their sharing by conjugation. The small fraction of genes that were exchanged through the complete sharing of plasmids also revealed the importance of plasmid mosaicism, partly due to mobile genetic elements. Taken together, our results highlight the importance of bacterial communities in the evolution of phytopathogenic bacteria of the Xanthomonas genus, and the need for a precise characterization of the content and the functioning of the Xanthomonadaceae environmental genome in order to fully apprehend the adaptation of these phytopathogenic bacteria