Pathogen derived resistance to Potato virus Y: mechanisms and risks

Selostus: Patogeenivälitteinen, siirtogeeninen kestävyys perunan Y-virusta vastaan: mekanismit ja riskit

Induced defence responses of cereals to pathogen attack

Selostus: Viljojen puolustusreaktiot taudinaiheuttajia vastaan

Normal pathogen-specific immune responses mounted by CTLA-4-deficient T cells: a paradigm reconsidered.

CTLA-4 is a critical negative regulator of T cell responses and CTLA-4-deficient (CTLA-4(-/-)) mice die of a lymphproliferative disease. Nevertheless, RAG-2-deficient mice reconstituted with a mixture of CTLA-4(-/-) and normal (CTLA-4(+/+)) bone marrow survive in the absence of any signs of disease, although 50% of their T cells do not express CTLA-4. Using such mixed chimeras, we analyzed the role of CTLA-4 in specific T cell responses to lymphocytic choriomeningitis virus, Leishmania major and mouse mammary tumor virus, which cause acute, chronic and persistent infections, respectively. The populations of antigen-specific CTLA-4(-/-)CD4(+) and CTLA-4(-/-)CD8(+) T cells became activated, expanded and contracted indistinguishably from CTLA-4(+/+)CD4(+) and CTLA-4(+/+)CD8(+) T cells after infection with all three pathogens. Thus, CTLA-4 is not involved in the down-regulation of specific T cell responses and peripheral deletion in a T cell-autonomous fashion.

Adding injury to insult: pathogen detection and responses.

Genomic approaches to the study of the expression of plant genes induced in response to disease and attack are now showing that there is an intimate association between pathogen perception and general stress detection.

Phenotypic plasticity in salmonid embryos : characterizing pathogen-induced stress effects on heritable variation in traits and reaction norms

Les pressions écologiques peuvent varier tant en nature qu'en intensité dans le temps et l'espace. C'est pourquoi, un phénotype unique ne peut pas forcément conférer la meilleure valeur sélective. La plasticité phénotypique peut être un moyen de s'accommoder de cette situation, en augmentant globalement la tolérance aux changements environnementaux. Comme pour tout trait de caractère, une variation génétique doit persister pour qu'évoluent les traits plastiques dans une population donnée. Cependant, les pressions extérieures peuvent affecter l'héritabilité, et la direction de ces changements peut dépendre du caractère en question, de l'espèce mais aussi du type de stress. Dans la présente thèse, nous avons cherché à élucider les effets des pressions pathogéniques sur les phénotypes et la génétique quantitative de plusieurs traits plastiques chez les embryons de deux salmonidés, la palée (Coregonus palaea), et la truite de rivière (Salmo trutta). Les salmonidés se prêtent à de telles études du fait de leur extraordinaire variabilité morphologique, comportementale et des traits d'histoire de vie. Par ailleurs, avec le déclin des salmonidés dans le monde, il est important de savoir combien la variabilité génétique persiste dans les normes de réaction afin d'aider à prédire leur capacité à répondre aux changements de leur milieu. Nous avons observé qu'une augmentation de la croissance des communautés microbiennes symbiotiques entraînait une mortalité accrue et une éclosion précoce chez la palée, et dévoilait la variance génétique additive pour ces deux caractères (Chapitres 1-2). Bien qu'aucune variation génétique n'ait été trouvée pour les normes de réaction, nous avons observé une variabilité de la plasticité d'éclosion. Néanmoins, on a trouvé que les temps d'éclosion étaient corrélés entre les environnements, ce qui pourrait limiter l'évolution de la norme de réaction. Le temps d'éclosion des embryons est lié à la taille des géniteurs mâles, ce qui indique des effets pléiotropiques. Dans le Chapitre 3, nous avons montré qu'une interaction triple entre la souche bactérienne {Pseudomonas fluorescens}, l'état de dévelopement de l'hôte ainsi que ses gènes ont une influence sur la mortalité, le temps d'éclosion et la taille des alevins de la palée. Nous avons démontré qu'une variation génétique subsistait généralement dans les normes de réaction des temps d'éclosion, mais rarement pour la taille des alevins, et jamais pour la mortalité. Dans le même temps, nous avons exhibé que des corrélations entre environnements dépendaient des caractères phénotypiques, mais contrairement au Chapitre 2, nous n'avons pas trouvé de preuve de corrélations transgénérationnelles. Le Chapitre 4 complète le chapitre précédent, en se plaçant du point de vue moléculaire, et décrit comment le traitement d'embryons avec P. fluorescens s'est traduit par une régulation négative d'expression du CMH-I indépendemment de la souche bactérienne. Nous avons non seulement trouvé une variation génétique des caractères phénotypiques moyens, mais aussi de la plasticité. Les deux derniers chapitres traitent de l'investigation, chez la truite de rivière, des différences spécifiques entre populations pour des normes de réaction induites par les pathogènes. Dans le Chapitre 5, nous avons illustré que le métissage entre des populations génétiquement distinctes n'affectait en rien la hauteur ou la forme des normes de réaction d'un trait précoce d'histoire de vie suite au traitement pathogénique. De surcroît, en dépit de l'éclosion tardive et de la réduction de la taille des alevins, le traitement n'a pas modifié la variation héritable des traits de caractère. D'autre part, dans le Chapitre 6, nous avons démontré que le traitement d'embryons avec des stimuli contenus dans l'eau de conspécifiques infectés a entraîné des réponses propre à chaque population en terme de temps d'éclosion ; néanmoins, nous avons observé peu de variabilité génétique des normes de réaction pour ce temps d'éclosion au sein des populations. - Ecological stressors can vary in type and intensity over space and time, and as such, a single phenotype may not confer the highest fitness. Phenotypic plasticity can act as a means to accommodate this situation, increasing overall tolerance to environmental change. As with any trait, for plastic traits to evolve in a population, genetic variation must persist. However, environmental stress can alter trait heritability, and the direction of this shift can be trait, species, and stressor-dependent. In this thesis, we sought to understand the effects of pathogen stressors on the phenotypes and genetic architecture of several plastic traits in the embryos of two salmonids, the whitefish (Coregonus palaea), and the brown trout (Salmo trutta). Salmonids lend themselves to such studies because their extraordinary variability in morphological, behavioral, and life-history traits. Also, with declines in salmonids worldwide, knowing how much genetic variability persists in reaction norms may help predict their ability to respond to environmental change. We found that increasing growth of symbiotic microbial communities increased mortality and induced hatching in whitefish, and released additive genetic variance for both traits (Chapters 1-2). While no genetic variation was found for survival reaction norms, we did find variability in hatching plasticity. Nevertheless, hatching time was correlated across environments, which could constrain evolution of the reaction norm. Hatching time in the induced environment was also correlated to sire size, indicating pleiotropic effects. In Chapter 3 we report that a three-way interaction between bacterial strain (Pseudomonas fluorescens), host developmental stage, and host genetics impacted mortality, hatching time, and hatchling size in whitefish. We also showed that genetic variation generally persisted in hatching age reaction norms, but rarely for hatchling length, and never for mortality. At the same time, we demonstrated that cross-environmental correlations were trait-dependent, and unlike Chapter 2, we found no evidence of cross-generational correlations. Chapter 4 expands on the previous chapter, moving to the molecular level, and describes how treatment of embryos with P. fluorescens resulted in strain-independent downregulation of MHC class I. Genetic variation was evident not only in trait means, but also in plasticity. In the last two chapters, we investigated population level differences in pathogen- induced reaction norms in brown trout. In Chapter 5, we found that interbreeding between genetically distinct populations did not affect the elevation or shapes of the reaction norms of early life-history traits after pathogen challenge. Moreover, despite delaying hatching and reducing larval length, treatment produced no discernable shifts in heritable variation in traits. On the other hand, in Chapter 6, we found that treatment of embryos with water-borne cues from infected conspecifics elicited population-specific responses in terms of hatching time; however, we found little evidence of genetic variability in hatching reaction norms within populations. We have made considerable progress in understanding how pathogen stressors affect various early life-history traits in salmonid embryos. We have demonstrated that the effect of a particular stressor on heritable variation in these traits can vary according to the trait and species under consideration, in addition to the developmental stage of the host. Moreover, we found evidence of genetic variability in some, but not all reaction norms in whitefish and brown trout.

Characterization of a Peruvian isolate of Metarhizium anisopliae var. acridum, a pathogen of grasshoppers

The objective of this study was to characterize the Peruvian isolate of Metarhizium anisopliae var. acridum, CG 863, obtained from the grasshopper Schistocerca interrita, a crop pest in Peru. The characterization was done by comparing this isolate with two other ones of M. anisopliae var. acridum, from Brazil and Australia, and with an isolate of M. anisopliae var. anisopliae. The three M. anisopliae var. acridum isolates had similar growth profiles in agar plates at 25°C and 37°C, and similar RAPD patterns according to the analysis of three primers. However, regarding these parameters and conidial size, these isolates were very distinct when compared to M. anisopliae var. anisopliae isolate. Bioassays indicated that the Peruvian isolate is as pathogenic as the Brazilian isolate against nymphs of Rhammatocerus schistocercoides.

Genomics of host-pathogen interactions.

The study of immunity against infection can be framed in the context of genomics. First, long-term association with pathogens results in genomic signatures that result from positive selection. Evolutionary pressures tailor species or individual responses to pathogens, that may be associated with skewed patterns of immunity. Second, recent human population expansion carries an increasing burden of genetic mutation that can result in sporadic immunodeficiencies, and more generally, in diversity in susceptibility to infection. This review highlights current concepts and tools for the analysis of genomes and stresses the interest of these approaches in immunity.

Pneumococcal penumonia presenting with septic shock: host-ant pathogen-related factors and outcomes

BACKGROUND: Host- and pathogen-related factors associated with septic shock in pneumococcal pneumonia are not well defined. The aim of this study was to identify risk factors for septic shock and to ascertain patient outcomes. Serotypes, genotypes and antibiotic resistance of isolated strains were also analysed. METHODS: Observational analysis of a prospective cohort of non-severely immunosuppressed hospitalised adults with pneumococcal pneumonia. Septic shock was defined as a systolic blood pressure of <90 mm Hg and peripheral hypoperfusion with the need for vasopressors for >4 h after fluid replacement. RESULTS: 1041 patients with pneumococcal pneumonia diagnosed by Gram stain and culture of appropriate samples and/or urine antigen test were documented, of whom 114 (10.9%) had septic shock at admission. After adjustment, independent risk factors for shock were current tobacco smoking (OR, 2.11; 95% CI, 1.02 to 4.34; p = 0.044), chronic corticosteroid treatment (OR, 4.45; 95% CI, 1.75 to 11.32; p = 0.002) and serotype 3 (OR, 2.24; 95% CI, 1.12 to 4.475; p = 0.022). No significant differences were found in genotypes and rates of antibiotic resistance. Compared with the remaining patients, patients with septic shock required mechanical ventilation more frequently (37% vs 4%; p<0.001) and had longer length of stay (11 vs 8 days; p<0.001). The early (10% vs 1%; p<0.001) and overall case fatality rates (25% vs 5%; p<0.001) were higher in patients with shock. CONCLUSIONS: Septic shock is a frequent complication of pneumococcal pneumonia and causes high morbidity and mortality. Current tobacco smoking, chronic corticosteroid treatment and infection caused by serotype 3 are independent risk factors for this complication.

Ancient dispersal of the human fungal pathogen Cryptococcus gattii from the Amazon rainforest

Over the past two decades, several fungal outbreaks have occurred, including the high-profile 'Vancouver Island' and 'Pacific Northwest' outbreaks, caused by Cryptococcus gattii, which has affected hundreds of otherwise healthy humans and animals. Over the same time period, C. gattii was the cause of several additional case clusters at localities outside of the tropical and subtropical climate zones where the species normally occurs. In every case, the causative agent belongs to a previously rare genotype of C. gattii called AFLP6/VGII, but the origin of the outbreak clades remains enigmatic. Here we used phylogenetic and recombination analyses, based on AFLP and multiple MLST datasets, and coalescence gene genealogy to demonstrate that these outbreaks have arisen from a highly-recombining C. gattii population in the native rainforest of Northern Brazil. Thus the modern virulent C. gattii AFLP6/VGII outbreak lineages derived from mating events in South America and then dispersed to temperate regions where they cause serious infections in humans and animals.

Cuticular defects lead to full immunity to a major plant pathogen.

In addition to its role as a barrier, the cuticle is also a source of signals perceived by invading fungi. Cuticular breakdown products have been shown previously to be potent inducers of cutinase or developmental processes in fungal pathogens. Here the question was addressed as to whether plants themselves can perceive modifications of the cuticle. This was studied using Arabidopsis thaliana plants with altered cuticular structure. The expression of a cell wall-targeted fungal cutinase in A. thaliana was found to provide total immunity to Botrytis cinerea. The response observed in such cutinase-expressing plants is independent of signal transduction pathways involving salicylic acid, ethylene or jasmonic acid. It is accompanied by the release of a fungitoxic activity and increased expression of members of the lipid transfer protein, peroxidase and protein inhibitor gene families that provide resistance when overexpressed in wild-type plants. The same experiments were made in the bodyguard (bdg) mutant of A. thaliana. This mutant exhibits cuticular defects and remained free of symptoms after inoculation with B. cinerea. The expression of resistance was accompanied by the release of a fungitoxic activity and increased expression of the same genes as observed in cutinase-expressing plants. Structural defects of the cuticle can thus be converted into an effective multi-factorial defence, and reveal a hitherto hidden aspect of the innate immune response of plants.

From pathogen defence to food allergy; The multiple facets of the mucosal immune system

Résumé destiné à un large public Le système immunitaire associé aux muqueuses gastro-intestinales doit être capable de protéger notre organisme contre l'invasion de pathogènes. Parallèlement, il doit identifier en Cant que tels, des composés inoffensifs comme la nourriture ou les milliards de bactéries qui résident dans notre intestin. Le travail présenté ici aborde ces deux aspects essentiels au bon fonctionnement de notre muqueuse intestinale. Dans une première partie, la protéine nommée pièce sécrétoire a été étudiée pour ses propriétés protectrices contre le pathogène viral rotavirus. Le rôle de la pièce sécrétoire est de transporter les anticorps que nous produisons vers la surface des muqueuses. En dehors de cette fonction bien connue, il se peut que cette protéine soit également capable de protéger notre organisme contre certains virus. L'hypothèse de travail était donc que la pièce sécrétoire se lie directement au virus, l'empêchant ainsi d'infecter des cellules épithéliales de l'intestin. En utilisant différentes techniques biochimiques, cette hypothèse s'est révélée fausse car aucune interaction entre la pièce sécrétoire et le virus n'a pu être observée, et logiquement, aucune protection n'a pu prendre place. En revanche, la pièce sécrétoire se lie à d'autres structures pathogéniques et permet ainsi de neutraliser leurs effets néfastes. La pièce sécrétoire participe donc activement à la protection de nos muqueuses, en plus de son rôle de transporteur. La deuxième partie de ce travail avait pour sujet les réactions inappropriées que le système immunitaire induit parfois contre un aliment, ou, autrement dit, les allergies alimentaires. Un modèle d'allergie alimentaire à donc été développé chez la souris et a permis de mesurer plusieurs symptômes et facteurs liés à l'allergie. Puis, ce modèle a été utilisé afin de tester les effets bénéfiques d'une bactérie lactique, dite probiotique, sur le développement de l'allergie. Il a été observé que, sous certaines circonstances, l'administration de la bactérie lactique protégeait entièrement les souris contre les réactions allergiques. L'effet bénéfique dépend donc du probiotique mais également d'autres facteurs encore inconnus â ce jour. Cette étude ouvre la voie sur la compréhension des mécanismes liés aux allergies alimentaires et sur l'impact que peuvent avoir les bactéries probiotiques sur cette maladie. Résumé Le système immunitaire associé aux muqueuses intestinales doit être capable de différencier les antigènes inoffensifs tels que 1a nourriture ou les bactéries commensales des microorganismes potentiellement dangereux. Cet aspect est essentiel pour le maintien de l'homéostase intestinale et fait l'objet du travail présenté ici. Dans un premier projet, les propriétés protectrices de la protéine appelée pièce sécrétoire (SC) ont été étudiées. SC est une protéine connue pour le transport des immunoglobulines à la surface des muqueuses. Cette protéine est fortement glycosylée paz des sucres complexes, ce qui nous a mené à postuler que SC puisse interagir avec le pathogène rotavirus. Cette hypothèse était soutenue par le fait que ce virus adhère aux cellules épithéliales par des résidus glycosylés. Des analyses biochimiques et biologiques ont démontré qu'aucune interaction entre SC et le virus ne prenait place, et que par conséquent SC n'offrait aucune protection contre ce pathogène. En revanche, SC interagit avec d'autres structures pathogéniques, comme la toxine A de Clostridium difficile, et la molécule d'adhésion intimine de la bactérie entéropathogène Escherichia coli. La liaison se fait par l'intermédiaire des sucres et confère ainsi une protection contre ces pathogènes. Ainsi, SC a été identifié comme agent neutralisant au niveau de l'intestin. La deuxième partie de ce travail abordait le sujet des allergies alimentaires, et avait pour but de tester les effets bénéfiques potentiels d'une bactérie probiotique, Lactobacillus paracasei NCC2461, contre les réactions allergiques. Un modèle marin d'allergie alimentaire a été mis au point, permettant de mesurer des immunoglobulines E, des symptômes allergiques, et la dégranulation de mastocytes. Lorsque le probiotique a été administré aux souris, celles-ci ont été complètement protégées des réactions allergiques dans une première expérience. Cependant, cette protection n'a pas été reproduite et suggère que des facteurs environnementaux encore inconnus sont critiques pour que le probiotique agisse positivement. Ce travail a permis de mettre en évidence la complexité de l'approche des traitements liés aux probiotiques et ouvre la voie sur la compréhension des mécanismes liés à l'allergie. Abstract The mucosal immune system associated to the gastrointestinal mucosa must efficiently distinguish between innocuous antigens, such as food proteins and commensal bacteria and potentially infectious agents. The work presented here deals with these two essential aspects guaranteeing intestinal homeostasis. In the first part of this work, the protective properties of secretory component (SC) toward the pathogen rotavirus were investigated. SC, which allows the transport of polymeric immunoglobulins (Ig) to mucosal surfaces, is highly glycosylated with complex glycan structures. The abundance and the nature of these carbohydrates led us to speculate that SC might interact with rotavirus, which is known to bind target cells with glycan receptors. Using various biological and biochemical techniques, we demonstrated that SC did not interact with rotaviruses, nor protected epithelial cells from infection. However, SC was shown to bind to Clostridium difficile toxin A and to the enteropathogenic Echerischia coli adhesion molecule intimin in a glycan-dependent fashion. These interactions allow in vitro protection of epithelial cells using physiological concentrations of SC. These data identify SC as a microbial scavenger at mucosal surfaces, and in the context of secretory IgA, further enhance the neutralising properties of the complex. The second project was inscribed in the domain of food allergy and aimed to test the modulatory functions of a probiotic strain of Lactobacillus paracasei toward allergic reactions. A model of food-mediated allergy was developed in the mouse using mucosal sensitisation. Several parameters associated to allergy were quantified after allergen challenge, and included allergen-specific IgE, allergic signs like diarrhea and temperature drop, and degranulation of mast cells. Administration of the probiotic strain was shown to completely protect mice from allergic reactions. However, these data were not reproduced, suggesting that unknown environmental factors are required so that protection mediated by the probiotic strain occurs. This study paves the way to the understanding of the mechanisms associated to allergy, and highlights the tremendous complexity that probiotic treatments will have to face.

Embryonic gene expression of Coregonus palaea (whitefish) under pathogen stress as analyzed by high-throughput RNA-sequencing.

Most fishes produce free-living embryos that are exposed to environmental stressors immediately following fertilization, including pathogenic microorganisms. Initial immune protection of embryos involves the chorion, as a protective barrier, and maternally-allocated antimicrobial compounds. At later developmental stages, host-genetic effects influence susceptibility and tolerance, suggesting a direct interaction between embryo genes and pathogens. So far, only a few host genes could be identified that correlate with embryonic survival under pathogen stress in salmonids. Here, we utilized high-throughput RNA-sequencing in order to describe the transcriptional response of a non-model fish, the Alpine whitefish Coregonus palaea, to infection, both in terms of host genes that are likely manipulated by the pathogen, and those involved in an early putative immune response. Embryos were produced in vitro, raised individually, and exposed at the late-eyed stage to a virulent strain of the opportunistic fish pathogen Pseudomonas fluorescens. The pseudomonad increased embryonic mortality and affected gene expression substantially. For example, essential, upregulated metabolic pathways in embryos under pathogen stress included ion binding pathways, aminoacyl-tRNA-biosynthesis, and the production of arginine and proline, most probably mediated by the pathogen for its proliferation. Most prominently downregulated transcripts comprised the biosynthesis of unsaturated fatty acids, the citrate cycle, and various isoforms of b-cell transcription factors. These factors have been shown to play a significant role in host blood cell differentiation and renewal. With regard to specific immune functions, differentially expressed transcripts mapped to the complement cascade, MHC class I and II, TNF-alpha, and T-cell differentiation proteins. The results of this study reveal insights into how P. fluorescens impairs the development of whitefish embryos and set a foundation for future studies investigating host pathogen interactions in fish embryos.

Waddlia: An emerging pathogen and a model organism to study the biology of chlamydiae.

Waddlia chondrophila is an emerging pathogen associated with abortion in cattle. In humans, a growing body of evidence supports its pathogenic role in miscarriage and in respiratory tract infection. The human pathogenicity of W. chondrophila is further supported by the presence of several virulence factors including a catalase, a functional T3SS and several adhesins. Despite this medical importance, no commercial tests are available and diagnostic of this strict intracellular bacterium mainly relies on serology, PCR and immunohistochemistry. So far, the epidemiology of W. chondrophila remains largely unexplored and zoonotic, waterborne or interhuman transmission has been considered. Apart from its pathogenic role, chlamydiologists are also interested in W. chondrophila in order to better understand biological mechanisms conserved and shared with Chlamydia spp. Indeed, W. chondrophila proved to be a useful model organism to study the pathobiology of chlamydiae thanks to its rapid replication, its large size allowing precise subcellular protein localization, as well as its growth in Dictyostelium amoebae.

Ralstonia solanacearum, a widespread bacterial plant pathogen in the post-genomic era

Ralstonia solanacearum is a soil-borne bacterium causing the widespread disease known as bacterial wilt. Ralstonia solanacearum is also the causal agent of Moko disease of banana and brown rot of potato. Since the last R. solanacearum pathogen profile was published 10 years ago, studies concerning this plant pathogen have taken a genomic and post-genomic direction. This was pioneered by the first sequenced and annotated genome for a major plant bacterial pathogen and followed by many more genomes in subsequent years. All molecular features studied now have a genomic flavour. In the future, this will help in connecting the classical field of pathology and diversity studies with the gene content of specific strains. In this review, we summarize the recent research on this bacterial pathogen, including strain classification, host range, pathogenicity determinants, regulation of virulence genes, type III effector repertoire, effector-triggered immunity, plant signalling in response to R. solanacearum, as well as a review of different new pathosystems.

Inonotus splitbergeri a stem pathogen of Eucalyptus globulus in Uruguay

Inonotus splitbergeri é relatado pela primeira vez o Uruguay causando podridáo-do-lenho de Eucalyptus globulus. Durante as tempestades ocorre o tombamento de árvores, mesmo daquelas totalmente enfolhadas.