20 results on '"Frey, Pascal"'
Search Results
2. Poplar rust systematics and refinement of Melampsora species delineation
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Vialle, Agathe, Frey, Pascal, Hambleton, Sarah, Bernier, Louis, and Hamelin, Richard C.
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- 2011
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3. The escalatory Red Queen: Population extinction and replacement following arms race dynamics in poplar rust.
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Persoons, Antoine, Hayden, Katherine J., Fabre, Bénédicte, Frey, Pascal, De Mita, Stéphane, Tellier, Aurélien, and Halkett, Fabien
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BIOLOGICAL extinction ,HOST-parasite relationships ,MELAMPSORA ,MICROBIAL virulence genetics ,COEXISTENCE of species - Abstract
Host-parasite systems provide convincing examples of Red Queen co-evolutionary dynamics. Yet, a key process underscored in Van Valen's theory - that arms race dynamics can result in extinction - has never been documented. One reason for this may be that most sampling designs lack the breadth needed to illuminate the rapid pace of adaptation by pathogen populations. In this study, we used a 25-year temporal sampling to decipher the demographic history of a plant pathogen: the poplar rust fungus, Melampsora larici-populina. A major adaptive event occurred in 1994 with the breakdown of R7 resistance carried by several poplar cultivars widely planted in Western Europe since 1982. The corresponding virulence rapidly spread in M. larici-populina populations and nearly reached fixation in northern France, even on susceptible hosts. Using both temporal records of virulence profiles and temporal population genetic data, our analyses revealed that (i) R7 resistance breakdown resulted in the emergence of a unique and homogeneous genetic group, the so-called cultivated population, which predominated in northern France for about 20 years, (ii) selection for Vir7 individuals brought with it multiple other virulence types via hitchhiking, resulting in an overall increase in the population-wide number of virulence types and (iii) - above all - the emergence of the cultivated population superseded the initial population which predominated at the same place before R7 resistance breakdown. Our temporal analysis illustrates how antagonistic co-evolution can lead to population extinction and replacement, hence providing direct evidence for the escalation process which is at the core of Red Queen dynamics. [ABSTRACT FROM AUTHOR]
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- 2017
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4. Characterization of the early response of poplar to rust infection using expression profiling
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Duplessis, Sébastien, Kohler, Annegret, Rinaldi, Cécile, Frey, Pascal, Martin, Francis, Interactions Arbres-Microorganismes (IAM), Institut National de la Recherche Agronomique (INRA)-Université de Lorraine (UL), and ProdInra, Migration
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[SDV] Life Sciences [q-bio] ,RUST TOLERANCE ,GENES ,MELAMPSORA ,[SDV]Life Sciences [q-bio] ,PEUPLIER ,food and beverages ,POPULUS TRICHOCARPA X DELTOIDES CV. BEAUPRÉ ,FOLIAR RUST - Abstract
International audience; Foliar rust diseases causes by Melampsora spp. have the potential to be very damaging to poplar plantations. The most effective method of reducing the risk is to select varieties that are rust tolerant. Plants respond to microbial attack by activating an array of inducible defense responses. Poplar molecular responses to Melampsora spp. infection are however poorly understood. To characterize the response of Populus trichocarpa x deltoides cv. Beaupré to virulent (98AG31) and avirulent (93ID6) strains of M. larici-populina and identify genes that may play a role in resistance, expression profiling of plants have been carried out. Approximately 200 (4.3%) of the ~ 4600 genes monitored showed reproducible and significant (t-test P>0.05) expression level changes in at least one of the interactions. In the incompatible interaction, defense- and stress12th New Phytologist Symposium 19 response genes (e.g., PR-2, PR-3, PR-5, PR-10) showed an increase in transcripts which peaked 48h post-contact. Decreased levels of transcripts encoding primary metabolism, photosynthesis and photorespiration enzymes was observed in both interactions. Expression profiling technologies, in combination with other tools, such as RNAi, will have a substantial impact on our understanding of poplar-rust interactions and defense signaling pathways.
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- 2004
5. Influence des peupleraires sauvages et cultivées et de la présence de mélèzes sur la structuration génétique des populations de Melampsora larici-populina, agent de la rouille foliaire
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Frey, Pascal, Gérard, P., Feau, N., Husson, Claude, Schipfer, A., Lefèvre, F., and Pinon, Jean
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Populus ,Génétique des populations ,Larix ,Melampsora ,Relation hôte pathogène ,Structure de la population ,H20 - Maladies des plantes - Abstract
La peupleraie cultivée, monoclonale et équienne, constitue un des écosystèmes forestiers les plus simplifiés, ce qui la rend très fragile face à des agressions biotiques et abiotiques. En effet, la plantation sur de grandes superficies d'un très faible nombre de cultivars à résistance totale vis-à-vis de la rouille foliaire à Melampsora larici-populina, a favorisé l'émergence et la dissémination très rapide de nouveaux pathotypes du parasite, capables de contourner toutes les résistances sélectionnées à ce jour. Parallèlement à la dégradation très rapide de l'état sanitaire des peupleraies cultivées, celui des peupleraies sauvages (ripisylves à Populus nigra) vis-à-vis de la rouille semble rester stable. Les bases de cette stabilité résident vraisemblablement dans la diversité génétique des peupleraies sauvages, et dans l'influence de cette diversité sur la structuration des populations de M. larici-populina. Pour tester cette hypothèse, nous proposons de comparer le rôle des peupleraies cultivées et des peupleraies sauvages sur la structuration des populations du parasite. Pour cela, nous comparons la variabilité phénotypique (pathotypes) et la diversité génétique (marqueurs moléculaires) de populations de M larici-populina collectées dans les deux types de peuplement. De plus, il faut prendre en compte le rôle du Mélèze, qui est l'hôte alternant du parasite sur lequel a lieu la reproduction sexuée. En effet, la présence du Mélèze favorise les recombinaisons génétiques chez le champignon, et donc constitue un moteur de diversité pour ses populations. Ainsi, pour chaque type de peuplement hôte (peupleraies cultivées et sauvages) nous comparons des sites avec et des sites sans Mélèze. Les premiers résultats concernent le pathotypage des populations récoltées à l'automne 2001 en peupleraies cultivées (Aisne et Haute-Saône) et sauvages (Hautes-Alpes et Alpes-de-Haute-Provence). Les populations collectées en peupleraies cultivées présentent une richesse (14 pathotypes en moyenne) nettement supérieure à celle des populations collectées en peupleraies sauvages (5 pathotypes en moyenne). De plus, les peupleraies cultivées hébergent des populations nettement plus complexes (Cj = 3.40 virulences par isolat) que les peupleraies sauvages (Cj = 0.58 virulence par isolat). Ces résultats suggèrent la sélection de pathotypes complexes sous l'effet des gènes de résistance race-spécifique déployés dans les peupleraies cultivées. Concernant la présence ou non de l'hôte alternant à proximité des peupleraies, les populations "sexuées" présentent en moyenne une richesse supérieure à celle des populations "asexuées". Ceci suggère un effet du Mélèze sur la richesse des populations, en augmentant le nombre de pathotypes rares. L'utilisation de marqueurs moléculaires (RAPD) permettra de compléter cette étude, en particulier pour l'évaluation du rôle de la reproduction sexuée sur la structuration des populations du champignon. (Texte intégral)
- Published
- 2002
6. Analyse du transcriptome du pathosystème Populus x interamericana / Melampsora laricipopulina
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Duplessis, Nathalie, Rouhier, Nicolas, Frey, Pascal, Kohler, Annegret, Jacquot, Jean-Pierre, and Martin, Francis
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Populus ,Melampsora ,Résistance aux maladies ,mécanisme de défense ,H20 - Maladies des plantes - Abstract
Melampsora larici-populina, J'agent responsable de la rouille foliaire du peuplier, entraîne une forte perte de rendement sur la production populicole. L'étude du pathosystème Peuplier/Melampsora est justifiée par le fait qu'actuellement plus aucun des cultivars européens de peuplier n'est résistant à la rouille. En particulier, des cultivars récents ont vu leurs résistances contournées avec l'apparition successive en 1994 et 1997 de deux nouveaux groupes de races (E4 et E5). Afin d'étudier les mécanismes de défense mis en place par le peuplier lors de son interaction avec ce champignon, nous avons entrepris le séquençage massif d'ESTs à partir de banques d'ADNc de l'hybride interaméricain (Populus trichocarpa x Populus deltoides) 'Beaupré'. Le cultivar 'Beaupré' est un modèle de choix car il présente une résistance race-spécifique aux groupes de races E1, E2 et E3, mais pas au groupe E4, ce qui nous permet de réaliser des analyses comparatives entre les interactions compatible et incompatible, induites respectivement par les isolats 98AG31 (groupe E4) et 93ID6 (groupe E1) de Melampsora larici-populina. L'analyse des patrons d'expression génique lors de ces interactions a été réalisée lors d'une expérience pilote. Nous nous sommes focalisés sur un groupe de 200 gènes foliaires, dont certains sont des marqueurs de stress (gènes codant des protéines PR, des protéines induites par le stress hydrique ou la blessure,...). Nous avons mis en évidence une réponse précoce d'un grand nombre de gènes dans les tissus foliaires lors de l'interaction incompatible. Près de 20% des gènes sont stimulés de 3 à 8 fois après 24 heures d'infection par l'isolat incompatible alors qu'aucun gène ne présente de forte modulation de l'expression dans le cas de l'interaction compatible. Les gènes dont l'expression est fortement stimulée lors de l'infection par l'isolat 93ID6 codent des protéines impliquées dans le métabolisme et la photosynthèse (protéines du PSII, Glutamine synthétase), ainsi que dans la réponse aux stress (thioredoxine, péroxidase, protéines induites par la blessure,...). Cette stimulation de l'expression a tendance à diminuer apres 48 heures et n'est plus maintenue 96 heures après l'infection. Lors de l'interaction compatible, peu de gènes présentent des modifications de leur niveau d'expression. L'analyse comparative à plus large échelle devrait nous permettre d'identifier de nombreux gènes marqueurs utilisables dans une sélection assistée par marqueurs de cultivars résistants. (Texte intégral)
- Published
- 2002
7. Genetic signatures of a range expansion in natura: when clones play leapfrog.
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Becheler, Ronan, Xhaard, Constance, Hayden, Katherine J., Frey, Pascal, De Mita, Stéphane, Halkett, Fabien, and Klein, Etienne K.
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BIOLOGICAL invasions ,MELAMPSORA ,DISPERSAL (Ecology) ,GENE frequency ,COLONIZATION (Ecology) - Abstract
The genetic consequences of range expansions have generally been investigated at wide geographical and temporal scales, long after the colonization event. A unique ecological system enabled us to both monitor the colonization dynamics and decipher the genetic footprints of expansion over a very short time period. Each year an epidemic of the poplar rust ( Melampsora larici-populina) expands clonally and linearly along the Durance River, in the Alps. The colonization dynamics observed in 2004 showed two phases with different genetic outcomes. Upstream, fast colonization maintained high genetic diversity. Downstream, the colonization wave progressively faltered, diversity eroded, and differentiation increased, as expected under recurrent founder events. In line with the high dispersal abilities of rust pathogens, we provide evidence for leapfrog dispersal of clones. Our results thus emphasize the importance of colonization dynamics in shaping spatial genetic structure in the face of high gene flow. [ABSTRACT FROM AUTHOR]
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- 2016
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8. Transcriptome analysis of poplar rust telia reveals overwintering adaptation and tightly coordinated karyogamy and meiosis processes.
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Hacquard, Stéphane, Delaruelle, Christine, Frey, Pascal, Tisserant, Emilie, Kohler, Annegret, and Duplessis, Sébastien
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RUST fungi ,MELAMPSORA ,TELIOSPORES ,MEIOSIS ,EXONS (Genetics) ,POLYMERASE chain reaction - Abstract
Most rust fungi have a complex life cycle involving up to five different spore-producing stages. The telial stage that produces melanized overwintering teliospores is one of these and plays a fundamental role for generating genetic diversity as karyogamy and meiosis occur at that stage. Despite the importance of telia for the rust life cycle, almost nothing is known about the fungal genetic programs that are activated in this overwintering structure. In the present study, the transcriptome of telia produced by the poplar rust fungus Melampsora larici-populina has been investigated using whole genome exon oligoarrays and RT-qPCR. Comparative expression profiling at the telial and uredinial stages identifies genes specifically expressed or up-regulated in telia including osmotins/thaumatin-like proteins (TLPs) and aquaporins that may reflect specific adaptation to overwintering as well numerous lytic enzymes acting on plant cell wall, reflecting extensive cell wall remodeling at that stage. The temporal dynamics of karyogamy was followed using combined RT-qPCR and DAPI-staining approaches. This reveals that fusion of nuclei and induction of karyogamy-related genes occur simultaneously between the 25 and 39 days post inoculation time frame. Transcript profiling of conserved meiosis genes indicates a preferential induction right after karyogamy and corroborates that meiosis begins prior to overwintering and is interrupted in Meiosis I (prophase I, diplonema stage) until teliospore germination in early spring. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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9. Exploring the role of asexual multiplication in poplar rust epidemics: impact on diversity and genetic structure.
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Barrès, Benoît, Dutech, Cyril, Andrieux, Axelle, Halkett, Fabien, and Frey, Pascal
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ASEXUAL reproduction ,POPLARS ,EPIDEMICS ,PLANT diversity ,RUST fungi ,PLANT life cycles ,MELAMPSORA - Abstract
Fungal plant pathogens, especially rust fungi ( Pucciniales), are well known for their complex life cycles, which include phases of sexual and asexual reproduction. The effect of asexual multiplication on population genetic diversity has been investigated in the poplar rust fungus Melampsora larici-populina using a nested hierarchical sampling scheme. Four hierarchical levels were considered: leaf, twig, tree and site. Both cultivated and wild poplar stands were sampled at two time points at the start and end of rust epidemics. A total of 641 fungal isolates was analysed using nine microsatellite markers. This study revealed that the genetic signature of asexual multiplication in the wild poplar stand was seen only at lower hierarchical levels (leaf and twig). Moreover, we observed an erosion of clonal structure through time, with an increase in both gene and genotypic diversity. New genotypes contributed to host infection over time, which demonstrates the importance of allo-infection in the epidemic process in this host-pathogen system. Compared with the wild stands, the nearly lack of detection of clonal structure in the cultivated stands reflects the higher infection level on cultivated poplars. More generally, this genetic analysis illustrates the utility of population genetics approach for elucidating the proportion of asexual reproduction in the multiplication of isolates during an epidemic, and for proper quantification of asexual dispersal in plant pathogens. [ABSTRACT FROM AUTHOR]
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- 2012
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10. Disentangling the genetic origins of a plant pathogen during disease spread using an original molecular epidemiology approach.
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XHAARD, CONSTANCE, BARRÈS, BENOÎT, ANDRIEUX, AXELLE, BOUSSET, LYDIA, HALKETT, FABIEN, and FREY, PASCAL
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PHYTOPATHOGENIC microorganisms ,MOLECULAR epidemiology ,BIOLOGICAL invasions ,PLANT genetics ,MELAMPSORA ,FUNGI - Abstract
The advent of molecular epidemiology has greatly improved our ability to identify the population sources and track the pathogen movement. Yet the wide spatial and temporal scales usually considered are useful only to infer historical migration pathways. In this study, Bayesian genetic assignments and a landscape epidemiology approach were combined to unravel genetic origin and annual spread during a single epidemic of a plant pathogen: the poplar rust fungus Melampsora larici-populina. The study focused on a particular area-the Durance River valley-which enabled inoculum sources to be identified and channelled spread of the epidemic along a one-dimensional corridor. Spatio-temporal monitoring of disease showed that the epidemic began in the upstream part of the valley and spread out downstream. Using genetic assignment tests, individuals collected at the end of the epidemic were sorted into two genetic groups; very few hybrids were detected, although individuals from both groups coexisted locally downstream in the valley. The epidemic originated from two genetically distinct inoculum sources. Individuals of each group then dispersed southwards along the Durance River and became mixed in poplar riparian stands. These two genetic groups were found previously at a wider spatial scale and proved to result from distinct evolutionary histories on either wild or cultivated poplars. This study showed that the two groups can mix during an epidemic but do not hybridize because they then reproduce asexually. In general, the methods employed here could be useful for elucidating the genetic origin and retracing the colonization history and migration pathways of recent epidemics. [ABSTRACT FROM AUTHOR]
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- 2012
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11. Isolation and characterization of 15 microsatellite loci in the poplar rust fungus, Melampsora larici-populina, and cross-amplification in related species.
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Barrès, Benoît, Dutech, Cyril, Andrieux, Axelle, Caron, Henri, Pinon, Jean, and Frey, Pascal
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MICROSATELLITE repeats ,RUST fungi ,MELAMPSORA ,MELAMPSORACEAE ,SALICACEAE - Abstract
We developed 15 microsatellite loci in the poplar rust fungus, Melampsora larici-populina, using two enrichment protocols. Polymorphism of each locus was assessed on a panel of 30 isolates, comprising three subpanels (world, regional and local scales). Thirteen loci were polymorphic with three to eight alleles detected. The 15 loci were also tested on five related Melampsora species, M. allii-populina, M. medusae f. sp. deltoidae, M. larici-tremulae, M. rostrupii and M. pinitorqua, and partial or global cross-amplification events were detected. [ABSTRACT FROM AUTHOR]
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- 2006
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12. Wettability of Poplar Leaves Influences Dew Formation and Infection by Melampsora larici-populina.
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Pinon, Jean, Frey, Pascal, and Husson, Claude
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MELAMPSORA , *LEAF diseases & pests , *PLANT diseases , *POPLARS , *RAINFALL , *DEW - Abstract
The wettability of leaves of 60 poplar (Populus spp.) clones from sections Aigeiros (black) and Tacamahaca (balsam) and their hybrids was assessed by measuring the contact angle of calibrated water droplets on their abaxial leaf surface. The frequency and duration of dew on these clones were recorded in two nurseries. Black poplar leaves had the highest wettability, with relatively flat-shaped water droplets and a short drying time, in both the laboratory and nursery. Conversely, round-shaped water droplets on balsam poplars dried more slowly in the laboratory. In the nursery, dew was more frequent and persisted longer. First-generation intersectional hybrids behaved like balsam poplars, but successive backcrosses with black poplar (P. deltoides) resulted in clones with leaves that were more wettable and possessed less frequent and persistent dew. Infection by Melampsora larici-populina on two hybrid clones (‘Robusta’ and ‘Beaupré’), assessed by the number of uredinia in the laboratory, was dependent on the duration of leaf moisture. Maximum infection occurred when water was present on the leaves for 12 h. Leaf wettability should be considered as an additional trait when breeding poplar for durable resistance to M. larici-populina, as this characteristic is likely to be a useful defense against all pathotypes of the pathogen. [ABSTRACT FROM AUTHOR]
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- 2006
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13. Phylogenetic species recognition reveals host-specific lineages among poplar rust fungi
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Vialle, Agathe, Feau, Nicolas, Frey, Pascal, Bernier, Louis, and Hamelin, Richard C.
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PHYLOGENY , *RUST fungi , *MELAMPSORA , *SALICACEAE , *SPECIES , *MITOCHONDRIA , *LOCUS (Genetics) - Abstract
Abstract: Fungal species belonging to the genus Melampsora (Basidiomycota, Pucciniales) comprise rust pathogens that alternate between Salicaceae and other plant hosts. Species delineation and identification are difficult within this group due to the paucity of observable morphological features. Several Melampsora rusts are highly host-specific and this feature has been used for identification at the species level. However, this criterion is not always reliable since different Melampsora rust species can overlap on one host but specialize on a different one. To date, two different species recognition methods are used to recognize and define species within the Melampsora genus: (i) morphological species recognition, which is based solely on morphological criteria; and (ii) ecological species recognition, which combines morphological criteria with host range to recognize and define species. In order to clarify species recognition within the Melampsora genus, we applied phylogenetic species recognition to Melampsora poplar rusts by conducting molecular phylogenetic analyses on 15 Melampsora taxa using six nuclear and mitochondrial loci. By assessing the genealogical concordance between phylogenies, we identified 12 lineages that evolved independently, corresponding to distinct phylogenetic species. All 12 lineages were concordant with host specialization, but only three belonged to strictly defined morphological species. The estimation of the species tree obtained with Bayesian concordance analysis highlighted a potential co-evolutionary history between Melampsora species and their reciprocal aecial host plants. Within the Melampsora speciation process, aecial host may have had a strong effect on ancestral evolution, whereas telial host specificity seems to have evolved more recently. The morphological characters initially used to define species boundaries in the Melampsora genus are not reflective of the evolutionary and genetic relationships among poplar rusts. In order to construct a more meaningful taxonomy, host specificity must be considered an important criterion for delineating and describing species within the genus Melampsora as previously suggested by ecological species recognition. [Copyright &y& Elsevier]
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- 2013
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14. The Poplar-Poplar Rust Interaction: Insights from Genomics and Transcriptomics.
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Hacquard, Stéphane, Petre, Benjamin, Frey, Pascal, Hecker, Arnaud, Rouhier, Nicolas, and Duplessis, Sébastien
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GENOMICS , *MELAMPSORA , *PLANTATIONS , *EPIDEMICS , *POPLARS , *FUNGI , *MICROBIAL virulence , *GENES - Abstract
Poplars are extensively cultivated worldwide, and their susceptibility to the leaf rust fungus Melampsora larici-populina leads to considerable damages in plantations. Despite a good knowledge of the poplar rust life cycle, and particularly the epidemics on poplar, the perennial status of the plant host and the obligate biotrophic lifestyle of the rust fungus are bottlenecks for molecular investigations. Following the completion of both M. larici-populina and Populus trichocarpa genome sequences, gene families involved in poplar resistance or in rust fungus virulence were investigated, allowing the identification of key genetic determinants likely controlling the outcome of the interaction. Specific expansions of resistance and defense-related genes in poplar indicate probable innovations in perennial species in relation with host-pathogen interactions. The genome of M. Laricipopulina contains a strikingly high number of genes encoding small secreted proteins (SSPs) representing hundreds of candidate effectors. Transcriptome analyses of interacting partners in compatible and incompatible interactions revealed conserved set of genes involved in poplar defense reactions as well as timely regulated expression of SSP transcripts during host tissues colonisation. Ongoing functional studies of selected candidate effectors will be achieved mainly on the basis of recombinant protein purification and subsequent characterisation. [ABSTRACT FROM AUTHOR]
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- 2011
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15. Optimization of a real-time PCR assay for the detection of the quarantine pathogen Melampsora medusae f. sp. deltoidae.
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Boutigny, Anne-Laure, Guinet, Cécile, Vialle, Agathe, Hamelin, Richard C., Andrieux, Axelle, Frey, Pascal, Husson, Claude, and Ioos, Renaud
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POLYMERASE chain reaction , *PLANT quarantine , *MELAMPSORA , *RUST fungi , *POPLAR tree diseases & pests , *PATHOGENIC fungi - Abstract
Abstract: Melampsora medusae (Mm), one of the causal agents of poplar rust, is classified as an A2 quarantine pest for European Plant Protection Organization (EPPO) and its presence in Europe is strictly controlled. Two formae speciales have been described within Mm, Melampsora medusae f. sp. deltoidae (Mmd), and Melampsora medusae f. sp. tremuloidae (Mmt) on the basis of their pathogenicity on Populus species from the section Aigeiros (e.g. Populus deltoides) or Populus (e.g. Populus tremuloides), respectively. In this study, a real-time polymerase chain reaction (PCR) assay was developed allowing the detection of Mmd, the forma specialis that is economically harmful. A set of primers and hydrolysis probe were designed based on sequence polymorphisms in the large ribosomal RNA subunit (28S). The real-time PCR assay was optimized and performance criteria of the detection method, i.e. sensitivity, specificity, repeatability, reproducibility, and robustness, were assessed. The real-time PCR method was highly specific and sensitive and allowed the detection of one single urediniospore of Mmd in a mixture of 2 mg of urediniospores of other Melampsora species. This test offers improved specificity over currently existing conventional PCR tests and can be used for specific surveys in European nurseries and phytosanitary controls, in order to avoid introduction and spread of this pathogen in Europe. [Copyright &y& Elsevier]
- Published
- 2013
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16. Three-year investigations on leaf rust of poplar cultivated for biomass production in Umbria, Central Italy
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Covarelli, Lorenzo, Beccari, Giovanni, Tosi, Laura, Fabre, Bénédicte, and Frey, Pascal
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BIOMASS production , *LEAF rust of wheat , *SPECIES specificity , *FIELD research , *MELAMPSORA - Abstract
Abstract: During disease surveys carried out in the years 2006, 2007 and 2008, severe natural rust infections on biomass poplar cultivations in clone experimental field trials in the province of Perugia (Umbria, Central Italy) were observed both in summer and autumn. The foliage of infected plants presented the typical rusty coloration for the presence of uredinia, mainly on the abaxial leaf surface, and teliospores which appeared at the end of the growing season. All tested clones showed to be susceptible to the disease, with significant incidence and severity differences among them. Clones ‘Sirio’, ‘Baldo’ and ‘AF8’ showed a lower susceptibility with respect to the other clones. Weather data suggested that the early summer attacks observed in 2008 were favored by the high rainfalls recorded in June and by the possible presence of asexual spores which were able to overwinter on infected leaf residues. Microscopic observations of the morphological characteristics of pathogen spores, the examination of infected leaf sections, species-specific PCR assays, and pathotype identification revealed that the recorded rust attacks were caused by the species Melampsora larici-populina (pathotype 2–4) and Melampsora allii-populina. This represents a comprehensive study on the occurrence of poplar leaf rust in central Italy, an area where poplar short rotation coppice (SRC) could potentially increase in the next years. [Copyright &y& Elsevier]
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- 2013
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17. Validation of Melampsora larici-populina reference genes for in planta RT-quantitative PCR expression profiling during time-course infection of poplar leaves
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Hacquard, Stéphane, Veneault-Fourrey, Claire, Delaruelle, Christine, Frey, Pascal, Martin, Francis, and Duplessis, Sébastien
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MELAMPSORA , *FUNGAL genetics , *REVERSE transcriptase polymerase chain reaction , *GENE expression , *POPLAR tree diseases & pests , *VITAMIN B1 , *RIBOSOMAL DNA - Abstract
Abstract: The foliar rust caused by Melampsora larici-populina (Mlp) is the main disease affecting poplar plantations in Europe. The biotrophic status of this fungus is a major limitation to address in planta transcripts profiling. Thus, identification of reference rust genes steadily expressed during plant tissue colonization is a crucial point. A quantitative PCR approach to assess fungal ITS amplification profile and Reverse Transcription quantitative-PCR was set to compare candidate reference genes amplification profiles in poplar infected tissues. We selected two M. larici-populina genes encoding an alpha-tubulin and the elongation factor-1-alpha that showed the highest expression stability across biological samples and for which transcript levels were correlated with fungal ITS amplification during time-course infection of poplar leaves. We report the use of these reference genes to assess in planta expression profiles of two genes involved in thiamine biosynthesis (THI1 and THI2) for which specific haustorium expression was previously described in the bean rust fungus Uromyces fabae. Mlp-THI1 and Mlp-THI2 showed similar expression profiles. Trancripts were barely detectable in urediniospores as well as during the early stages of infection compared to those reported in the bean rust, whereas a strong induction was observed after haustorial formation after 24 hpi. These data are in frame with the results obtained in U. fabae and consistent with a metabolic reorientation that likely occurs after the fungus derived nutrients from its host in the haustorial structure essential for fungal biotrophy. [Copyright &y& Elsevier]
- Published
- 2011
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18. Fungal pathogen (mis-) identifications: A case study with DNA barcodes on Melampsora rusts of aspen and white poplar
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Feau, Nicolas, Vialle, Agathe, Allaire, Mathieu, Tanguay, Philippe, Joly, David L., Frey, Pascal, Callan, Brenda E., and Hamelin, Richard C.
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PATHOGENIC fungi , *IDENTIFICATION of fungi , *CASE studies , *BAR codes , *MELAMPSORA , *RUST diseases , *ASPEN (Trees) , *POPULUS alba - Abstract
Abstract: Wide variation and overlap in morphological characters have led to confusion in species identification within the fungal rust genus Melampsora. The Melampsora species with uredinial–telial stages on white poplar and aspens are especially prone to misidentification. This group includes the Melampsora populnea species complex and the highly destructive pine twisting rust, Melampsora pinitorqua, which alternates between hosts in Populus section Populus and Pinus. Our objective was to compare morphologically based identification to genetic material extracted from Melampsora species pathogenic to aspen and white poplar. We compared morphometric traits and DNA barcodes obtained from internal transcribed spacer (ITS), large ribosomal RNA subunit (28S), and mitochondrial cytochrome oxidase 1 (CO1) sequences to delimit within this taxonomically difficult group. Eight different Melampsora species were initially defined based on host specificity and morphometric data. DNA barcodes were then overlaid on these initial species definitions. The DNA barcodes, specifically those defined on ITS and 28S sequences, provided a highly accurate means of identifying and resolving Melampsora taxa. We highlighted species misidentification in specimens from Canadian herbaria related to either Melampsora medusae f. sp. tremuloidae or Melampsora aecidioides. Finally, we evidenced that the north-American species found on Populus alba, M. aecidioides is closely related but distinct from the four species of the M. populnea complex (Melampsora larici-tremulae, Melampsora magnusiana, Melampsora pinitorqua, and Melampsora rostrupii) found in Eurasia. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
19. Genetic structure of the poplar rust fungus Melampsora larici-populina: Evidence for isolation by distance in Europe and recent founder effects overseas
- Author
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Barrès, Benoît, Halkett, Fabien, Dutech, Cyril, Andrieux, Axelle, Pinon, Jean, and Frey, Pascal
- Subjects
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GENETICS , *MELAMPSORA , *PATHOGENIC microorganisms , *MICROORGANISMS , *PLANT dispersal , *EMBRYOLOGY - Abstract
Abstract: Dispersal has a great impact on the genetic structure of populations, but remains difficult to estimate by direct measures. In particular, gradual and stochastic dispersal are often difficult to assess and to distinguish, although they have different evolutionary consequences. Plant pathogens, especially rust fungi, are suspected to display both dispersal modes, though on different spatial scales. In this study, we inferred dispersal capacities of the poplar rust fungus Melampsora larici-populina by examining the genetic diversity and structure of 13 populations from eight European and two overseas countries in the Northern hemisphere. M. larici-populina was sampled from both cultivated hybrid poplars and on the wild host, Populus nigra. The populations were analyzed with 11 microsatellite and 8 virulence markers. Although isolates displayed different virulence profiles according to the host plant, neutral markers revealed little population differentiation with respect to the type of host. This suggests an absence of reproductive isolation between populations sampled from cultivated and wild poplars. Conversely, studying the relationship between geographic and genetic structure allowed us to distinguish between isolation by distance (IBD) patterns and long distance dispersal (LDD) events. The European populations exhibited a significant IBD pattern, suggesting a regular and gradual dispersal of the pathogen over this spatial scale. Nonetheless, the genetic differentiation between these populations was low, suggesting an important gene flow on a continental scale. The two overseas populations from Iceland and Canada were shown to result from rare LDD events, and exhibited signatures of strong founder effects. Furthermore, the high genetic differentiation between both populations suggested that these two recent introductions were independent. This study illustrated how the proper use of population genetics methods can enable contrasted dispersal modes to be revealed. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
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20. Comparison of Genetic and Virulence Diversity of Melampsora larici-populina Populations on Wild and Cultivated Poplar and Influence of the Alternate Host.
- Author
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Gérard, Pierre R., Husson, Claude, Pinon, Jean, and Frey, Pascal
- Subjects
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MELAMPSORA , *POPLARS , *MICROBIAL virulence , *LARCHES , *PLANT-pathogen relationships , *RAPD technique - Abstract
The aims of this study were, first, to compare the genetic and virulence diversity between populations of the rust fungus Melampsora larici-populina on wild and cultivated poplar stands and, second, to investigate the influence of the presence of the alternate host of the pathogen, larch, on which its sexual reproduction occurs, on these diversities. Nine French M. larici-populina populations collected from poplar trees in autumn and four populations collected from larch trees during the following spring were analyzed using both virulence factors and neutral markers. In all, 30 pathotypes were identified within the 13 populations studied. The pathotypic structure clearly distinguished the cultivated stands with high richness and complexity from the wild stands with low richness and complexity. High linkage disequilibria between virulences indicated preferential virulence associations, probably due to selection by the host. In all, 19 random amplified polymorphic DNA (RAPD) markers were used, which revealed a very high genetic diversity in the 743 isolates analyzed. The nine populations from poplar appeared moderately differentiated, indicating long-distance gene flow, and no isolation by distance was found. Linkage disequilibria between RAPD markers generally were low, indicating frequent recombination, but they were not lower in populations located near larch, probably due to long-distance dispersal. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
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