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Descripción
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| Host-pathogen co-evolution is a central question in Biology as it is at the root of pathogen emergence, host switch and host range expansion, and the composition and dynamics of ecosystems. However, contrary to agroecosystems, evidences for plant-virus co-evolution in wild ecosystems are almost non-existent. To understand plant-virus co-evolution, we propose to use as a model system the wild pepper Capsicum annuum var. glabriusculum (chiltepin), which is the wild ancestor of the domesticated C. annuum. Wild populations of chiltepin are found in the tropical dry forests of Mexico (1), where they are exploited for their small pungent fruits. Their cultivation by traditional local farmers has recently started in several regions. A large collection of samples representing wild and cultivated chiltepin populations in Mexico has been obtained and characterised on the basis of microsatellite marker variation (2). Tobamovirus resistance in Capsicum spp. is controlled by the L gene. The different alleles of this gene (from L1 to L4) confer resistance to different Tobamovirus pathotypes (from P0 to P1,2,3) according to the gene-for-gene model. The L resistance gene has recently been cloned and characterised as a single-gene locus encoding a CC-NB-LRR protein, which targets the coat protein (CP) of tobamoviruses (3). This recognition initiates signalling pathways leading to resistance by hypersensitive response (HR). In the absence of the resistance gene (L+ allele), or in the absence of L/CP recognition, the virus is not detected by the host resistance system, which results in a successful infection. L-gene resistance is only expressed at temperatures below 28ºC, except for allele L1a, which is thermoresistant. L1a recognises pathotypes P0 and P1 at 24ºC, and only the former one at 30ºC (4). In this study, we assessed the L gene frequency in different chiltepin populations, and we confirmed the strict correlation between the presence of the L gene and a resistance phenotype. Interestingly, the frequency of L gene was significantly higher in the wild populations than in the cultivated ones, which suggests that the pre-domestication of this species has not focused on Tobamovirus resistance. The analysis of more than 100 full-length L gene sequences showed a high variability, even if most of the sequences were closed to the L1 and L1a alleles. A strong geographical structure of polymorphisms at this gene was observed, which could correspond to local adaptations of chiltepin populations toward various Tobamovirus pathotypes (i.e., P0 and P1 are recognised by L1 and L1a, respectively) and/or different environmental conditions (i.e., the high temperature-tolerant L1a allele and other related alleles were more frequent in the warmest regions of Mexico). Finally, we identified several co-variations and sites under positive selection, mainly located in the domain involved in the CP recognition. Interestingly, one co-variation was detected between two sites under positive selection and discriminating L1 and L1a alleles, which could correspond to a major adaptive signature of the L gene in Mexico. The possible role of these sites in virus recognition at different temperatures is being analysed by protein co-expression assays. Altogether, these results suggest that the L resistance gene is a target for selection by virus infection, which could support the hypothesis of Tobamovirus-chiltepin co-evolution potentially influenced by environmental conditions. | |
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Internacional
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Si |
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Nombre congreso
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EMBO Workshop. Green viruses, from gene to landscape |
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Tipo de participación
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960 |
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Lugar del congreso
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Hyères-les-Palmiers, Francia |
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Revisores
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Si |
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ISBN o ISSN
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00-0000-00 |
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DOI
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Fecha inicio congreso
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07/09/2013 |
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Fecha fin congreso
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11/09/2913 |
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Desde la página
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101 |
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Hasta la página
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101 |
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Título de las actas
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Programme and Abstracts Book |