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Descripción
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| Because infection by virulent parasites has a negative impact on host fitness, hosts have developed defences against parasites. Virulence in parasites and defences in hosts may result in host-parasite co-evolution. In plants, the two major defence strategies are resistance, defined as the host ability to restrict the multiplication of the parasite, and tolerance, defined as the host ability to reduce the negative effects of infection on its fitness. While large efforts have been done to understand plant resistance, tolerance of plants to viruses has received little attention. We have approached the analysis of plant tolerance to viruses using the Arabidopsis thaliana and Cucumber mosaic virus (CMV) system because CMV aturally infects wild A. thaliana populations with high incidence (1) and, therefore this is a suitable system to address plant-virus co-evolution. Our previous work based on the analysis of the response of 21 wild genotypes of A. thalianato infection by various CMV strains showed that tolerance depended on the host genotype and showed a moderate heritability. Moreover, it demonstrated that the more tolerant Arabidopsis genotypes modified their developmental pattern and timing, so that upon infection resources werere-allocated from vegetative growth to increase the production of reproductive structures and seeds (2). Genetic mapping of tolerance determinants allowed the identification of three QTLs for tolerance that co-located with genes known to regulate the transition from vegetative to reproductive growth, which are then good candidate genes for tolerance based on life-history trait modification. As tolerance is a quantitative trait with a moderate heritability that appears associated to changes in the host developmental programme, it can be predicted that its expression will depend on the environment. To approach this question, four Arabidopsis accessions largely differing in their degree of tolerance were chosen for further analysis. Their response to CMV infection was analysed in a range of temperature and light conditions. This showed that environmental conditions are involved in the outcome of infection, which varied from high susceptibility to high tolerance. Still, the response pattern over environmental conditions was genetically determined, and differed largely for the accessions previously rated as tolerant and for those rated as susceptible. The role of tolerance in plant defence might be questioned by this strong genotype x environment interaction affecting its expression: if tolerance is effective in only a limited set of conditions, it might have no role in plant-virus co-evolution. To test the possible role of tolerance as a defence mechanism of Arabidopsis to CMV in nature, we analysed its variation over wild Arabidopsis genotypes, and compared it with the variation in resistance, which can hardly be questioned as a defence mechanism. For this, 12 wild Arabidopsis populations were sampled over the Iberian Peninsula and 10 random individuals per population were assayed for resistance and tolerance to two CMV strains. Assays were done in two environmental conditions, simulating a mild or a severe Iberian winter. Results indicated that Arabidopsis populations were highly polymorphic for both resistance and tolerance, both traits showing moderate to high heritabilities. In addition, both, resistance and tolerance, depended on the host and virus genotypes and on their interaction, a requirement for a possible role in plant-virus co-evolution. Finally, comparisons of the variation for these traits within and among populations,with that quantified for neutral genetic markers, suggest that both, resistance and tolerance to CMV, are under selection in Iberian Arabidopsis population. Overall, these results provided information on the mechanisms of tolerance, including its expression and its putative genetic determinants, and strongly support a role for tolerance in plant defence. | |
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Internacional
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Si |
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ISSN o ISBN
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00-0000-00 |
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Entidad relacionada
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Nacionalidad Entidad
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Sin nacionalidad |
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Lugar del congreso
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Hyères-les-Palmiers (Francia) |