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PATRON DE POLYMORPHISME ET SIGNATURE MOLECULAIRE DE L'ADAPTATION AU MILIEU SALIN DE HELIANTHUS PARADOXUS

Abstract : The homoploid hybrid sunflower species, Helianthus paradoxus, is derived from two wild sunflower species H. annuus and H. petiolaris, and is adapted to salt marshes. My thesis work characterized the genetic basis of the natural selection that created the adaptation of H. paradoxus to this extreme habitat.
I searched for signatures of selection at the whole genome scale, as well as at a finer scale of 20 to 90 cM within individual chromosomes. Accordingly, I analyzed the genetic diversity of three natural populations of H. paradoxus and its parental species using microsatellite markers. For the analysis, I used microsatellite markers that are located near three survivorship QTLs, and compared their genetic diversity to markers from putative unselected regions. Genetic diversity was significantly lower around the survivorship QTL in the hybrid species but not in the parental species, signaling for the signature of selection in the H. paradoxus genome detectable at this scale. At the finer scale, I found a mosaic pattern of genetic diversity. To overcome unknown mapping locations of genetic markers in H. paradoxus, a method to group and order markers based on measure of linkage disequilibrium in natural populations was developed. Congruence of the order according to the sunflower genetic map and the linkage disequilibrium ordering depended on the populations and the genetic scale tested.
In addition, a physiological and gene expression study was developed to understand the mechanisms of H. paradoxus adaptation to salty habitat. The hybrid species exhibited a high plasticity response, and performed better than its parental species in a saline habitat. Leaves of H. paradoxus were more succulent and have a higher concentration of sodium and sulfate, compared to the parental species. Several candidate genes, implied in various salinity response pathways and located for some within the mapped QTL regions, were differentially expressed in the hybrid species and the two parental species. These results confirm that these genes are potential candidate genes for studying H. paradoxus adaptation to saline marshes, and probably played a major role in the process of speciation.
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Submitted on : Wednesday, December 12, 2007 - 10:31:50 PM
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  • HAL Id : tel-00196521, version 1
  • PRODINRA : 251036

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Cécile Edelist. PATRON DE POLYMORPHISME ET SIGNATURE MOLECULAIRE DE L'ADAPTATION AU MILIEU SALIN DE HELIANTHUS PARADOXUS. Ecologie, Environnement. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00196521⟩

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