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Caractérisation génétique et moléculaire d'une incompatibilité nucléo-cytoplasmique chez Arabidopsis Thaliana

Abstract : The genome of plants is compartmentalized between nucleus and organelles (chloroplasts and mitochondria). These compartments have different inheritance patterns (nuclear genes have Mendelian inheritance; organelles genes are maternally inherited) and this has consequences for their co-adaptation, which is under the influence of two forces: on the one hand, a functional co-adaption whose failure leads to Bateson-Dobzhanski-Muller incompatibilities, on a second hand a genomic conflict, sometimes revealed by nucleo-cytoplasmic male sterility. The wealth of genetic resources at our disposal for Arabidopsis thaliana makes it an interesting model to study the co-evolution between genetic compartments. As part of this problem, this thesis is devoted to a male sterility presenting a nucleo-cytoplasmic determinism and which emerged as a result of a cross between two accessions (Sha x Mr-0) while the reciprocal cross (Mr-0 x Sha) produced male fertile F1 individuals. Results preliminary to this thesis have shown that male sterility results from an interaction between the cytoplasm of Sha and dominant alleles carried by chromosomes 1 and 3. The objectives of this thesis were to describe the phenotype of the male sterility, as well as to identify both cytoplasmic and nuclear factors, and also to start the study of the underlying molecular mechanisms, which are responsible of this male sterility. I followed a strategy of genetic mapping to identify involved nuclear factors by positional cloning. I localized the maintainer locus on chromosome 3 in an interval of 53 kb and began a molecular analysis of this region in the two parental accessions. This now allows a candidate gene approach for this maintainer. I also showed that the maintainer locus on chromosome 1 probably consists of two closely linked loci, whose alleles Mr-0 are both required for the expression of the male sterility. In parallel, reciprocal crosses involving either Mr-0 or Sha with accessions of the collection allowed us to identify at least one other accession with maintainer alleles (Etna-2), and a dozen accessions carrying the male sterility-inducing cytoplasm (all from Central Asia). A comparative analysis of cytoplasmic genomes of Sha and Kz-9, which has a cytoplasm very close to Sha but not inducing sterility, revealed a mitochondrial gene, candidate for male sterility and called orf117Sha. It is specific to accessions inducing sterility and its putative product shows 57% identity and 71% similarity with orf108, a gene involved in cytoplasmic male sterility in alloplasmic Brassicas (Ashutosh et al, 2008 ; Kumar et al, 2012).During the mapping and cytological observations, I have highlighted genetic incompatibilities that cause distortions of segregation through the male descent in the progeny of heterozygous plants. These incompatibilities, probably independent of the cytoplasm, create genetic barriers between the two parental accessions of the cross that I studied. I propose that the cross Sha x Mr-0 reveals an ongoing evolutionary process that can eventually lead to speciation events in Arabidopsis thaliana.
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Submitted on : Monday, July 2, 2012 - 1:53:32 PM
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  • PRODINRA : 244921

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Nicolas Gobron. Caractérisation génétique et moléculaire d'une incompatibilité nucléo-cytoplasmique chez Arabidopsis Thaliana. Sciences agricoles. Université Paris Sud - Paris XI, 2012. Français. ⟨NNT : 2012PA112077⟩. ⟨tel-00713647⟩

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