Thèse de doctorat en Sciences biologiques. Sciences du végétal
Sous la direction de Françoise Budar.
Soutenue en 2009
à Paris 11 , en partenariat avec Université de Paris-Sud. Faculté des sciences d'Orsay (Essonne) (autre partenaire) .
Nucleo-cytoplasmic male sterility (CMS) systems are natural systems controlled by two genetic factors: a cytoplasmic determinant causing male sterility and a nuclear determinant able to restore fertility. The Ogura CMS system is widely used for the production of hybrid seeds in cultivated Brassicas. The restorer locus of the Ogura system (Rfo) includes three highly related genes encoding PentatricoPeptide Repeat (PPR) proteins. Two of the most important questions regarding restorers of fertility concern the molecular mechanisms by which PPR restorers counter sterility, and the evolutionary relationships between related PPR genes found at restorer loci. The present study launched a functional analysis of the Rfo restorer protein (PPRB) and a study of the evolution of the Rfo locus in radish. A structure-function analysis of PPRB was undertaken in order to identify the protein domains or residues that are essential for impairing ORF138 accumulation. A functional test for the restorer activity was developed, based on the relative quantification of ORF138 in transgenic roots. For the evolutionary study the sequence of an allele of the Rfo locus obtained from a non-restorer genotype was determined. This allele carries two PPR genes closely related to those of the restorer sequence. The comparison of the two allele sequences showed that the Rfo locus evolved rapidly that intergenic and intragenic recombination operated during its evolution. Overall, the results described in this thesis contributes to a better understanding of the structural and biochemical features important for Rfo restoration activity and sheds light on the peculiar evolution of the Rfo locus.