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Evolution de la gynodioécie-gynomonoécie : approches expérimentales chez Silene nutans & approche théorique

Abstract : In flowering plants, gynodioecy -- a system in which females and hermaphrodites coexist within populations -- is the most common sexual system after hermaphroditism. The evolution and maintenance of gynodiocy and its underlying polymorphism have puzzled evolutionary biologists since the 19th century. The main principles of its evolution are well known but some points remain vague. During my PhD, I explored three aspects of gynodioecy using an experimental approach in the species Silene nutans and a theoretical approach. First, I studied the genetic determination of gynodioecy using controlled crosses that showed that the genetic determination of sex was cytonuclear, i.e. controlled by several cytoplasmic male sterility (CMS) genes and several nuclear restorers of fertility. Second, I focused on gynomonoecious plants -- those that carry both pistillate (female) flowers and perfect (hermaphrodite) flowers -- that are frequently found in Silene nutans as in other gynodioecious species. I showed that the floral and reproductive traits of this third sex phenotype were often intermediate between those of females and hermaphrodites but varied with varying proportions of pistillate flowers on the plant. Contrary to what was previously thought, the plasticity of the gynomoneocious phenotype was found to be limited, suggesting a genetic determination whose characterization is still in progress. The third part of my PhD was motivated by recent evidences of heteroplasmy -- the coexistence of different mitochondrial genomes within an individual -- and occasional transmission of the mitochondrial genome through pollen in Silene vulgaris. I showed theoretically that the occurrence of a cytoplasmic male sterility gene can favor the evolution of paternal leakage of mitochondria. I also investigated mitochondrial inheritance in Silene nutans by genotyping progenies from controlled crosses.
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Submitted on : Friday, February 10, 2012 - 2:02:25 PM
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Claire Garraud. Evolution de la gynodioécie-gynomonoécie : approches expérimentales chez Silene nutans & approche théorique. Sciences agricoles. Université Paris Sud - Paris XI, 2011. Français. ⟨NNT : 2011PA112014⟩. ⟨tel-00668797⟩



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