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Étude des causes génétiques de la plasticité phénotypique par une approche de cartographie de QTLs : cas de la levure oenologique Saccharomyces cerevisiae

Abstract : The yeast S. cerevisiae is the only species able to complete the alcoholic fermentation of grape must which is the main step of the wine-making process. Because of the high technological variability found in this species, selection work is carried out with the aim of using efficient yeasts for the industry. These strains show important differences both in their fermentation kinetics and their metabolite yield which affects the wines quality. In addition to these important phenotypic variations, the phenotypic response of yeasts varies considerably and not homogeneously against environmental variations. Understanding the genetic mechanisms that explain these differentiated responses to environmental variations is a non-trivial scientific question. This is of particular importance in oenology, where the winemaking conditions are highly variable (vintages, grape variety, terroirs, oenological practices...). In order to obtain yeasts ensuring the success of the fermentations under a wide range of conditions, we propose here to better understand these mechanisms of interaction Gene x Environment in an oenological context. The identification of genetic locus (Quantitative Trait Loci (QTL)) controlling quantitative characters is made possible by QTL mapping approaches. These approaches require the study of a large progeny in segregation that must be characterized genetically and phenotypically. The establishment of a statistical link between genotype and phenotype allows the localization of QTLs that have an impact on phenotyped characters. During this thesis a phenotyping method that allows us to follow the fermentations of several hundred individuals has been developed. Thanks to it, two progenies genotyped by whole genome sequencing have been phenotyped in different environmental conditions. This lead to the identification of many QTLs and to the estimation of their impact in strain robustness. The implication of the alleles of 3 genes showing a strong interaction with environment and pleiotropic effects linked to the SO2 metabolism has been proved molecularly. The results achieved are discussed in the context of QTL exploitation for the selection of more efficient yeast.
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Emilien Peltier. Étude des causes génétiques de la plasticité phénotypique par une approche de cartographie de QTLs : cas de la levure oenologique Saccharomyces cerevisiae. Biochimie, Biologie Moléculaire. Université de Bordeaux, 2017. Français. ⟨NNT : 2017BORD0945⟩. ⟨tel-01806339⟩

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