Seed maturation is characterized by the acquisition ofthe various components that collectively constitute thephysiological quality or vigor of the seed: desiccation tolerance(DT, i.e. the capacity to survive complete drying), seedstorability or longevity (the capacity to remain alive duringstorage), dormancy, as well as fast and uniform germinationand seedling emergence under stressful conditions. Thesetraits are pivotal to ensure rapid and homogenous seedlingestablishment required for stable yield and are a majoreconomic challenge for the seed industry. Despite theiragronomic importance, the mechanisms regulating theiracquisition, including longevity, are still poorly understood. InMedicago truncatula, a gene co-expression network inferredthat transcription factors such asMtABL (ABA INSENSITIVE4-LIKE), MtABI5 (ABA INSENSITIVE5) and MtHSFA2.2 (HEATSHOCK FACTOR A2.2) are putative regulators of seedlongevity. The aim of this thesis was to characterize theirroles in Medicago truncatula and Pisum sativum using Tnt1insertion and EMS mutants. ABL and ABI5 are positiveregulators of longevity while defects in hsfa2.2 do not affectit. Transcriptomic and biochemical analyses show that ABLand ABI5 are involved in the regulation of photosynthesisassociated genes, chlorophyll loss and accumulation ofraffi nose family oligosaccharides (RFO). ABI5 is also involvedin the accumulation of stress proteins such as LEA proteins.By establishing a link between degreening, RFO contents andlongevity, our work offers new opportunities to tackle a

La phase de maturation des graines est caractĂ©risĂ©e par l’ac-quisition successive de composantes qui constituent la qua-litĂ© physiologique d’un lot de semences, Ă  savoir la tolĂ©ranceĂ  la dessiccation (capacitĂ© Ă  survivre au retrait total de l’eaucellulaire), la longĂ©vitĂ© (capacitĂ© de survivre Ă  l’Ă©tat sec pen-dant le stockage), la dormance ainsi que la vigueur germina-tive (capacitĂ© Ă  germer de façon rapide et homogène quelquessoient les conditions de l’environnement). La production desemences Ă  haute qualitĂ© germinative reprĂ©sente un enjeumajeur pour les semenciers car elle constitue un levier clefpour augmenter les rendements agricoles. Cependant, lesmĂ©canismes rĂ©gulant l’acquisition de la qualitĂ© germinativeet en particulier la longĂ©vitĂ© restent peu connus. Une Ă©tudeprĂ©alable d’un rĂ©seau de co-expression gĂ©nique de facteursde transcription avait identifi Ă© trois gènes candidats associĂ©sĂ  la longĂ©vitĂ© chez Medicago truncatula :MtABL (ABA INSEN-SITIVE4-LIKE), MtABI5 (ABA INSENSITIVE5) et MtHSFA2.2(HEAT SHOCK FACTOR A2.2). L’objectif de cette thèse Ă©tait devalider ces gènes et d’en comprendre leur fonction chez Medicagotruncatula et le pois par la caractĂ©risation de mutantsd’insertion et EMS. ABL et ABI5 jouent un rĂ´le dans la matu-ration en rĂ©gulant positivement la longĂ©vitĂ© alors que celle-ci n’est pas affectĂ©e dans les mutants hsfa2.2. Des Ă©tudestranscriptomiques et biochimiques montrent que ABL et ABI5rĂ©gulent de manière complexe la photosynthèse, la dĂ©grada-tion de la chlorophylle et l’accumulation des oligosaccharide