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Analyse fonctionnelle de BclA, un transporteur de peptides antimicrobiens impliqué dans la différenciation des bactéroïdes au cours de la symbiose Aeschynomene/Bradyrhizobium

Abstract : Plants of the legume family have acquired the ability to host in specific symbiotic organs, the roots nodules, nitrogen fixing bacteria, called bacteroids. This symbiosis allows plants to fulfill all their nitrogen requirements. Some legume plants produce in their nodules a large family of antimicrobials peptides called the NCRs (Nodule-specific Cysteine-Rich). Their antimicrobial activities allow the host plant to control the intracellular bacterial population. NCRs peptides also govern terminal differentiation of the bacteroids. During my PhD work, I participated in the identification and characterization of BclA. This bacterial ABC transporter is involved in bacteroid differentiation during the Aeschynomene- Bradyrhizobium symbiosis. In order to better understand its symbiotic function, I studied the link between BclA and a peptidoglycan-modifying enzyme, the DD-carboxypeptidase 1. I was able to show that these two factors act in an independent manner in the establishment of bacteroid differentiation. A functional analysis of BclA and an experimental evolution on Sinorhizobium bacA mutant, an orthologue of bclA, conferred a better understanding of the in vivo role of these transporters. The results obtained during my thesis suggest that the BclA and BacA function is to ensure bacterial resistance to NCRs, as a prerequisite for the bacterial differentiation process, but is not needed for differentiation per se. Furthermore, their NCR uptake activities do not seem to be the mechanism underlying the resistance.
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Quentin Barrière. Analyse fonctionnelle de BclA, un transporteur de peptides antimicrobiens impliqué dans la différenciation des bactéroïdes au cours de la symbiose Aeschynomene/Bradyrhizobium. Biologie végétale. Université Paris Saclay (COmUE), 2018. Français. ⟨NNT : 2018SACLS460⟩. ⟨tel-03017576⟩

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