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Rôle des enzymes ALDH10 dans la voie de biosynthèse de la carnitine et la physiologie de la plante chez Arabidopsis

Abstract : Carnitine is a non-proteinogenic amino acid present in all living organisms. Its role in theintracellular transport of fatty acids is well characterized in animals. In plants also, carnitine islinked to lipid metabolism, but its precise role remains poorly understood. In animals andyeasts, carnitine is synthetized from trimethyllysine (TML) through 4 enzymatic steps. The identification in plant tissues of TML and γ-butyrobetaine, the direct precursor of carnitine,suggests that its biosynthesis follows the same steps. A bioinformatics research of candidatesidentified the two ALDH10 enzymes as possibly involved in the synthesis of γ-butyrobetaine.The present study deals with the characterization of the AtALDH10s, to elucidate their role incarnitine biosynthesis and plant physiology. Firstly, the two AtALDH10s were characterized in vitro. This study demonstrates their capability to synthetize γ-butyrobetaine, as well as osmoprotectants. Secondly, an Arabidopsis loss-of-function for the two AtALDH10 has beenobtained and characterized. This mutant is more sensitive to salt stress, bears a longer main shoot and more secondary shoots, and smaller siliques containing less seeds. Its viable seeds are enriched in proteins and fatty acids, and the seedling development is faster. These resultssuggest an intervention of AtALDH10s in the resistance to osmotic stress, the control of plant architecture and the early development. The γ-butyrobetaine content is reduced in the mutant, confirming the involvement of AtALDH10s in the synthesis of γ-butyrobetaine in planta. The residual content of γ-butyrobetaine seems to be sufficient to maintain an unchanged level of carnitine in the mutant. These results raise the question of the regulation of the carnitine biosynthesis pathway and suggest that γ-butyrobetaine could be involved in response to osmotic stress, signalisation pathways and plant architecture. Besides this work, a bioinformatic research lead to the identification of a protein with a structure close to that of the enzyme involved in the conversion of γ-butyrobetaine into carnitine in humans. However, the characterization of this protein did not confirm its involvement in carnitine biosynthesis. The identification and characterization of mutants impaired in enzymatic activities linked to carnitine, such as its biosynthesis or its intervention in the transport of fatty acids, would be valuable to pave the way of a better understanding of the role of carnitine in plants.
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Submitted on : Tuesday, May 25, 2021 - 12:40:09 PM
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Florian Jacques. Rôle des enzymes ALDH10 dans la voie de biosynthèse de la carnitine et la physiologie de la plante chez Arabidopsis. Biotechnologies. Université de Technologie de Compiègne, 2019. Français. ⟨NNT : 2019COMP2487⟩. ⟨tel-03234451⟩



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