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Identification et étude fonctionnelle de protéines virales impliquées dans la suppression de l'extinction post-transcriptionnelle de gènes ou PTGS

Abstract : Posttranscriptional Gene Silencing (PTGS) is a widespread phenomenon conserved among organisms such as fungi, plants or mammals. This system specifically recognizes double-stranded RNA molecules and degrades them to small fragments of 21-23 nt in size. PTGS is thought to act as an antiviral defence system in plants. Plant viruses have evolved a counter-strategy against PTGS and it has been shown that some of them encode proteins which act as suppressors of PTGS. Surprisingly, those proteins, such as HCPro from potyviruses or 2b from cucumoviruses, do not share sequence or structural homologies and have distinct roles in the viral infection cycle. In this thesis I describe the identification and functional characterization of new viral proteins involved in suppression of PTGS. Thus, we have shown that the P15 and P14 proteins from two closely related viruses, PCV (Peanut Clump Virus) and BNYVV (Beet Necrotic Yellow Vein Virus), are suppressors of PTGS with different properties. P15 protein localizes to peroxisomes and seems to be active in a multimeric form, whereas P14 localizes in the cytoplasm and nucleolus and is a "weaker" suppressor of PTGS. We have also identified the P0 protein from BWYV (Beet Western Yellows Virus) as a very effective suppressor of PTGS when expressed out of its viral context. Strikingly, P0 expression is strongly down-regulated during viral infection. Finally, we have used transgenic plants expressing BWYV's minor capsid protein and silenced by BWYV infection to confirm that P0 is indeed important for viral protection against PTGS.
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Submitted on : Friday, January 7, 2005 - 12:22:08 AM
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Sébastien Pfeffer. Identification et étude fonctionnelle de protéines virales impliquées dans la suppression de l'extinction post-transcriptionnelle de gènes ou PTGS. Biochimie [q-bio.BM]. Université Louis Pasteur - Strasbourg I, 2002. Français. ⟨tel-00007938⟩

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