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L‘extinction de gènes chez les plantes révèle un mécanisme de défense antiviral surmonté par les phytovirus Volume 7, issue 5, septembre-octobre 2003

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Laboratory of RNA Molecular Biology, The Rockefeller University, 1230 York Avenue, Box 186, New York, NY 10021, USA Institut de biologie moléculaire des plantes du CNRS, Université Louis‐Pasteur, 12, rue du Général Zimmer, 67084 Strasbourg  Cedex

Posttranscriptional gene silencing or PTGS is a widespread phenomenon conserved in plants and animals and triggered by double stranded (ds) RNA. dsRNA is recognized by an Rnase III like nuclease and cleaved in short RNA molecules of 21 to 23 nucleotides in length ; these short interfering RNAs are then going to target a cellular multienzeymatic complex on all homologous RNA to degrade them. In plants, PTGS is now known to act as an antiviral defence system, especially against RNA viruses that use a double stranded replication intermediate. To comfort this theory, it has been shown that plant viruses have developed a counter strategy to suppress PTGS. Some viral proteins involved in suppression of PTGS have been identified and, interestingly, they don‘t share any sequence or structure homology.