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Plant Cell Advance Online Publication Published on November 9, 2007; 10.1105/tpc.107.055319
Received August 23, 2007 Arabidopsis FIERY1, XRN2, and XRN3 Are Endogenous RNA Silencing Suppressors
1 Laboratoire de Biologie Cellulaire, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique (INRA), 78026 Versailles Cedex, France * To whom correspondence should be addressed. E-mail: amallory{at}versailles.inra.fr.
The eukaryotic defense response posttranscriptional gene silencing (PTGS) is directed by short-interfering RNAs and thwarts invading nucleic acids via the RNA slicing activity of conserved ARGONAUTE (AGO) proteins. PTGS can be counteracted by exogenous or endogenous suppressors, including the cytoplasmic exoribonuclease XRN4, which also degrades microRNA (miRNA)-guided mRNA cleavage products but does not play an obvious role in development. Here, we show that the nuclear exoribonucleases XRN2 and XRN3 are endogenous PTGS suppressors. We also identify excised MIRNA loops as templates for XRN2 and XRN3 and show that XRN3 is critical for proper development. Independently, we identified the nucleotidase/phosphatase FIERY1 (FRY1) as an endogenous PTGS suppressor through a suppressor screen in a hypomorphic ago1 genetic background. FRY1 is one of six Arabidopsis thaliana orthologs of yeast Hal2. Yeast hal2 mutants overaccumulate 3'-phosphoadenosine 5'-phosphate, which suppresses the 5'
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