Arabidopsis FIERY1, XRN2, and XRN3 are endogenous RNA silencing suppressors.
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'-->3' exoribonucleases Xrn1 and Rat1. fry1 mutant plants recapitulate developmental and molecular characteristics of xrn mutants and likely restore PTGS in ago1 hypomorphic mutants by corepressing XRN2, XRN3, and XRN4, thus increasing RNA silencing triggers. We anticipate that screens incorporating partially compromised silencing components will uncover additional PTGS suppressors that may not be revealed using robust silencing systems.
Gy
Isabelle
I
Laboratoire de Biologie Cellulaire, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique (INRA), 78026 Versailles Cedex, France.
Gasciolli
Virginie
V
Lauressergues
Dominique
D
Morel
Jean-Benoit
JB
Gombert
Julie
J
Proux
Florence
F
Proux
Caroline
C
Vaucheret
Hervé
H
Mallory
Allison C
AC
D017360:Arabidopsis / Q000235:genetics* / Q000821:virology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D060565:Argonaute Proteins; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017799:Cucumovirus / Q000502:physiology; D005095:Exoribonucleases / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D016153:Genes, Suppressor; D035683:MicroRNAs / Q000737:chemistry / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D009690:Nucleic Acid Conformation; D009708:Nucleotidases / Q000235:genetics* / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D019076:Transgenes
C117457:AGO1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060565:Argonaute Proteins; D035683:MicroRNAs; D009687:Nuclear Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D005095:Exoribonucleases; C511588:XRN2 protein, Arabidopsis; C526974:Xrn3 protein, Arabidopsis; D009708:Nucleotidases; D010744:Phosphoric Monoester Hydrolases; C053087:inositol-1,4-bisphosphate 1-phosphatase