Abstract
Multisubunit RNA polymerases IV and V (Pol IV and Pol V) evolved as specialized forms of Pol II that mediate RNA-directed DNA methylation (RdDM) and transcriptional silencing of transposons, viruses, and endogenous repeats in plants. Among the subunits common to Arabidopsis thaliana Pols II, IV, and V are 93% identical alternative ninth subunits, NRP(B/D/E)9a and NRP(B/D/E)9b. The 9a and 9b subunit variants are incompletely redundant with respect to Pol II; whereas double mutants are embryo lethal, single mutants are viable, yet phenotypically distinct. Likewise, 9a or 9b can associate with Pols IV or V but RNA-directed DNA methylation is impaired only in 9b mutants. Based on genetic and molecular tests, we attribute the defect in RdDM to impaired Pol V function. Collectively, our results reveal a role for the ninth subunit in RNA silencing and demonstrate that subunit diversity generates functionally distinct subtypes of RNA polymerases II and V.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Arabidopsis / enzymology*
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Arabidopsis / genetics
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Arabidopsis Proteins / chemistry
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Arabidopsis Proteins / genetics
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Arabidopsis Proteins / metabolism*
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Crosses, Genetic
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DNA Methylation / genetics
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DNA, Bacterial / genetics
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DNA-Directed RNA Polymerases / chemistry
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DNA-Directed RNA Polymerases / genetics
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DNA-Directed RNA Polymerases / metabolism*
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Gene Expression Regulation, Plant
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Gene Silencing
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Molecular Sequence Data
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Mutation / genetics
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Phylogeny
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Plants, Genetically Modified
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Protein Subunits / chemistry
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Protein Subunits / genetics
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Protein Subunits / metabolism*
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RNA Polymerase II / chemistry
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RNA Polymerase II / genetics
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RNA Polymerase II / metabolism*
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Sequence Alignment
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Transgenes
Substances
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Arabidopsis Proteins
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DNA, Bacterial
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Protein Subunits
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RNA, Messenger
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T-DNA
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RNA Polymerase II
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RNA polymerase IV, Arabidopsis
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RNA polymerase V, Arabidopsis
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DNA-Directed RNA Polymerases