An RNA-dependent RNA polymerase is required for paramutation in maize

Nature. 2006 Jul 20;442(7100):295-8. doi: 10.1038/nature04884.


Paramutation is an allele-dependent transfer of epigenetic information, which results in the heritable silencing of one allele by another. Paramutation at the b1 locus in maize is mediated by unique tandem repeats that communicate in trans to establish and maintain meiotically heritable transcriptional silencing. The mop1 (mediator of paramutation1) gene is required for paramutation, and mop1 mutations reactivate silenced Mutator elements. Plants carrying mutations in the mop1 gene also stochastically exhibit pleiotropic developmental phenotypes. Here we report the map-based cloning of mop1, an RNA-dependent RNA polymerase gene (RDRP), most similar to the RDRP in plants that is associated with the production of short interfering RNA (siRNA) targeting chromatin. Nuclear run-on assays reveal that the tandem repeats required for b1 paramutation are transcribed from both strands, but siRNAs were not detected. We propose that the mop1 RDRP is required to maintain a threshold level of repeat RNA, which functions in trans to establish and maintain the heritable chromatin states associated with paramutation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Base Sequence
  • Cloning, Molecular
  • Gene Expression Regulation, Plant / genetics
  • Molecular Sequence Data
  • Mutagenesis / genetics*
  • Mutation / genetics*
  • RNA-Dependent RNA Polymerase / chemistry
  • RNA-Dependent RNA Polymerase / genetics
  • RNA-Dependent RNA Polymerase / metabolism*
  • Tandem Repeat Sequences / genetics
  • Transcription, Genetic / genetics
  • Zea mays / enzymology*
  • Zea mays / genetics*


  • RNA-Dependent RNA Polymerase

Associated data

  • GENBANK/DQ414253
  • GENBANK/DQ417752
  • GENBANK/DQ417753
  • GENBANK/DQ417754
  • GENBANK/DQ417755
  • GENBANK/DQ419917