Plant nuclear RNA polymerase IV mediates siRNA and DNA methylation-dependent heterochromatin formation

Cell. 2005 Mar 11;120(5):613-22. doi: 10.1016/j.cell.2005.02.007.


All eukaryotes have three nuclear DNA-dependent RNA polymerases, namely, Pol I, II, and III. Interestingly, plants have catalytic subunits for a fourth nuclear polymerase, Pol IV. Genetic and biochemical evidence indicates that Pol IV does not functionally overlap with Pol I, II, or III and is nonessential for viability. However, disruption of the Pol IV catalytic subunit genes NRPD1 or NRPD2 inhibits heterochromatin association into chromocenters, coincident with losses in cytosine methylation at pericentromeric 5S gene clusters and AtSN1 retroelements. Loss of CG, CNG, and CNN methylation in Pol IV mutants implicates a partnership between Pol IV and the methyltransferase responsible for RNA-directed de novo methylation. Consistent with this hypothesis, 5S gene and AtSN1 siRNAs are essentially eliminated in Pol IV mutants. The data suggest that Pol IV helps produce siRNAs that target de novo cytosine methylation events required for facultative heterochromatin formation and higher-order heterochromatin associations.

Publication types

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

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Catalytic Domain / genetics
  • Cell Nucleus / enzymology*
  • Cell Nucleus / genetics
  • DNA Methylation
  • DNA-Directed RNA Polymerases / genetics
  • DNA-Directed RNA Polymerases / metabolism*
  • Evolution, Molecular
  • Heterochromatin / enzymology*
  • Heterochromatin / genetics
  • Molecular Sequence Data
  • Mutation / genetics
  • Phylogeny
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism*
  • tRNA Methyltransferases / metabolism


  • Arabidopsis Proteins
  • Heterochromatin
  • Protein Subunits
  • RNA, Small Interfering
  • tRNA Methyltransferases
  • RNA polymerase IV, Arabidopsis
  • DNA-Directed RNA Polymerases

Associated data

  • GENBANK/AY862891