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Letters to Nature

Nature 427, 164-167 (8 January 2004) | doi:10.1038/nature02269; Received 4 August 2003; Accepted 5 December 2003

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Vernalization requires epigenetic silencing of FLC by histone methylation

Ruth Bastow1, Joshua S. Mylne1, Clare Lister1, Zachary Lippman2, Robert A. Martienssen2 & Caroline Dean1

  1. Department of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK
  2. Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA

Correspondence to: Caroline Dean1 Email: caroline.dean@bbsrc.ac.uk

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To ensure flowering in favourable conditions, many plants flower only after an extended period of cold, namely winter. In Arabidopsis, the acceleration of flowering by prolonged cold, a process called vernalization, involves downregulation of the protein FLC, which would otherwise prevent flowering1, 2. This lowered FLC expression is maintained through subsequent development by the activity of VERNALIZATION (VRN) genes3, 4. VRN1 encodes a DNA-binding protein4 whereas VRN2 encodes a homologue of one of the Polycomb group proteins, which maintain the silencing of genes during animal development3. Here we show that vernalization causes changes in histone methylation in discrete domains within the FLC locus, increasing dimethylation of lysines 9 and 27 on histone H3. Such modifications identify silenced chromatin states in Drosophila and human cells5, 6, 7. Dimethylation of H3 K27 was lost only in vrn2 mutants, but dimethylation of H3 K9 was absent from both vrn1 and vrn2, consistent with VRN1 functioning downstream of VRN2. The epigenetic memory of winter is thus mediated by a 'histone code' that specifies a silent chromatin state conserved between animals and plants.