Erasure of CpG methylation in Arabidopsis alters patterns of histone H3 methylation in heterochromatin

Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland

Communicated by Steven P. Briggs, Diversa Corporation, San Diego, CA, May 15, 2003 (received for review March 5, 2003)

Abstract

In mammals and plants, formation of heterochromatin is associated with hypermethylation of DNA at CpG sites and histone H3 methylation at lysine 9. Previous studies have revealed that maintenance of DNA methylation in Neurospora and Arabidopsis requires histone H3 methylation. A feedback loop from DNA methylation to histone methylation, however, is less understood. Its recent examination in Arabidopsis with a partial loss of function in DNA methyltransferase 1 (responsible for maintenance of CpG methylation) yielded conflicting results. Here we report that complete removal of CpG methylation in an Arabidopsis mutant null for DNA maintenance methyltransferase results in a clear loss of histone H3 methylation at lysine 9 in heterochromatin and also at heterochromatic loci that remain transcriptionally silent. Surprisingly, these dramatic alterations are not reflected in heterochromatin relaxation.

Footnotes

↵ * To whom correspondence should be addressed. E-mail: tariq{at}fmi.ch.
↵ † Present address: Department of Plant Biology, University of Geneva, 30 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.
↵ ‡ Present address: National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba 305-8602, Ibaraki, Japan.
Abbreviations: ChIP, chromatin immunoprecipitation; H3K9^Me, histone H3 dimethylated at lysine 9; H3K4^Me, histone H3 dimethylated at lysine 4; DAPI, 4′,6-diamidino-2-phenylindole.