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EMBO reports 7, 12, 1273–1278 (2006)
doi:10.1038/sj.embor.7400791
AOP Published online: 3 November 2006
MOM1 mediates DNA-methylation-independent silencing of repetitive sequences in Arabidopsis
Isabelle Vaillant1, Ingo Schubert2, Sylvette Tourmente1 & Olivier Mathieu1
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1 UMR CNRS 6547, BIOMOVE, Université Blaise Pascal, 24 Avenue des Landais, 63177 Aubière Cedex, France
2 Department of Cytogenetics, Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, D-06466 Gatersleben, Germany
To whom correspondence should be addressed
Olivier Mathieu Tel: +33 4 73 40 77 31; Fax: +33 4 73 40 77 77; E-mail: olivier.mathieu@univ-bpclermont.fr
Received 1 May 2006; Accepted 21 July 2006; Published online 3 November 2006.
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Abstract
The heterochromatic regions around centromeres of animal and plant chromosomes are composed of tandem repetitive sequences, interspersed with transposons and transposon derivatives. These sequences are largely transcriptionally silent and highly methylated, and are associated with specifically modified histones. Although embedded in heterochromatin, Arabidopsis 5S ribosomal RNA genes are among the most highly transcribed genes. However, some 5S genes are silenced, and we show here that this silencing can be suppressed by a reduction in CG methylation. Importantly, we show that mutation of MORPHEUS' MOLECULE 1 (MOM1) releases 5S repeat silencing independently of chromatin properties, as illustrated by the absence of detectable alteration of DNA and histone H3 methylation patterns. MOM1 also prevents transcription of 180-bp satellite repeats and 106B dispersed repeats but not of transposons. Our results provide evidence that transcription of densely methylated and highly repetitive heterochromatic sequences is controlled by two distinct epigenetic silencing pathways, one dependent on and the other independent of DNA methylation.
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