Transcription of the 5S rRNA heterochromatic genes is epigenetically controlled in Arabidopsis thaliana and Xenopus laevis

doi:doi:10.1038/sj.hdy.6800964

Heredity (2007) 99, 5–13; doi:10.1038/sj.hdy.6800964; published online 9 May 2007

Transcription of the 5S rRNA heterochromatic genes is epigenetically controlled in Arabidopsis thaliana and Xenopus laevis

J Douet¹ and S Tourmente¹

¹Unité Mixte de Recherche CNRS 6547 BIOMOVE, Université Blaise Pascal, Aubière Cedex, France

Correspondence: Dr S Tourmente, Unité Mixte de Recherche CNRS 6547 BIOMOVE, Université Blaise Pascal, 24 Avenue des Landais, 63177 Aubière Cedex, France. E-mail: sylvette.tourmente@univ-bpclermont.fr

Received 6 December 2006; Revised 13 February 2007; Accepted 16 February 2007; Published online 9 May 2007.

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Abstract

5S ribosomal DNA is a highly conserved tandemly repeated multigenic family. As suggested for a long time, we have shown that only a fraction of the 5S rRNA genes are expressed in Arabidopsis thaliana. In Xenopus laevis, there is a developmental control of the expression of the 5S rRNA genes with only one of the two 5S rDNA families expressed during oogenesis. For both Arabidopsis and Xenopus, the strongest transcription of 5S rRNA, respectively in the seed and during oogenesis is correlated with heterogeneity in the transcribed 5S rRNAs. Epigenetic mechanisms such as modification of the chromatin structure are involved in the transcriptional regulation of the 5S rRNA genes in both organisms. In Arabidopsis, two silencing pathways, methylation-dependent (RNAi) and methylation-independent (MOM pathway), are involved in the silencing of a 5S rDNA fraction.