Nucleolar rDNA folds into condensed foci with a specific combination of epigenetic marks

SUMMARY Arabidopsis thaliana 45S ribosomal genes (rDNA) are located in tandem arrays called nucleolus organizing regions on the termini of chromosomes 2 and 4 (NOR2 NOR4) encode rRNA, a crucial structural element ribosome. The current model rDNA organization suggests that inactive rRNA accumulate condensed chromocenters nucleus at nucleolar periphery, while delineates active genes. We challenge perspective all intranucleolar is by showing subset assembles into foci marked H3.1 H3.3 histones also contain repressive H3K9me2 histone mark. By using plant lines containing low number copies, we further found relate to folding rDNA, which appears be common mechanism regulation inside nucleolus. mark represents typical modification bulk as show genome‐wide approaches, similar H2A.W variant. euchromatin marks H3K27me3 H3K4me3, contrast, do not colocalize with their overall levels very low. demonstrate promoter an important regulatory region where distribution variants modifications modulated response activity.