title: Plant 45S rDNA clusters are fragile sites and their instability is associated with epigenetic alterations.
abstract: Our previous study demonstrated that 45S ribosomal DNA (45S rDNA) clusters were chromosome fragile sites expressed spontaneously in Lolium. In this study, fragile phenotypes of 45S rDNA were observed under aphidicolin (APH) incubation in several plant species. Further actinomycin D (ActD) treatment showed that transcriptional stress might interfere with chromatin packaging, resulting in 45S rDNA fragile expression. These data identified 45S rDNA sites as replication-dependent as well as transcription-dependent fragile sites in plants. In the presence of ActD, a dramatic switch to an open chromatin conformation and accumulated incomplete 5' end of the external transcribed spacer (5'ETS) transcripts were observed, accompanied by decreased DNA methylation, decreased levels of histone H3, and increased histone acetylation and levels of H3K4me2, suggesting that these epigenetic alterations are associated with failure of 45S rDNA condensation. Furthermore, the finding that γ-H2AX was accumulated at 45S rDNA sites following ActD treatment suggested that the DNA damage signaling pathway was associated with the appearance of 45S rDNA fragile phenotypes. Our data provide a link between 45S rDNA transcription and chromatin-packaging defects and open the door for further identifying the molecular mechanism involved.
authors.affiliation: State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Min
authors.initials: M
authors.lastname: Huang
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Lu
authors.initials: L
authors.lastname: Zhang
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.forename: Pu
authors.initials: P
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Hu
authors.forename: Shihan
authors.initials: S
authors.lastname: Yan
authors.forename: Lin
authors.initials: L
authors.lastname: Zhao
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Junjun
authors.initials: J
authors.lastname: Tan
authors.forename: Xincheng
authors.initials: X
authors.lastname: Liu
authors.forename: Shibin
authors.initials: S
authors.lastname: He
authors.forename: Lijia
authors.initials: L
authors.lastname: Li
mesh_terms: D016590:Aphidicolin / Q000008:administration & dosage; D002843:Chromatin / Q000235:genetics; D043283:Chromosome Fragile Sites / Q000187:drug effects / Q000235:genetics*; D019175:DNA Methylation / Q000187:drug effects; D003609:Dactinomycin / Q000008:administration & dosage; D044127:Epigenesis, Genetic; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018745:Genome, Plant / Q000187:drug effects; D042822:Genomic Instability / Q000187:drug effects; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D008129:Lolium / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics*
chemical_list: D002843:Chromatin; D006657:Histones; D012335:RNA, Ribosomal; C088179:RNA, ribosomal, 45S; D003609:Dactinomycin; D016590:Aphidicolin; D011495:Histone-Lysine N-Methyltransferase