title: The cytological and molecular role of domains rearranged methyltransferase3 in RNA-dependent DNA methylation of Arabidopsis thaliana.
abstract: BACKGROUND
  Plants have evolved a unique epigenetic process to target DNA cytosine methylation: RNA-directed DNA methylation (RdDM). During RdDM, small RNAs (smRNAs) guide methylation of homologous DNA loci. In Arabidopsis thaliana, the de novo DNA methyltransferase that ultimately methylates cytosines guided by smRNAs in all sequence contexts is Domains Rearranged Methyltransferase 2 (DRM2). Recent reports have shown that DRM2 requires the catalytic mutated paralog DRM3 to exert its function through a still largely unknown process. To shed light on how DRM3 affects RdDM, we have further characterized its role at the molecular and cytological levels.
  
  
  RESULTS
  Although DRM3 is not required for RdDM loci transcriptional silencing, it specifically affects loci's DNA methylation. Interestingly, DRM3 and DRM2 regulate the DNA methylation in a subset of loci differently.Fluorescence In Situ Hybridization and immunolocalization analyses showed that DRM3 is not required for the large-scale nuclear organization of heterochromatin during interphase, with the notable exception of the 45S ribosomal RNA loci. DRM3 localizes exclusively to the nucleus and is enriched in a round-shaped domain located in the nucleolar periphery, in which it colocalizes with components of the RdDM pathway.
  
  
  CONCLUSIONS
  Our analyses reinforce the previously proposed chaperone role of DRM3 in RdDM. Overall, our work further demonstrates that DRM3 most likely functions exclusively with DRM2 in RdDM and not with other A. thaliana DNA methyltransferases. However, DRM3's regulation of DNA methylation is likely target- or chromatin context-dependent. DRM3 hypothetically acts in RdDM either upstream of DRM2, or in a parallel step.
authors.forename: Pedro
authors.initials: P
authors.lastname: Costa-Nunes
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Kim
authors.forename: Evelyn
authors.initials: E
authors.lastname: Hong
authors.affiliation: Department of Biology, University of New Mexico, MSC03 2020, 1 University of New Mexico, Albuquerque, NM 87131, USA. opontes@unm.edu.
authors.forename: Olga
authors.initials: O
authors.lastname: Pontes
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000378:metabolism; D060565:Argonaute Proteins / Q000378:metabolism; D002466:Cell Nucleolus / Q000378:metabolism; D042002:Chromatin Assembly and Disassembly; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D018506:Gene Expression Regulation, Plant; D006570:Heterochromatin / Q000378:metabolism; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D009697:Nucleolus Organizer Region / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D018749:RNA, Plant / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C471209:AGO4 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060565:Argonaute Proteins; D006570:Heterochromatin; D018749:RNA, Plant; D034741:RNA, Small Interfering; D008780:Methyltransferases; C470732:DRM2 protein, Arabidopsis