title: RNA-directed DNA methylation mediated by DRD1 and Pol IVb: a versatile pathway for transcriptional gene silencing in plants.
abstract: RNA-directed DNA methylation, which is one of several RNAi-mediated pathways in the nucleus, has been highly elaborated in the plant kingdom. RNA-directed DNA methylation requires for the most part conventional DNA methyltransferases, histone modifying enzymes and RNAi proteins; however, several novel, plant-specific proteins that are essential for this process have been identified recently. DRD1 (defective in RNA-directed DNA methylation) is a putative SWI2/SNF2-like chromatin remodelling protein; DRD2 and DRD3 (renamed NRPD2a and NRPD1b, respectively) are subunits of Pol IVb, a putative RNA polymerase found only in plants. Interestingly, DRD1 and Pol IVb appear to be required not only for RNA-directed de novo methylation, but also for full erasure of methylation when the RNA trigger is withdrawn. These proteins thus have the potential to facilitate dynamic regulation of DNA methylation. Prominent targets of RNA-directed DNA methylation in the Arabidopsis thaliana genome include retrotransposon long terminal repeats (LTRs), which have bidirectional promoter/enhancer activities, and other types of intergenic transposons and repeats. Intergenic solitary LTRs that are targeted for reversible methylation by the DRD1/Pol IVb pathway can potentially act as switches or rheostats for neighboring plant genes. The resulting alterations in gene expression patterns may promote physiological flexibility and adaptation to the environment.
authors: Gregor Mendel Institute for Molecular Plant Biology, Austrian Academy of Sciences, Dr. Bohr-Gasse 3, A-1030 Vienna, Austria.
authors: Bruno
authors: B
authors: Huettel
authors: Tatsuo
authors: T
authors: Kanno
authors: Lucia
authors: L
authors: Daxinger
authors: Etienne
authors: E
authors: Bucher
authors: Johannes
authors: J
authors: van der Winden
authors: Antonius J M
authors: AJ
authors: Matzke
authors: Marjori
authors: M
authors: Matzke
mesh_terms: D001483:Base Sequence; D042002:Chromatin Assembly and Disassembly; D019175:DNA Methylation; D018744:DNA, Plant / Q000235:genetics* / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000378:metabolism; D020868:Gene Silencing; D017343:Genes, Plant; D006657:Histones / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D010944:Plants / Q000235:genetics* / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics* / Q000378:metabolism*; D020079:Terminal Repeat Sequences
chemical_list: D018744:DNA, Plant; D006657:Histones; D010940:Plant Proteins; D018749:RNA, Plant; D012321:DNA-Directed RNA Polymerases