title: An RNA-dependent RNA polymerase is required for paramutation in maize.
abstract: Paramutation is an allele-dependent transfer of epigenetic information, which results in the heritable silencing of one allele by another. Paramutation at the b1 locus in maize is mediated by unique tandem repeats that communicate in trans to establish and maintain meiotically heritable transcriptional silencing. The mop1 (mediator of paramutation1) gene is required for paramutation, and mop1 mutations reactivate silenced Mutator elements. Plants carrying mutations in the mop1 gene also stochastically exhibit pleiotropic developmental phenotypes. Here we report the map-based cloning of mop1, an RNA-dependent RNA polymerase gene (RDRP), most similar to the RDRP in plants that is associated with the production of short interfering RNA (siRNA) targeting chromatin. Nuclear run-on assays reveal that the tandem repeats required for b1 paramutation are transcribed from both strands, but siRNAs were not detected. We propose that the mop1 RDRP is required to maintain a threshold level of repeat RNA, which functions in trans to establish and maintain the heritable chromatin states associated with paramutation.
authors.affiliation: Department of Plant Sciences, 303 Forbes Hall, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Alleman
authors.forename: Lyudmila
authors.initials: L
authors.lastname: Sidorenko
authors.forename: Karen
authors.initials: K
authors.lastname: McGinnis
authors.forename: Vishwas
authors.initials: V
authors.lastname: Seshadri
authors.forename: Jane E
authors.initials: JE
authors.lastname: Dorweiler
authors.forename: Joshua
authors.initials: J
authors.lastname: White
authors.forename: Kristin
authors.initials: K
authors.lastname: Sikkink
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Chandler
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D012324:RNA-Dependent RNA Polymerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020080:Tandem Repeat Sequences / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics*
chemical_list: D012324:RNA-Dependent RNA Polymerase