title: An SNF2 protein associated with nuclear RNA silencing and the spread of a silencing signal between cells in Arabidopsis.
abstract: The silencing phenotype in Arabidopsis thaliana lines with an inverted repeat transgene under the control of a phloem-specific promoter was manifested in regions around veins due to a mobile signal of silencing. Genetic analysis implicates RNA-DEPENDENT RNA POLYMERASE2 (RDR2) and an RNA polymerase IVa subunit gene (NRPD1a) in the signaling mechanism. We also identified an SNF2 domain-containing protein (CLASSY1) that acts together with RDR2 and NRPD1a in the spread of transgene silencing and in the production of endogenous 24-nucleotide short interfering RNAs (siRNAs). Cytochemical analysis indicates that CLASSY1 may act in the nucleus with NRPD1a and RDR2 in the upstream part of RNA silencing pathways that generate a double-stranded RNA substrate for Dicer-like (DCL) nucleases. DCL3 and ARGONAUTE4 act in a downstream part of the pathway, leading to endogenous 24-nucleotide siRNA production, but are not required for intercellular signaling. From genetic analysis, we conclude that another downstream part of the pathway associated with intercellular signaling requires DCL4 and at least one other protein required for 21-nucleotide trans-acting siRNAs. We interpret the effect of polymerase IVa and trans-acting siRNA pathway mutations in terms of a modular property of RNA silencing pathways.
authors.affiliation: Sainsbury Laboratory, John Ines Centre, Norwich NR4 7UH, United Kingdom.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Smith
authors.forename: Olga
authors.initials: O
authors.lastname: Pontes
authors.forename: Iain
authors.initials: I
authors.lastname: Searle
authors.forename: Nataliya
authors.initials: N
authors.lastname: Yelina
authors.forename: Faridoon K
authors.initials: FK
authors.lastname: Yousafzai
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Herr
authors.forename: Craig S
authors.initials: CS
authors.lastname: Pikaard
authors.forename: David C
authors.initials: DC
authors.lastname: Baulcombe
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D019951:DNA Polymerase beta / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D035683:MicroRNAs / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D030821:Plants, Genetically Modified; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C523533:CLASSY1 protein, Arabidopsis; D047908:Intracellular Signaling Peptides and Proteins; D035683:MicroRNAs; D034741:RNA, Small Interfering; C519655:RDR2 protein, Arabidopsis; D012324:RNA-Dependent RNA Polymerase; D019951:DNA Polymerase beta