title: PolIVb influences RNA-directed DNA methylation independently of its role in siRNA biogenesis.
abstract: DNA-dependent RNA polymerase (Pol)IV in Arabidopsis exists in two isoforms (PolIVa and PolIVb), with NRPD1a and NRPD1b as their respective largest subunits. Both isoforms are implicated in production and activity of siRNAs and in RNA-directed DNA methylation (RdDM). Deep sequence analysis of siRNAs in WT Arabidopsis flowers and in nrpd1a and nrpd1b mutants identified >4,200 loci producing siRNAs in a PolIV-dependent manner, with PolIVb reinforcing siRNA production by PolIVa. Transposable element identity and pericentromeric localization are both features that predispose a locus for siRNA production via PolIV proteins and determine the extent to which siRNA production relies on PolIVb. Detailed analysis of DNA methylation at PolIV-dependent loci revealed unexpected deviations from the previously noted association of PolIVb-dependent siRNA production and RdDM. Notably, PolIVb functions independently in DNA methylation and siRNA generation. Additionally, we have uncovered siRNA-directed loss of DNA methylation, a process requiring both PolIV isoforms. From these findings, we infer that the role of PolIVb in siRNA production is secondary to a role in chromatin modification and is influenced by chromatin context.
authors.affiliation: Sainsbury Laboratory, Norwich NR4 7UH, United Kingdom.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Mosher
authors.forename: Frank
authors.initials: F
authors.lastname: Schwach
authors.forename: David
authors.initials: D
authors.lastname: Studholme
authors.forename: David C
authors.initials: DC
authors.lastname: Baulcombe
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D015152:Blotting, Northern; D042002:Chromatin Assembly and Disassembly / Q000502:physiology; D019175:DNA Methylation; D012321:DNA-Directed RNA Polymerases / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D021122:Protein Subunits / Q000235:genetics; D034741:RNA, Small Interfering / Q000096:biosynthesis* / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D029681:Arabidopsis Proteins; D021122:Protein Subunits; D034741:RNA, Small Interfering; C499181:RNA polymerase IV, Arabidopsis; D012321:DNA-Directed RNA Polymerases