title: Unique functionality of 22-nt miRNAs in triggering RDR6-dependent siRNA biogenesis from target transcripts in Arabidopsis.
abstract: RNA interference pathways can involve amplification of secondary siRNAs by RNA-dependent RNA polymerases. In plants, RDR6-dependent secondary siRNAs arise from transcripts targeted by some microRNAs (miRNAs). Here, Arabidopsis thaliana secondary siRNAs from mRNA as well as trans-acting siRNAs are shown to be triggered through initial targeting by a 22-nucleotide (nt) miRNA that associates with AGO1. In contrast to canonical 21-nt miRNAs, 22-nt miRNAs primarily arise from foldback precursors containing asymmetric bulges. Using artificial miRNA constructs, conversion of asymmetric foldbacks to symmetric foldbacks resulted in the production of 21-nt forms of miR173, miR472 and miR828. Both 21- and 22-nt forms associated with AGO1 and guided accurate slicer activity, but only 22-nt forms were competent to trigger RDR6-dependent siRNA production from target RNA. These data suggest that AGO1 functions differentially with 21- and 22-nt miRNAs to engage the RDR6-associated amplification apparatus.
authors.affiliation: Molecular and Cellular Biology Program, Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, USA.
authors.forename: Josh T
authors.initials: JT
authors.lastname: Cuperus
authors.forename: Alberto
authors.initials: A
authors.lastname: Carbonell
authors.forename: Noah
authors.initials: N
authors.lastname: Fahlgren
authors.forename: Hernan
authors.initials: H
authors.lastname: Garcia-Ruiz
authors.forename: Russell T
authors.initials: RT
authors.lastname: Burke
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takeda
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Sullivan
authors.forename: Sunny D
authors.initials: SD
authors.lastname: Gilbert
authors.forename: Taiowa A
authors.initials: TA
authors.lastname: Montgomery
authors.forename: James C
authors.initials: JC
authors.lastname: Carrington
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001483:Base Sequence; D018506:Gene Expression Regulation, Plant; D035683:MicroRNAs / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D035683:MicroRNAs; D009711:Nucleotides; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C514575:RDR6 protein, Arabidopsis; D012324:RNA-Dependent RNA Polymerase