title: Characterization of silencing suppressor 2b of cucumber mosaic virus based on examination of its small RNA-binding abilities.
abstract: Double-stranded (ds) RNAs and imperfect hairpin RNAs of endogenous genes trigger post-transcriptional gene silencing (PTGS) and are cleaved by a Dicer-like nuclease into small interfering RNAs (siRNAs) and microRNs (miRNAs), respectively. Such small RNAs (siRNAs and miRNAs) then guide an RNA-induced silencing complex (RISC) for sequence-specific RNA degradation. While PTGS serves as an antiviral defense in plants, many plant viruses encode suppressors as a counter defense. Here we demonstrate that the PTGS suppressor (2b) of a severe strain (CM95R) of cucumber mosaic virus (CMV) can bind to in vitro synthesized siRNAs and even to long dsRNAs to a lesser extent. However, the 2b suppressor weakly bound to a miRNA (miR171) duplex in contrast to another small RNA-binding suppressor, p19 of tombusvirus that can effectively bind miRNAs. Because the 2b suppressor of an attenuated strain of CMV (CM95), which differs in a single amino acid from the 2b of CM95R, could barely bind siRNAs, we hypothesized that the weak suppressor activity of the attenuated strain resulted from a loss of the siRNA-binding property of 2b via a single amino acid change. Here we consider that 2b interferes with the PTGS pathway by directly binding siRNAs (or long dsRNA).
authors.affiliation: Cell Biology and Manipulation Laboratory, Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Goto
authors.forename: Takashi
authors.initials: T
authors.lastname: Kobori
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Kosaka
authors.forename: Tomohide
authors.initials: T
authors.lastname: Natsuaki
authors.forename: Chikara
authors.initials: C
authors.lastname: Masuta
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D017799:Cucumovirus / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant / Q000235:genetics; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D019697:Onions / Q000166:cytology / Q000235:genetics / Q000821:virology; D032306:Petunia / Q000166:cytology / Q000235:genetics / Q000821:virology; D030821:Plants, Genetically Modified; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D035683:MicroRNAs; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D014764:Viral Proteins