Plant and Cell Physiology Advance Access published online on June 13, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm074
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Characterization of silencing suppressor 2b of Cucumber mosaic virus based on examination of its small RNA-binding abilities
1 Cell Biology and Manipulation Laboratory, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
2 Kyoto Prefectural Institute of Agricultural Biotechnology, Kyoto 619-0244, Japan
3 Laboratory of Plant Pathology, Faculty of Agriculture, Utsunomiya University, Utsunomiya 321-8505, Japan
Corresponding author: Chikara Masuta. Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo, 060-8589. Telephone number; 81-11-706-2807, FAX: 81-11-706-2483, E-mail: masuta{at}res.agr.hokudai.ac.jp
| Abstract |
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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 siRNAs and 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 CMV95R, could barely bind siRNAs, we hypothesized that the weak suppressor activity of the attenuated strain resulted from a loss in 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).
Keywords: Cucumber mosaic virus - PTGS - siRNA - viral suppressor
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