Journal Article

The Mechanism Selecting the Guide Strand from Small RNA Duplexes is Different Among <i>Argonaute</i> Proteins

Atsushi Takeda, Shintaro Iwasaki, Toshiaki Watanabe, Maki Utsumi and Yuichiro Watanabe

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 49, issue 4, pages 493-500
Published in print April 2008 | ISSN: 0032-0781
Published online April 2008 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcn043
The Mechanism Selecting the Guide Strand from Small RNA Duplexes is Different Among Argonaute Proteins

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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Double-stranded RNA induces RNA silencing and is cleaved into 21–24 nt small RNA duplexes by Dicer enzyme. A strand of Dicer-generated small RNA duplex (called the guide strand) is then selected by a thermodynamic mechanism to associate with Argonaute (AGO) protein. This AGO–small RNA complex functions to cleave mRNA, repress translation or modify chromatin structure in a sequence-specific manner. Although a model plant, Arabidopsis thaliana, contains 10 AGO genes, their roles and molecular mechanisms remain obscure. In this study, we analyzed the roles of Arabidopsis AGO2 and AGO5. Interestingly, the 5′ nucleotide of small RNAs that associated with AGO2 was mainly adenine (85.7%) and that with AGO5 was mainly cytosine (83.5%). Small RNAs that were abundantly cloned from the AGO2 immunoprecipitation fraction (miR163-LL, which is derived from the Lower Left of mature miR163 in pre-miR163, and miR390) and from the AGO5 immunoprecipitation fraction (miR163-UL, which is derived from the Upper Left of mature miR163 in pre-miR163, and miR390*) are derived from the single small RNA duplexes, miR163-LL/miR163-UL and miR390/miR390*. Each strand of the miR163-LL/miR163-UL duplex is selectively sorted to associate with AGO2 or AGO5 in a 5′ nucleotide-dependent manner rather than in a thermodynamic stability-dependent manner. Furthermore, we showed that both AGO2 and AGO5 have the ability to bind cucumber mosaic virus-derived small RNAs. These results clearly indicate that the mechanism selecting the guide strand is different among AGO proteins and that multiple AGO genes are involved in anti-virus defense in plants.

Keywords: Arabidopsis; Argonaute (AGO); Cucumber mosaic virus (CMV); MicroRNA (miRNA); 5′ Nucleotide of small RNA; RNA silencing

Journal Article.  3790 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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