Nucleic Acids Research Advance Access originally published online on November 7, 2006
Nucleic Acids Research 2006 34(21):6233-6246; doi:10.1093/nar/gkl886
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Nucleic Acids Research, 2006, Vol. 34, No. 21 6233-6246
© 2006 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
Four plant Dicers mediate viral small RNA biogenesis and DNA virus induced silencing
1 Institute of Botany, University of Basel Schönbeinstrasse 6, 4056 Basel, Switzerland 2 Friedrich Miescher Institute for Biomedical Research Maulbeerstrasse 66, 4058 Basel, Switzerland 3 North Carolina State University Raleigh, NC 27695-7612, USA
*To whom correspondence should be addressed. Tel: +1 41 61 2672977; Fax: +1 41 61 2673504; Email: Mikhail.Pooggin{at}unibas.ch
Received September 18, 2006. Accepted October 9, 2006.
Like other eukaryotes, plants use DICER-LIKE (DCL) proteins as the central enzymes of RNA silencing, which regulates gene expression and mediates defense against viruses. But why do plants like Arabidopsis express four DCLs, a diversity unmatched by other kingdoms? Here we show that two nuclear DNA viruses (geminivirus CaLCuV and pararetrovirus CaMV) and a cytoplasmic RNA tobamovirus ORMV are differentially targeted by subsets of DCLs. DNA virus-derived small interfering RNAs (siRNAs) of specific size classes (21, 22 and 24 nt) are produced by all four DCLs, including DCL1, known to process microRNA precursors. Specifically, DCL1 generates 21 nt siRNAs from the CaMV leader region. In contrast, RNA virus infection is mainly affected by DCL4. While the four DCLs are partially redundant for CaLCuV-induced mRNA degradation, DCL4 in conjunction with RDR6 and HEN1 specifically facilitates extensive virus-induced silencing in new growth. Additionally, we show that CaMV infection impairs processing of endogenous RDR6-derived double-stranded RNA, while ORMV prevents HEN1-mediated methylation of small RNA duplexes, suggesting two novel viral strategies of silencing suppression. Our work highlights the complexity of virus interaction with host silencing pathways and suggests that DCL multiplicity helps mediate plant responses to diverse viral infections.
*Correspondence may also be addressed to Thomas Hohn. Tel: +1 41 61 6977266; Fax: +1 41 61 2673504; Email: hohn{at}fmi.ch
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