HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: rna.541307v1 13/8/1268    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Moissiard, G. Articles by Voinnet, O. Search for Related Content PubMed PubMed Citation Articles by Moissiard, G. Articles by Voinnet, O. Social Bookmarking                   What's this?

Transitivity in Arabidopsis can be primed, requires the redundant action of the antiviral Dicer-like 4 and Dicer-like 2, and is compromised by viral-encoded suppressor proteins

Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, 67084 Strasbourg Cedex, France

In plants, worms, and fungi, RNA-dependent RNA polymerases (RDRs) amplify the production of short-interfering RNAs (siRNAs) that mediate RNA silencing. In Arabidopsis, RDR6 is thought to copy endogenous and exogenous RNA templates into double-stranded RNAs (dsRNAs), which are subsequently processed into siRNAs by one or several of the four Dicer-like enzymes (DCL14). This reaction produces secondary siRNAs corresponding to sequences outside the primary targeted regions of a transcript, a phenomenon called transitivity. One recognized role of RDR6 is to strengthen the RNA silencing response mounted by plants against viruses. Accordingly, suppressor proteins deployed by viruses inhibit this defense. However, interactions between silencing suppressors and RDR6 have not yet been documented. Additionally, the mechanism underlying transitivity remains poorly understood. Here, we report how several viral silencing suppressors inhibit the RDR6-dependent amplification of virus-induced and transgene-induced gene silencing. Viral suppression of primary siRNA accumulation shows that transitivity can be initiated with minute amounts of DCL4-dependent 21-nucleotide (nt)-long siRNAs, whereas DCL3-dependent 24-nt siRNAs appear dispensable for this process. We further show that unidirectional (35') transitivity requires the hierarchical and redundant functions of DCL4 and DCL2 acting downstream from RDR6 to produce 21- and 22-nt-long siRNAs, respectively. The 35' transitive reaction is likely to be processive over >750 nt, with secondary siRNA production progressively decreasing as the reaction proceeds toward the 5'-proximal region of target transcripts. Finally, we show that target cleavage by a primary small RNA and 35' transitivity can be genetically uncoupled, and we provide in vivo evidence supporting a key role for priming in this specific reaction.

Keywords: Dicer; RNA-dependent RNA polymerase; transitivity; siRNA; viral suppressors

CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				E. M. Tretter, J. P. Alvarez, Y. Eshed, and J. L. Bowman Activity Range of Arabidopsis Small RNAs Derived from Different Biogenesis Pathways Plant Physiology, May 1, 2008; 147(1): 58 - 62. [Full Text] [PDF]

				H. B. Scholthof Heterologous Expression of Viral RNA Interference Suppressors: RISC Management Plant Physiology, December 1, 2007; 145(4): 1110 - 1117. [Full Text] [PDF]

				T. Csorba, A. Bovi, T. Dalmay, and J. Burgyan The p122 Subunit of Tobacco Mosaic Virus Replicase Is a Potent Silencing Suppressor and Compromises both Small Interfering RNA- and MicroRNA-Mediated Pathways J. Virol., November 1, 2007; 81(21): 11768 - 11780. [Abstract] [Full Text] [PDF]