Primary and secondary siRNAs in geminivirus-induced gene silencing

Aregger, M. and Borah, B. K. and Seguin, J. and Rajeswaran, R. and Gubaeva, E. G. and Zvereva, A. S. and Windels, D. and Vazquez, F. and Blevins, T. and Farinelli, L. and Pooggin, M. M.. (2012) Primary and secondary siRNAs in geminivirus-induced gene silencing. PLoS Pathogens, Vol. 8, H. 9 , e1002941.

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Official URL: http://edoc.unibas.ch/dok/A6070621

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In plants, RNA silencing-based antiviral defense is mediated by Dicer-like (DCL) proteins producing short interfering (si)RNAs. In Arabidopsis infected with the bipartite circular DNA geminivirus Cabbage leaf curl virus (CaLCuV), four distinct DCLs produce 21, 22 and 24 nt viral siRNAs. Using deep sequencing and blot hybridization, we found that viral siRNAs of each size-class densely cover the entire viral genome sequences in both polarities, but highly abundant siRNAs correspond primarily to the leftward and rightward transcription units. Double-stranded RNA precursors of viral siRNAs can potentially be generated by host RDR-dependent RNA polymerase (RDR). However, genetic evidence revealed that CaLCuV siRNA biogenesis does not require RDR1, RDR2, or RDR6. By contrast, CaLCuV derivatives engineered to target 30 nt sequences of a GFP transgene by primary viral siRNAs trigger RDR6-dependent production of secondary siRNAs. Viral siRNAs targeting upstream of the GFP stop codon induce secondary siRNAs almost exclusively from sequences downstream of the target site. Conversely, viral siRNAs targeting the GFP 3'-untranslated region (UTR) induce secondary siRNAs mostly upstream of the target site. RDR6-dependent siRNA production is not necessary for robust GFP silencing, except when viral siRNAs targeted GFP 5'-UTR. Furthermore, viral siRNAs targeting the transgene enhancer region cause GFP silencing without secondary siRNA production. We conclude that the majority of viral siRNAs accumulating during geminiviral infection are RDR1/2/6-independent primary siRNAs. Double-stranded RNA precursors of these siRNAs are likely generated by bidirectional readthrough transcription of circular viral DNA by RNA polymerase II. Unlike transgenic mRNA, geminiviral mRNAs appear to be poor templates for RDR-dependent production of secondary siRNAs.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Ehemalige Einheiten Umweltwissenschaften > Pflanzenphysiologie Pathogenabwehr (Boller)
UniBasel Contributors:Borah, Basanta Kumar and Rajeswaran, Rajendran and Gubaeva, Ekaterina and Zvereva, Anna and Pooggin, Mikhail and Windels, David and Vazquez, Franck and Seguin, Jonathan
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:Public Library of Science
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:13 Oct 2017 07:46
Deposited On:01 Mar 2013 11:07

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