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Updated: Jun 30, 2026

Virus-induced Gene Silencing (VIGS) in Nicotiana benthamiana and Tomato
Published on: June 10, 2009
The CaMV transactivator/viroplasmin interferes with RDR6-dependent trans-acting and secondary siRNA pathways in
Padubidri V Shivaprasad1, Rajendran Rajeswaran, Todd Blevins
1Institute of Botany, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland.
Abstract:
Several RNA silencing pathways in plants restrict viral infections and are suppressed by distinct viral proteins. Here we show that the endogenous trans-acting (ta)siRNA pathway, which depends on Dicer-like (DCL) 4 and RNA-dependent RNA polymerase (RDR) 6, is suppressed by infection of Arabidopsis with Cauliflower mosaic virus (CaMV). This effect was associated with overaccumulation of unprocessed, RDR6-dependent precursors of tasiRNAs and is due solely to expression of the CaMV transactivator/viroplasmin (TAV) protein. TAV expression also impaired secondary, but not primary, siRNA production from a silenced transgene and increased accumulation of mRNAs normally silenced by the four known tasiRNA families and RDR6-dependent secondary siRNAs. Moreover, TAV expression upregulated DCL4, DRB4 and AGO7 that mediate tasiRNA biogenesis. Our findings suggest that TAV is a general inhibitor of silencing amplification that impairs DCL4-mediated processing of RDR6-dependent double-stranded RNA to siRNAs. The resulting deficiency in tasiRNAs and other RDR6-/DCL4-dependent siRNAs appears to trigger a feedback mechanism that compensates for the inhibitory effects.
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