RNA-Dependent RNA Polymerase 1 from Nicotiana tabacum Suppresses RNA Silencing and Enhances Viral Infection in Nicotiana benthamiana

Apr 20, 2010The Plant cell

A tobacco plant enzyme blocks RNA defense and helps virus infection in a related plant

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Abstract

Nicotiana benthamiana transformed with RDR1 from Nicotiana tabacum shows hypersusceptibility to Plum pox potyvirus and other viruses.

RDR6 is necessary for posttranscriptional gene silencing and antiviral silencing in plants.
RDR1 is involved in antiviral defense but may not trigger silencing in the same way as RDR6.
Nt-RDR1 exhibits silencing suppression activity that resembles RDR6-silenced plants.
Nt-RDR1 does not affect the accumulation of RDR6-dependent small interfering RNAs but suppresses RDR6-mediated silencing.
RDR1 may play a dual role in antiviral defense, contributing to salicylic acid-mediated defense while suppressing RDR6 activity.

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Endogenous eukaryotic RNA-dependent RNA polymerases (RDRs) produce double-stranded RNA intermediates in diverse processes of small RNA synthesis in RNA silencing pathways. RDR6 is required in plants for posttranscriptional gene silencing induced by sense transgenes (S-PTGS) and has an important role in amplification of antiviral silencing. Whereas RDR1 is also involved in antiviral defense in plants, this does not necessarily proceed through triggering silencing. In this study, we show that Nicotiana benthamiana transformed with RDR1 from Nicotiana tabacum (Nt-RDR1 plants) exhibits hypersusceptibility to Plum pox potyvirus and other viruses, resembling RDR6-silenced (RDR6i) N. benthamiana. Analysis of transient induction of RNA silencing in N. benthamiana Nt-RDR1 and RDR6i plants revealed that Nt-RDR1 possesses silencing suppression activity. We found that Nt-RDR1 does not interfere with RDR6-dependent siRNA accumulation but turns out to suppress RDR6-dependent S-PTGS. Our results, together with previously published data, suggest that RDR1 might have a dual role, contributing, on one hand, to salicylic acid-mediated antiviral defense, and suppressing, on the other hand, the RDR6-mediated antiviral RNA silencing. We propose a scenario in which the natural loss-of-function variant of RDR1 in N. benthamiana may be the outcome of selective pressure to maintain a high RDR6-dependent antiviral defense, which would be required to face the hypersensitivity of this plant to a large number of viruses.

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RNA-Dependent RNA Polymerase 1 from Nicotiana tabacum Suppresses RNA Silencing and Enhances Viral Infection in Nicotiana benthamiana

Abstract

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