Distinct Effects of p19 RNA Silencing Suppressor on Small RNA Mediated Pathways in Plants

Abstract

RNA silencing is one of the main defense mechanisms employed by plants to fight viruses. In change, viruses have evolved silencing suppressor proteins to neutralize antiviral silencing. Since the endogenous and antiviral functions of RNA silencing pathway rely on common components, it was suggested that viral suppressors interfere with endogenous silencing pathway contributing to viral symptom development. In this work, we aimed to understand the effects of the tombusviral p19 suppressor on endogenous and antiviral silencing during genuine virus infection. We showed that ectopically expressed p19 sequesters endogenous small RNAs (sRNAs) in the absence, but not in the presence of virus infection. Our presented data question the generalized model in which the sequestration of endogenous sRNAs by the viral suppressor contributes to the viral symptom development. We further showed that p19 preferentially binds the perfectly paired ds-viral small interfering RNAs (vsiRNAs) but does not select based on their sequence or the type of the 5’ nucleotide. Finally, co-immunoprecipitation of sRNAs with AGO1 or AGO2 from virus-infected plants revealed that p19 specifically impairs vsiRNA loading into AGO1 but not AGO2. Our findings, coupled with the fact that p19-expressing wild type Cymbidium ringspot virus (CymRSV) overcomes the Nicotiana benthamiana silencing based defense killing the host, suggest that AGO1 is the main effector of antiviral silencing in this host-virus combination.

Biochemical and genetic functional dissection of the P38 viral suppressor of RNA silencing

“…Further technical refinement beyond the BYL-based RISC loading, dsRNA processing and binding assays should not only provide novel insights into the molecular activities of VSRs but also help uncover the VSR-targeted molecular mechanisms underlying (antiviral) RNA silencing pathways. Ultimately, however, findings made in vitro or upon transgenic VSR expression in isolation of the virus should be pondered in the context of authentic infections, which are likely to provide a much more complex and accurate view of VSR function and their effects in planta, as recently shown in unraveling studies of the Hc-Pro and P19 proteins during real infections (Garcia-Ruiz et al 2015;Kontra et al 2016).…”

Cross-Talk in Viral Defense Signaling in Plants

“…As genome analysis techniques are developed, understanding of plant–virus interactions increases. Kontra et al (2016) recently reported that the tombusviral P19 suppressor preferentially affects virus-derived small interfering RNAs rather than endogenous host miRNAs in virus-infected plants. The authors suggested that the relationship between VSRs and host RNA silencing, as well as their contribution to the virulence of viruses, should be reconsidered.…”

Antiviral Functions of ARGONAUTE Proteins During Turnip Crinkle Virus Infection Revealed by Image-based Trait Analysis in Arabidopsis

“…The Arabidopsis thaliana ( Arabidopsis ) genome encodes ten AGO proteins, several of which have demonstrated antiviral roles [16]. AGO1 [14, 17–19] and AGO2 [15, 20–22] have been identified as prominent antiviral AGOs against several RNA viruses, while other AGOs, including AGO5, AGO7, and AGO10, have limited antiviral roles in some cases [14, 15]. For DNA viruses, AGO4 is the main effector protein in the antiviral silencing machinery [23, 24].…”