The silencing suppressor P25 of Potato virus X interacts with Argonaute1 and mediates its degradation through the proteasome pathway

Abstract

Previous evidence has indicated that the P25 protein encoded by Potato virus X (PVX) inhibits either the assembly or function of the effector complexes in the RNA silencing-based antiviral defence system (Bayne et al., Cell-to-cell movement of Potato Potexvirus X is dependent on suppression of RNA silencing. Plant J.44, 471-482). This finding prompted us to investigate the possibility that P25 targets the Argonaute (AGO) effector nuclease of RNA silencing. Co-immunoprecipitation and Western blot analysis indicated that there is a strong interaction between P25 and AGO1 of Arabidopsis when these proteins are transiently co-expressed in Nicotiana benthamiana. P25 also interacts with AGO1, AGO2, AGO3 and AGO4, but not with AGO5 and AGO9. As an effective suppressor, the amount of AGO1 accumulated in the presence of P25 was dramatically lower than that infiltrated with HcPro, but was restored when treated with a proteasome inhibitor MG132. These findings are consistent with the idea that RNA silencing is an antiviral defence mechanism and that the counter-defence role of P25 is through the degradation of AGO proteins via the proteasome pathway. Further support for this idea is provided by the observation that plants treated with MG132 are less susceptible to PVX and its relative Bamboo mosaic virus.

ARGONAUTE2 Mediates RNA-Silencing Antiviral Defenses againstPotato virus Xin Arabidopsis

“…However, attempts to coimmunoprecipitate multiple AGO proteins with 12K and 16K did not reveal any interactions (data not shown). Recently, it was reported that the PVX P25 protein is able to interact with AGO1, AGO2, AGO3, and AGO4, as well as destabilizing AGO1 (Chiu et al, 2010). Using comparable methodology, we are similarly unable to detect interactions between P25 and a number of AGO proteins, including Arabidopsis and tobacco AGO2 (data not shown).…”

In Planta Recognition of a Double-Stranded RNA Synthesis Protein Complex by a Potexviral RNA Silencing Suppressor

“…A recent study suggested that PVX-TGBp1 interacts with AGO1 and leads to its degradation via a proteasome-dependent pathway (Chiu et al, 2010). Although we have not investigated whether PlAMV-TGBp1 interacts with AGO1, we showed that the TAS2 primary transcript was normally cleaved in the PlAMVTGBp1 transformants ( Figure 2B, lanes 3 to 5; Supplemental Figure 2), suggesting that PlAMV-TGBp1 does not significantly inhibit the slicing activity of AGO1.…”

Functional and Genetic Analysis Identify a Role for Arabidopsis ARGONAUTE5 in Antiviral RNA Silencing

“…A previous study has shown that PVX P25 may counteract RNA silencing by destabilizing AGO1 (Chiu et al, 2010). To better understand the importance of P25 in the modulation of RNA silencing efficiency, we monitored AGO protein accumulation in the presence of P25.…”

“…Although the PVX VSR, P25, destabilizes Arabidopsis AGO1, this virus does not normally systemically infect Arabidopsis Columbia-0 (Col-0) (Chiu et al, 2010;Jaubert et al, 2011). However, PVX can effectively infect Arabidopsis if a VSR is supplied in trans from a second virus or if RNA silencing is attenuated by mutation of DCL-encoding genes or AGO2 Andika et al, 2015).…”