Cell‐to‐cell movement of Potato Potexvirus X is dependent on suppression of RNA silencing

Abstract

SummaryRNA silencing in transgenic and virus-infected plants involves a mobile silencing signal that can move cell-tocell and systemically through the plant. It is thought that this signal can influence long-distance movement of viruses because protein suppressors of silencing encoded in viral genomes are required for long-distance virus movement. However, until now, it was not known whether the mobile signal could also influence short-range virus movement between cells. Here, through random mutation analysis of the Potato Potexvirus X (PVX) silencing suppressor P25, we provide evidence that it does. All mutants that were defective for silencing suppression were also non-functional in viral cell-to-cell movement. However, we identified mutant P25 proteins that were functional as silencing suppressors but not as movement proteins and we conclude that suppression of silencing is not sufficient to allow virus movement between cells: there must be a second P25 function that is independent of silencing but also required for cell-to-cell movement. Consistent with this hypothesis, we identified two classes of suppressor-inactive P25 mutants. One class of these mutants is proposed to be functional for the accessory function because their failure to support PVX movement could be complemented by heterologous suppressors of silencing. The second class of P25 mutants is considered defective for both the suppressor and second functions because the heterologous silencing suppressors did not restore virus movement. It is possible, based on analyses of short interfering RNA accumulation, that P25 suppresses silencing by interfering with either assembly or function of the effector complexes of RNA silencing.

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

“…We introduced amino acid substitutions in the GKS/T motif of the NTPase/RNA helicase domain (Morozov and Solovyev, 2003) to generate TGBp1 AKT . In addition, based on the previously characterized mutation of PVX TGBp1, we constructed three other PlAMV-TGBp1 mutants; TGBp1 E82A is predicted to retain RNA silencing suppressor activity, while TGBp1 P110L and TGBp1 T192A are predicted to have lost the activity (Bayne et al, 2005). Agroinfiltration-mediated transient coexpression assays of GFP and TGBp1 mutants showed that TGBp1 E82A retained RNA silencing suppressor activity whereas TGBp1 AKT and TGBp1 P110L lost it ( Figure 3C).…”

ARGONAUTE2 Mediates RNA-Silencing Antiviral Defenses againstPotato virus Xin Arabidopsis

“…4A). PVX encodes three genes required for viral movement, known as the triple gene block (TGB), including P25, which also possesses VSR activity (Voinnet et al, 2000;Bayne et al, 2005). We expressed 12K with a version of PVX that expresses GFP but lacks the TGB (PVX-GFPDTGB), to determine whether the 12K protein could substitute for a lack of P25 as a VSR.…”

Experimental and bioinformatic evidence that raspberry leaf blotch emaravirus P4 is a movement protein of the 30K superfamily

“…As an alternative approach, we decided to examine whether the RLBV P4 protein could rescue the cell-to-cell movement of PVX expressing GFP but with an in-frame deletion within the TGB1 gene that prevents PVX cell-to-cell movement (Bayne et al, 2005).…”