The P1 Protein of Watermelon mosaic virus Compromises the Activity as RNA Silencing Suppressor of the P25 Protein of Cucurbit yellow stunting disorder virus.

Maria Luisa Domingo-Calap,Mariona Estapé,Juan José López-Moya,Ornela Chase,Ana Beatriz Moreno

doi:10.3389/fmicb.2021.645530

Abstract

Mixed viral infections in plants involving a potyvirus and other unrelated virus often result in synergistic effects, with significant increases in accumulation of the non-potyvirus partner, as in the case of melon plants infected by the potyvirus Watermelon mosaic virus (WMV) and the crinivirus Cucurbit yellow stunting disorder virus (CYSDV). To further explore the synergistic interaction between these two viruses, the activity of RNA silencing suppressors (RSSs) was addressed in transiently co-expressed combinations of heterologous viral products in Nicotiana benthamiana leaves. While the strong RSS activity of WMV Helper Component Proteinase (HCPro) was unaltered, including no evident additive effects observed when co-expressed with the weaker CYSDV P25, an unexpected negative effect of WMV P1 was found on the RSS activity of P25. Analysis of protein expression during the assays showed that the amount of P25 was not reduced when co-expressed with P1. The detrimental action of P1 on the activity of P25 was dose-dependent, and the subcellular localization of fluorescently labeled variants of P1 and P25 when transiently co-expressed showed coincidences both in nucleus and cytoplasm. Also, immunoprecipitation experiments showed interaction of tagged versions of the two proteins. This novel interaction, not previously described in other combinations of potyviruses and criniviruses, might play a role in modulating the complexities of the response to multiple viral infections in susceptible plants.

Highlights

The simultaneous presence of two unrelated viruses in mixedinfected plants can lead to different outcomes, including synergisms, antagonisms, and neutral interactions (Syller, 2012; Syller and Grupa, 2016; Moreno and López-Moya, 2020)
Since P1 and HCpro are naturally expressed in cis as part of a larger polyprotein, the construct P1-Helper Component Proteinase (HCPro) with the two gene products in cis was tested, showing again a strong RNA silencing suppressors (RSSs) activity, indistinguishable of the activity exhibited by the Watermelon mosaic virus (WMV) HCPro alone (Figure 1B)
Our recent analysis of melon plants co-infected by WMV and Cucurbit yellow stunting disorder virus (CYSDV) revealed a complex scenario, with dynamic changes along the progress of the infections, that could even affect the transmissibility of the viruses by their insect vectors: briefly, the initial synergism and boost of CYSDV accumulation was later moderated and accompanied by a sort of recovery phenotype (Domingo-Calap et al, 2020)

Summary

Introduction

The simultaneous presence of two unrelated viruses in mixedinfected plants can lead to different outcomes, including synergisms, antagonisms, and neutral interactions (Syller, 2012; Syller and Grupa, 2016; Moreno and López-Moya, 2020). One remarkable exception to the potyvirus-assisted synergistic interactions was reported in sweet potato crops, where the potyvirus partners were benefited in co-infections with the crinivirus Sweet potato chlorotic stunt virus (SPCSV; Tairo et al, 2005; Untiveros et al, 2007; Clark et al, 2012). For this exception, a gene product different of HCPro, the P1N-PISPO, was associated to RSS activity in the potyvirus Sweet potato feathery mottle virus (SPFMV; Mingot et al, 2016; Untiveros et al, 2016)

Methods

Results

Conclusion