Trigger and Suppression of Antiviral Defenses by Grapevine Pinot Gris Virus (GPGV): Novel Insights into Virus-Host Interaction

Abstract

Grapevine Pinot gris virus (GPGV) is an emerging trichovirus that has been putatively associated with a novel grapevine disease known as grapevine leaf mottling and deformation (GLMD). Yet the role of GPGV in GLMD disease is poorly understood since it has been detected both in symptomatic and symptomless grapevines. We exploited a recently constructed GPGV infectious clone (pRI::GPGV-vir) to induce an antiviral response in Nicotiana benthamiana plants. In silico prediction of virus-derived small interfering RNAs (vsiRNAs) and gene expression analyses revealed the involvement of DCL4, AGO5 and RDR6 genes during GPGV infection, suggesting the activation of the post-transcriptional gene-silencing (PTGS) pathway as a plant antiviral defense. PTGS suppression assays in transgenic N. benthamiana 16c plants revealed the ability of the GPGV coat protein to suppress RNA silencing. This work provides novel insights on the interaction between GPGV and its host, revealing the ability of the virus to trigger and suppress antiviral RNA silencing.

The conundrum of the connection of grapevine Pinot gris virus with the grapevine leaf mottling and deformation syndrome

“…This observation prompted investigations into the onset of recovery in GPGV‐infected plants in relation to the activation of antiviral RNA silencing involved in GPGV infection. Hence, when in a subsequent study an infectious clone of GPGV (pRI::GPGV‐vir) was inoculated in wild‐type and transgenic (16c line) N. benthamiana plants, in silico prediction of virus‐derived small interfering RNAs (vsiRNAs) and gene expression analyses revealed the involvement of Dicer‐like 4 ( DCL4 ), Argonaute protein 5 ( AGO5 ) and RNA‐dependent RNA polymerase 6 ( RDR6 ) genes during GPGV infection, suggesting the activation of the posttranscriptional gene‐silencing (PTGS) pathway as a plant antiviral defence (Tarquini, Pagliari, et al, 2021). Thus, the observed attenuation or disappearance of disease symptoms in GPGV‐infected grapevines may be explained by the well‐established association between the activation of the PTGS pathway and the onset of symptom recovery (Ghoshal & Sanfaçon, 2015; Kørner et al, 2018; Križnik et al, 2020; Smith et al, 2011).…”

“…Indeed, Tarquini, Pagliari, et al (2021) demonstrated the ability of GPGV to suppress the antiviral PTGS in transgenic (16c line) N . benthamiana plants by assessing the expression level of green fluorescent protein (GFP) in 16c plants and by quantifying GFP ‐derived small interfering RNAs (siRNAs) using stem‐loop primers.…”

“…One scenario supported by current evidence for the progression of molecular events mediating GPGV–host interaction includes the production of GPGV‐derived siRNAs directly within the lumen of the altered ER. Here, dsRNA precursors would be produced during virus replication, with subsequent prompt recruitment by AGO5 in the same location (Pagliari et al, 2021; Tarquini, Pagliari, et al, 2021).…”

“…During this time, plants may not perceive the presence of the virus or the onset of infection, and this averts the activation of antiviral defence (Laliberté & Sanfaçon, 2010; Miller & Krijnse‐Locker, 2008). When GPGV particles are released into the cytosol, following disruption of the ER membranes, the plants trigger antiviral RNA silencing, which involves the activation of AGO5 at the rough ER, and thus determines the onset of recovery (Tarquini, Pagliari, et al, 2021).…”

“…Hence, it was speculated that some factors may inhibit the activation of antiviral RNA silencing machinery, which allows maintenance of high levels of viral titre and severe disease effects (Bertazzon et al, 2017(Bertazzon et al, , 2020. Indeed, Tarquini, Pagliari, et al (2021) demonstrated the ability of GPGV to suppress the antiviral PTGS in transgenic (16c line) N. benthamiana plants by assessing the expression level of green fluorescent protein (GFP) in 16c plants and by quantifying GFP-derived small interfering RNAs (siRNAs) using stem-loop primers. Low transcriptional levels of GFP mRNA combined with high levels of GFP-derived siRNA clearly demonstrated that the GPGV CP can suppress antiviral host defence, behaving as a viral suppressor of RNA silencing (VSR) (Tarquini, Pagliari, et al, 2021).…”