Pattern-triggered immunity induced by dsRNA against plant viruses involves two distinct branches, one of which depends on Coronatine insensitive1 (COI1)

Abstract

Double-stranded RNA (dsRNA) is a conserved molecular signature of RNA virus generated during infection that can activate antiviral pattern-triggered immunity (PTI) in plants. However, the effectiveness of dsRNA-induced PTI against viruses from diverse taxa, its impact on different stages of the infection, as well as effectors used by viruses other than tobamoviruses to counteract this defense response remain poorly explored. Here, we established an Agrobacterium-mediated transient expression assay for inducing PTI through intracellular production of nonspecific dsRNA in Nicotiana benthamiana. Expression of nonspecific dsRNA restricted cell-to-cell movement and accumulation of three RNA viruses representing different taxonomic groups: Tobacco mosaic virus, Turnip mosaic virus, and Tobacco rattle virus. Co-expression of dsRNA together with a P25 movement protein (MP) mutant of Potato virus X (PVX) defective in RNA silencing suppression, prevented dsRNA-induced callose accumulation at plasmodesmata (PD) and restored efficient viral cell-to-cell movement. Interestingly, dsRNA also reduced viral RNA accumulation at the cellular level, revealing an impact of dsRNA-based PTI on virus replication independently of cell-to-cell movement. We further showed that the dsRNA-induced antiviral response required jasmonic acid (JA) signaling. Silencing of the JA receptor Coronatine insensitive1 (COI1) abolished dsRNA-induced PD callose deposition and the associated restriction of virus movement and accumulation. Accordingly, dsRNA-induced expression of defense-related genes was compromised in COI1-silenced plants. Next, we conducted RNA-seq analysis to identify early biological processes involved in COI1-dependent, dsRNA-induced immunity. The differential expression of 198 genes, some potentially involved in the regulation of callose accumulation, in COI1-silenced plants suggested that JA signaling contributes to shaping the transcriptional response to nonspecific dsRNA. Together, our findings establish nonspecific dsRNA-induced PTI as a multilayered antiviral response that restricts pathogen replication and cell-to-cell movement, and identify a heterologous MP, PVX P25, as an effector that counteracts the PD component of this defense response in a COI1-dependent manner.