Viral RNA signature triggers two layers of plant antiviral defense

What the study found

In a bioRxiv preprint, the authors describe an assay that used Agrobacterium to produce nonspecific double-stranded RNA (dsRNA) inside plant cells. They report that this reduced the accumulation and cell-to-cell movement of three RNA viruses from different taxonomic groups: Tobacco mosaic virus, Turnip mosaic virus and Tobacco rattle virus.

The researchers also found reduced viral RNA accumulation within individual cells, which they interpret as an effect on replication independent of movement between cells. At connections between cells called plasmodesmata, dsRNA induced deposits of callose, a plant material associated with restricted viral movement.

When the team silenced COI1, a receptor involved in jasmonic acid signaling, the callose response and associated restrictions on viral movement and accumulation were lost. A mutant of the Potato virus X movement protein P25 also prevented the callose buildup and restored efficient viral movement, despite being defective in suppression of RNA silencing.

Why it matters

The findings suggest that recognition of a shared viral RNA signature can engage more than one antiviral defense. The authors' RNA-sequencing analysis identified 198 differentially expressed genes in COI1-silenced plants, suggesting that jasmonic acid signaling helps shape the response to dsRNA. The P25 result also points to a viral protein that can counter the defense at plasmodesmata.

Limits and unknowns

This is a preprint, and the account is based on its abstract. The abstract does not provide sample sizes, effect sizes, detailed experimental conditions or the full gene list. The work used a model plant and an experimental dsRNA-expression assay; the abstract does not establish whether the same responses occur across crop species or under field conditions.