Double-stranded RNA does more than trigger plant defence
In his doctoral thesis at SLU, Aimer Gutiérrez-Díaz shows that the RNA-based defence mechanisms plants use against viruses influence plant fertility, virus transmission and the behavior of viral proteins inside cells. His findings reveal that double-stranded RNA is more than a simple alarm signal during infection.
A molecular warning with several roles
Viruses often produce double-stranded RNA, or dsRNA, when they multiply. Plants recognise it and cut it into short pieces that guide RNA silencing, a defence system that targets matching viral RNA. This mechanism is attracting interest for RNA-based biopesticides, which could target specific pests and pathogens while reducing the use of broad chemical treatments. But dsRNA also has other roles in infected cells that are less well understood. dsRNA is usually presented as a warning sign that activates defence and Aimer's results show that it can also change the behaviour of viral proteins inside the plant cell.
Reaching the next generation
To understand how RNA silencing affects reproduction, the thesis compares six viruses infecting Arabidopsis plants with an intact defence system, and in plants lacking three Dicer-like proteins that help cut viral dsRNA. The study followed the infection beyond the leaves, into flowering shoots and seed production.
Turnip mosaic virus (TuMV) was especially useful as a visible test case. Using TuMV viral constructs carrying a gene for green fluorescent protein (GFP) that makes infected tissues glow under ultraviolet light, the team could follow the spread of the virus through the plant (See image below). They also studied HC-Pro, a viral protein that blocks RNA silencing. When the plant's RNA-silencing defence was genetically weakened, even TuMV lacking HC-Pro could spread through the plant. As with most of the viruses studied, wild-type TuMV then prevented normal development of the flowering shoots and no seeds were produced.
Turnip rosette virus (TRoV) was an important exception. Despite infecting plants in the same weakened defence background, TRoV-infected plants still produced viable seeds. TRoV was also detected more frequently in the next generation than in plants with intact RNA silencing. The results show that a virus cannot be judged only by how much it accumulates. To be inherited through seeds, it must reach reproductive tissues without eliminating the plant's ability to produce offspring.
The second study focused on P6, a multifunctional protein from Cauliflower mosaic virus. P6 was already known to interact with TOR, a plant regulator of protein production, and to bind dsRNA. What remained unclear was how P6 coordinates these interactions. A combined approach using structural predictions (figure 2) and experiments with P6 mutants points to a disordered region that favours nucleic-acid interactions and the transition from a soluble form into less soluble viroplasm-associated states. Viroplasms are viral factories where viral components are concentrated and new virus particles are assembled. This transition may redirect P6 from stimulating viral protein production towards supporting virus formation within viroplasms.
Towards more informed RNA-based crop protection
Aimer's findings do not make dsRNA-based crop protection less promising. Instead, they show why it is important to understand the wider effects of dsRNA. Evaluating an RNA treatment, it may not be enough to ask whether the target RNA decreases. Effects on plant growth, reproduction, virus transmission and viral proteins that interact with dsRNA may also matter. Understanding these layers can support the design of more reliable and precise crop-protection tools.
Read more
The thesis findings can be explored through an interactive website, where the main experiments and conclusions are presented in an accessible visual format. The website offers a closer look at how RNA silencing affects plant reproduction and virus inheritance, and how dsRNA changes the behaviour of the CaMV protein P6.
Read the thesis:
Aimer Gutiérrez-Díaz is a PhD student at the Plant Biology Department, BioCenter, Ultuna. He will defend his doctoral thesis on 2 October at 12:30 in Lennart-Kennes hall at SLU in Uppsala.
Read more about the event