Crop Protection: RNA-based substances open new means to combat widespread plant viruses

The new RNA-based active agent ensures that plants protect against cucumber mosaic virus (CMV), the most common virus in agriculture and horticulture. They were developed by researchers at Halle Wittenberg (MLU) at Martin Luther University.

Active ingredients have broad spectral effects. A set of RNA molecules supports the plant’s immune system in the fight against viruses. In laboratory experiments, 80-100% of treated plants survived high viral infectious diseases, as reported by the team in their nucleic acid studies.

Their paper has been selected by the journal as a “groundbreaking article.” Researchers are currently working on shifting ideas from labs to practice.

Cucumber mosaic viruses are particularly devastating viruses for crops. Approximately 90 aphids transmit the virus, affecting over 1,200 plant species. These include numerous crops such as squash, cucumbers, grains, medicinal and aromatic plants. Infected plants are easily identified by their distinctive mosaic patterns of leaves.

Once infected, the plants cannot flourish and the fruits cannot be sold. To date, no approved agents exist for the CMV. However, new work by MLU researchers could provide a long-term solution. The basic idea is to fight the virus by pointing the plant’s natural defenses in the right direction.

When a virus infects a plant, it uses the plant’s cells as its host. Viruses grow through their genetic material in the form of ribonucleic acid (RNA) molecules in plant cells. When injected, these foreign RNA molecules trigger an initial response from the plant’s immune system. Special enzyme scissors recognize and cleave viral RNA molecules.

This process spreads throughout the plant and produces small interfering RNAs (siRNAs) that trigger the second step of the immune response. siRNA molecules bind to special protein complexes and lead to viral RNA molecules. Going there, the proteins begin to degrade harmful RNA molecules of the virus by converting them into harmless, degradable fragments.

“In general, this defense process is not very effective. Viral infections produce many different siRNA molecules, but only a few have protective effects,” says Professor Sven-Erik Behrens of the Institute for Biochemistry and Biotechnology at MLU. His team developed a method to identify highly efficient siRNA molecules along the way.

In a more important step, some of these siRNA molecules could be combined into so-called efficient double-stranded RNA molecules (edsRNAs). This is especially suitable for use in plants. These edsrnas act as a kind of “package” that is degraded into sirnas immediately after they enter plant cells. In this way, a large number of highly effective siRNA molecules can exert protective antiviral effects in the spot.

The team conducted numerous laboratory experiments at the model plant Nicotania Benthamiana, and was able to demonstrate that Edsluna-based active agents ensured protection from cucumber mosaic virus.

“The plants in our experiments were infected with very high viral loads. All of our untreated plants died,” explains Behrens.

In contrast, 80-100% of the treated plants survived. EdsRNA agents have another special advantage. Once the package is degraded, efficient siRNA molecules are produced that attack viruses only at various sites. This greatly improves the protection effect.

“RNA viruses such as cucumber mosaic viruses are dangerous because they can evolve rapidly. Furthermore, the genetic material of this virus is made up of three separate parts that are mixed and further increase the possibility of new mutations.

The team has also optimized the process of efficient siRNA screening and can adapt procedures to target new viral mutations within 2-4 weeks.

“Time is a key factor. When new virus variants appear, the active agent can be changed very quickly accordingly,” explains Behrens. This approach may also be applied to other pathogens and pests.

Until now, substances have been administered manually into the lab by injection or rubbing onto plant leaves. The team is working with Professor Karsten Mäder, a pharmacist and drug delivery expert at MLU, to make RNA-based substances more durable and easy to apply to plants.

For example, you can spray it. At the same time, researchers are planning a field trial to test RNA-based substances under real conditions. And they are talking to businesses about future industrial production.

Furthermore, it will be a while before products that fight cucumber mosaic viruses enter the market as potential new crop protection products still need to go through the approval process.

“However, we believe our approach is feasible. The first crop protection product with RNA-based active ingredients has recently been approved in the US,” says Behrens.