The German name of the “cucumber mosaic virus” may sound harmless, but it is a particularly vicious pathogen. It causes wilted leaves, stunted fruits and leads to billions of  crop damage every year. It affects around 1,200 plant species – not just squash and cucumbers, as the name suggests, but also herbs and grains. “The virus is mainly carried by insects, such as aphids, so farmers are eager to control them”, says Professor Sven-Erik Behrens from the Institute of Biochemistry and Biotechnology at the MLU. “They don’t hold back when using chemical pesticides – even if it means destroying insects that don’t harm the plants or even benefit them”. According to the “Pesticide Atlas”, approximately four million tons of insecticides, fungicides and herbicides are used in agriculture worldwide every year. In addition to the collateral damage to the environment, as described above, there is a risk that people will ingest residues in their food.

Behrens has also dedicated his research to fighting plant pests. However, he doesn’t want to bombard viruses with chemical weapons, but instead wants to stop their reproduction process at cellular level. “To do this, we intervene in the plant’s molecular defence system”, he explains. “Although plants are hardly comparable to animals or humans, this is very much like a vaccination”. Almost two years ago, the Federal Ministry of Education and Research (BMBF) commissioned the biochemist to evaluate the widespread use of novel vaccines targeting plant viruses based on RNA molecules. As part of this “RNA Protect” project, he is also applying his findings to harmful insects and fungi. The project has received around 1.3 million euros from the BMBF, and the funding will stop at the end of this year.

Back in 2019, Behrens and his research team at the MLU developed a method of “vaccinating” plants with efficient “small interfering RNAs” (siRNAs). Infected plants initially produce these siRNAs themselves by cutting up viral ribonucleic acid molecules with enzyme scissors. These RNA snippets guide protein complexes to the viral RNAs, which – in the best-case scenario – are then broken down into harmless fragments and degraded. Unfortunately, this endogenous defence mechanism is not very efficient. “When a plant is infected with a virus, it produces a very large number of different siRNA molecules, but only a few of them have a protective effect”, says Behrens. “We’ve developed a reliable method of identifying the exact siRNAs that are particularly effective against viral RNAs, so that they can be used in a targeted manner. And we’ve now successfully transferred this method to other pathogens”.

A few months ago, the research team led by Sven-Erik Behrens managed to expand the range of methods used to guide the enzyme scissors – the plant cell police – straight to the weak points of the viral RNA. This method does not use siRNAs, but rather artificially produced DNA molecules known as “antisense oligonucleotides” (ASOs). “The active principles of siRNAs and ASOs may be very similar, but the active enzyme complexes are completely different”, explains Behrens. However, both methods are equally effective; around 90 percent of plants “vaccinated” in a laboratory trial were protected against infection with a model virus.

“The basic method of RNA or DNA-based vaccination works reliably”, explains Behrens. “We’re now working on transferring the principle to agricultural practice”. The biggest challenge is to transport the nucleic acids outside the laboratory to the place where they are to have their effect. That’s why the biochemists are working with Professor Karsten Mäder, an MLU pharmacist who specialises in packing active ingredients in carrier systems in such a way that they are not released until they reach the organism of plants, insects or fungi. Behrens: “The nucleic acid molecules themselves are unstable and quickly broken down. That’s why we encase them in particles made of natural material, similar to the RNA vaccines designed to fight the coronavirus”. This should make it possible to apply nucleic acid-based vaccines as a spray, for example.

Although only a few grams of the vaccine’s active ingredient will be needed for one field, cost-effective production is a major hurdle. “Until now, specific RNA molecules have been produced synthetically with enzymes, which is a relatively complex process”, says Behrens. “We want to take a different approach and produce the vaccine microbially in yeast”. Behrens can draw on experience gained with “Verovaccines”, a Halle-based spin-off that he founded at the MLU in 2017. The company is developing novel vaccines to target animal diseases using genetically modified lactic yeast. The MLU biochemists are working on this process in collaboration with researchers from the Delft University of Technology in the Netherlands. As part of the “RNA Protect” project, a new experimental fermenter has been installed at the Institute of Biochemistry and Biotechnology to show the effort and expense involved in mass production and the key factors in this regard.

And expectations are high, because the new nucleic acid-based vaccines have enormous potential for agriculture, environmental protection and the conservation of species. “As we can precisely identify and control the target structures, the process is much more targeted than any chemical agent and results in much less pollution”, explains Behrens. “What’s more, RNA and DNA are biomolecules that are broken down relatively quickly in natural processes”. Another advantage of the now patented method is that the active ingredients in the vaccines can be adapted very quickly to new pathogens. In order to rule out “off-target effects” – undesirable effects on related species – as much as possible, Behrens’ team is working with MLU bioinformaticians PD Jan Grau and Professor Ivo Große as well as the Federal Office of Consumer Protection and Food Safety (BVL).

When the “RNA Protect” project stops receiving funding, research on the topic will be far from over. “We’re currently exploring different options to secure follow-up financing”, says Sven-Erik Behrens, “from additional public funding for basic research to more targeted private funding for the development of RNA-based vaccines against a specific pathogen by the industry”. Another conceivable option would be to set up an own company using the patented method in the next two to three years.