RNA interference (RNAi) as an innovation in plant protection

Climate change, shrinking arable land, and the spread of pests pose considerable challenges for agriculture. To ensure successful harvests and thus an adequate food supply, a wide range of pesticides are used to protect crops from pests. However, conventional pesticides can remain in the environment and have negative effects on the organisms living there. Therefore, research is continuously being conducted to reduce the harmful side effects of plant protection methods and develop alternatives to conventional pesticides. For several years now, RNA interference (RNAi)-based plant protection methods have been a focus of research and represent a promising alternative. This is due, on the one hand, to the rapid degradability of RNA molecules and the possibility of targeting the active ingredients very specifically at pests. Since RNAi-based plant protection differs from conventional pesticides in its mode of action and application, it is necessary to adapt the classic methods for assessing the environmental risk of RNAi applications. Staff at Fraunhofer IME in Schmallenberg are involved in two projects to record the state of development and determine an environmental risk assessment strategy for RNAi plant protection.

RNA interference (RNAi) – what is it and what is it good for?

The RNAi mechanism is originally a natural defense mechanism of the immune system of eukaryotes against viruses. In plant protection, this mechanism is exploited to specifically shut down genes in the pest that are essential for its survival. To do this, a double-stranded RNA (dsRNA) complementary to the target gene in the pest is produced, which is cleaved into smaller molecules in the organism and incorporated into the RNA-induced silencing complex (RISC). The target RNA is then bound by this complex, thereby preventing the production of the corresponding protein. This can inhibit, for example, the growth, reproduction, or survival of the harmful organism.

In plant protection, crops can be genetically modified to produce dsRNA themselves (host-induced gene silencing; HIGS), or RNA sprays can be applied to the plant surface (spray-induced gene silencing; SIGS). By feeding on the plant, the pest ingests the dsRNA, which then blocks the production of vital proteins in the organism. Since the dsRNA sequences can be developed to be very specific to the pest, it is assumed that RNA applications pose a lower risk to non-target organisms. In addition, dsRNA itself is very unstable in the environment, so the persistence in the environment is considered to be low compared to that of most chemical products. At the same time, however, this instability poses a problem for the effectiveness of dsRNA. For this reason, research is constantly being conducted into new formulation techniques to stabilize the RNA.

Project 1: Environmental effects of RNAi-based GM plants and methods for transient modification of organisms
 

In a project funded by the Federal Agency for Nature Conservation (BfN), various work packages were used to determine the current status and development of RNAi-based plant protection and to provide an overview of the development of risk assessment strategies.

In a Horizon Scan of the literature between 2013 and 2023, the current status of RNAi developments was recorded and published by Kirsten Germing, research assistant of the Ecotoxicology Department (Germing et al 2025, see below). The literature was evaluated according to the crop to be protected, the target organism (pest), the function of the target gene, the method of application (e.g., HIGS or SIGS), and the stage of development of the method. The literature review showed that the development of applications is focused on spray methods. Research work on the use of RNAi for a variety of target organisms and crops was identified. Many developments are no longer in the initial phase; the greatest challenge in current research has proven to be the development of the application method and the development of stabilizing formulations. Three developments are currently in commercial application in the USA: the two genetically modified corn varieties SmartStax® Pro and Vorceed™ Enlist®, which express dsRNA against the corn rootworm, and the dsRNA spray Catantha, which is used against the Colorado potato beetle.

In a follow-up study, literature was collected to provide an overview of the molecular RNAi mechanisms and the possible classification and detection of RNAi effects in genetically modified plants (Diaz et al 2025, see below). In this study, we identified that RNAi probably acts very specifically and that no effects have been detected in the crop plant to date. However, detecting these effects is a major challenge and evidence is hard to find in the literature. To identify these effects, the further development of molecular biological methods and bioinformatic approaches is recommended.

The state of research on potential effects on non-target organisms was investigated in a further work package (Hommen et al 2026, in preparation). The evaluation of the literature showed that existing risk assessment strategies can in principle be adapted to RNAi applications. Bioinformatic methods in particular should be integrated more strongly into risk assessment, as they can be used to estimate unintended sequence homologies with regard to the specific mechanism of action of RNAi applications.

The interim results of the project were presented at a workshop at the BfN in October 2024 and discussed with national and international experts from research, industry, and regulatory authorities.

Project 2: Strategy development for the environmental risk assessment of RNAi-based pesticides (SIGS)
 

Hannah-Philine Dey, research assistant of the Ecotoxicogenomics Department, is working on her doctoral thesis, funded by the German Federal Environment Agency, to develop the basis for a new strategy for the environmental risk assessment of dsRNA sprays. The study examines the extent to which the current data requirements for European approval of conventional pesticides are transferable to RNAi-based pesticides and how they may need to be adapted to take the new mechanism of action into account.

Two aspects are being focused on separately: First, a bioinformatic analysis is being carried out, followed by an experimental part. With the help of molecular biological analysis of messenger RNA (mRNA), this will determine the extent to which bioinformatics can make adequate predictions about the environmental risk to non-target organisms. This offers the opportunity for environmental risk assessment to narrow down the required ecotoxicological tests more specifically.

In the second part of the project, an assessment strategy will be developed that will allow novel formulation technologies to be taken into account in future environmental risk assessments. To this end, a method based on a universal signaling molecule has been established that can be used for as many non-target organisms as possible at the same time and that enables the environmental risk assessment of formulations for RNAi sprays.

In view of the efforts to reduce the use of conventional chemical pesticides, research into RNAi plant protection is a promising approach. With these two projects, we are contributing to the further development of environmental risk assessment to ensure that the approval of safe RNAi applications is advanced.