Ecological risk assessment for DvSnf7 RNA: A plant-incorporated protectant with targeted activity against western corn rootworm

Abstract

MON 87411 maize, which expresses DvSnf7 RNA, was developed to provide an additional mode of action to confer protection against corn rootworm (Diabrotica spp.). A critical step in the registration of a genetically engineered crop with an insecticidal trait is performing an ecological risk assessment to evaluate the potential for adverse ecological effects. For MON 87411, an assessment plan was developed that met specific protection goals by characterizing the routes and levels of exposure, and testing representative functional taxa that would be directly or indirectly exposed in the environment. The potential for toxicity of DvSnf7 RNA was evaluated with a harmonized battery of non-target organisms (NTOs) that included invertebrate predators, parasitoids, pollinators, soil biota as well as aquatic and terrestrial vertebrate species. Laboratory tests evaluated ecologically relevant endpoints such as survival, growth, development, and reproduction and were of sufficient duration to assess the potential for adverse effects. No adverse effects were observed with any species tested at, or above, the maximum expected environmental concentration (MEEC). All margins of exposure for NTOs were >10-fold the MEEC. Therefore, it is reasonable to conclude that exposure to DvSnf7 RNA, both directly and indirectly, is safe for NTOs at the expected field exposure levels.

Responses of two ladybird beetle species (Coleoptera: Coccinellidae) to dietary RNAi

“…Selection of the correct sequence is thus central to the development of any RNAi‐based plant protection product. In general, species phylogenetically related to the target organism are more likely to be susceptible to the dsRNA than distantly related species . This has been confirmed in several studies.…”

“…For example, the Snf7 genes from both Cerotoma trifurcata and Galerucella calamariensis (both Coleoptera: Chrysomelidae) possess 90.8% identity with Snf7 from D. v. virgifera , but the number of 21‐nt‐long matches was 18 in the former and 3 in the latter non‐target species . Although a single 21‐nt‐long sequence match can induce toxicity in a highly susceptible insect, toxicity of the dsRNA is expected to be positively related to the number of potential 21‐nt‐long matches . Our bioinformatics analyses thus predicted that C. septempunctata would be more susceptible than A. bipunctata to Dvv dsRNA, and that prediction was confirmed in the feeding bioassays.…”

“…Thus, the level at which the Dvv dsRNA would be expressed in the plant tissue is unknown. As a proxy, we can base our assessment on the known expression levels of Dvv Snf7 dsRNA in MON 87411 maize, which were reported to reach a maximum of 33.8 ng/g FW leaf (mean of 14.4 ng/g FW) . Because we provided the test insects with sucrose solution containing dsRNA at concentrations of 0.25 or 2 µg µL −1 , our margins of exposure (MOE) were 15 000 and 60 000, respectively, when calculated for the maximum expression levels of Dvv Snf7 dsRNA in leaves.…”

“…To inform the non‐target risk assessment, the effects of the insecticidal compound is tested on a range of surrogate species representing species of economic and ecological importance . The ERA framework established for Bt ‐transgenic crops has also been regarded as suitable for the evaluation of non‐target risks of RNAi‐based GE plants . Researchers have also used bioinformatics analyses to detect 21‐nt‐long sequence matches between the designed dsRNA and the target gene in non‐target species since this indicates that there will be bioactivity …”

Gene silencing by RNAi via oral delivery of dsRNA by bacteria in the South American tomato pinworm, Tuta absoluta

“…The production of transgenic plants expressing insect dsRNA represents a powerful approach to be used in the control of insect pests, and commercial products using RNAi by expressing insect dsRNA in plants are close to a commercial launch . Transgenic plants expressing insect dsRNA have been the main goal as the method to selectively control insect pests.…”