Management of Pest Insects and Plant Diseases by Non-Transformative RNAi

Abstract

Since the discovery of RNA interference (RNAi), scientists have made significant progress towards the development of this unique technology for crop protection. The RNAi mechanism works at the mRNA level by exploiting a sequence-dependent mode of action with high target specificity due to the design of complementary dsRNA molecules, allowing growers to target pests more precisely compared to conventional agrochemicals. The delivery of RNAi through transgenic plants is now a reality with some products currently in the market. Conversely, it is also expected that more RNA-based products reach the market as non-transformative alternatives. For instance, topically applied dsRNA/siRNA (SIGS – Spray Induced Gene Silencing) has attracted attention due to its feasibility and low cost compared to transgenic plants. Once on the leaf surface, dsRNAs can move directly to target pest cells (e.g., insects or pathogens) or can be taken up indirectly by plant cells to then be transferred into the pest cells. Water-soluble formulations containing pesticidal dsRNA provide alternatives, especially in some cases where plant transformation is not possible or takes years and cost millions to be developed (e.g., perennial crops). The ever-growing understanding of the RNAi mechanism and its limitations has allowed scientists to develop non-transgenic approaches such as trunk injection, soaking, and irrigation. While the technology has been considered promising for pest management, some issues such as RNAi efficiency, dsRNA degradation, environmental risk assessments, and resistance evolution still need to be addressed. Here, our main goal is to review some possible strategies for non-transgenic delivery systems, addressing important issues related to the use of this technology.

Risk Assessment Considerations for Genetically Modified RNAi Plants: EFSA’s Activities and Perspective

“…At present, RNAi-based GMPs have been designed to express either a double-stranded RNA (dsRNA) or an artificial microRNA (miRNA) precursor. These molecules are cleaved by Dicer/Dicer-like proteins into a pool of small RNAs that are 20-30 nucleotides long (small interfering RNAs [siRNAs] or miRNAs) and which specifically bind the target/messenger RNA (mRNA) with perfect or nearly perfect complementarity (Burand and Hunter, 2013;Koch and Kogel, 2014;Cagliari et al, 2019). siRNAs and miRNAs bind to an Argonaute protein forming the RNAi-induced silencing complex which, based on sequence homology, targets cognate RNAs.…”

Validating the potential of double-stranded RNA targeting Colorado potato beetle mesh gene in laboratory and field trials

“…Thus, dsRNAs application by non-transformative strategies, i.e. through sprayinduced gene silencing, is currently a more realistic option (Cagliari et al 2019). We have shown in laboratory trials as well as in the field that spraying with insecticidal dsRNA is a highly efficient strategy for managing CPB.…”

“…The observed field mortality was slightly lower compared to laboratory trials, which is reasonable, as larval treatment on the field was not as controlled and uniform as in the laboratory. In addition, reduced dsRNA stability in the field is expected due to direct sunlight exposure and lack of formulation to improve dsRNA stability (Cagliari et al 2019). Compared to the wide-spectrum insecticide spinosad (Kirst 2010), dsMESH has an inherent lag phase in observed mortality, which can be attributed to its mode of action.…”

Enhancing RNAi Efficiency to Decipher the Functional Response of Potential Genes in Bemisia tabaci AsiaII-1 (Gennadius) Through dsRNA Feeding Assays

“…Recently the corn plants expressing dsRNA against reproductive genes of Diabrotica virgifera virgifera has demonstrated the potential of this technology through RNAi based transgenic plants (Niu et al, 2017). Alternatively, dsRNA-based sprays under curtailed conditions have also been proven to be effective against different insects (Palli, 2014;Cagliari et al, 2019).…”