A Perspective on RNAi-Based Biopesticides

Abstract

Sustainable agriculture relies on practices and technologies that combine effectiveness with a minimal environmental footprint. RNA interference (RNAi), a eukaryotic process in which transcript expression is reduced in a sequence-specific manner, can be co-opted for the control of plant pests and pathogens in a topical application system. Double-stranded RNA (dsRNA), the key trigger molecule of RNAi, has been shown to provide protection without the need for integration of dsRNA-expressing constructs as transgenes. Consequently, development of RNA-based biopesticides is gaining momentum as a narrow-spectrum alternative to chemical-based control measures, with pests and pathogens targeted with accuracy and specificity. Limitations for a commercially viable product to overcome include stable delivery of the topically applied dsRNA and extension of the duration of protection. In addition to the research focus on delivery of dsRNA, development of regulatory frameworks, risk identification, and establishing avoidance and mitigation strategies is key to widespread deployment of topical RNAi technologies. Once in place, these measures will provide the crop protection industry with the certainty necessary to expend resources on the development of innovative dsRNA-based products. Readily evident risks to human health appear minimal, with multiple barriers to uptake and a long history of consumption of dsRNA from plant material. Unintended impacts to the environment are expected to be most apparent in species closely related to the target. Holistic design practices, which incorporate bioinformatics-based dsRNA selection along with experimental testing, represent important techniques for elimination of adverse impacts.

Keywords: RNAi; biopesticide; crop protection; dsRNA; topical application.

Figure 1

Topical application of BioClay allows for extended RNAi-mediated protection from plant viruses. BioClay is a complex of double-stranded RNA (dsRNA) and layered double hydroxide (LDH). BioClay is prepared by mixing dsRNA and LDH in solution and is applied as a foliar spray. Moisture and carbon dioxide combine to allow acid release of the dsRNA, with LDH degrading to its constituents. The dsRNA can subsequently be taken up by the plant and prime its RNA machinery to degrade homologous viral RNAs. Due to the stabilization and slow release of dsRNA, resistance to the target virus relative to naked dsRNA can be extended from days to weeks.

Figure 2

As a crop protection measure, topically-applied dsRNA should be effective against specific pests and pathogens while avoiding unintended adverse consequences. Topically applied double-stranded RNA (dsRNA) can be used to generate resistance to pathogenic viruses and fungi, and pests such as insects. Off-target impacts to be avoided include silencing of crucial host plant and other non-target organism genes. Potential routes of exposure to humans including operators applying the dsRNA along with consumers of treated products could occur via dermal exposure, inhalation, and ingestion.