RNAi as a Foliar Spray for Gene Silencing

RNA interference (RNAi) is a useful technology that is being used more frequently to protect crops against viruses, fungi, and insect pests. A non-transgenic technique that depends on spray application of double-stranded RNA (dsRNA) to induce RNAi is called spray-induced gene silencing (SIGS). It has gained popularity due to its safety and environmental benefits, as well as its broad host range and excellent target specificity. While some chewing insects can respond strongly to sprayed dsRNA on plants by producing RNAi, many other target species require plant uptake and systemic transport of dsRNA; whereas many fungal diseases are mostly found in internal plant tissues, pests like sucking insects require the presence of dsRNA in vascular tissues. After application of dsRNA; three possible outcomes are migration to vascular tissues and systemic transport as intact molecules, breakdown, and cellular absorption and processing into siRNAs which is preferable for protection against viruses, fungi, and also pests.

Figure. Functional crop protection via a foliar dsRNA spray to induce RNAi (Hoang et al. 2022) (A). Plant uptake of dsRNA can be divided into two stages: foliar uptake where sprayed dsRNA molecules from the leaf surfaces enter the interior of the leaf tissue, and cellular uptake where dsRNA molecules get taken up into plant cells. Following foliar uptake, sprayed dsRNAs may diffuse through the leaf interior and cellular uptake may occur. (B). Once dsRNA penetrates the cell wall pores and cell membrane to enter the cytoplasm, the plant RNAi machinery can process dsRNAs into siRNAs. Produced siRNAs can lead to the degradation of viral transcripts in local cells and also be transported to adjacent cells. siRNAs are likely to participate in long-distance signaling through vascular bundles to other parts of the plant. It is uncertain how non-processed dsRNA in the apoplastic pathway are translocated systemically. (C). dsRNA/siRNAs from the plant surfaces or in the plant system can be taken up by different targets and trigger an RNAi response depending on their sensitivity to dsRNA or siRNA.

Dr. Md. Monirul Islam
Senior Scientist
ASRBC, ACI Seed

References:
Hoang, B.T.L.; Fletcher, S.J.; Brosnan, C.A.; Ghodke, A.B.; Manzie, N.; Mitter, N. RNAi as a Foliar Spray: Efficiency and Challenges to Field Applications. Int. J. Mol. Sci. 2022, 23, 6639.