Abstract
RNA interference (RNAi) was discovered almost 20 years ago and has been exploited worldwide to silence genes in plants and animals. A decade later, it was found that transforming plants with an RNAi construct targeting an insect gene could protect the plant against feeding by that insect. Production of double‐stranded RNA (dsRNA) in a plant to affect the viability of a herbivorous animal is termed trans‐kingdom RNAi (TK‐RNAi). Since this pioneering work, there have been many further examples of successful TK‐RNAi, but also reports of failed attempts and unrepeatable experiments. Recently, three laboratories have shown that producing dsRNA in a plant's chloroplast, rather than in its cellular cytoplasm, is a very effective way of delivering TK‐RNAi. Our review examines this potentially game‐changing approach and compares it with other transgenic insect‐proofing schemes. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Highlights
A significant constraint to crop production is the damage caused by insects, with arthropod pests causing global crop losses of 13–18%, with an estimated value loss of US$470 billion annually.[1]
This production of double-stranded RNA (dsRNA) in a plant affecting the viability of an insect is termed trans-kingdom RNA interference (RNAi) (TK-RNAi)
8 producing the guide dsRNA in a plant’s chloroplasts rather than in its cellular cytoplasm has recently been shown to enhance the effectiveness of TK-RNAi.[9,10,11,12]
Summary
A significant constraint to crop production is the damage caused by insects, with arthropod pests causing global crop losses of 13–18%, with an estimated (in 2014) value loss of US$470 billion annually.[1]. 2.1 RNAi machinery: plant cell versus insect cell versus chloroplast The endogenous gene silencing capability of a plant cell has many different facets that may be regarded as a suite of overlapping pathways, including the RNAi pathway (duplexed RNA-induced targeted RNA degradation) These pathways control the expression of developmentally regulated genes, repress the activity of repetitive elements in the plant genome, and provide resistance against invading nucleic acids such as viruses.[15] They are mediated by four (in dicots) or five (in monocots) different Dicer-like RNase III-like endonucleases (DCLs) that collectively process duplexed RNA into 21-, 22-, and 24-nt siRNAs, and appropriate highly structured RNA transcripts into ∼21-nt microRNAs.[15,16,17] The siRNAs and microRNAs are loaded onto specific effector proteins of the multi-member Argonaute (AGO) family that have RNA cleavage or binding capability.[18,19] In the RNAi pathway, DCL2 and DCL4 produce siRNAs that predominantly guide AGO1 and AGO720 which cleave target RNAs. Further, siRNAs are generated through a process that involves siRNAs, target RNAs, and at least one RNA-directed RNA polymerase, RDR6 (Fig. 1). The choice of target gene, length of dsRNA, method of dsRNA delivery, and capacity of the target species to traffic dsRNA all appear to be factors in the strength of eRNAi outcome
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