Protection of Crops Against Insect Pests Using RNA Interference

Abstract

RNA interference (RNAi) caused by exogenous double-stranded RNA (dsRNA) has developed into a powerful technique for down-regulating gene expression in a wide range of organisms, following its discovery in the nematode Caenorhabditis elegans. Not only does import of dsRNA into cells to produce small interfering RNAs (siRNAs) take place readily in C. elegans, but also systemic RNAi effects can be shown to occur, which persist over distinct developmental stages. These effects are mediated by amplification of siRNAs and export to other cells in the organism. However, the sensitivity to RNAi in C. elegans, where specific genes can be down-regulated by feeding dsRNA, or even by soaking nematodes in dsRNA solutions, have not been duplicated in other organisms, nor have systemic and persistent RNAi effects been widely observed. Uptake of dsRNA was limited in the model insect species Drosophila melanogaster (fruit fly), and no evidence of systemic and persistent RNAi effects was observed. However, more recent research has shown that full RNAi effects can occur in insects, although they are variable from species to species. Down-regulation of gene expression through delivery of dsRNA to insects can cause mortality, through a range of altered phenotypes, such as interference with developmental processes, or metabolism, or responses to the environment, and systemic and persistent RNAi effects have been reported, most notably in the beetle Tribolium confusum. Whereas injection of dsRNA remains the method of choice for delivery to insects, in some species feeding dsRNA has also been shown to produce RNAi effects. Further, expression of dsRNAs directed against insect genes in transgenic plants has been shown to result in RNAi effects and to afford protection against insect herbivores. This technology has the potential to be the basis of a new generation of pest-resistant GM crops, complementing existing technologies, but further development to improve efficacy of protection, and range of species affected, will be necessary.