RNAi-mediated Gene Silencing and Its Implications for Agriculture

Background RNA interference (RNAi) has emerged as a powerful genetic tool for scientific research over the past several years. RNAi is known as a conserved integral part of the gene regulation processes present in all eukaryotes that utilizes small RNAs (sRNAs) to direct the silencing of gene expression at i.a. the post-transcriptional level. Posttranscriptional gene silencing (PTGS) starts with the initial processing or cleavage of a precursor double-stranded (ds) RNA into short 21–25 nucleotide small-interfering RNA (siRNA) duplexes by an RNaseIII-like enzyme called Dicer. Double-stranded siRNAs are incorporated into an RNAinduced silencing complex (RISC). The activated RISC subsequently unwinds the siRNA in an ATP-dependent reaction, thereby generating an antisense (or guide) strand that targets complementary mRNA transcripts via basepairing interactions. Subsequent degradation of the targeted mRNA causes inhibition of protein biosynthesis1. The consequence of RNAi is a loss of function phenotype that, ideally, is identical to that of a genetic null mutant. Therefore RNAi has been utilized not only in fundamental research for the assessment of gene function, but also in various fields of applied research, such as human and veterinary medicine and agriculture. The first investigations on the potential of RNAi in agriculture research focused on the “proof of concept” that lethal outcomes are possible by gene silencing through RNAi signals in vitro. To that end agricultural pests such as insects, nematodes, and fungi underwent feeding, soaking, and microinjection experiments where RNAi signals were exogenously applied with overwhelming results. Encouraged by the fact that agricultural pests can be killed by exogenously supplied RNAi targeting their essential genes, some scientists have done pioneering work on the level of in vivo RNAi and found first evidence that plant predation can be controlled by lethal RNAi signals generated in planta. We owe it to them that today the RNAi technique has provided possibilities for improved plant production in more efficient agricultural systems.