The previous issue of the IPM Chronicle discussed the development of gene editing techniques to enhance crops. The discussion will now turn to a molecular technique that provides the ability to turn off (silence) genes within an organism’s cells. This process of silencing genes can be accomplished through a process called ribonucleic acid interference or RNAi.
Developed in the 1990s, RNAi is now being studied as a tool for managing various pest species. So what is RNAi, and how exactly can it be used for pest management? Before these questions can be answered, one must first understand the connection between DNA and proteins.
DNA is the molecule that contains all the information needed to build and maintain an organism. More specifically, genes (sections of a DNA molecule) provide the information necessary to build specific protein molecules that carry out the various functions of a cell. However, a gene does not build a protein directly. The bridge between DNA and protein synthesis is RNA. In the simplest sense, RNA molecules convert the information stored in DNA into proteins.
There are many types of RNA molecules involved in protein synthesis, and each performs a specific function. The role of RNAi is to turn down the production of specific proteins within a cell, or remove foreign RNA molecules that may have been inserted by an invading organism, such as a virus.
Advantages of RNAi
By exploiting the RNAi pathway, scientists can target specific RNA sequences for removal before they can be used to make a protein. Thus, RNAi technology can potentially be used to silence a gene’s activity that is essential for the development and survival of particular pest species. There are many potential advantages of using RNAi technology in pest management. The ability to target an individual pest species without harming non-target species in the environment is the most important benefit. In addition, the likelihood of a pest developing resistance would be extremely low, especially if multiple genes are targeted simultaneously. Delivery of RNAi can be conducted in a manner similar to pesticides, such as in a spray or powder. Additionally, RNAi could be delivered to pests through the genetic engineering of transgenic plants, similar to Bt crops.
RNAi is currently being studied for control of several important agricultural insect pests including western corn rootworm ( Diabrotica v. virgifera), Colorado potato beetle ( Leptinotarsa decemlineata), cotton bollworm ( Helicoverpa armigera), beet armyworm ( Spodoptera exigua), green peach aphid ( Myzus persicae) and silverleaf whitefly ( Bemisia tabaci). RNAi technology is also being used to develop plant varieties resistant to viruses, such as cucumber and tobacco mosaic virus and tomato spotted wilt virus (among many others), and is being considered to combat herbicide-resistant weeds. In addition to its many potential agricultural uses, RNAi technology is being used to study gene function for the treatment of a variety of human diseases, such as cancer, HIV, hepatitis and malaria.