Crystal (Cry) proteins are produced by the soil bacterium Bacillus thuringiensis (Bt) and have been used extensively for decades in organic farming, in insect vector control (mosquito, black fly), and in transgenic crops. These proteins kill insects and nematodes (invertebrates) but are non-toxic to mammals and other vertebrates. Most importantly, the use of Cry proteins has resulted in increases in crop yields while simultaneously allowing for significant decreases in the use of hazardous chemical pesticides. However, a critical issue that needs to be addressed for the continued effectiveness of Cry proteins is the emergence of resistance in the invertebrate targets of these proteins. This issue is the focus of the current research. In prior studies, it was found that an invertebrate-specific carbohydrate acts as a receptor for a Cry protein and that loss of this carbohydrate receptor leads to resistance against this Cry protein. The first aim of this project is to gain a three-dimensional understanding of how the carbohydrate receptor is recognized specifically by the Cry protein. The second aim of this project uses the nematode C. elegans, which has provided a unique and powerful genetic system for dissecting host resistance, to identify, on a genome-wide scale, genes that are important for Cry protein resistance. The intellectual merits of the first aim of this project include determining detailed molecular contacts between a Cry protein and the carbohydrate receptor. This information will enable rational engineering of the toxin and provide information on how Cry proteins discriminate between invertebrates and vertebrates. The intellectual merits of the second aim include discovering new genes that, when reduced in expression or function, confer Bt toxin resistance. This information will uncover new steps and pathways involved in evolution of resistance to Cry proteins. The broad impacts of this research to society are to: 1) maintain the long-term utility of Bt toxins; 2) better establish the foundation for mammalian safety, thus providing a greater sense of security about use of these proteins in food crops; and 3) lay the foundation for rational design of Bt toxin variants with improved potency against pests and with less likelihood of being resisted.
