Plant-parasitic nematodes (PPNs) are estimated to cause over $170 billion in lost agricultural production globally each year, with losses of over $13 billion in the United States alone. To meet expected food demand in 2050, when the world is projected to have an additional 2 billion people, it is imperative that we reduce crop losses to PPNs. The goal of this project is to develop genetic-based resistance to PPNs using soybean and the soybean cyst nematode (SCN) as model pathosystem. Plants have the ability to detect disease-causing organisms (pathogens) and then activate a robust defense response that ultimately leads to localized cell death to stop the invader. To detect pathogens, plants use sensor proteins that are modified by enzymes that pathogens secrete during the infection process. This project focuses on identifying enzymes secreted by SCN that are required for infection of soybean. Once such enzymes are identified, sensor proteins will be designed that can activate defense responses in soybean upon modification by these SCN enzymes. Such a system would thus confer resistance to infection by PPNs without the use of costly and environmentally damaging pesticides and should be transferrable to a wide array of important crop plants that are damaged by PPNs.
Many plant pathogens depend on proteases to infect host plants. The Innes laboratory has developed a novel method for engineering resistance to such pathogens based on detecting these specific proteases. In Arabidopsis, cleavage of the host kinase PBS1 by the pathogen protease AvrPphB activates a strong defense response. The AvrPphB recognition sequence within PBS1 (seven amino acids) can be replaced by the recognition sequence for other pathogen proteases. These ?decoy? kinases can then be cleaved by the matching protease, which activates resistance. Thus, by manipulating the PBS1 amino acid sequence, it is possible to engineer recognition of many pathogen proteases. This proposal seeks to extend this discovery to the crop plant soybean by engineering resistance to its single most important pathogen in North America, soybean cyst nematode (SCN). Prior work has shown that modification of soybean PBS1 so that it is cleaved by the NIa protease of soybean mosaic virus (SMV) confers complete immunity to infection by SMV. To assess whether proteases secreted by SCN contribute to virulence, the expression of candidate protease genes will be reduced using RNA interference and then the impact on soybean root infection will be assessed. Proteases that contribute to infection will then be further analyzed by identifying their targets in soybean root cells using biotin proximity labeling, and their cleavage sites identified using mass-spectrometry. SCN protease cleavage sites will then be inserted into soybean PBS1 genes using CRISPR-Prime genome editing, thus generating soybean lines that are resistant to SCN infection and free of transgenes.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
