Large amounts of nitrogen fertilizer are used to increase yields of cereal crops worldwide, resulting in higher crop input costs, greater energy requirements for crop production, and negative impacts on water quality due to excess nitrogen. Despite the widespread use of nitrogen fertilizer, little is known about the genes that control nitrogen use efficiency in cereal crops. This project will identify and characterize genes regulating nitrogen use efficiency in maize, a model system for plant genomics research and an economically important cereal crop. Experiments that integrate physiological, genetic, and functional genomics approaches will identify genes whose expression changes in response to nitrogen, from its uptake by roots to its use by developing seeds. Emphasis will be placed on key regulatory genes that are associated with nitrogen use efficiency in environments and germplasm relevant to crop production, including ongoing breeding efforts for improving maize nitrogen use efficiency in west central Africa. To this end, the project includes a Developing Country Collaboration with the International Institute for Tropical Agriculture (IATA) in Nigeria to enhance ongoing breeding programs aimed at improving NUE for maize in Western and Central Africa. This project will provide training opportunities in the biology of the maize crop, plant genomics, and bioinformatics.
All project data and results will be made available through scientific publications, outreach to scientific and public audiences, and through the project website, www.nitrogenes.uiuc.edu.
for NSF DBI-0501700 Gene Discovery for Maize Response to Nitrogen. Stephen Moose PI and Fred Below co-PI, University of Illinois Edward S. Buckler co-PI, United States Department of Agriculture and Cornell University. One of the key innovations to agriculture during the 20th century was the use of nitrogen fertilizers and improved crop varieties to boost cereal production. Corn yields increased more than five-fold and currently nearly all commercial production of corn (known scientifically as maize) benefits from application of nitrogen fertilizer. However, these benefits are also associated with increased costs of crop production, and the potentially negative environmental impacts that arise from excess fertilizer use. An important goal to enhance the economic and environmental sustainability of corn production is to reduce the amount of nitrogen required to maintain high grain yield. Despite the strong interest in genetic improvement of corn nitrogen use efficiency, the complex nature of this trait has limited past progress. The goal of this project was to use the most recent advances in maize genetics and genomics to understand how the activities of corn genes change in response to nitrogen supply under conditions relevant to commercial corn production, and to identify those genes with promise in improving nitrogen use efficiency. The project produced four major outputs that provide a strong foundation for future enhancement of nitrogen use efficiency of corn and other related cereal and bioenergy crops. We first developed approaches to accurately measure nitrogen use efficiency in large and diverse populations of corn. We found that variation in flowering time and degree of hybrid vigor often obscures true genetic differences in nitrogen use, but that measuring total biomass (grain plus stalks, leaves, and cobs) as well as amounts of amino acids in plant tissues greatly helps identify varieties with potential for improvement. Our second output was a thorough analysis of which corn genes respond to nitrogen, in roots, leaves, cobs and seeds. This effort confirmed that genes known to respond to nitrogen in other plant species also do so in maize, but many new maize genes were discovered that are only active when nitrogen is limiting for growth. Our third major objective used advanced genetic mapping strategies to document genetic variation in nitrogen use genes (which we have named "NitroGenes"), and we identified a small set of genes that contribute to improved nitrogen use. An interesting finding from these studies is that it appears that past selection for high grain yields with nitrogen fertilizer led to the loss of genes found in older maize varieties that are important to maintaining yields when available nitrogen is low. Efforts are ongoing to bring these genes back into modern germplasm. Our final output builds on the aforementioned discoveries, where we have used the tools of molecular breeding and biotechnology to better understand the functions and regulation of some of the most promising candidates for improving nitrogen use efficiency, and to modify these genes in ways that we predict will improve both grain yields at low N, or produce even higher yields when nitrogen fertilizers are applied. Our project was also very active in educating and training the next generation of young scientists engaged in crop improvement. Twenty undergraduate students, six graduate students, and five full-time scientists worked on the project. Project results were presented at scientific conferences in the U.S. and abroad, to a variety of farmer groups, and to the interested public from grade school to retirees. Because of the commercial interest in improving nitrogen use efficiency, our project collaborated with each of the major agricultural biotechnology companies that produce sell corn hybrids, and many of the students who participated in the project are either employed with these companies or are pursuing advanced degrees in the plant sciences. We also joined forces with laboratories in both Germany and Nigeria to conduct portions of the project, which included scientist exchanges among the different research groups. The collaboration with the International Institute for Tropical Agriculture located in Nigeria was especially valuable in providing education and training to scientists who are now enabled to apply our discoveries to improving maize in Western Africa, where poor soils and low incomes limit the potential benefits gained from nitrogen fertilizers. A final important contribution of our project is in providing additional data regarding corn varieties that may be particularly well-suited as a high-yielding annual crop for sustainable bioenergy production.
