Genetic and Genomic Analysis of Plant Response to Limiting Nutrient Environments

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Within the next 50 years, considerable stress will be placed on worldwide crop production from a combination of factors including increased human population, an increase in the crops used per person and many environmental issues. To significantly increase yields per area planted worldwide will require considerable effort to meet this challenge in an economically and environmentally sustainable fashion. Available nitrogen is a major limiting factor in crop production. Nitrogen fertilizer is now the single largest input cost for many crops and farmers in developing countries cannot afford fertilizer, leading to lower yields. Therefore crop lines that utilize available nitrogen more efficiently would significantly reduce costs in the developed world and increase yields in the developing world. In addition, use of large amounts of N fertilizer in agriculture causes significant and irreversible environmental damage. Thus, current practices of nitrogen fertilizer use are unsustainable and, given the need for enhanced crop yields over the next half-century, increasing nitrogen application is clearly problematic. Many studies have been done on a wide variety of crops demonstrating that there is significant genetic variability in utilizing nitrogen fertilizer. Although significant efforts and progress have been made, there are still much to be understood on the genetic basis of these differences. It is crucial to understand the underlying role of different genes on nitrogen acquisition and use in order to develop crops that use nitrogen more efficiently. We have done considerable research on how plants respond to conditions where the nitrogen nutrient limits plant growth in order to understand which genes are important for this response. This proposal places primary emphasis on how metabolic pathways are regulated that might affect the plant response to nitrogen stress adaptation as well as how they remobilize the acquired organic nitrogen for seed production. The focus will be on two basic processes. First, we will look at a set of genes that regulate chlorophyll amounts particularly under low nitrogen conditions. We have demonstrated that these regulatory genes modulate the number of chloroplasts present as well as the amount of chlorophyll and starch. Changing the activity of this gene can lead to changes in all of these. Second, we will study some key aspects of biomass formation and nitrogen remobilization. The amount of biomass produced and the percentage of the nutrients from this biomass that ends up in the seed are the key determinants of crop yield. Finally, nitrogen limitation is only one of the many types of stress that crop plants typically endure under field conditions. The proposed studies will also include a delineation of responses to multiple nutrient/stress conditions like drought and planting density stress, using genomic methodologies and bioinformatics analyses. By delineating how plants respond to different combinations of stress, we will gain understanding of the combinatorial nature of how these affect plant growth and development. From earlier studies, we know that this response is not additive and that each combination has some unique elements. Thus, we hope to develop more sophisticated indicators of crop response to these important conditions that significantly affect crop yield.