The amino acids threonine and methionine are not only essential protein building blocks, but also serve as precursors for other important plant metabolites. Although the basic biochemical pathways for the synthesis of methionine and threonine in plants have been identified, relatively little is known about the catabolism of these amino acids and their partitioning into downstream metabolic networks. Work on Arabidopsis lines with increased seed threonine and methionine levels identified two mutations that are the subject of ongoing research. One of the mutations is in threonine aldolase, a threonine catabolic enzyme that has not been previously studied in plants. Further research will accomplish the following goals: 1. The biochemical characteristics of Arabidopsis threonine aldolase, the role of this enzyme in plant amino acid metabolism, and the effects of mutations in the Arabidopsis threonine aldolase genes will be investigated; and 2. A second mutation causing ten-fold increases in seed methionine and threonine will be characterized, and the function of this gene in plant amino acid metabolism will be determined. Broader Impact: Methionine and threonine are two of the essential amino acids that cannot be synthesized by humans and other animals. Many crop plants, in particular legumes, have sub-optimal levels of methionine or threonine for the mammalian diet. Therefore, there is interest in discovering new plant genes that can be employed to raise levels of these amino acids in crops through biotechnology or plant breeding. The project will also provide research opportunities for high school, undergraduate, and graduate students. An established summer internship program will be used to recruit students, including underrepresented minorities, from local high schools and from colleges throughout the USA. These students will be trained in the most modern techniques of metabolic biochemistry and molecular genetics to prepare them for future careers in industry or academics.
