The proteins in all living organisms are constructed using a set of twenty different amino acids, and plants serve as the primary source of these protein building blocks in the human diet. Plants also use specific amino acids in a variety of other ways including combating insect pests, plant diseases, and surviving environmental hardship. Therefore, it is ultimately important to understand how plants supply amino acids to their various organs. One example of this importance relates to the nutritional quality of seeds. Amino acid content is an important factor affecting the nutritional value of seed crops. Knowing how amino acids are accumulated in seeds, whether they are produced endogenously or are delivered there from elsewhere in the plant, would be critical to devising strategies to improve nutritional quality. This proposal focuses on the amino acid histidine. Examination of mutants of the plant species Arabidopsis thaliana that are unable to synthesize histidine showed that they die at the earliest stages of seed development. The mutants die even if they are borne by a maternal plant that is able to produce histidine. This observation suggests that the maternal plant cannot supply this amino acid to its seeds. The aim of the current proposal is to learn how histidine is accumulated in seeds. To address this issue a series of experiments are proposed to explore the following questions. If the parent plant cannot supply histidine, is it because this amino acid is actively excluded from developing seeds, or is it because the parent plant does not produce enough histidine to supply its seeds? If histidine is actively excluded, why is this so? Is it an indication that histidine plays some special role in seed development and if so, what is this function? If developing seeds produce their own histidine, what genes are necessary for the process and how does the expression of these genes control histidine production?
Intellectual Merit The current proposal challenges common presumptions on how amino acids are supplied for seed development. Until now it was thought that all of them are supplied to developing seeds by the maternal plant. Apparently this is not true for histidine. Studying how plants allocate histidine will lead to insights into the allocation of other amino acids. Therefore, the proposed work will expand our understanding of how plants control synthesis and utilization of amino acids, processes that are essential for the growth and development of plants, and to human use of plant resources.
Broader Impacts The proposed activities will provide research and training for a postdoctoral fellow, undergraduates, and high school students. Laboratory experiences for undergraduates and high school students in particular are critical for the training of future scientists, policy makers, and informed citizens. The P.I. has a strong track record of involving undergraduate and high school students in vibrant research projects. The students are frequently from demographic groups that are underrepresented in the biological sciences. Moreover, the "educational" mindset in the P.I.'s group translates into opportunities for the postdoctoral fellow to develop teaching skills.