Lysine Biosynthesis in Plants

The objective of this proposal is to learn how lysine is synthesized by plants. Lysine is one of the key amino acids that limit the nutritional value of crops used for animal diets. The complete set of genes needed for lysine biosynthesis in plants is not known. In broad outline it is recognized that plants synthesize lysine using a pathway that includes the compound diaminopimelic acid (DAP). Bacteria also use this compound. However, bacteria use three different variations of the DAP pathway and it is unknown which, if any, of them is used by plants.

Preliminary evidence indicates that plants contain a novel enzyme that catalyzes in a single step a reaction that in the bacteria Escherichia coli requires three different enzymes, the products of the dapC, dapD, and dapE genes. It is hypothesized that the plant enzyme synthesizes L,L-diaminopimelate from tetrahydrodipicolinate. This enzyme is found in corn, pea, Arabidopsis thaliana and a moss, Physcomitrella patens. The discovery of L,L-diaminopimelate aminotransferase indicates that plants may produce lysine differently than all previously known mechanisms.

In the proposed experiments the gene encoding L,L-diaminopimelate aminotransferase will be cloned. The reaction catalyzed by the enzyme will be studied. The role of the aminotransferase in lysine biosynthesis will be confirmed by observing whether a knockout mutation of the gene produces a strain that requires lysine-feeding to grow. The expression of the L,L-diaminopimelate aminotransferase gene will be studied to determine whether its expression pattern compares with other genes for lysine biosynthesis. The organisms that will be used in this study are A. thaliana and P. patens.

Intellectual Merit Statement

The proposed work may finally solve the longstanding open question of how plants produce lysine. The information may prove useful in developing strategies to improve the nutritional value of crops.

Broader Impact Statement

The proposed activities will provide research and training to a postdoctoral fellow, undergraduates, and high school students. Laboratory experiences for undergraduates and high school students in particular are necessary for the training of future scientists, policy makers, and informed citizens.