The aim of this project is to develop strategies for metabolic engineering of plants enriched in folates and soluble methionine by manipulating the network of tetrahydrofolate-bound one-carbon (C1) units in plastids. Plants will be engineered to consist of simultaneous expression of methionine synthase and 5,10-methylenetetrahydrofolate enzymes in plastids. Two methods for over-expression will be tested: chloroplast-targeted expression from strong constitutive nuclear gene promoters, and ectopic expression from the genes incorporated into the plastid genome. Metabolic engineering will be carried out in tobacco (Nicotiana tabacum), a species in which plastid transformation can be routinely obtained. Isozymes of serine hydroxymethyltransferase (SHMT) will also be studied, as this enzyme may be a rate-limiting step of folate biosynthesis. Understanding the biochemical properties and subcellular localization of SHMT is essential for planning and interpretation of the proposed metabolic engineering experiments, a study that will be carried out in Arabidopsis thaliana, a model species in plant biology, in which genomic resources are available. The research can lead to the generation of plants enriched in folates and methionine. Folate deficiency in humans has been linked to anemia, birth defects and vascular diseases. Engineered plants with increased folate content will represent a dietary source of natural folates, and could potentially solve the problem of poor folate uptake, and the associated health disorders, for human populations. Methionine is an essential amino acid for humans and nonruminant animals. Crops used for animal feed do not have optimal methionine content, so they must be fortified with supplemental methionine. The high cost of this supplementation has prompted recent interest in metabolic engineering of plants with increased methionine content. The research program, in collaboration with Dr. Pal Maliga at Rutgers University, will train students and post-doctorals in all aspects of metabolic engineering.
