Richard T. Sayre

Department of Plant Biology, Ohio State University, Columbus OH, 43210

Phone (614) 292-9030; email: sayre.2@osu.edu.

There are three major research programs in our lab including; 1) molecular studies on the structure and function of the photosynthetic electron transport complexes in chloroplasts, 2) studies on the regulation of cyanogenesis and its molecular manipulation in the tropical root crop cassava, and 3) the biochemical characterization and genetic manipulation of heavy metal binding proteins in algae for use in bioremediation of heavy metal contaminated sites.

The focus areas of our photosynthesis research program include; 1) the characterization of the structure/function relationships in photosynthetic reaction center complexes, and 2) the study of energy transfer mechanisms in photosystem II. Our lab uses recombinant DNA techniques to generate site-directed mutations in chloroplast genes encoding proteins of the photosynthetic apparatus. The mutants are then characterized using a variety of biochemical and biophysical techniques. Notable accomplishments include; 1) mapping the molecular topology of PSII membrane proteins using antibodies generated against synthetic peptides, 2) development of chloroplast DNA co-transformation protocols and the generation of the first site-directed mutations in chloroplast genes, and 3) identification of functional residues in photosystem II reaction centers which are associated with water oxidizing chemistry and light harvesting processes. Presently we are testing models for the structural and functional organization of the reaction center chlorophylls involved in primary charge separation.

The objectives of our research program on cyanogenesis in cassava are; 1) to characterize the biochemistry of cyanogenic glycoside synthesis, transport and turnover, and 2) to develop transgenic plants which are less toxic (low cyanogenic) for human consumption. Towards these objectives we have demonstrated that cyanogenic enzymes are expressed in tissue specific patterns. The effect of these patterns of expression is a reduced ability to efficiently remove cyanogens from cassava root food products. Our research program also focuses on the biochemistry, physiology and cell biology of cyanogen synthesis. Recently, we have demonstrated that cyanogens are synthesized in the vacuole. In addition, we are isolating cytochrome P450(s) involved in the first dedicated step of cyanogen synthesis by yeast complementation. In order to alter cyanogenesis in cassava, we also have developed Agrobacterium Ti plasmid vectors for cassava transformation and tissue culture systems for regeneration of recalcitrant cassava cultivars. Recently, we have begun studies on the genetic manipulation of starch production in cassava.

The most recent addition to our research program is a collaborative project involving soil and analytical chemists and focuses on the biochemistry of heavy metal binding in algae. The objectives of the program are to characterize the chemistry of heavy metal binding factors in algae and to generate transgenic algae which over-express heavy metal binding proteins. These recombinant algae will be used for the bioremediation of heavy metal contaminated waters. Initial accomplishments include the characterization of heavy metal binding sites in algae and the generation of transgenic algae expressing novel heavy metal binding proteins and genes which reduce heavy metal stress. This work also has recently lead to the identification of ABC-type, xenobiotic transporters which apparently export toxic or foreign substance out of the cell.