**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE INTERMEDIATES AND IMMEDIATE END-PRODUCTS OF THE SHIKIMATE PATHWAY SERVE IN PLANTS AS PRECURSORS TO THOUSANDS OF COMPOUNDS WITH AGRONOMIC, NUTRITIONAL, AND INDUSTRIAL RELEVANCE. A COMPLETE SET OF ENZYMES NECESSARY FOR THE SHIKIMATE PATHWAY IS KNOWN TO BE LOCATED IN THE SUBCELLULAR COMPARTMENT KNOWN AS THE PLASTID. WHILE THIS COMPARTMENT IS GENERALLY ACCEPTED AS THE SOLE SITE OF SYNTHESIS OF SHIKIMATE PATHWAY PRODUCTS, IT IS NECESSARY FOR PLANT CELLS TO MAINTAIN POOLS OF THE KEY INTERMEDIATE SHIKIMATE AND THE CLOSELY RELATED COMPOUND QUINATE OUTSIDE OF THE PLASTIDS FOR THE PRODUCTION OF SEVERAL MAJOR METABOLITES. THIS APPARENT CONTRADICTION IN OUR CURRENT UNDERSTANDING OF PLANT METABOLISM PREVENTS EFFECTIVE TARGETING OF ENHANCED PRODUCTION OF VALUABLE SHIKIMATE PATHWAY-DERIVED PHYTOCHEMICALS VIA EITHER TRADITIONAL BREEDING OR BIOENGINEERING STRATEGIES.DHDSDH ENZYMES WITH APPARENT EXTRA-PLASTIDIAL LOCALIZATIONSMAY HELP RESOLVE THIS APPARENT CONTRADICTION IN OUR CURRENT UNDERSTANDING OF PLANT METABOLISM. WE WILL USE A COMBINATION OF IN VITRO BIOCHEMISTRY, REVERSE GENETICS, AND METABOLIC ANALYSIS TO EXPLORE THE LINK BETWEEN DIFFERENT DHDSDH ISOFORMS AND DOWNSTREAM PHYTOCHEMICALS THAT INFLUENCE FOOD QUALITY AND/OR HAVE AGRONOMIC AND INDUSTRIAL RELEVANCE. USING TOMATO AND BEET AS OUR EXPERIMENTAL SYSTEMS, WE WILL DETERMINE THE BIOCHEMICAL PROPERTIES AND VERIFY THE SUBCELLULAR LOCALIZATION OF DHDSDH ENZYMES, INCLUDING THOSE PRESUMED TO BE CYTOSOLIC, THEREBY DETERMINING THE METABOLIC POTENTIAL OF THESE ENZYMES. THIS WILL BE COMPLEMENTED BY EXAMINING THE REAL IN PLANTA IMPACT OF ALTERNATIVE DHDSDH ISOFORMS IN TOMATO AND BEET, INCLUDING DETERMINING WHETHER THE METABOLIC ROLES OF THESE ISOZYMES MAY BE INTEGRATED WITH A MORE COMPLETE CYTOSOLIC SHIKIMATE PATHWAY, AS POSITED NEARLY FOUR DECADES AGO. THIS WILL INVOLVE THE CREATION OF GENETICALLY MODIFIED PLANTS IN WHICH THE LEVELS OF THESE ENZYMES HAVE BEEN ALTERED AND MEASURING THE IMPACT OF THESE ALTERATIONS ON SHIKIMATE PATHWAY INTERMEDIATES AND PRODUCTS, INCLUDING SEVERAL CHEMICALS THAT CONFER DESIRABLE CHARACTERISTICS ON CROP SPECIES. RESULTS GENERATED FROM THIS WORK WILL IMPACT OUR FUNDAMENTAL UNDERSTANDING OF PHYTOCHEMICAL METABOLISM, PROVIDING TARGETS FOR FUTURE DEVELOPMENT OF ENHANCED CROP VARIETIES. THIS IS EXPECTED TO ULTIMATELY FACILITATE DEVELOP OF CROPS WITH BETTER RESISTANCE TO PESTS AND ABIOTIC STRESSES, IMPROVED NUTRITIONAL VALUE, AND FLAVORS AND COLORS THAT ARE MORE DESIREABLE TO CONSUMERS. DUE TO THE INDUSTRIAL POTENTIAL OF MANY SHIKIMATE PATHWAY-DERIVED COMPOUNDS AS LUBRICANTS, PLASTIC ALTERNATIVES, AND FUELS, THIS RESEARCH WILL ALSO BUILD ON EXISTING GROUNDWORK INTENDED TO DEVELOP PLANT-BASED PLATFORMS FOR SUSTAINABLE PRODUCTION OF PETROCHEMICAL REPLACEMENTS AS SOCIETY MOVES TOWARDS THE GOAL OF POST-PETROLEUM LIFESTYLES.