**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PHOSPHOENOLPYRUVATE CARBOXYLASE (PPC) IS A KEY CARBON CAPTURE ENZYME IN PLANTS AND BACTERIA THAT PRODUCES OXALOACETATE AS A PRECURSOR TO MANY IMPORTANT BIOMOLECULES. A PRIOR PROJECT TO IDENTIFY ARABIDOPSIS MUTANTS WITH INCREASED ALUMINUM RESISTANCE RESULTED IN ISOLATION OF SEVERAL LINES THAT HAD INCREASED GROWTH ASSOCIATED WITH RELEASE OF HIGHER LEVELS OF ALUMINUM CHELATING MALATE INTO THE ROOT GROWTH ENVIRONMENT. RECENT ANALYSIS OF THESE MUTANT LINES REVEALED THAT THREE OF THESE MUTANTS WERE THE RESULT OF SIMPLE CHANGES TO AN ARABIDOPSIS GENE THAT ENCODES PHOSPHOENOLPYRUVATE CARBOXYLASE 1. PRELIMINARY STUDIES INDICATE THAT THE IDENTIFIED MUTATIONS ACTUALLY IMPROVE RATE OF OUTPUT OF THIS ENZYME IN ARABIDOPSIS, WHICH IS CONSISTENT WITH THE INCREASED RELEASE OF OXALOACETATE-DERIVED MALATE. MOST IMPORTANTLY, THE OBSERVED CHANGES THAT SEEMINGLY REDUCE OR DESTROY PROPER REGULATION OF THIS ENZYME AFFECT POSITIONS THAT ARE CONSERVED IN ALL PPCS SO FAR SEQUENCED FROM PLANTS SUGGESTING THAT THESE CHANGES HAVE UTILITY FOR IMPROVING CARBON CAPTURE AND THE RELATED OUTCOMES IN PLANTS IN GENERAL. THIS PROPOSAL IS FOCUSED ON DEVELOPING NEW KNOWLEDGE OF HOW THIS POORLY UNDERSTOOD CLASS OF ENZYMES FUNCTIONS AT THE BIOCHEMICAL LEVEL ALONG WITH ATTEMPTING TO DETERMINE WHETHER THESE IDENTIFIED CHANGES WILL HAVE A UNIVERSAL IMPACT ON PPCS. FOR THIS WORK, PPCS FROM ARABIDOPSIS AND MAIZE WILL SERVE AS THE FOCUS OF ANALYSES REGARDING THE IMPACT OF THESE AMINO ACID CHANGES ON PROTEIN ACTIVITY. THIS WILL INCLUDE AN EXTENSIVE ANALYSIS OF HOW THESE AMINO ACID CHANGES IMPACT A RANGE OF KINETIC PARAMETERS AS WELL AS ALLOSTERIC REGULATION. IN CONJUNCTION WITH THE KINETIC ANALYSES, STRUCTURAL STUDIES TO ASSESS HOW THESE AMINO ACID CHANGES AFFECT CONFORMATIONAL CHANGES OF THE ENZYME AS IT PROGRESSES THROUGH THE CATALYTIC MECHANISM WILL BE PERFORMED. AS A COMPLEMENT TO THE IN VITRO STUDIES, WORK WILL BE PERFORMED WITH TRANSGENIC ARABIDOPSIS AND MAIZE TO DETERMINE THE IMPACTS OF THESE AMINO ACID CHANGES ON PPC DEPENDENT OUTPUTS. THIS WILL FOCUS ON PROCESSES SUCH AS ALUMINUM RESISTANCE FOR ARABIDOPSIS AND MAIZE ROOTS, WITH THE EXPECTATION BEING THAT TRANSLATION OF OUR AMINO ACID CHANGES INTO A MAIZE PPC WILL CONFER SIMILAR POSITIVE EFFECTS FOR ROOT GROWTH OF THIS VALUABLE CROP PLANT IN ALUMINUM TOXIC ENVIRONMENTS. ADDITIONALLY, THESE AMINO ACID CHANGES HAVE BEEN INTRODUCED INTO A MAIZE PPC THAT IS RESPONSIBLE FOR C4 PHOTOSYNTHESIS AND TRANSGENIC LINES WILL BE TESTED TO DETERMINE WHETHER THEY HAVE INCREASED CARBON CAPTURE AS A RESULT OF THE MODIFICATIONS TO THE PPC. THROUGH THIS RESEARCH, IT IS EXPECTED THAT A DETAILED UNDERSTANDING OF HOW PPCS FUNCTION AND THE EFFECTS OF THE AMINO ACID CHANGES ON THIS ENZYMATIC MECHANISM WILL BE DEVELOPED WHILE AT THE SAME TIME THE EFFORTS SHOULD PROVIDE CLARITY ABOUT WHETHER THESE CAN BE USED TO IMPROVE CARBON CAPTURE BY PLANTS IN GENERAL.