ResearchCrossroads

Summary
9315928 Chollet The experimental plan is composed of three areas of research on the control of higher plant phosphoenolpyruvate carboxylase (PEPC) activity in vivo by regulatory phosphorylation and allosteric metabolite effectors. Specific research objectives include (i) the continued scrutiny of the highly regulated PEPC-kinase signal- transduction chain by in situ studies with intact C4 and CAM plants using an integrated biochemical, immunological and/or molecular- genetic approach, and the further elucidation of the complex C4 PEPC-kinase signal-transduction chain by in situ studies with intact C4-mesophyll cells and protoplasts. The outcome of these objectives could strongly affect our basic understanding of the regulation of PEPC activity by L-malate, the negative allosteric effector. Conversely, project (ii) will focus on the opposing control of C4/CAM PEPC activity exerted by positive phosphorylated effectors (e.g., glucose 6-P, triose-P) by mapping this activator binding domain with photoaffinity-labeling and site-directed mutagenesis techniques. Finally, project (iii) will critically assess the possible regulatory phosphorylation of nonphotosynthetic PEPC in leaves and root-nodules from C3 plants by integrative in vivo (detached leaves and nodules), in situ (intact leaf protoplasts), and in vitro (isolated PEPC and PEPC-kinase) analysis. Results from these three projects will not only delineate important details of the control of C4- and CAM- photosynthesis, and details of general C/N metabolism in plants at the level of cytosolic PEPC, but at the same time will provide much needed insight into enzyme regulation in higher plants by reversible protein phosphorylation. %%% This project is focused on the posttranslational regulation of the carbon dioxide (CO2)-fixing enzyme phosphoenolpyruvate carboxylase (PEPC) in higher plants. While this enzyme is best known for its role in CO2 fixation during C4 photosynthesis and Crassulacean acid metabolism (CA M) in crops as maize, sorghum, sugarcane, and pineapple (CAM), it also functions in general plant carbon/nitrogen metabolism. Besides these important physiological and functional considerations, the PEPC enzyme represents one of the few well- known examples in higher plants of an enzyme that is controlled by the opposing action of a protein phosphatase and a protein-serine kinase. Consequently, this complex regulatory phosphorylation cycle forms the central focus of many of our present studies. Understanding about how the cycle operates is important in regulation of CO2 assimilation and in plant metabolism in general. It can form the basis for biotechnological engineering of plants to improve growth and productivity. This project is supported jointly by Metabolic Biochemistry Program, MCB and the Plant Integrative Biology Program, IBN. ***

Principal Investigator	Raymond Chollet
Co-Principal Investigator(s)
Recipient Organization	University of Nebraska-Lincoln
Granting Organization	Division of Molecular and Cellular Biosciences (MCB - NSF)

Reference	Dates	Fiscal Year	Funded Amount
			0

Keywords
Agriculture |Life Science Biological |