Poster: Enzymology

Abs # 263: Analysis of phosphoenolpyruvate carboxylase kinase genes in C₃ plants

Presenter:	Sullivan, Stuart , 9907448s@student.gla.ac.uk
Authors	Sullivan, Stuart  (A)   Hartwell, James  (B)   Nimmo, Hugh  (A)
Affiliations:	(A): University of Glasgow (B): University of York

Phosphoenolpyruvate carboxylase (PEPc) is a ubiquitous cytosolic plant enzyme. In C₄ and CAM plants PEPc is responsible for the primary fixation of atmospheric CO₂. In C₃ plants it has a general role in the carbon economy of the plant by recapturing respiratory CO₂. In most plant tissues it is the major anaplerotic enzyme replenishing carbon-skeletons removed from the TCA cycle, for functions such as amino acid biosynthesis. Other biological roles associated with PEPc activity include: guard cell movement, a pH stat, N₂ fixation in legume root nodules and fruit ripening. PEPc is an allosteric enzyme; it is activated by glucose 6-phosphate and triose phosphates, and is inhibited by L-malate. The sensitivity of PEPc to these metabolites is dependent upon the phosphorylation status of a single serine residue near its N-terminus. The phosphorylation status of PEPc is controlled by the level of expression of phosphoenolpyruvate carboxylase kinase (PEPc kinase). PEPc kinase activity and the phosphorylation status of PEPc are increased by different signals in different tissues. In legume root nodules, PEPc provides dicarboxcylic acids (malate, succinate) for both bacteroid respiration and amino acid synthesis. Therefore PEPc is an important control point for nodule metabolism. We are interested in the expression and roles of PEPc kinase in C₃ plants, using soybean as one model system. We have isolated four putative PEPc kinase genes from soybean and have demonstrated the biochemical function of the product for three of these genes. We report on the expression patterns of the four genes using RT-PCR analysis.