PHOSPHOENOLPYRUVATE CARBOXYLASE - STRUCTURE, REGULATION AND EVOLUTION

Plant phosphoenolpyruvate carboxylase (EC 4.1.1.31; PEPC) is encoded by a small multigene family in which the expression of each member is controlled individually by exogenous (light, environmental) and/or endogenous (hormonal and developmental) stimuli. The involvement of putative trans-acting factors and consensus cis-elements of promoters in the specific transcriptional regulation of the PEPC genes is discussed. At the post-translational level, the regulatory strategy of the plant enzyme is mainly to offset the negative effect of the feedback inhibitor, L-malate, the end-product of the oxaloacetate reduction. All plant PEPC-forms are under positive and negative allosteric control by metabolite effecters and possess a consensus phosphorylation site containing a target serine residue near their N-terminus (e.g. Ser8 in C-4 PEPC from sorghum). In C-4 and Crassulacean acid metabolism (CAM) plants, a complex signal-transduction chain activates a Ca2+-independent protein-serine kinase responsible for regulatory phosphorylation of PEPC. A more thorough understanding of the functional and regulatory properties of the bacterial and C-4 enzymes has emerged by exploiting recombinant proteins and site-directed mutagenesis. In these newly opened areas, PEPC offers one of the best characterized paradigms of plant signaling. Finally, some emerging ideas on the evolution and phylogenetic relationships of the various PEPC isoforms are presented.