Evolution of C < inf > 4 < /inf > phosphoenolpyruvate carboxylase in the genus Alternanthera: Gene families and the enzymatic characteristics of the C < inf > 4 < /inf > isozyme and its orthologues in C < inf > 3 < /inf > and C < inf > 3 < /inf > /C < inf > 4 < /inf > Alternantheras

Abstract

Phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.3) is a key enzyme of C4 photosynthesis. It has evolved from ancestral non-photosynthetic (C3) isoforms and thereby changed its kinetic and regulatory properties. We are interested in understanding the molecular changes, as the C4 PEPCases were adapted to their new function in C4 photosynthesis and have therefore analysed the PEPCase genes of various Alternanthera species. We isolated PEPCase cDNAs from the C4 plant Alternanthera pungens H.B.K., the C3/C4 intermediate plant A. tenella Colla, and the C3 plant A. sessilis (L.) R.Br. and investigated the kinetic properties of the corresponding recombinant PEPCase proteins and their phylogenetic relationships. The three PEPCases are most likely derived from orthologous gene classes named ppcA. The affinity constant for the substrate phosphoenolpyruvate (K0.5 PEP) and the degree of activation by glucose-6-phosphate classified the enzyme from A. pungens (C 4) as a C4 PEPCase isoform. In contrast, both the PEPCases from A. sessilis (C3) and A. tenella (C3/C4) were found to be typical C3 PEPCase isozymes. The C4 characteristics of the PEPCase of A. pungens were accompanied by the presence of the C4-invariant serine residue at position 775 reinforcing that a serine at this position is essential for being a C4 PEPCase (Svensson et al. 2003). Genomic Southern blot experiments and sequence analysis of the 3′ untranslated regions of these genes indicated the existence of PEPCase multigene family in all three plants which can be grouped into three classes named ppcA, ppcB and ppcC. © Springer-Verlag 2005.