Functional evolution of C4 pyruvate, orthophosphate dikinase

Pyruvate, orthophosphate dikinase (PPDK) plays a controlling role in the PEP-regeneration phase of the C-4 photosynthetic pathway. Earlier studies have fully documented its biochemical properties and its post-translational regulation by the PPDK regulatory protein (PDRP). However, the question of its evolution into the C-4 pathway has, until recently, received little attention. One assumption concerning this evolution is that changes in catalytic and regulatory properties of PPDK were necessary for the enzyme to fulfil its role in the C-4 pathway. In this study, the functional evolution of PPDK from its ancient origins in the Archaea to its ascension as a photosynthetic enzyme in modern C-4 angiosperms is reviewed. This analysis is accompanied by a comparative investigation into key catalytic and regulatory properties of a C-3 PPDK isoform from Arabidopsis and the C-4 PPDK isoform from Zea mays. From these analyses, it is proposed that PPDK first became functionally seated in C-3 plants as an ancillary glycolytic enzyme and that its transition into a C-4 pathway enzyme involved only minor changes in enzyme properties per se.