Regulation of pyruvate, orthophosphate dikinase by ADP-/Pi-dependent reversible phosphorylation in C3 and C4 plants

Pyruvate, orthophosphate dikinase (PPDK, E.C. 2.7.9.1) is a cardinal carbon-assimilating, stromal enzyme of the C4 photosynthetic pathway. Like several other photosynthetic pathway enzymes, its activity is strictly and reversibly regulated by light. This regulation is conferred by the PPDK regulatory protein (RP), a bifunctional protein kinase/phosphatase that catalyzes the ADP-/Pi-dependent, reversible phosphorylation of an active-site threonine residue. In this minireview, we highlight how plastidic PPDK in leaves and developing seeds of C3 plants is regulated in an identical manner as C4 PPDK via a putative C3-RP isoform. Additionally, we also detail the progress in research concerning C4 RP, since this highly unusual regulatory enzyme was last reviewed nearly two decades ago.