Proposed C4 pathways in maize. CO2 fixation genes on the cladogram of Figure 2 are mapped onto the biochemical pathway. NADP-MDH, NADP-malate dehydrogenase; PEPC, phosphoenolpyruate carboxylase; PEPCK, phosphoenolpyruvate carboxykinase; PEPT, PEP transferase; PPDK, pyruvate orthophosphate dikinase; RuBPC, Rubisco.