Two major metabolic factors for an efficient NADP-malic enzyme type C(4) photosynthesis

Compared to the large number of studies focused on the factors controlling C(3) photosynthesis efficiency, there are relatively fewer studies of the factors controlling photosynthetic efficiency in C(4) leaves. Here, we used a dynamic systems model of C(4) photosynthesis based on maize (Zea mays) to identify features associated with high photosynthetic efficiency in NADP-malic enzyme (NADP-ME) type C(4) photosynthesis. We found that two additional factors related to coordination between C(4) shuttle metabolism and C(3) metabolism are required for efficient C(4) photosynthesis: (1) accumulating a high concentration of phosphoenolpyruvate through maintaining a large PGA concentration in the mesophyll cell chloroplast and (2) maintaining a suitable oxidized status in bundle sheath cell chloroplasts. These identified mechanisms are in line with the current cellular location of enzymes/proteins involved in the starch synthesis, the Calvin–Benson cycle and photosystem II of NADP-ME type C(4) photosynthesis. These findings suggested potential strategies for improving C(4) photosynthesis and engineering C(4) rice.