Exploiting differences in the energy budget among C subtypes to improve crop productivity.

C crops of agricultural importance all belong to the NADP-malic enzyme (ME) subtype, and this subtype has been the template for C introductions into C crops, like rice, to improve their productivity. However, the ATP cost for the C cycle in both NADP-ME and NAD-ME subtypes accounts for > 40% of the total ATP requirement for CO assimilation. These high ATP costs, and the associated need for intense cyclic electron transport and low intrinsic quantum yield , are major constraints in realizing strong improvements of canopy photosynthesis and crop productivity. Based on mathematical modelling, we propose a C ideotype that utilizes low chloroplastic ATP requirements present in the nondomesticated phosphoenolpyruvate carboxykinase (PEP-CK) subtype. The ideotype is a mixed form of NAD(P)-ME and PEP-CK types, requires no cyclic electron transport under low irradiances, and its theoretical is c. 25% higher than that of a C crop type. Its cell-type-specific ATP and NADPH requirements can be fulfilled by local energy production. The ideotype is projected to have c. 10% yield advantage over NADP-ME-type crops and > 50% advantage over C counterparts. The ideotype provides a unique (theoretical) case where could be improved, thereby paving a new avenue for improving photosynthesis in both C and C crops.