Promotion of Cyclic Electron Transport around Photosystem I with the Development of C4 Photosynthesis

C-4 photosynthesis is present in approximately 7,500 species classified into 19 families, including monocots and eudicots. In the majority of documented cases, a two-celled CO2-concentrating system that uses a metabolic cycle of four-carbon compounds is employed. C-4 photosynthesis repeatedly evolved from C-3 photosynthesis, possibly driven by the survival advantages it bestows in the hot, often dry, and nutrient-poor soils of the tropics and subtropics. The development of the C-4 metabolic cycle greatly increased the ATP demand in chloroplasts during the evolution of malic enzyme-type C-4 photosynthesis, and the additional ATP required for C-4 metabolism may be produced by the cyclic electron transport around PSI. Recent studies have revealed the nature of cyclic electron transport and the elevation of its components during C-4 evolution. In this review, we discuss the energy requirements of C-3 and C-4 photosynthesis, the current model of cyclic electron transport around PSI and how cyclic electron transport is promoted during C-4 evolution using studies on the genus Flaveria, which contains a number of closely related C-3, C-4 and C-3-C-4 intermediate species.