A scheme for C evolution derived from a comparative analysis of the closely related C, C-C intermediate, C-like, and C species in the genus Flaveria.

A comparative analysis of the genus Flaveria showed a C evolutionary process in which the anatomical and metabolic features of C photosynthesis were gradually acquired through C-C intermediate stages. C photosynthesis has been acquired in multiple lineages of angiosperms during evolution to suppress photorespiration. Crops that perform C photosynthesis exhibit high rates of CO assimilation and high grain production even under high-temperature in semiarid environments; therefore, engineering C photosynthesis in C plants is of great importance in the application field. The genus Flaveria contains a large number of C, C-C intermediate, C-like, and C species, making it a good model genus to study the evolution of C photosynthesis, and these studies indicate the direction for C engineering. C photosynthesis was acquired gradually through the C-C intermediate stage. First, a two-celled C cycle called C photosynthesis was acquired by localizing glycine decarboxylase activity in the mitochondria of bundle sheath cells. With the development of two-cell metabolism, anatomical features also changed. Next, the replacement of the two-celled C cycle by the two-celled C cycle was induced by the acquisition of cell-selective expression in addition to the upregulation of enzymes in the C cycle during the C-C intermediate stage. This was supported by an increase in cyclic electron transport activity in response to an increase in the ATP/NADPH demand for metabolism. Suppression of the C cycle in mesophyll cells was induced after the functional establishment of the C cycle, and optimization of electron transport by suppressing the activity of photosystem II also occurred during the final phase of C evolution.