Recruitment of pre-existing networks during the evolution of C photosynthesis.

During C photosynthesis, CO is concentrated around the enzyme RuBisCO. The net effect is to reduce photorespiration while increasing water and nitrogen use efficiencies. Species that use C photosynthesis have evolved independently from their C ancestors on more than 60 occasions. Along with mimicry and the camera-like eye, the C pathway therefore represents a remarkable example of the repeated evolution of a highly complex trait. In this review, we provide evidence that the polyphyletic evolution of C photosynthesis is built upon pre-existing metabolic and genetic networks. For example, cells around veins of C species show similarities to those of the C bundle sheath in terms of C acid decarboxylase activity and also the photosynthetic electron transport chain. Enzymes of C photosynthesis function together in gluconeogenesis during early seedling growth of C Furthermore, multiple C genes appear to be under control of both light and chloroplast signals in the ancestral C state. We, therefore, hypothesize that relatively minor rewiring of pre-existing genetic and metabolic networks has facilitated the recurrent evolution of this trait. Understanding how these changes are likely to have occurred could inform attempts to install C traits into C crops.This article is part of the themed issue 'Enhancing photosynthesis in crop plants: targets for improvement'.