Abstract
During C(4) photosynthesis, CO(2) is concentrated around the enzyme RuBisCO. The net effect is to reduce photorespiration while increasing water and nitrogen use efficiencies. Species that use C(4) photosynthesis have evolved independently from their C(3) ancestors on more than 60 occasions. Along with mimicry and the camera-like eye, the C(4) 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(4) photosynthesis is built upon pre-existing metabolic and genetic networks. For example, cells around veins of C(3) species show similarities to those of the C(4) bundle sheath in terms of C(4) acid decarboxylase activity and also the photosynthetic electron transport chain. Enzymes of C(4) photosynthesis function together in gluconeogenesis during early seedling growth of C(3)Arabidopsis thaliana Furthermore, multiple C(4) genes appear to be under control of both light and chloroplast signals in the ancestral C(3) 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(4) traits into C(3) crops.This article is part of the themed issue 'Enhancing photosynthesis in crop plants: targets for improvement'.