C4 rice: a challenge for plant phenomics

There is now strong evidence that yield potential in rice (Oryza sativa L.) is becoming limited by 'source' capacity, i.e. photosynthetic capacity or efficiency, and hence the ability to fill the large number of grain 'sinks' produced in modern varieties. One solution to this problem is to introduce a more efficient, higher capacity photosynthetic mechanism to rice, the C-4 pathway. A major challenge is identifying and engineering the genes necessary to install C-4 photosynthesis in rice. Recently, an international research consortium was established to achieve this aim. Central to the aims of this project is phenotyping large populations of rice and sorghum (Sorghum bicolor L.) mutants for 'C-4-ness' to identify C-3 plants that have acquired C-4 characteristics or revertant C-4 plants that have lost them. This paper describes a variety of plant phenomics approaches to identify these plants and the genes responsible, based on our detailed physiological knowledge of C-4 photosynthesis. Strategies to asses the physiological effects of the installation of components of the C-4 pathway in rice are also presented.