6. Climate-Resilient Future Crop: Development of C₄ Rice

Rice is the most important crop in the world. It is a staple food for more than half of the human population and a primary food source for the world’s poorest people. Asia currently accounts for 90% of global rice production but it will need to increase this by 50% within the next 30 years. By this time the region will be home to nearly 90% of the global population increase and will likely be experiencing extreme climatic conditions. Agriculture will be challenged by diminishing water resources, reduced nutrient inputs and an increase in abiotic stresses. Rice yield increases have already stagnated and so a new paradigm is needed to meet these future challenges. Most crop plants, like rice and wheat, have a simple and less efficient photosynthetic mechanism (C₃ photosynthesis) that as a consequence results in considerable loss of water through stomatal pores on their leaves that open widely to let in more carbon dioxide. They also make a large amount of photosynthetic protein to maximise their photosynthetic rate that requires a large investment of nitrogen and hence fertiliser application. However, a few plants have evolved a more efficient C₄ photosynthetic pathway that greatly alleviates these problems. The installation of a C₄ photosynthetic pathway into major crops like rice could potentially increase yields by 50%, double the water-use efficiency and reduce fertiliser use by 40%. This is because plants with a C₄ photosynthetic pathway concentrate CO₂ within the leaf prior to photosynthetic fixation leading to increased photosynthetic efficiency and large reductions in the requirement for scarce resources like water and nitrogen (fertiliser). These modifications would be particularly advantageous in future climate scenarios where water scarcity and global temperature are predicted to increase.