Enhancing photosynthetic CO2 use efficiency in rice: approaches and challenges

It is estimated that 925 million people mainly in developing countries suffer from malnutrition due to food shortage. This situation will deteriorate as world population will reach 9 billion by 2050. It is obvious that current rate of increase in crop yields is not sufficient to solve the problem of food security worldwide, especially in Asia, where at least 50 % increase in rice yield is needed to satisfy the increasing population. Depending on advanced development of modern biotechnology, several strategies have been provided for ‘supercharging’ photosynthesis to increase rice yield. In this review, we updated four major approaches: namely improving the performance of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), establishment of photorespiratory bypass, installing single-cell and two-celled C₄ photosynthesis. The first approach aimed at direct manipulation of Rubisco for more efficient catalytic character by directed molecular evolution. The second approach focused on reducing the loss of photorespiratory CO₂ by direct manipulation of photorespiratory pathway. The last two concentrated on introduction of C₄ pathway into rice, based on the observation that the efficiency of C₄ photosynthesis is 50 % higher than that of C₃ photosynthesis.