Evolution of C4 photosynthetic genes and overexpression of maize C4 genes in rice

C3 plants including many agronomically important crops exhibit a lower photosynthetic efficiency due to inhibition of photosynthesis by O-2 and the associated photorespiration. C4 plants had evolved the C4 pathway to overcome low CO2 and photorespiration. This review first focuses on the generation of a system for high level expression of the C4-specific gene for pyruvate, orthophosphate dikinase (Pdk), one of the key enzyme in C4 photosynthesis. Based on the results with transgenic rice plants, we have demonstrated that the regulatory system controlling the Pdk expression in maize is not unique to C4 plants but rice (C3 plant) posses a similar system. Second, we discuss the possibility of the high level expression of maize C4-specific genes in transgenic rice plants. Introduction of the maize intact phosphoenolpyruvate carboxylase gene (Ppc) caused 30-100 fold higher PEPC activities than non-transgenic rice. These results demonstrated that intact C4-type genes are available for high level expression of C4 enzymes in rice plants.