Characterization of a C4 maize pyruvate orthophosphate dikinase expressed in C3 transgenic rice plants

Pyruvate orthophosphate dikinase (PPDK) is a key enzyme in plants that utilize the C4 photosynthetic pathway to fix CO2. The enzymatic reaction catalyzed by PPDK is critically controlled by light and is one of the rate-limiting steps of the C4 pathway. The intact maize (Zea mays) C4-PPDK gene, containing its own promoter, terminator sequences and exon/intron structure was introduced into rice (Oryza sativa L. Indica “IR64”), a C3 plant. Expression of C4-PPDK in most transgenic rice lines resulted in increased CO2 assimilation rates compared to untransformed control plants. Most of the transformants showed higher photosynthetic activities than that of wild-type plant. Total nitrogen in the flag leaves of C4-PPDK transgenics was analyzed. Results showed an increase in total nitrogen compared to untransformed control plants suggesting that C4-PPDK expression in rice promoted nitrogen absorption from the soil. In addition, the photosynthesis rate of some transgenic IR64 lines was also increased in the greenhouse. Molecular analysis revealed that the intact PPDK gene integrated in the rice genome and affected the phenotypes of plants particularly tillers and enhanced yield of transgenic IR64 rice plants in the greenhouse.