The Function of a Maize-Derived Phosphoenol pyruvate Carboxylase (PEPC) in Phosphorus-Deficient Transgenic Rice

Transgenic rice ( Oryza sativa L., a C₃ plant) lines carrying a complete phospho enol pyruvate carboxylase (PEPC) gene from maize (a C₄ plant) were tested for their performance in terms of organic acid synthesis and organic acid exudation into the rhizosphere under phosphorus (P)-deficient conditions. High PEPC activity increased the fraction of photosynthetically fixed carbon allocated to the organic acid pool, and P deficiency enhanced oxalate exudation from the roots of the transgenic plants. There was no evidence that the transformed PEPC was involved in internal P recycling in the plant. However, the root PEPC activity was positively correlated with the oxalate exudation and negatively correlated with the root P concentration, and a higher root PEPC activity led to a higher oxalate exudation. Thus, it is suggested that C₄-PEPC transgenic rice plants had acquired the ability to exude oxalate, which enhanced their capacity to adapt to low P soil conditions.