Physiological and phenotypical characterization of transgenic rice double crosses with overexpressed maize phosphoenolpyruvate carboxylase and pyruvate, phosphate dikinase

The success of the First Green Revolution in the 1960s paved the way to an increase in the production of major crops including wheat and rice. However, the amount of rice being produced now will not be enough to feed the growing population by 2050. Currently, efforts are underway to produce a rice prototype with C4 photosynthetic pathway. In this study, rice double crosses overexpressing maize phosphoenolpyruvate carboxylase (ZmPEPC) and pyruvate, phosphate dikinase (ZmPPDK) were characterized molecularly and phenotypically. Polymerase chain reaction and western blot analysis identified homozygous lines of ZmPEPC-28xZmPPDK-02, ZmPEPC-28xZmPPDK-11 and ZmPEPC-28xZmPPDK-29. Southern blot analysis showed that there was only one gene copy number for both ZmPEPC and ZmPPDK for all the crossing events. In addition, cytological immunolocalization had shown that ZmPEPC had intense expression in both the mesophyll and bundle sheath cells. On the other hand, ZmPPDK exhibited specific expression in the bundle sheath cell. Significantly lower glucose and fructose content were observed that the ZmPEPC-28xZmPPDK-02 event. Moreover, the three events exhibited significantly higher tillering in all of the crossing events compared with the wild type. It was also observed that the ZmPEPC-28xZmPPDK-29 had significantly improved tillering when compared to its parents. The height observed for ZmPEPC-28xZmPPDK-02 was significantly higher than the wild type and ZmPEPC-28xZmPPDK-11 was significantly shorter than the control and its parents. There were no significant differences observed in the biomass and yield of the three events when the compared with the wild type control, however, improved yield was observed in ZmPEPC-28xZmPPDK-11 compared with their parents. Further assessment on the starch content and metabolite profiling using GC-MS will be performed for a more in-depth characterization of the crosses.