Characterization of novel symbiotic Fix^- mutant of Lotus joponicus, Ljsym104, that shows impaired nitrogen fixation activity.

Abstract

Nitrogen fixation activity of rhizobia inside the root nodules is strictly controlled by interactions with the host plants. The early steps of the interactions between rhizobia and host legumes have been revealed by genetic method using symbiotic mutants of the model legume plants such as Lotus joponicus. Meanwhile, the information about the host plant genes that are crucial for the interactions in the later stages of symbiosis, such as nodule organogenesis and the control of nitrogen fixation is still limited. The Fix^- mutants, which form apparently normal nodules that contain endosymbiotic rhizobia but exhibit low or no nitrogen fixation activity, are the useful materials to identify the plant genes involved in development of rhizobial nitrogen fixation under symbiotic conditions.
In this study, we characterized a novel Fix^- mutant of Lotus joponicus, Ljsym104. This mutant forms small white nodules with low nitrogen fixation activity, and shows nitrogen deficiency symptoms under symbiotic conditions. Further characterization of Ljsym104 mutants and the causal gene, LjSYM104, will be presented.