Abstract
The most of rhizobium bacteria develop N2 fixing activity only when they made endosymbiosis in the nodules formed in their compatible host legume plants. This indicates that rhizobial N2 fixation is strictly controlled by interactions with host legumes. To elucidate regulatory mechanisms of symbiotic N2 fixation by host plants, we have focused on Fix- mutants of Lotus japonicus, which develop apparently normal nodules with rhizobial endosymbiosis but exhibit no or very low N2 fixation activity. We have identified thus far four genes, Sst1, Ign1, Sen1 and Fen1, which are essential for functional symbiosis with rhizobia. Among them, Sst1 was demonstrated to encode nodule-specific sulfate transporter localized in peribacteroid membrane and plays a role for transporting sulfate required for nitrogenase. However, the exact functions of the other genes are still unknown. Here, we present the results on possible functions of Sen1 and Fen1 genes from the resent experiments using recombinant proteins.
