Identification of a plant molecule involved in a surveillance system for the symbiotic nitrogen fixation and its localization in the symbiotic tissues

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Lipopolysaccharide (LPS) of bacteria induces the plant resistance in pathogenic combination and is also involved in the establishment of symbiosis between legumes and rhizobia. However, LPS recognition system is still unknown in plants. Referring LBP of mammals, four LBP-candidates were identified on the genome of Lotus japonicus and referred to as LjLBPs. N-terminal barrel of LjLBPs bound with LPS of Escherichia coli. Hairy roots transformed with the fusion genes of LjLBPs and mOrange revealed the localization of LjLBPs. LjLBPs were secreted to the outside of the roots and, in the nodule, targeted to the rhizobia that penetrated into the host plant cells. We investigated the symbiotic phenotype of the hairy roots carrying RNAi- and overexpressing- constructs, and mutant lines generated by EMS treatment or LORE1 insertion. However, we could not establish the idea that LjLBPs were essential for the symbiosis between L. japonicus and its microsymbiont Mesorhizobium loti.