Lipopolysaccharide-binding protein genes of Lotus japonicus are related to the symbiosis with Mesorhzobium loti

Abstract

Lipopolysaccharide (LPS) is a structural component of the outer membrane of Gram-negative bacteria and LPS of pathogen induces the plant resistant. LPS is also involved in the establishment of symbiosis between legumes and rhizobia. Thus, the elucidation of the LPS recognition system is essential for understanding the plant-bacteria interaction. However, LPS recognition system is not clear in plants. In animal, LPS receptor and LPS binding protein (LBP) have been identified. Referring LPS recognition systems of animal, we tried to clone LBP gene of Lotus japonicus. As the result of BLAST research in the genome library of L. japonicus, four high regions showed high similarity with human LBP. We referred to these genes as LjLBP1, 2, 3 and 4 respectively. N-terminal domain of LjLBP1 and LjLBP2 showed the LPS binding activity. Symbiosis was aborted in the nodules formed on RNAi hairy roots of LjLBP. These results suggest that LjLBP is necessary for the normal symbiosis.