Abstract
Lipopolysaccharide (LPS) of rhizobia is involved in establishing symbiosis between rhizobia and their host legumes. However, LPS signaling system is still not clear in plant. In mammals, LPS binding protein (LBP) forms a complex with LPS and activates innate immune system. On the genome of Lotus japonicus, four genes, LjLBP1, 2, 3, and 4, were identified as candidates for plant LBP.
Expression level of LjLBPs was analyzed with or without microsymbiont Mesorhizobium loti. The expression of LjLBP3/4 was strongly repressed in nodulated plants 28 days after inoculation compared with that of plants supplied with 0.5 mM NH4Cl. Whereas expression of LjLBP1 and LjLBP2 was stable at low level. LjLBP3/4 was up-ragulated transiently at 4h after inoculation of M.loti, Ralsonia solanacearum and Pseudomonas syringae pv. pisi. Furthermore, RNAi of LjLBPs resulted in the failure of symbiosis. These results indicate that the expression of each LBP is regulated in different manner, and LPS signaling via LBP of the host plant will be essential for establishing symbiosis especially after the microsymbionts invasion.
