Involvement of nonsymbiotic hemoglobin in Mesorhizobium-Lotus symbiosis

Abstract

Two distinct nonsymbiotic hemoglobin genes (LjHb1, LjHb2) of Lotus japonicus were characterized by their expression profiles. Both genes were expressed in several tissues of mature plants and enhanced expression was observed in root nodules. LjHb1 was strongly induced under hypoxia and low temperature, and by plant hormones ABA and BA, whereas LjHb2 was induced only by the application of sucrose. LjHb1 was also induced transiently by the inoculation of symbiotic rhizobium, M. loti. Microscopic observation with SNAP (NO generator) and DAF-FM (NO detector) revealed that LjHb1 was induced by NO. NO binding ability of LjHb1 recombinant protein and the phenotype of hairy root over-expressing LjHb1 supported that LjHb1 was involved in the Mesorhizobium-Lotus symbiosis.