Abstract
Symbiotic nitrogen fixation by collaboration between legumes and Rhizobium is an important system in the global nitrogen cycle and molecular aspect has been revealed at the early stage of the host-symbiont recognition. To understand the response of a host plant against its symbiont and pathogen, we examined expression of class 1 hemoglobin gene (LjHb1) and production of nitric oxide (NO) of Lotus japonicus. When a symbiotic rhizobium, Mesorhizobium loti, was inoculated, expression of LjHb1 and NO production were induced transiently in the roots at 4 h after inoculation. While, inoculation of pathogens (Ralstonia solanacearum and Pseudomonas syringae) induced continuous NO production in roots without expression of LjHb1. NO was also detected in nitrogen fixing root nodules. Over-expression of LjHb1 enhanced the activity of nitrogenase. Class 1 Hb may be involved in the host-symbiont recognition and in support of symbiotic nitrogen fixation by modulating NO.
