Abstract
Formation of nitorogen-fixing root nodules is induced by mutual interactions between legume plants and rhizobium bacteria. Nodulation process is genetically controlled by both host plants and microsymbionts. To clarify the plant genes involved in nitrogen-fixing symbiosis, we isolated a number of mutant lines of a model legume Lotus japonicus through regeneration after extensive in vitro culture, that show no or little nitrogen fixation activity after rhizobium inoculation. Genetic analyses showed that the mutations are recessive and monogenic in 18 lines. The mutant phenotypes were characterized in respect to rhizobium infection, nodulation, and their behaviours to mycorrhiza infection. Mutant genes were mapped on the linkage map with DNA markers using F2 plants derived from cross between Gifu and Miyakojima accessions. At present, we identified one nod- / myc+, one nod - / myc-, and four fix- (or hist- )/ myc+ loci in these mutant plants.
