Abstract
Leguminous plants form root nodules for symbiotic nitrogen fixation with soil bacteria Rhizobia. To utilize symbiotic nitrogen fixation, it is indispensable to understand the molecular mechanism of nodulation process. Fix- mutants, which form root nodules but have defect in nitrogen fixation activity, are useful materials to clarify the molecular mechanism which nitrogen fixation by endosymbiotic bacteria is controlled by host plant genes. A novel Fix- mutant Ljsym89 was isolated from L. japonicus Gifu plants by EMS mutagenesis. Preliminary observations of the mutant nodules at 14 dpi by optical and electron microscopy revealed that the Ljsym89 nodules show abnormal structures of bacteroids, together with typical symptoms of premature senescence, such as enlargement of symbiosomes and disintegration of the infected cells. Here, we report further characterization of a novel Fix- mutant Ljsym89 and positional cloning of its causal gene.
