Abstract
We isolated a nodule symbiotic mutant 56M from M2 progeny of Lotus japonicus lines regenerated from callus. 56M formed white or greenish nodules upon inoculation with Mesorhizobium loti under nitrogen-free condition and the shoot growth was remarkably retarded with symptoms of nitrogen deficiency. The cytoplasmic structure in Rhizobium-infected cells of 56M was disorganized and aggregated at 3 weeks after M. loti inoculation. The growth of 56M in the presence of nitrate was the same as wild type. The number of nodules under nitrogen-free condition and the dose-response of nitrate on nodule formation were the same as wild type as well. The infection process of M. loti on 56M appears to be normal and then the symbiosis is collapsed much earlier.
The segregation of F2 phenotype indicated that 56M mutant was monogenic and recessive. Map-based cloning to isolate 56M is under way. The 56M locus could be positioned on chromosome 5.
