Abstract
The nodule number of legume roots is tightly regulated through root-to-shoot long-distance signaling. Hypernodulation mutants deficient in the negative regulation of nodulation, also termed autoregulation of nodulation, have been isolated and characterized. However, genes responsible for autoregulation have not been identified besides HAR1 of the model legume Lotus japonicus and its orthologous genes from other legumes. HAR1 has been shown to regulate the nodule number by the shoot genotype. Thus, the isolation of root-regulated hypernodulation mutants would extend our understanding of nodule autoregulation at molecular level.
In the present study, novel L. japonicus hypernodulation mutants were isolated by C6+ ion beam irradiation. Grafting experiments allowed us to find two root-regulated hypernodulation mutant lines 716-1 and 1836-1. Both mutants showed no dwarf phenotypes, but a lower lateral root number than wild-type MG-20. Mapping of the causative genes indicated that 716-1 and 1836-1 have mutations in different loci.
