Identification of a Nitrate Tolerant Supernodulating Mutant in Lotus japonicus

Abstract

In an attempt to identify new genes involved in the process of nodule development and regulation of nodulation in the model legume Lotus japonicus the progeny of about 1,000 primary transformant plants has been screened for mutant nodulation phenotypes. Among other very interesting nodulation mutants a family segregating supernodulating (Nod++) mutants of Lotus japonicus was identified. The segregation in this family, as well as in the F2 progeny of the back cross to wild type plants, was 3:1, demonstrating monogenic recesive inheritance. Depending on the growth conditions mutant plants develop between 3–10 fold increased number of nodules as compared to wild type plants. Furthermore, suppression of the nodulation is not observed even in the presence of high concentrations of nitrate in the medium. The inability to grow when plants are heavily nodulated, even though different forms of combined nitrogen are supplied, and the abnormal phenotype of the root system are other interesting characteristics of this supernodulating mutant. Southern blot analysis indicated that the mutant is not tagged. Thus, the mutant has been crossed to a different ecotype (namely Funakura) and to the diploid species Lotus filicaulis in order to approach the map based cloning of the mutant locus. The F2 population of these crosses are currently been analyzed for linked markers.