Screening of novel Fixation minus mutants of Lotus japonicus mutagenized by ion-beam

Abstract

The legumes form nodules for the symbiosis with Rhizobia to fix nitrogen. Fix^- mutants of legume plants form nodules but fail to develop rhizobial nitrogen fixation. This indicates that host plant genes are crucial for development and/or maintenance of nitrogen fixation activity of endosymbiotic rhozobia. Molecular genetic studies of the Fix^- mutants are useful to clarify the host-plant mechanisms controlling symbiotic nitrogen fixation. However, numbers of Fix^- mutants isolated are still limited.
Here, we report the screening of Fix^- mutants from Lotus japonicus MG-20 "Miyakojima" mutagenized by heavy ion beam irradiation. Approximately 72,000 M2 seeds derived from 2,400 M₁ lines were cultured with Rhizobia under nitrogen-free condition. A total of 26 candidate mutants showed reproducibility of the Fix^- phenotypes in M₃ generation. So far, rough mapping suggested 5 mutant lines could be novel Fix^- mutants.