A Study on Ion-beam-induced Mutations in Rice under Cross-ministerial Research Program, “SIP”

Since 2014, we have been involved in the scientific research program, Cross-ministerial Strategic Innovation Promotion Program (SIP), directed by the Council for Science, Technology and Innovation (CSTI). The project, “Technologies for Creating Next-Generation Agriculture, Forestry and Fisheries” is one of the 11 projects produced and run under SIP. One of the major goals in this project is establishing new breeding techniques including sophistication of the ion-beam breeding technique. With collaborating other irradiation research facilities such as RIKEN Nishina Center and Institute of Radiation Breeding (IRB), we are going to analyze DNA of rice mutants by exome analysis1). This study is aimed to uncover features of induced mutations caused by ion beams in TIARA, and figure out similarities and differences of characteristics of mutations obtained in the other facilities. Rice cultivar Nipponbare was chosen for the material of the experiment, because genome sequence of Nipponbare has been released to the public. Seeds of Nipponbare were irradiated with 40 Gy of 320-MeV 12C6+ ions (LET on surface = 76 keV/μm), after adjusting their water content to 12~13%, and sown on soil to grow M1 plants in a greenhouse at TARRI, QST. M2 seeds were harvested from every M1 plants and sown again on soil to estimate mutagenic effect by counting the number of chlorophyll mutants in the M2 lines at seedling stage. Several types of chlorophyll mutants, which show pale or white leaf color, were identified. The appearance rate of the chlorophyll mutants was 6.6% (134 / 2,039 M2 lines), suggesting that the irradiation properly worked and caused mutations in the rice genome as expected. We also screened morphological mutants in this mutagenized population in a green house and identified several mutant candidates with altered visible phenotype. Seeds of these mutant candidates were harvested and the mutant phenotype was confirmed in next (M3) generation. At the end of March 2016, we have successfully confirmed mutant phenotypes in 8 independent M3 lines. These mutants were put on the list for exome analysis that will be performed in the project. Some M2 lines were send to IRB to be screened in the paddy field in IRB