Molecular nature of mutations induced by high-LET irradiation with argon and carbon ions in Arabidopsis thaliana

Linear energy transfer (LET) is an important parameter to be considered in heavy-ion mutagenesis. However, in plants, no quantitative data are available on the molecular nature of the mutations induced with high-LET radiation above 101–124 keV μm−1. In this study, we irradiated dry seeds of Arabidopsis thaliana with Ar and C ions with an LET of 290 keV μm−1. We analyzed the DNA alterations caused by the higher-LET radiation. Mutants were identified from the M2 pools. In total, 14 and 13 mutated genes, including bin2, egy1, gl1, gl2, hy1, hy3–5, ttg1, and var2, were identified in the plants derived from Ar- and C-ions irradiation, respectively. In the mutants from both irradiations, deletion was the most frequent type of mutation; 13 of the 14 mutated genes from the Ar ion-irradiated plants and 11 of the 13 mutated genes from the C ion-irradiated plants harbored deletions. Analysis of junction regions generated by the 2 types of irradiation suggested that alternative non-homologous end-joining was the predominant pathway of repair of break points. Among the deletions, the proportion of large deletions (>100 bp) was about 54% for Ar-ion irradiation and about 64% for C-ion irradiation. Both current results and previously reported data revealed that the proportions of the large deletions induced by 290-keV μm−1 radiations were higher than those of the large deletions induced by lower-LET radiations (6% for 22.5–30.0 keV μm−1 and 27% for 101–124 keV μm−1). Therefore, the 290 keV μm−1 heavy-ion beams can effectively induce large deletions and will prove useful as novel mutagens for plant breeding and analysis of gene functions, particularly tandemly arrayed genes.