Responsible Gene Analysis of Phenotypic Mutants Revealed the Linear Energy Transfer (LET)-Dependent Mutation Spectrum in Rice

Linear energy transfer (LET) is an important parameter for ion beam mutagenesis. We irradiated rice seeds with carbon ions (LET: 23, 30, 50, or 57 keV μm-1), neon ions (LET: 63 or 70 keV μm-1), or argon ions (LET: 290 keV μm-1). We subsequently isolated 56 mutants and analyzed the mutations in the responsible genes for mutant phenotypes to evaluate the effects of different LETs in rice. Mutations were classified as single nucleotide variants, small deletions (<100 bp), large deletions (≥100 bp), and chromosomal rearrangements (inversions and translocations). The carbon and neon ions (23-70 keV μm-1) tended to induce small deletions, whereas the argon ions mainly induced large deletions. These results were consistent with the findings of our previous studies on Arabidopsis mutants irradiated with carbon ions (23 or 30 keV μm-1) or argon ions (290 keV μm-1). Moreover, the deletions caused by argon ions were larger than those induced by carbon or neon ions. Therefore, in rice and Arabidopsis, carbon ion (23 or 30 keV μm-1) irradiations are more likely to induce single-gene mutations, whereas irradiation with argon ions (290 keV μm-1) tends to cause large deletions, that can be useful to disrupt tandemly arrayed genes.