| Summary: | <p>Abstract</p> <p>Background</p> <p>Heavy-ion mutagenesis is recognised as a powerful technology to generate new mutants, especially in higher plants. Heavy-ion beams show high linear energy transfer (LET) and thus more effectively induce DNA double-strand breaks than other mutagenic techniques. Previously, we determined the most effective heavy-ion LET (LET<sub>max</sub>: 30.0 keV μm<sup>-1</sup>) for <it>Arabidopsis </it>mutagenesis by analysing the effect of LET on mutation induction. However, the molecular structure of mutated DNA induced by heavy ions with LET<sub>max </sub>remains unclear. Knowledge of the structure of mutated DNA will contribute to the effective exploitation of heavy-ion beam mutagenesis.</p> <p>Results</p> <p>Dry <it>Arabidopsis thaliana </it>seeds were irradiated with carbon (C) ions with LET<sub>max </sub>at a dose of 400 Gy and with LET of 22.5 keV μm<sup>-1 </sup>at doses of 250 Gy or 450 Gy. The effects on mutation frequency and alteration of DNA structure were compared. To characterise the structure of mutated DNA, we screened the well-characterised mutants <it>elongated hypocotyls </it>(<it>hy</it>) and <it>glabrous </it>(<it>gl</it>) and identified mutated DNA among the resulting mutants by high-resolution melting curve, PCR and sequencing analyses. The mutation frequency induced by C ions with LET<sub>max </sub>was two-fold higher than that with 22.5 keV μm<sup>-1 </sup>and similar to the mutation frequency previously induced by ethyl methane sulfonate. We identified the structure of 22 mutated DNAs. Over 80% of the mutations caused by C ions with both LETs were base substitutions or deletions/insertions of less than 100 bp. The other mutations involved large rearrangements.</p> <p>Conclusions</p> <p>The C ions with LET<sub>max </sub>showed high mutation efficiency and predominantly induced base substitutions or small deletions/insertions, most of which were null mutations. These small alterations can be determined by single-nucleotide polymorphism (SNP) detection systems. Therefore, C ions with LET<sub>max </sub>might be useful as a highly efficient reverse genetic system in conjunction with SNP detection systems, and will be beneficial for forward genetics and plant breeding.</p>
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