Abstract
Protons may have contributed to the evolution of plants as a major component of cosmic-rays and also have been used for mutagenesis in plants. Although the mutagenic effect of protons has been well-characterized in animals, no comprehensive phenotypic and genomic analyses has been reported in plants. Here, we investigated the phenotypes and whole genome sequences of Arabidopsis M2 lines derived by irradiation with proton beams and gamma-rays, to determine unique characteristics of proton beams in mutagenesis. We found that mutation frequency was dependent on the irradiation doses of both proton beams and gamma-rays. On the basis of the relationship between survival and mutation rates, we hypothesized that there may be a mutation rate threshold for survived individuals after irradiation. There were no significant differences between the total mutation rates in groups derived using proton beam or gamma-ray irradiation at doses that had similar impacts on survival rate. However, proton beam irradiation resulted in a broader mutant phenotype spectrum than gamma-ray irradiation, and proton beams generated more DNA structural variations (SVs) than gamma-rays. The most frequent SV was inversion. Most of the inversion junctions contained sequences with microhomology and were associated with the deletion of only a few nucleotides, which implies that preferential use of microhomology in non-homologous end joining was likely to be responsible for the SVs. These results show that protons, as particles with low linear energy transfer (LET), have unique characteristics in mutagenesis that partially overlap with those of low-LET gamma-rays and high-LET heavy ions in different respects.
Highlights
Life on Earth has been exposed to ionizing radiation during its evolutionary history (Todd, 1994)
The survival rates of Arabidopsis were investigated 4 weeks after sowing dry seeds irradiated with 100 MeV proton beams (LET = 0.7306 keV/μm) or gamma-rays (LET = 0.2 keV/μm) at different irradiation doses (Figure 1)
The Dq calculated following Hase et al (2012) was 13% lower for proton beam irradiation (754 Gy) than it was for gamma-ray irradiation (860 Gy), which indicates that the negative effect of proton beams on plant survival was slightly higher than that of gamma-rays
Summary
Life on Earth has been exposed to ionizing radiation during its evolutionary history (Todd, 1994). These relationships among LET, spectrum of DNA mutation, and impact on gene function are supported by the results of Kazama et al (2008, 2011) They showed that ion beams with LETmax of 30.0 KeV μm−1 produced the highest phenotypic mutation rate among ion beams with various LETs, because radiation with this LET maximized null mutations of genes by inducing frequent SBSs and small InDels (Kazama et al, 2011). Yamaguchi et al (2009) showed that irradiation at the shoulder dose, from which the survival rate of plants from the irradiated seeds decreases rapidly according to increasing dose, maximized the number of phenotypic mutants in M2 generation per irradiated seeds This relationship between irradiation dose and mutation frequency was applicable to gamma-rays and diverse ion beams. On the basis of the obtained results, we discuss the implications of proton beam-induced mutation on the plant DNA repair mechanism and the applicability of proton beam irradiation to plant mutagenesis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
