LET dependence on killing effect and mutagenicity in the model filamentous fungus Neurospora crassa

Abstract

Purpose: To assess the unique biological effects of different forms of ionizing radiation causing DNA double-strand breaks (DSBs), we compared the killing effect, mutagenesis frequency, and mutation type spectrum using the model filamentous fungus Neurospora.

Materials and methods: Asexual spores of wild-type Neurospora and two DSB repair-deficient strains [one homologous recombination- and the other non-homologous end-joining (NHEJ) pathway-deficient] were irradiated with argon (Ar)-ion beams, ferrous (Fe)-ion beams, or X-rays. Relative biological effectiveness (RBE), forward mutation frequencies at the ad-3 loci, and mutation spectra at the ad-3B gene were determined.

Results: The canonical NHEJ (cNHEJ)-deficient strain showed resistance to higher X-ray doses, while other strains showed dose-dependent sensitivity. In contrast, the killing effects of Ar-ion and Fe-ion beam irradiation were dose-dependent in all strains tested. The rank order of RBE was Ar-ion > Fe-ion > C-ion. Deletion mutations were the most common, but deletion size incremented with the increasing value of linear energy transfer (LET).

Conclusions: We found marked differences in killing effect of a cNHEJ-deficient mutant between X-ray and high-LET ion beam irradiations (Ar and Fe). The mutation spectra also differed between irradiation types. These differences may be due to the physical properties of each radiation and the repair mechanism of induced damage in Neurospora crassa. These results may guide the choice of irradiation beam to kill or mutagenize fungi for agricultural applications or further research.

Keywords:

• High-LET ion beam
• homologous recombination repair
• non-homologous end-joining
• large deletion
• multiple mutations

Acknowledgements

The authors are sincerely grateful to Dr. Akihisa Takahashi for useful comments and critical reviewing of the manuscript. This experiment was performed at the RIBF operated by the RIKEN Nishina Center and Center for Nuclear Study, University of Tokyo. We thank the RIKEN Research Resources Center of the Brain Science Institute for performing DNA sequencing. L.M. was supported by the Junior Research Associate Program of RIKEN. The data of C-ion irradiation were reprinted from Fungal Biology, 117, Ma et al. The type of mutations induced by carbon-ion-beam irradiation of the filamentous fungus Neurospora crassa, 227–238, (2013), with permission from Elsevier.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Liqiu Ma

Liqiu Ma, PhD, is a researcher of Gunma University Heavy Ion Medical Center. He currently focuses on systemic immune responses following carbon-ion radiotherapy.

Yusuke Kazama

Yusuke Kazama, PhD, is a team leader of Plant Genome Evolution Research Team at RIKEN Nishina Center.

Tomonari Hirano

Tomonari Hirano, PhD, is an associate professor of faculty of agriculture, University of Miyazaki.

Ryouhei Morita

Ryouhei Morita, PhD, is a technical scientist of Beam Mutagenesis Group at RIKEN Nishina Center.

Shuuitsu Tanaka

Shuuitsu Tanaka, PhD, is a professor of Genetics at Saitama University.

Tomoko Abe

Tomoko Abe, PhD, is a group director of Beam Mutagenesis Group at RIKEN Nishina Center.

Shin Hatakeyama

Shin Hatakeyama, PhD, is an associate professor of faculty of science, Saitama University.