Rapid survey of de novo mutations in naturally growing tree species following the March 2011 disaster in Fukushima: The effect of low-dose-rate radiation.

De novo mutation frequency in two Japanese tree species as a function of ambient radiation dose rate. [Display omitted] • Trees in contaminated areas following a nuclear accident were surveyed genetically. • De novo mutations (DNMs) were detected via RADseq, comparing parents and offspring. • Low-dose-rate radiation (up to 6.86 μGy h−1) did not affect the occurrence of DNMs. • Unknown factors other than low-dose-rate radiation had stronger effects on DNMs. • Haploid or phased reference genomes were effective for detecting DNMs. The impact of low-dose-rate radiation on genetics is largely unknown, particularly in natural environments. The Fukushima Dai-ich Nuclear Power Plant disaster resulted in the creation of contaminated natural lands. In this study, de novo mutations (DNMs) in germ line cells were surveyed from double-digest RADseq fragments in Japanese cedar and flowering cherry trees exposed to ambient dose rates ranging from 0.08 to 6.86 μGy h−1. These two species are among the most widely cultivated Japanese gymnosperm and angiosperm trees for forestry and horticultural purpose, respectively. For Japanese flowering cherry, open crossings were performed to produce seedlings, and only two candidate DNMs were detected from uncontaminated area. For Japanese cedar, the haploid megagametophytes were used as next generation samples. The use of megagametophytes from open crossing for next generation mutation screening had many advantages such as reducing exposure to radiation in contaminated areas because artificial crossings are not needed and the ease of data analysis owing to the haploid nature of megagametophytes. A direct comparison of the nucleotide sequences of parents and megagametophytes revealed an average of 1.4 candidate DNMs per megagametophyte sample (range: 0–40) after filtering procedures were optimized based on the validation of DNMs via Sanger sequencing. There was no relationship between the observed mutations and the ambient dose rate in the growing area or the concentration of 137Cs in cedar branches. The present results also suggest that mutation rates differ among lineages and that the growing environment has a relatively large influence on these mutation rates. These results suggested there was no significant increase in the mutation rate of the germplasm of Japanese cedar and flowering cherry trees growing in the contaminated areas. [ABSTRACT FROM AUTHOR]