Diversity in DNA sequence, structure, and heterozygosity of nuclear rRNA gene region in Neopyropia yezoensis

DNA sequence reads of Neopyropia yezoensis (susabi-nori), its relative N. tenera (asakusa-nori), and their hybrids available in the sequence read archive produced assembled sequences of the nuclear rRNA gene region for 82 samples. Analysis of the assembled sequences revealed structural differences in the region of nuclear rRNA genes, with 17 forms depending on the presence or absence of introns and their lengths. The samples were divided into three groups based on differences in DNA sequences: Japanese N. yezoensis, Chinese N. yezoensis, and N. tenera/hybrids of N. tenera and N. yezoensis that exist in both countries. Despite genetic differentiation, the Japanese and Chinese N. yezoensis exhibit common structural forms. One sample of Chinese N. yezoensis presented almost 1:1 heterozygosity, whereas five other samples of Chinese N. yezoensis showed non-1:1 heterozygosity. In the latter case, neither the ratio of alleles nor the ratio of the number of introns was 1:1, suggesting the existence of an ongoing mechanism to eliminate the nuclear rRNA gene region on one of the homologous chromosomes in N. yezoensis.