8Pyropia species, such as nori (P. yezoensis), are important marine crops. We analysed the genome 9 sequences of 39 Pyropia species grown in Japan. Analysis of organellar genomes showed that the 10 chloroplast and mitochondrial genomes of P. yezoensis have different evolutionary histories. The 11 genetic diversity of Japanese P. yezoensis used in this study is lower than that of Chinese wild P. 12 yezoensis. Nuclear genome analysis revealed nearly 90% of the analysed loci as allodiploid in the 13 hybrid between P. yezoensis and P. tenera. Although the genetic diversity of Japanese P. yezoensis is 14 low, analysis of nuclear genomes genetically separated each accession. Accessions isolated from the 15 sea were often genetically similar to those being farmed. Study of genetic heterogeneity within a single 16 strain of P. yezoensis showed that accessions with frequent abnormal budding formed a single, 17 genetically similar group. The results will be useful for breeding and the conservation of Pyropia 18
species. 19 20In this study, we conducted a phylogenetic analysis of 39 Pyropia accessions grown in Japan using 46 chloroplast DNA sequences assembled from short reads. We also used whole-genome resequencing to 47 analyse the nuclear genomes of 34 accessions of P. yezoensis, one accession of the closely related P. 48 tenera, and one hybrid between P. yezoensis and P. tenera. Particularly, we focused on the analysis of 49 some kinds of seaweed in the Ariake sound, Japan, where seaweed production is the most active. 50
51Results 52Samples used in this study 53 Table 1 summarises the samples used in this study, and Figure 1 shows the isolation site of each 54 sample. In addition to 34 accessions of P. yezoensis, we used P. haitanensis, P. dentata Kjellman, P. 55 tenuipedalis Miura, P. tenera, and the hybrid between P. yezoensis and P. tenera in this study. Many 56 are pure accessions because they were cultured from a monospore (a single haploid cell). 57 58
Chloroplast and mitochondrial genomes 59To elucidate the relationships among the 39 accessions, we analysed their chloroplast DNA 60 sequences. Using the GetOrganelle 31 program, which is a toolkit for assembling the organelle genome 61 from short reads, we attempted to determine the whole chloroplast DNA sequences. Of the 39 total 62 cases, we successfully assembled the whole chloroplast genome of 30 samples, and 9 cases (Pyr_16, 63Pyr_18, Pyr_21, Pyr_29, Pyr_23, Pyr_25, Pyr_28, Pyr_33, and Pyr_34) were unsuccessful. The 64 chloroplast genomes of Pyropia species contain two direct repeats carrying ribosomal RNA (rRNA) 65 operon copies. 26 The circular chloroplast genome has a large single-copy section and a short single-66 copy section between two rRNA repeats. Mapping of the short reads to the assembled chloroplast 67 genome detected two types of reads in the rRNA operons ( Supplementary Figure 1) in all 39 cases, 68reflecting the presence of two non-identical direct repeats carrying two different rRNA operons. 26 The 69 presence of two types of reads in the rRN...