The unique color and type characteristics of watermelon fruits are regulated by many molecular mechanisms. However, it still needs to be combined with more abundant genetic data to fine-tune the positioning. We assembled genomes of two Korean inbred watermelon lines (cv. 242-1 and 159-1) with unique color and fruit-type characteristics and identified 23,921 and 24,451 protein-coding genes in the two genomes, respectively. To obtain more precise results for further study, we resequenced one individual of each parental line and an F2 population composed of 87 individuals. This identified 1,539 single-nucleotide polymorphisms (SNPs) and 80 InDel markers that provided a high-density genetic linkage map with a total length of 3,036.9 cM. Quantitative trait locus mapping identified 15 QTLs for watermelon fruit quality-related traits, including β-carotene and lycopene content in fruit flesh, fruit shape index, skin thickness, flesh color, and rind color. By investigating the mapping intervals, we identified 33 candidate genes containing variants in the coding sequence. Among them, Cla97C01G008760 was annotated as a phytoene synthase with a single-nucleotide variant (A → G) in the first exon at 9,539,129 bp of chromosome 1 that resulted in the conversion of a lysine to glutamic acid, indicating that this gene might regulate flesh color changes at the protein level. These findings not only prove the importance of a phytoene synthase gene in pigmentation but also explain an important reason for the color change of watermelon flesh.

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As a preliminary step of genome analysis, we produced a total of 28–44 Gb DNA sequencing data of whole-genome for thirteen Svalbard plants. We estimated genome sizes using these data with a k-mer-based computation tool and found that genome sizes of eight species ranged from 180–894 Mb: Cochlearia groenlandica 180 Mb, Dryas octopetala 204 Mb, Eriophorum scheuchzeri ssp. arcticum 306 Mb, Oxyria digyna 352 Mb, Salix polaris 383 Mb, Betula nana 689 Mb, Cassiope tetragona 798 Mb, and Silene uralensis ssp. arctica 894 Mb. We could not estimate the genome size of the other five species. We also analyzed variations in DNA sequences by identifying putative telomeric-repeat motifs in the thirteen Svalbard plants. Eleven out of thirteen species contained the canonical plant telomeric-repeat motif, TTTAGGG (Arabidopsis-type), whereas S. oppositifolia contained the Chlamydomonas-type telomeric-repeat motif (TTTTAGGG) and P. dahlianum had a novel telomeric-repeat motif, TTCAGGG. These findings provide a quantitative guideline for whole-genome sequencing analysis of Arctic plants in the future. The findings in this study provide a quantitative guideline for whole-genome sequencing analysis of Arctic plants, and they also show the potential of Arctic plants to be a new source of telomere diversity.