Chloroplast genome-based genetic resources for Japan's threatened subalpine forests via genome skimming

The Japanese subalpine zone is dominated by a distinct and ecologically important conifer rich forest biome, subalpine coniferous forests, that are an outlier of the extensive boreal forests of Eurasia. While being relatively intact compared to other forest biomes in Japan, subalpine coniferous forests are under significant threat from deer browsing, global warming and small populations size effects. However, there is a severe lack of genetic resources available for the study of this biomes major constituent plant species. This study aims to develop chloroplast genome-based genetic resources for 12 widespread subalpine tree and shrub species via genome skimming of whole genomic DNA using short reads (100-150 bp in length). For 10 species, whole chloroplast genomes were assembled via de novo-based methods from 4-10 individuals per species sampled from across their ranges in Japan and, for non-Japanese endemic species, elsewhere in northeast Asia. A total of 566 single nucleotide polymorphisms for Japanese samples and 768 for all samples (varying from 2 to 202 per species) were identified which were distributed in geographically restricted lineages in most species. In addition, between 9 to 58 polymorphic simple sequence repeat regions were identified per species. For two Ericaceae species (Rhododendron brachycarpum and Vaccinium vitis-idaea) characterized by large chloroplast genomes, de novo assembly failed, but single nucleotide polymorphisms could be identified using reference mapping. This data will be useful for genetic studies of the taxonomic relationship of populations within Japan and to other parts of northeast Asia, investigating phylogeographic patterns within species, conservation genetics and has potential application for studies of environmental and ancient DNA.