Tae-Hee KimP, Ye-Rim Choi, Hee-Joo Choi, Ara Cho, Hee-Young Gil*

Division of Forest Biodiversity, Korea National Arboretum, Pocheon, Korea

Euonymus japonicus Thunb. (Celastraceae) is a widely distributed evergreen shrub with high tolerance to sea winds and salinity, making it suitable for coastal forest restoration. Despite its ecological significance, genetic studies of E. japonicus remain limited. Here, we present a draft genome assembly of E. japonicus generated using PacBio long-read sequencing. The assembled genome consists of 132 contigs with a total length of 285.3 Mb, an N50 of 8.6 Mb, and 98.1% completeness based on BUSCO analysis, providing a high-quality reference for population genetic analyses. Using this reference genome, we analyzed genetic diversity and population structure of 107 individuals from 13 populations in Korea and China based on 3RAD sequencing and identified 12,357 high-quality single nucleotide polymorphisms. Population structure analyses using ADMIXTURE and principal component analysis revealed partially shared genetic ancestry between Chinese and some Korean populations, suggesting historical connectivity or gene flow across regions. However, analysis of molecular variance (AMOVA) indicated significant genetic differentiation among populations (F_ST = 0.145, P = 0.001), with 14.5% of the total genetic variation attributable to differences among populations, while most variation was distributed within individuals. These results suggest that although E. japonicus populations share common genetic backgrounds across East Asia, population-level genetic structure has been maintained. Our study demonstrates that the draft genome assembly enables robust assessment of genetic diversity and population structure in E. japonicus and provides valuable genetic insights for the selection and management of plant materials in coastal forest restoration and conservation programs on the Korean Peninsula.