De Novo Genome Assembly and Phylogenetic Analysis of Cirsium nipponicum

Background: Cirsium nipponicum, a pharmaceutically valuable plant from the Asteraceae family, has been utilized for over 2000 years. Unlike other thistles, it is native to East Asia and found exclusively on Ulleung Island on the Korea Peninsula. Despite its significance, the genome information of C. nipponicum has remained unclear. Methods: In this study, we assembled the genome of C. nipponicum using both short reads from Illumina sequencing and long reads from Nanopore sequencing. Results: The assembled genome is 929.4 Mb in size with an N50 length of 0.7 Mb, covering 95.1% of BUSCO core groups listed in edicots_odb10. Repeat sequences accounted for 70.94% of the assembled genome. We curated 31,263 protein-coding genes, of which 28,752 were functionally annotated using public databases. Phylogenetic analysis of 11 plant species using single-copy orthologs revealed that C. nipponicum diverged from Cynara cardunculus approximately 15.9 million years ago. Gene family evolutionary analysis revealed significant expansion and contraction in genes involved in abscisic acid biosynthesis, late endosome to vacuole transport, response to nitrate, and abaxial cell fate specification. Conclusions: This study provides a reference genome of C. nipponicum, enhancing our understanding of its genetic background and facilitating an exploration of genetic resources for beneficial phytochemicals.