Telomere-to-telomere reference genome for Panax ginseng highlights the evolution of saponin biosynthesis

Abstract Ginseng (Panax ginseng) is a representative of Chinese traditional medicine, also used worldwide, while the triterpene saponin ginsenoside is the most important effective compound within it. Ginseng is an allotetraploid, with complex genetic background, making the study of its metabolic evolution challenging. In this study, we assembled a telomere-to-telomere ginseng reference genome, constructed of 3.45 Gb with 24 chromosomes and 77 266 protein-coding genes. Additionally, the reference genome was divided into two subgenomes, designated as subgenome A and B. Subgenome A contains a larger number of genes, whereas subgenome B has a general expression advantage, suggesting that ginseng subgenomes experienced asymmetric gene loss with biased gene expression. The two subgenomes separated approximately 6.07 million years ago, and subgenome B shows the closest relation to Panax vietnamensis var. fuscidiscus. Comparative genomics revealed an expansion of gene families associated with ginsenoside biosynthesis in both ginseng subgenomes. Furthermore, both tandem duplications and proximal duplications play crucial roles in ginsenoside biosynthesis. We also screened functional genes identified in previous research and found that some of these genes located in colinear regions between subgenomes have divergence functions, revealing an unbalanced evolution in both subgenomes and the saponin biosynthesis pathway in ginseng. Our work provides important resources for future genetic studies and breeding programs of ginseng, as well as the biosynthesis of ginsenosides.