Advances in Transcriptomic Studies and Ginsenoside Biosynthesis of American Ginseng

American ginseng（Panax quinquefolius L.）, belonging to the Araliaceae family, is one of the most widely used traditional herbs in the world. Its major bioactive constituents are triterpene saponins known as ginsenosides. Up to date, it is still a big challenge to sequence and assemble the large and repeat-enriched genome of tetraploid American ginseng, using whole genome shotgun（WGS） sequencing strategy. The lack of American ginseng genome information has significantly impeded its genetic and functional genomic studies. With the development of next-generation sequencing（NGS） technologies, sequencing and analysis of transcriptomes have become powerful tools for the discovery of novel genes and elucidation of specific biosynthetic pathways of secondary metabolites. Here we summarized the recent advances in the transcriptomic studies of American ginseng, including high-throughput transcriptome sequencing, assembly, and functional gene annotation and classification. Based on the results of transcriptomic data mining and co-expression analyses, many candidate genes possibly involved in the biosynthetic pathway of ginsenosides have been found, thereby providing an unparalleled opportunity to fully understand the mechanism of ginsenoside biosynthesis and its regulations in American ginseng. Advances in transcriptomic studies will contribute to the molecular breeding and planting management of American ginseng and to the development of novel ginsenoside-type drugs.