Transcript profiles of Panax quinquefolius from flower, leaf and root bring new insights into genes related to ginsenosides biosynthesis and transcriptional regulation

American ginseng (Panax quinquefolius L.) has been used for a wide range of therapeutic purposes in China. The major bioactive phytochemicals responsible for this plant's pharmacological features are ginsenosides. Thus far, little is known regarding the genes involved in ginsenosides biosynthesis in this species. As a non-model plant, information about its genomes is generally not available. In this study, we generated 6678 expressed sequence tags (ESTs) from the flower, leaf and root cDNA libraries of American ginseng. Assembly of ESTs resulted in 3349 unigenes including 534 contigs (with ESTs number ranging from 2 to 52) and 2815 singletons. By analyzing the predominant transcripts within specific tissues, a gene expression pattern was obtained in a tissue-specific manner. They were assigned according to the functional classification of unigenes to broad ranges of Gene Ontology categories which include biological processes, cellular components and molecular functions. Based on blastx search results, 24 unigenes representing candidates related to ginsenosides biosynthesis were identified. Cloning and characterization of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR, EC: 1.1.1.34), the rate-limiting enzyme in mevalonic acid pathway, demonstrated that it belonged to the plant HMGR family and was highly expressed in leaves. Putative transcription factors were detected in 63 unigenes, including zinc finger, WRKY, homeobox and MADS-box family proteins. Five hundred and eighty-eight simple sequence repeat motifs were identified, of which, dimer was the most abundant motif. These data will provide useful information on transcript profiles, gene discovery, transcriptional regulation, flower biogenesis and marker-assisted selections. The analysis and information from this study will greatly contribute to the improvement of this medicinal plant as well as of other species in the Araliaceae family, for the purpose of ensuring adequate drug resources.