Abstract
Background: Platycodon grandiflorum is the only species in the genus Platycodon of the family Campanulaceae, which has been traditionally used as a medicinal plant for its lung-heat-clearing, antitussive, and expectorant properties in China, Japanese, and Korean. Oleanane-type triterpenoid saponins were the main chemical components of P. grandiflorum and platycodin D was the abundant and main bioactive component, but little is known about their biosynthesis in plants. Hence, P. grandiflorum is an ideal medicinal plant for studying the biosynthesis of Oleanane-type saponins. In addition, the genomic information of this important herbal plant is unavailable.Principal findings: A total of 58,580,566 clean reads were obtained, which were assembled into 34,053 unigenes, with an average length of 936 bp and N50 of 1,661 bp by analyzing the transcriptome data of P. grandiflorum. Among these 34,053 unigenes, 22,409 unigenes (65.80%) were annotated based on the information available from public databases, including Nr, NCBI, Swiss-Prot, KOG, and KEGG. Furthermore, 21 candidate cytochrome P450 genes and 17 candidate UDP-glycosyltransferase genes most likely involved in triterpenoid saponins biosynthesis pathway were discovered from the transcriptome sequencing of P. grandiflorum. In addition, 10,626 SSRs were identified based on the transcriptome data, which would provide abundant candidates of molecular markers for genetic diversity and genetic map for this medicinal plant.Conclusion: The genomic data obtained from P. grandiflorum, especially the identification of putative genes involved in triterpenoid saponins biosynthesis pathway, will facilitate our understanding of the biosynthesis of triterpenoid saponins at molecular level.
Highlights
The root tissue of P. grandiflorum was used for transcriptome sequencing and analysis because roots have traditionally been used for medicinal purpose
The high quality reads obtained in this study have been deposited in the National Center for Biotechnology Information (NCBI) SRA database
We found that five unigenes were highly homologous to CYP93E1 of Glycine max, M. truncatula, and Glycyrrhiza uralensis (Seki et al, 2008), which catalyzes the C24 hydroxylation of β-amyrin and sophoradiol in soyasaponin biosynthesis (Shibuya et al, 2006; Li et al, 2007; Seki et al, 2008; Fukushima et al, 2013), proteins encoded by these unigenes might be responsible for the C-24 hydroxylation in P. grandiflorum
Summary
Oleanane-type triterpenoid saponins are the main chemical components of P. grandiflorum, mainly including platycodin D, D2, D3, deapioplatycodin D, D2, polygalacin D and platyconic acid A (Kim J.W. et al, 2013). Oleanane-type triterpenoid saponins were the main chemical components of P. grandiflorum and platycodin D was the abundant and main bioactive component, but little is known about their biosynthesis in plants. Principal findings: A total of 58,580,566 clean reads were obtained, which were assembled into 34,053 unigenes, with an average length of 936 bp and N50 of 1,661 bp by analyzing the transcriptome data of P. grandiflorum Among these 34,053 unigenes, 22,409 unigenes (65.80%) were annotated based on the information available from public databases, including Nr, NCBI, Swiss-Prot, KOG, and KEGG. Conclusion: The genomic data obtained from P. grandiflorum, especially the identification of putative genes involved in triterpenoid saponins biosynthesis pathway, will facilitate our understanding of the biosynthesis of triterpenoid saponins at molecular level
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