Abstract
BackgroundP. vietnamensis var. fuscidiscus, called “Yesanqi” in Chinese, is a new variety of P. vietnamensis, which was first found in Jinping County, the southern part of Yunnan Province, China. Compared with other Panax plants, this species contains higher content of ocotillol-type saponin, majonoside R2. Despite the pharmacological importance of ocotillol-type saponins, little is known about their biosynthesis in plants. Hence, P. vietnamensis var. fuscidiscus is a suitable medicinal herbal plant species to study biosynthesis of ocotillol-type saponins. In addition, the available genomic information of this important herbal plant is lacking.ResultsTo investigate the P. vietnamensis var. fuscidiscus transcriptome, Illumina HiSeq™ 2000 sequencing platform was employed. We produced 114,703,210 clean reads, assembled into 126,758 unigenes, with an average length of 1,304 bp and N50 of 2,108 bp. Among these 126,758 unigenes, 85,214 unigenes (67.23%) were annotated based on the information available from the public databases. The transcripts encoding the known enzymes involved in triterpenoid saponins biosynthesis were identified in our Illumina dataset. A full-length cDNA of three Squalene epoxidase (SE) genes were obtained using reverse transcription PCR (RT-PCR) and the expression patterns of ten unigenes were analyzed by reverse transcription quantitative real-time PCR (RT-qPCR). Furthermore, 15 candidate cytochrome P450 genes and 17 candidate UDP-glycosyltransferase genes most likely to involve in triterpenoid saponins biosynthesis pathway were discovered from transcriptome sequencing of P. vietnamensis var. fuscidiscus. We further analyzed the data and found 21,320 simple sequence repeats (SSRs), 30 primer pairs for SSRs were randomly selected for validation of the amplification and polymorphism in 13 P. vietnamensis var. fuscidiscus accessions. Meanwhile, five major triterpene saponins in roots of P. vietnamensis var. fuscidicus were determined using high performance liquid chromatography (HPLC) and evaporative light scattering detector (ELSD).ConclusionsThe genomic resources generated from P. vietnamensis var. fuscidiscus provide new insights into the identification of putative genes involved in triterpenoid saponins biosynthesis pathway. This will facilitate our understanding of the biosynthesis of triterpenoid saponins at molecular level. The SSR markers identified and developed in this study show genetic diversity for this important crop and will contribute to marker-assisted breeding for P. vietnamensis var. fuscidiscus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1332-8) contains supplementary material, which is available to authorized users.
Highlights
P. vietnamensis var. fuscidiscus, called “Yesanqi” in Chinese, is a new variety of P. vietnamensis, which was first found in Jinping County, the southern part of Yunnan Province, China
The genomic resources generated from P. vietnamensis var. fuscidiscus provide new insights into the identification of putative genes involved in triterpenoid saponins biosynthesis pathway
After the cyclization of 2,3-oxidosqalene by oxidosqualene cyclase (OSC), the triterpene skeletons are modified by hydroxylation and glycosidation that leads to the production of various ginsenosides, that are further catalyzed by cytochrome Cytochrome P450 (P450) monoxygenases (CYP450s) and uridine diphosphate (UDP)-dependent glycosyl-transferases (UGTs) [8] (Figure 1)
Summary
P. vietnamensis var. fuscidiscus, called “Yesanqi” in Chinese, is a new variety of P. vietnamensis, which was first found in Jinping County, the southern part of Yunnan Province, China. Compared with other Panax plants, this species contains higher content of ocotillol-type saponin, majonoside R2. Despite the pharmacological importance of ocotillol-type saponins, little is known about their biosynthesis in plants. Fuscidiscus is a suitable medicinal herbal plant species to study biosynthesis of ocotillol-type saponins. The Panax genus comprises approximately 14 species, more than 150 naturally occurring ginsenosides have been isolated from different parts of plants [1] and most of the saponins possess four types of aglycone moieties, i.e. protopanaxadiol, protopanaxatriol, ocotillol, and oleanolic acid types. Only one species, P. vietnamensis have been found accumulates surprisingly high content of ocotillol-type saponins, mainly majonoside R2, which is as high as 5.3% of the dried rhizome and exhibited anti-tumor and hepatocytoprotective activities [4,5,6]. Despite the pharmacological importance of ocotillol-type saponins, little is known about their biosynthesis [1]. P. vietnamensis is the only species found in the narrow habitat in central Vietnam with high content of ocotillol-type saponins, which is in the list of endanger species
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