Abstract
Dracocephalum tanguticum Maxim, a Lamiaceae species endemic to the Qinghai-Tibetan Plateau and adjacent regions, is an important ornamental, medicinal and aromatic herb. In this study, a comprehensive transcriptome of 18 libraries from six organs namely, roots, stems, leaves, sepals, flowers and seeds of D. tanguticum were generated. More than 100 Gb of sequence data were obtained and assembled de novo into 187,447 transcripts, including 151,463 unigenes, among which the six organs shared 17.7% (26,841). In addition, all unigenes were assigned to 362 pathways, in which ‘biosynthesis of secondary metabolites’ is the second enriched pathway. Furthermore, rosmarinic acid (RA) is one of the multifunctional phenolic bioactive compounds produced in some Lamiaceae species. The six organs of D. tanguticum were confirmed to produce RA. A total of 22 predicted biosynthetic genes related to RA from the transcriptome were further isolated. Two of these genes were identified as candidates by evaluating the correlation coefficient between the RA contents and the expression of the predicted biosynthetic genes in the six organs. The new sequence information will improve the knowledge of D. tanguticum, as well as provide a reference tool for future studies of biosynthetic genes related to RA in this species.
Highlights
Dracocephalum tanguticum Maxim, a Lamiaceae species endemic to the Qinghai–Tibetan Plateau (QTP) and adjacent regions, is an important ornamental, medicinal and aromatic herb
Since rosmarinic acid (RA) biosynthetic genes are commonly shared by biosynthesis of many different secondary metabolites, elucidation of the potential pathway for RA biosynthesis genes would aid the required molecular manipulation to improve the quantity of RA in D. tanguticum
All unigenes were assigned to 362 pathways, ‘biosynthesis of secondary metabolites’ is the second enriched pathway among them
Summary
Dracocephalum tanguticum Maxim, a Lamiaceae species endemic to the Qinghai–Tibetan Plateau (QTP) and adjacent regions, is an important ornamental, medicinal and aromatic herb. The high-altitude QTP region has unique climate factors, including low oxygen levels, intense ultraviolet light, and large temperature difference between day and night, as well as prolonged daytime during the short growing seasons, which usually commences on April and ends in October for D. tanguticum All of these harsh factors may be beneficial for the biosynthesis of protective secondary metabolites in D. tanguticum. In the phenylalanine-derived pathway of RA biosynthesis, phenylalanine ammonia-lyase (PAL) catalyses the oxidative desamination of phenylalanine, forming t-cinnamic acid, and cinnamic acid; 4-hydroxylase (C4H) introduces the para-hydroxyl group into the aromatic ring of t-cinnamic acid; and 4-hydroxycinnamic acid CoA-ligase (4CL) catalyses the activation of cinnamic acids with coenzyme A These three enzymes are commonly shared by biosynthesis of many different secondary metabolites, such as flavonoids, lignans, coumarins, salicylic acid, stilbenes, and so on[17, 18]. Since RA biosynthetic genes are commonly shared by biosynthesis of many different secondary metabolites, elucidation of the potential pathway for RA biosynthesis genes would aid the required molecular manipulation to improve the quantity of RA in D. tanguticum
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