Abstract
The rare wild species of snow lotus Saussurea involucrata is a commonly used medicinal herb with great pharmacological value for human health, resulting from its uniquely high level of phenylpropanoid compound production. To gain information on the phenylpropanid biosynthetic pathway genes in this critically important medicinal plant, global transcriptome sequencing was performed. It revealed that the phenylpropanoid pathway genes were well represented in S. involucrata. In addition, we introduced two key phenylpropanoid pathway inducing transcription factors (PAP1 and Lc) into this medicinal plant. Transgenic S. involucrata co-expressing PAP1 and Lc exhibited purple pigments due to a massive accumulation of anthocyanins. The over-expression of PAP1 and Lc largely activated most of the phenylpropanoid pathway genes, and increased accumulation of several phenylpropanoid compounds significantly, including chlorogenic acid, syringin, cyanrine and rutin. Both ABTS (2,2′-azinobis-3-ethylbenzotiazo-line-6-sulfonic acid) and FRAP (ferric reducing anti-oxidant power) assays revealed that the antioxidant capacity of transgenic S. involucrata lines was greatly enhanced over controls. In addition to providing a deeper understanding of the molecular basis of phenylpropanoid metabolism, our results potentially enable an alternation of bioactive compound production in S. involucrata through metabolic engineering.
Highlights
Snow lotus is a well-known and rare traditional Chinese medicinal herb, the aerial part of which has been used commonly to treat a wide spectrum of clinical diseases, including arthritis, stomachache, and gynecological diseases [1,2]
Transcriptome sequencing of wild S. involucrata In order to obtain global transcriptome information for further investigation of the phenylpropanoid pathway in S. involucrata, Illumina sequencing was performed with pooled cDNA samples from leaf, stem and inflorescence organs of wild S. involucrata
Metabolic engineering of the phenylpropanoid pathway by co-expression of the key transcription factors PAP1 and Lc was successfully achieved in the snow lotus species S. involucrata
Summary
Snow lotus is a well-known and rare traditional Chinese medicinal herb, the aerial part of which has been used commonly to treat a wide spectrum of clinical diseases, including arthritis, stomachache, and gynecological diseases [1,2]. Among the few available endangered and rare wild snow lotus species in China, S. involucrata is of high quality for medicinal purposes due to its relatively higher total polyphenol/flavonoid content and antioxidant activity [4]. Polyphenol/flavonoid compounds are important plant secondary metabolites for both plant defense and human health They are derived from the general phenylpropanoid biosynthetic pathway, which is comprised of several biosynthetic branches, including lignin, stilbenes, flavonoids, and anthocyanins [5]. Given that PAP1 and Lc have been shown to successfully induce phenylpropanoid biosynthesis, are of two distinct gene families, and are derived from different species, these two transcription factors were here selected as high potential candidates for use as metabolic engineering tools in S. involucrata, which has not been modified genetically to generate whole transgenic plant previously
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