Background Dendrobium officinale, an endangered Chinese herb, possesses extensive therapeutic effects and contains bioactive ingredients such as major polysaccharides, alkaloids, and minimal flavonoids. We first obtained the protocorm-like bodies (PLBs) of this plant through tissue culture in order to determine the distribution of the main secondary metabolites in each organelle and the PLBs. We then analyzed the correlation between gene expression level from comparative transcriptome sequencing and metabolite content in different organs to identify putative genes encoding enzymes involved in the biosynthesis of polysaccharides, alkaloids, and flavonoids. Results We used seeds as explants for protocorm induction and PLB propagation of D. officinale. The optimal medium formula for PLB propagation was 1/2 MS + α-NAA 0.5 mg·L− 1 + 6-BA 1.0 mg·L− 1 + 2, 4-D 1.5–2.0 mg·L− 1 + potato juice 100 g·L− 1. Stems, PLBs and leaves of D. officinale had the highest content of polysaccharides, alkaloids and flavonoids, respectively. Naringenin was only produced in stem; however, PLBs with high alkaloid content can replace other organs producing alkaloids. The hot water extraction method outperformed the ultrasound-assisted extraction method for extracting polysaccharides from D. officinale. A comparative transcriptome analysis of PLBs and leaves of D. officinale revealed differential expression of genes encoding enzymes involved in polysaccharide, alkaloid and flavonoid biosynthetic pathways. Putative genes encoding enzymes involved in these biosynthetic pathways were identified. Notably, we identified genes encoding the alkaloid biosynthesis enzymes strictosidine β-D-Glucosidase, geissoschizine synthase and vinorine synthase in D. officinale. Conclusions The identification of candidate genes encoding enzymes involved in metabolite biosynthesis will help to explore and protect this endangered species and facilitate further analysis of the molecular mechanism of secondary metabolite biosynthesis in D. officinale.

Platycodin D and platycoside E are two triterpenoid saponins in Platycodon grandiflorus, differing only by two glycosyl groups structurally. Studies have shown β-Glucosidase from bacteria can convert platycoside E to platycodin D, indicating the potential existence of similar enzymes in P. grandiflorus. An L9(34) orthogonal experiment was performed to establish a protocol for calli induction as follows: the optimal explant is stems with nodes and the optimum medium formula is MS + NAA 1.0 mg/L + 6-BA 0.5 mg/L to obtain callus for experimental use. The platycodin D, platycoside E and total polysaccharides content between callus and plant organs varied wildly. Platycodin D and total polysaccharide content of calli was found higher than that of leaves. While, platycoside E and total polysaccharide content of calli was found lower than that of leaves. Associating platycodin D and platycoside E content with the expression level of genes involved in triterpenoid saponin biosynthesis between calli and leaves, three contigs were screened as putative sequences of β-Glucosidase gene converting platycoside E to platycodin D. Besides, we inferred that some transcription factors can regulate the expression of key enzymes involved in triterpernoid saponins and polysaccharides biosynthesis pathway of P. grandiflorus. Totally, a candidate gene encoding enzyme involved in converting platycoside E to platycodin D, and putative genes involved in polysaccharide synthesis in P. grandiflorus had been identified. This study will help uncover the molecular mechanism of triterpenoid saponins biosynthesis in P. grandiflorus.

Salvia miltiorrhiza has numerous compounds with extensive clinical application. “Sweating”, a processing method of Traditional Chinese Medicine (TCM), results in great changes in pharmacology and pharmacodynamics. Previously, chromatogram of 10 characteristic metabolites in S. miltiorrhiza showed a significant difference after “Sweating”. Due to the complexity of TCM, changes in metabolites should be investigated metabolome-wide after “Sweating”. An untargeted UPLC/MS-based metabolomics was performed to discover metabolites profile variation of S. miltiorrhiza after “Sweating”. Multivariate analysis was conducted to screen differential metabolites. Analysis indicated distinct differences between sweated and non-sweated samples. 10,108 substance peaks had been detected altogether, and 4759 metabolites had been identified from negative and positive ion model. 287 differential metabolites were screened including 112 up-regulated and 175 down-regulated and they belong to lipids and lipid-like molecules, and phenylpropanoid and polyketides. KEGG analysis showed the pathway of linoleic acid metabolism, and glyoxylate and dicarboxylate metabolism were mainly enriched. 31 and 49 identified metabolites were exclusively detected in SSM and NSSM, respectively, which mainly belong to carboxylic acids and derivatives, polyketides and fatty acyls. By mapping tanshinones and salvianolic acids to 4759 identified metabolites library, 23 characteristic metabolites had been identified, among which 11 metabolites changed most. We conclude that “Sweating’’ has significant effect on metabolites content and composition of S. miltiorrhiza.

Background: Dendrobium officinale, an endangered Chinese herb, has extensive therapeutic effects and contains bioactive ingredients including a large number of polysaccharides and alkaloids, and minimal flavonoids. Firstly, this study attempts to obtain the protocorm-like bodies of this plant through tissue culture to produce the main secondary metabolites whose distribution in each organelle and protocorm like bodies is analyzed. Then, analysis of the correlation between comparative transcriptome sequence and the metabolite content in different organs enables the discovery of putative genes encoding enzymes involved in the biosynthesis of polysaccharides and alkaloids, and flavonoids.Results: The optimum condition for protocorm-like bodies (PLBs) induction and propagation of D. officinale is established. For protocorm induction, we use the seed as the explant, and the optimum medium formula for PLBs propagation is 1/2 MS + α-NAA 0.5 mg·L-1 +6-BA 1.0 mg·L-1 + 2, 4-D 1.5-2.0 mg·L-1 + potato juice 100 g·L-1. The distribution of polysaccharides, alkaloids and flavonoids in D. officinale organs was clarified. Stems, PLBs and leaves have the highest content of polysaccharides, alkaloids and flavonoids, respectively. PLBs replace organs to produce alkaloids in D. officinale, and naringenin was only produced in stem. Hot water extraction (HWE) method was found outperforming the ultrasound-assisted extraction (UAE) method for polysaccharides from D. officinale. A comparative transcriptome analysis of the protocorm-like bodies and leaves of D. officinale showed genes encoding enzymes involved in polysaccharides, alkaloids and flavonoids biosynthetic pathway were differentially expressed. Putative genes encoding enzymes involved in polysaccharides, alkaloids and flavonoids synthetic pathway were identified. Notably, genes encoding enzymes of strictosidine beta-glucosidase, geissoschizine synthase and vinorine synthase in alkaloids biosynthesis of D. officinale are first reported.Conclusions: Our works, especially the identification of candidate genes encoding enzymes involved in metabolites biosynthesis will help to explore and protect the endangered genetic resources and will also facilitate further analysis of the molecular mechanism of secondary metabolites’ biosynthesis in D. officinale.

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