Ginsenosides in Panax genus and their biosynthesis

Abstract

Ginsenosides are a series of glycosylated triterpenoids which belong to protopanaxadiol (PPD)-, protopanaxatriol (PPT)-, ocotillol (OCT)- and oleanane (OA)-type saponins known as active compounds of Panax genus. They are accumulated in plant roots, stems, leaves, and flowers. The content and composition of ginsenosides are varied in different ginseng species, and in different parts of a certain plant. In this review, we summarized the representative saponins structures, their distributions and the contents in nearly 20 Panax species, and updated the biosynthetic pathways of ginsenosides focusing on enzymes responsible for structural diversified ginsenoside biosynthesis. We also emphasized the transcription factors in ginsenoside biosynthesis and non-coding RNAs in the growth of Panax genus plants, and highlighted the current three major biotechnological applications for ginsenosides production. This review covered advances in the past four decades, providing more clues for chemical discrimination and assessment on certain ginseng plants, new perspectives for rational evaluation and utilization of ginseng resource, and potential strategies for production of specific ginsenosides.

Keywords: ABA, abscisic acid; ADP, adenosine diphosphate; AtCPR (ATR), Arabidopsis thaliana cytochrome P450 reductase; BARS, baruol synthase; Biosynthetic pathway; Biotechnological approach; CAS, cycloartenol synthase; CDP, cytidine diphosphate; CPQ, cucurbitadienol synthase; CYP, cytochrome P450; DDS, dammarenediol synthase; DM, dammarenediol-II; DMAPP, dimethylallyl diphosphate; FPP, farnesyl pyrophosphate; FPPS (FPS), farnesyl diphosphate synthase; GDP, guanosine diphosphate; Ginsenoside; HEJA, 2-hydroxyethyl jasmonate; HMGR, HMG-CoA reductase; IPP, isopentenyl diphosphate; ITS, internal transcribed spacer; JA, jasmonic acid; JA-Ile, (+)-7-iso-jasmonoyl-l-isoleucine; JAR, JA-amino acid synthetase; JAZ, jasmonate ZIM-domain; KcMS, Kandelia candel multifunctional triterpene synthases; LAS, lanosterol synthase; LUP, lupeol synthase; MEP, methylerythritol phosphate; MVA, mevalonate; MVD, mevalonate diphosphate decarboxylase; MeJA, methyl jasmonate; NDP, nucleotide diphosphate; Non-coding RNAs; OA, oleanane or oleanic acid; OAS, oleanolic acid synthase; OCT, ocotillol; OSC, oxidosqualene cyclase; PPD, protopanaxadiol; PPDS, PPD synthase; PPT, protopanaxatriol; PPTS, PPT synthase; Panax species; RNAi, RNA interference; SA, salicylic acid; SE (SQE), squalene epoxidase; SPL, squamosa promoter-binding protein-like; SS (SQS), squalene synthase; SUS, sucrose synthase; TDP, thymine diphosphate; Transcription factors; UDP, uridine diphosphate; UGPase, UDP-glucose pyrophosphosphprylase; UGT, UDP-dependent glycosyltransferase; WGD, whole genome duplication; α-AS, α-amyrin synthase; β-AS, β-amyrin synthase.

Graphical abstract

Figure 1

Representative and hot ginsenosides in Panax species. (A) PPD or PPT-type ginsenosides. (B) Ocotillo-type ginsenosides. (C) Oleanane-type ginsenosides. (D) Dehydrated ginsenosides. Ginsenoside metabolites (hot compounds) are marked by asterisk. Chikusetsusaponin III, stipuleanoside R1 and R2 are branched glycosides, sapogenins link to C-1 of Glc or GluA (marked by red).

Figure 2

Phylogenetic tree of Panax plants based on ITS gene by Neighbor-Joining method. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches. The ID of ITS in GenBank are shown in the tree. P. japonicus from China was also treated as P. sinensis by Jun Wen et al..

Figure 3

CYPs in the biosynthesis of different ginsenoside skeletons. CYPs marked in red and dark are identified from Panax species and other species, respectively. Solid arrows are proven pathways, dashed arrows are unproven pathways, and double arrows are multiple steps (similarly hereinafter). The abbreviations are indicated as followed, β-AS: β-amyrin synthase, CYP (s): cytochrome P450 (s), DDS: dammarenediol synthase, OSC (s): oxidosqualene cyclase (s), SE: squalene epoxidase.

Figure 4

Comparison of different cyclization mechanisms among DDS, β-AS and other OSCs. Products labeled in black are generated via protosteryl cation, while products labeled in green are synthesized via dammarenyl cation. The abbreviations are indicated as follows, α-AS: α-amyrin synthase, β-AS: β-amyrin synthase, BARS1: baruol synthase, CAS: cycloartenol synthase, CCC: chair-chair-chair, CBC: chair-boat-chair, CPQ: cucurbitadienol synthase, LAS: lanosterol synthase, LUP: lupeol synthase, MdOSC4: oxidosqualene cyclase 4 of Malus domestica, PgDDS: dammarenediol synthase of P. ginseng.

Figure 5

UGTs catalyzing ginsenoside biosynthesis identified from Panax species (A)−(D) show UGTs involved in PPD-, PPT-, OCT- and OA-type ginsenoside biosynthesis, respectively. The abbreviations are indicated as follows, Pg: P. ginseng, Pj: P. japonicus var. major, Pn: P. notginseng, Pq: P. quinquefolius, Pz: P. zingiberensis, Gp: G. pentaphyllum.

Figure 6

Transcription factors identified involved in ginsenoside biosynthesis. HMGR, FPPS, SS, SE, β-AS and DDS are regulated by at least one TF from Panax species, TFs regulating other steps of ginsenoside biosynthesis is unresolved. The color of the hollow arrow corresponds to the color of the transcription factors, which regulate the enzyme encoding gene. The abbreviations are indicated as follows, β-AS: β-amyrin synthase, CD-ME: 4-diphosphocytidyl-2-C-methylerythritol, CD-MEP: 4-diphosphocytidyl-2-C-methyl-d-erythritol 2-phosphate, DS/DDS: dammarenediol-II synthase, DMAPP: dimethylallyl diphosphate, DXP: 1-deoxyxylulose 5-phosphate, FPP: farnesyl diphosphate, FPS/FPPS: farnesyl diphosphate synthase, GAP: glyceraldehyde-3-phosphate, HMBPP: 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate, HMG-CoA (S)-3-hydroxy-3-methylglutaryl-coenzyme A, HMGR: HMG-CoA reductase, IP: isopentenyl phosphate, IPP: isopentenyl diphosphate, MDP: mevalonate-5-diphosphate, MEcPP: 2-C-methyl-d-erythritol-2,4-cyclodiphosphate, MEP: methylerythritol phosphate, MP: mevalonate-5-phosphate, MVA (3R)-3,5-dihydroxy-3-methylpentanoic acid, SS/SQS: squalene synthase, SE/SQE: squalene epoxidases.

Figure 7

Omics-based gene mining technology and their applications in ginsenoside biosynthesis.