UV-B Radiation Enhances Epimedium brevicornu Maxim. Quality by Improving the Leaf Structure and Increasing the Icaritin Content

Epimedium brevicornu Maxim. is a herbal plant with various therapeutic effects, and its aboveground tissues contain flavonol compounds such as icaritin that can be used to produce new drugs for the treatment of advanced liver cancer. Previous studies have shown that ultraviolet-B (UV-B, 280-315 nm) stress can increase the levels of flavonoid substances in plants. In the current study, we observed the microstructure of E. brevicornu leaves after 0, 5, 10, 15, and 20 d of UV-B radiation (60 μw·cm-2) and quality formation mechanism of E. brevicornu leaves after 0, 10, and 20 d of UV-B radiation by LC‒ESI‒MS/MS. The contents of flavonols such as icariside I, wushanicaritin, icaritin, and kumatakenin were significantly upregulated after 10 d of radiation. The results indicated that UV-B radiation for 10 d inhibited the morphological development of E. brevicornu but increased the content of active medicinal components, providing a positive strategy for epimedium quality improvement.

De novo biosynthesis of anticarcinogenic icariin in engineered yeast

Icariin (ICA) has wide applications in nutraceuticals and medicine with strong anticancer activities. However, the structural complexity and low abundance in plants of ICA lead to the unsustainable and high-cost supply from chemical synthesis and plant extraction. Here, the whole biosynthesis pathway of ICA was elucidated, then was constructed in Saccharomyces cerevisiae, including a 13-step heterologous ICA pathway from eleven kinds of plants as well as deletions or overexpression of ten yeast endogenous genes. Spatial regulation of 8-C-prenyltransferase to mitochondria and three-stage sequential control of 4'-O-methyltransferase, 3-OH rhamnosyltransferase, and 7-OH glycosyltransferase expression successfully achieved the de novo synthesis of ICA with a titer of 130 μg/L under shake-flask culture. The ICA synthesis from glucose represents the longest reconstructed pathway of flavonoid in microbe so far. This study provides a potential choice for the sustainable microbial production of number of complex flavonoids.

Screening of superior anti-osteoporotic flavonoids from Epimedii Folium with dual effects of reversing iron overload and promoting osteogenesis

Iron overload is a risk factor for postmenopausal osteoporosis (PMOP) and lowering iron levels to regulate the labile plasma iron is the preferred therapy. Icariin (ICA), baohuoside I (BHS) and icaritin (ICT) are three flavonoids obtained from Epimedii Folium that are efficient in facilitating osteogenesis. In this study, an active flavonoid with dual effects of reversing iron overload and promoting osteogenesis was screened based on pharmacokinetics, iron complexation properties and the potential to downregulate iron overload, reversing PMOP. As a result, the in vivo absorption of three compounds was ICA > ICT > BHS, while the exposure in muscle and bone was BHS > ICT > ICA. In vitro complexation showed that only ICT complexed with Fe (III) at a 1:1 ratio on 3-OH and the ICT-Fe (III) complex (m/z 424.3750) was identified by UPLC-Q-TOF-MS. In vivo dynamic detection also showed that the concentration of ICT-Fe (III) complexes varied with the concentration of ICT in plasma. The behavioral blunting and bone loss in zebrafish induced by Fe (III) were significantly reversed by ICT in a dose-dependent manner. Pharmacokinetic-pharmacodynamic analysis showed that ICT was negatively correlated with serum ferritin and positively correlated with osteogenic markers including alkaline phosphatase, osteocalcin and osteoprotegerin. Bone loss in ovariectomized rats was significantly altered after ICT intervention, with reduced serum ferritin levels and improved osteogenic marker levels. These results demonstrated that ICT had favorable musculoskeletal penetration and iron complexation capability to shrink labile plasma iron, showing superior performance in anti-PMOP through the dual effects of reversing iron overload and promoting osteogenesis.

Time-series transcriptome provides insights into the gene regulation network involved in the icariin-flavonoid metabolism during the leaf development of Epimedium pubescens

Herba Epimedii (Epimedium) leaves are rich in prenylated flavonol glycosides (PFGs) with high medicinal value. However, the dynamics and regulatory network of PFG biosynthesis remain largely unclear. Here, we combined metabolite profiling (targeted to PFGs) and a high-temporal-resolution transcriptome to elucidate PFGs' regulatory network in Epimedium pubescens and identified key candidate structural genes and transcription factors (TFs) involved in PFG accumulation. Chemical profile analysis revealed that PFG content was quite different between buds and leaves and displayed a continuous decline with leaf development. The structural genes are the determinant reasons, and they are strictly regulated by TFs under temporal cues. We further constructed seven time-ordered gene co-expression networks (TO-GCNs) of PFG biosynthesis genes (including EpPAL2, EpC4H, EpCHS2, EpCHI2, EpF3H, EpFLS3, and EpPT8), and three flavonol biosynthesis routines were then predicted. The TFs involved in TO-GCNs were further confirmed by WGCNA analysis. Fourteen hub genes, comprising 5 MYBs, 1 bHLH, 1 WD40, 2 bZIPs, 1 BES1, 1 C2H2, 1 Trihelix, 1 HD-ZIP, and 1 GATA were identified as candidate key TFs. The results were further validated by TF binding site (TFBS) analysis and qRT-PCR. Overall, these findings provide valuable information for understanding the molecular regulatory mechanism of PFGs biosynthesis, enriching the gene resources, which will guide further research on PFG accumulation in Epimedium.

Construction of the first high-density genetic linkage map and QTL mapping of flavonoid and leaf-size related traits in Epimedium

BACKGROUND

Leaves are the main medicinal organ in Epimedium herbs, and leaf flavonoid content is an important criterion of Epimedium herbs. However, the underlying genes that regulate leaf size and flavonoid content are unclear, which limits the use of breeding for Epimedium development. This study focuses on QTL mapping of flavonoid and leaf-size related traits in Epimedium.

RESULTS

We constructed the first high-density genetic map (HDGM) using 109 F1 hybrids of Epimedium leptorrhizum and Epimedium sagittatum over three years (2019-2021). Using 5,271 single nucleotide polymorphism (SNP) markers, an HDGM with an overall distance of 2,366.07 cM and a mean gap of 0.612 cM was generated by utilizing genotyping by sequencing (GBS) technology. Every year for three years, 46 stable quantitative trait loci (QTLs) for leaf size and flavonoid contents were discovered, including 31 stable loci for Epimedin C (EC), one stable locus for total flavone content (TFC), 12 stable loci for leaf length (LL), and two stable loci for leaf area (LA). For flavonoid content and leaf size, the phenotypic variance explained for these loci varied between 4.00 and 16.80% and 14.95 and 17.34%, respectively.

CONCLUSIONS

Forty-six stable QTLs for leaf size and flavonoid content traits were repeatedly detected over three years. The HDGM and stable QTLs are laying the basis for breeding and gene investigation in Epimedium and will contribute to accelerating the identification of desirable genotypes for Epimedium breeding.

Screening and characterization of a β-xylosidase from Bifidobacterium breve K-110 and its application in the biotransformation of the total flavonoids of epimedium to icariin with α-l-rhamnosidase

Among the flavonoids of epimedium, epimedin B, epimedin C, and icariin are considered to be representative components and their structures are quite similar. Besides sharing the same backbone, the main difference is the sugar groups attached at the positions of C-3 and C-7. Despite their structural similarities, their potencies differ significantly, and only icariin is currently included in the Chinese Pharmacopoeia as a quality marker (Q-marker) for epimedium flavonoids. Furthermore, icariin has the functions of anti-aging, anti-inflammation, antioxidation, anti-osteoporosis, and ameliorating fibrosis. We used bioinformatics to look for the GH43 family β-xylosidase genes BbXyl from Bifidobacterium breve K-110, which has a length of 1347 bp and codes for 448 amino acids. This will allow us to convert epimedin B and epimedin C into icariin in a specific way. The expression level of recombinant BbXyl in TB medium containing 1 % inulin as carbon source, with an inducer concentration of 0.05 mmol/L and a temperature of 28 °C, was 86.4 U/mL. Previous studies found that the α-l-rhamnosidase BtRha could convert epoetin C to produce icariin, so we combined BbXyl and BtRha to catalyze the conversion of epimedium total flavonoids in vitro and in vivo to obtain the product icariin. Under optimal conditions, in vitro hydrolysis of 5 g/L of total flavonoids of epimedium eventually yielded a concentration of icariin of 678.1 μmol/L. To explore the conversion of total flavonoids of epimedium in vivo. Under the optimal conditions, the yield of icariin reached 97.27 μmol/L when the total flavonoid concentration of epimedium was 1 g/L. This study is the first to screen xylosidases for the targeted conversion of epimedin B to produce icariin, and the first to report that epimedin B and epimedin C in the raw epimedium flavonoids can convert efficiently to icariin by a collaborative of β-xylosidase and α-l-rhamnosidase.

A Novel 3-O-rhamnoside: 2″-O-xylosyltransferase Responsible for Terminal Modification of Prenylflavonol Glycosides in Epimedium pubescens Maxim

Prenylated flavonol glycosides in Epimedium plants, as key medicinal components, are known to have great pharmaceutical activities for human health. Among the main prenylated flavonol glycosides, the modification mechanism of different sugar moieties is still not well understood. In the current study, a novel prenylated flavonol rhamnoside xylosyltransferase gene (EpF3R2″XylT) was cloned from E. pubescens, and the enzymatic activity of its decoding proteins was examined in vitro with different prenylated flavonol rhamnoside substrates and different 3-O-monosaccharide moieties. Furthermore, the functional and structural domains of EpF3R2″XylT were analyzed by bioinformatic approaches and 3-D protein structure remodeling. In summary, EpF3R2″XylT was shown to cluster with GGT (glycosyltransferase that glycosylates sugar moieties of glycosides) through phylogenetic analysis. In enzymatic analysis, EpF3R2″XylT was proven to transfer xylose moiety from UDP-xylose to prenylated flavonol rhamnoside at the 2″-OH position of rhamnose. The analysis of enzymatic kinetics showed that EpF3R2″XylT had the highest substrate affinity toward icariin with the lowest K_m value of 75.96 ± 11.91 mM. Transient expression of EpF3R2″XylT in tobacco leaf showed functional production of EpF3R2″XylT proteins in planta. EpF3R2″XylT was preferably expressed in the leaves of E. pubescens, which is consistent with the accumulation levels of major prenylflavonol 3-O-triglycoside. The discovery of EpF3R2″XylT will provide an economical and efficient alternative way to produce prenylated flavonol trisaccharides through the biosynthetic approach.

Enzymatic synthesis of anhydroicaritin, baohuoside and icariin

Anhydroicaritin (1a), baohuoside (1b) and icariin (1c) were recognized as major pharmacologically active ingredients of Epimedium plants. Their primary means of acquisition were chemical isolation from plants. However, it suffers from low yield, environmental pollution and shortage of plants. Herein, to remedy these problems, biosynthesis was explored to obtain the three active ingredients. Fortunately, with SfFPT as 8-prenyltransferase, EpPF3RT and Ep7GT as glycosyltransferases, kaempferide (1) was transferred to 1a, 1b and 1c enzymatically. Thus, we report the details of this method. This approach represents a promising environmental friendly alternative for the production of these compounds from an abundant analogue.

Genome-wide analysis of UGT gene family identified key gene for the biosynthesis of bioactive flavonol glycosides in Epimedium pubescens Maxim

Epimedium pubescens Maxim. is a well-known traditional Chinese medicinal herb with flavonol glycosides as the major pharmaceutically active compounds. UDP-glycosyltransferases (UGTs) are a group of enzymes responsible for the glycosylation of flavonoid glycosides. In this study, a genome-wide analysis was performed to identify UGT family genes in E. pubescens. As a result, a total of 339 putative UGT genes were identified, which represents the largest UGT gene family known thus far, implying a significant expansion of the UGT gene family in E. pubescens. All EpUGTs were unevenly distributed across six chromosomes, and they were classified into 17 major groups. The expression profiles showed that UGT genes were differentially expressed in roots, leaves, flowers, shoots and fruits. In particular, several EpUGTs were highly induced by high light intensity, which was consistent with the accumulation level of bioactive flavonoids in E. pubescens. Six UGT79 genes that were preferentially expressed in roots or leaves were successfully expressed in E. coli, and only the recombinant EpGT60 protein was found to be active toward 8-prenylkaempferol and icaritin to produce the key bioactive compounds baohuoside II and baohuoside I. The optimal temperature, pH, k_m and V_max were determined for the recombinant EpGT60 protein. In addition, expression of recombinant EpGT60 in E. coli cell culture led to successful production of baohuoside II when fed 8-prenylkaempferol. Our study provides a foundation for further functional characterization of UGT genes in E. pubescens and provides key candidate genes for bioengineering bioactive flavonoids in E. pubescens.

Complete biosynthesis of the potential medicine icaritin by engineered Saccharomyces cerevisiae and Escherichia coli

Icaritin is a prenylflavonoid present in the Chinese herbal medicinal plant Epimedium spp. and is under investigation in a phase III clinical trial for advanced hepatocellular carcinoma. Here, we report the biosynthesis of icaritin from glucose by engineered microbial strains. We initially designed an artificial icaritin biosynthetic pathway by identifying a novel prenyltransferase from the Berberidaceae-family species Epimedium sagittatum (EsPT2) that catalyzes the C8 prenylation of kaempferol to yield 8-prenlykaempferol and a novel methyltransferase GmOMT2 from soybean to transfer a methyl to C4'-OH of 8-prenlykaempferol to produce icaritin. We next introduced 11 heterologous genes and modified 12 native yeast genes to construct a yeast strain capable of producing 8-prenylkaempferol with high efficiency. GmOMT2 was sensitive to low pH and lost its activity when expressed in the yeast cytoplasm. By relocating GmOMT2 into mitochondria (higher pH than cytoplasm) of the 8-prenylkaempferol-producing yeast strain or co-culturing the 8-prenylkaempferol-producing yeast with an Escherichia coli strain expressing GmOMT2, we obtained icaritin yields of 7.2 and 19.7 mg/L, respectively. Beyond the characterizing two previously unknown plant enzymes and conducting the first biosynthesis of icaritin from glucose, we describe two strategies of overcoming the widespread issue of incompatible pH conditions encountered in basic and applied bioproduction research. Our findings will facilitate industrial-scale production of icaritin and other prenylflavonoids.

Flavonoids, terpenoids, and polyketide antibiotics: Role of glycosylation and biocatalytic tactics in engineering glycosylation

Flavonoids, terpenoids, and polyketides are structurally diverse secondary metabolites used widely as pharmaceuticals and nutraceuticals. Most of these molecules exist in nature as glycosides, in which sugar residues act as a decisive factor in their architectural complexity and bioactivity. Engineering glycosylation through selective trimming or extension of the sugar residues in these molecules is a prerequisite to their commercial production as well to creating novel derivatives with specialized functions. Traditional chemical glycosylation methods are tedious and can offer only limited end-product diversity. New in vitro and in vivo biocatalytic tools have emerged as outstanding platforms for engineering glycosylation in these three classes of secondary metabolites to create a large repertoire of versatile glycoprofiles. As knowledge has increased about secondary metabolite-associated promiscuous glycosyltransferases and sugar biosynthetic machinery, along with phenomenal progress in combinatorial biosynthesis, reliable industrial production of unnatural secondary metabolites has gained momentum in recent years. This review highlights the significant role of sugar residues in naturally occurring flavonoids, terpenoids, and polyketide antibiotics. General biocatalytic tools used to alter the identity and pattern of sugar molecules are described, followed by a detailed illustration of diverse strategies used in the past decade to engineer glycosylation of these valuable metabolites, exemplified with commercialized products and patents. By addressing the challenges involved in current bio catalytic methods and considering the perspectives portrayed in this review, exceptional drugs, flavors, and aromas from these small molecules could come to dominate the natural-product industry.

Advances in engineering UDP-sugar supply for recombinant biosynthesis of glycosides in microbes

Plant glycosides are of great interest for industries. Glycosylation of plant secondary metabolites can greatly improve their solubility, biological activity, or stability. This allows some plant glycosides to be used as food additives, cosmetic products, health products, antisepsis and anti-cancer drugs. With the continuous expansion of market demand, a variety of biological fermentation technologies has emerged. This review focuses on recombinant microbial biosynthesis of plant glycosides, which uses UDP-sugars as precursors, and summarizes various strategies to increase the yield of glycosides with a key concentration on UDP-sugar supply based on four aspects, i.e., gene overexpression, UDP-sugar recycling, mixed fermentation, and carbon co-utilization. Meanwhile, the application potential and advantages of various techniques are introduced, which provide guidance to the development of high-yield strains for recombinant microbial production of plant glycosides. Finally, the technical challenges of glycoside biosynthesis are pointed out with discussions on future directions of improving the yield of recombinantly synthesized glycosides.