Introducing the glycyrrhizic acid and glabridin rich genotypes from the cultivated Iranian licorice (Glycyrrhiza glabra L.) populations to exploit in production systems

Currently, the stable, uniform, and highly efficient production of raw materials for pharmaceutical companies has received special attention. To meet these criteria and reduce harvesting pressure on the natural habitats of licorice (Glycyrrhiza glabra L.), cultivation of this valuable plant is inevitable. In the present study, to introduce the glycyrrhizic acid (GA)- and glabridin-rich genotypes from cultivated Iranian licorice, forty genotypes from eight high-potential wild populations were cultivated and evaluated under the same environmental conditions. The GA content varied from 5.00 ± 0.04 mg/g DW (TF2 genotype) to 23.13 ± 0.02 mg/g DW (I5 genotype). The highest and lowest glabridin content were found in the K2 (0.72 ± 0.021 mg/g DW) and M5 (0.02 ± 0.002 mg/g DW) genotypes, respectively. The rutin content in the leaves of the studied genotypes varied from 1.27 ± 0.02 mg/g DW in E4 to 3.24 ± 0.02 mg/g DW in BO5 genotypes. The genotypes from the Ilam population were characterized by higher vegetative growth and yield traits in the aerial parts and roots. The average root dry yield was 2.44 tons per hectare (t/ha) among the studied genotypes and a genotype from Ilam (I5) yielded the maximum value (3.08 ± 0.034 t/ha). The highest coefficient of variation among the genotypes was observed for leaf width (CV = 34.9%). The GA and glabridin-rich genotypes introduced in this study can be used in the future breeding programs to release new bred licorice cultivars.

The polysaccharides from seeds of Glycyrrhiza uralensis ameliorate metabolic disorders and restructure gut microbiota in type 2 diabetic mice

T2D and its complications are significant threats to human health and are among the most concerning metabolic diseases worldwide. Previous studies have revealed that Glycyrrhiza uralensis polysaccharide extract (GUP) exhibits remarkable antioxidant capabilities and inhibits alpha-glucosidase activity. However, whether GUP improves glycemic control in T2D is unknown. This study aims to investigate the effects of GUP on glucose and lipid metabolism as well as the intestinal microbiota in HFD/STZ-induced T2D. The results demonstrated that GUP could significantly ameliorate hyperglycemia, insulin resistance, oxidative stress, and reduce liver lipid levels in T2D mice. Furthermore, it also enhanced the integrity of the intestinal barrier in T2D mice by reducing the levels of pro-inflammatory cytokines and serum LPS levels. Interestingly, GUP treatment significantly lowered serum creatinine and urea nitrogen levels, mitigating renal function deterioration and interstitial fibrosis. Additionally, GUP intervention increased the α diversity of gut microbiota, promoting beneficial species like Akkermansia, Lactobacillus, Romboutsia and Faecalibaculum, while decreasing harmful ones such as Bacteroides, Escherichia-Shigella, and Clostridium sensu stricto 1 in T2D mice. Overall, this study highlights the potential of GUP in alleviating complications and enhancing intestinal health in T2D mice, providing valuable insights into dietary strategies for diabetes control and overall health improvement.

Multi-Omics Elucidates Difference in Accumulation of Bioactive Constituents in Licorice (Glycyrrhiza uralensis) under Drought Stress

Licorice is a frequently applied herb with potential edible and medicinal value based on various flavonoids and triterpenes. However, studies on detailed flavonoid and triterpene metabolism and the molecular basis of their biosynthesis in licorice are very limited, especially under drought conditions. In the present study, we carried out transcriptome, proteome, and metabolome experiments. To ultimately combine three omics for analysis, we performed a bioinformatics comparison, integrating transcriptome data and proteome data through a Cloud platform, along with a simplified biosynthesis of primary flavonoids and triterpenoids in the KEGG pathway based on metabolomic results. The biosynthesis pathways of triterpenes and flavonoids are enriched at both gene and protein levels. Key flavonoid-related genes (PAL, 4CL, CHS, CHI, CYP93C, HIDH, HI4OMT, and CYP81E1_7) and representative proteins (HIDH, CYP81E1_7, CYP93C, and VR) were obtained, which all showed high levels after drought treatment. Notably, one R2R3-MYB transcription factor (Glyur000237s00014382.1), a critical regulator of flavonoid biosynthesis, achieved a significant upregulated expression as well. In the biosynthesis of glycyrrhizin, both gene and protein levels of bAS and CYP88D6 have been found with upregulated expression under drought conditions. Most of the differentially expressed genes (DEGs) and proteins (DEPs) showed similar expression patterns and positively related to metabolic profiles of flavonoid and saponin. We believe that suitable drought stress may contribute to the accumulation of bioactive constituents in licorice, and our research provides an insight into the genetic study and quality breeding in this plant.

Abiotic factors and endophytes co-regulate flavone and terpenoid glycoside metabolism in Glycyrrhiza uralensis

Recently, endorhizospheric microbiota is realized to be able to promote the secondary metabolism in medicinal plants, but the detailed metabolic regulation metabolisms and whether the promotion is influenced by environmental factors are unclear yet. Here, the major flavonoids and endophytic bacterial communities in various Glycyrrhiza uralensis Fisch. roots collected from seven distinct places in northwest China, as well as the edaphic conditions, were characterized and analyzed. It was found that the soil moisture and temperature might modulate the secondary metabolism in G. uralensis roots partially through some endophytes. One rationally isolated endophyte Rhizobium rhizolycopersici GUH21 was proved to promote the accumulation of isoliquiritin and glycyrrhizic acid significantly in roots of the potted G. uralensis under the relatively high-level watering and low temperature. Furthermore, we did the comparative transcriptome analysis of G. uralensis seedling roots in different treatments to investigate the detailed mechanisms of the environment-endophyte-plant interactions and found that the low temperature went hand in hand with the high-level watering to activate the aglycone biosynthesis in G. uralensis, while GUH21 and the high-level watering cooperatively promoted the in planta glucosyl unit production. Our study is of significance for the development of methods to rationally promote the medicinal plant quality. KEY POINTS: • Soil temperature and moisture related to isoliquiritin contents in Glycyrrhiza uralensis Fisch. • Soil temperature and moisture related to the hosts' endophytic bacterial community structures. • The causal relation among abiotic factors-endophytes-host was proved through the pot experiment.

The effects of plastic film mulching and straw mulching on licorice root yield and soil organic carbon content in a dryland farming

The increasing worldwide demand for traditional herbs has been met by growing cultivated herbs. It is undoubtedly very important to seek a reasonable cultivation mode for the yield, quality and long-term production stability of traditional herbs. In this study, licorice (Glycyrrhiza uralensis Fisch.) was investigated using a field experiment and a process-based model (Denitrification-Decomposition (DNDC) model) to study the effects of mulching methods on root yield and soil organic carbon (SOC) long-term changes. The field experiment contained four treatments: plat planting without mulching (CK), ridge-furrow maize straw mulching (SM), ridge-furrow plastic film mulching (RP), and plat planting with plastic film mulching (FP). Licorice root yield was significantly higher in the SM, RP, and FP than in the CK. SM, RP and FP treatments increased the accumulation of liquiritin and glycyrrhizin in licorice roots. The SM significantly increased SOC content, SOC stocks, SOC sequestration rate, dissolved organic carbon (DOC) content and microbial biomass carbon (MBC) compared to CK, but there was no significant difference in SOC and DOC among CK, RP and FP. The DNDC model was calibrated based on the field test data and showed that under the four CMIP6 SSPs scenarios, the predicted root yield of each treatment was increasing obviously. The production and stability of RP and FP were greater than CK and SM. The SOC under SM showed an increasing trend, whereas it continuously decreased under CK, RP, and FP in the future. The SOC of simulated RS treatment of straw incorporation plus a plastic film mulch was always at the highest value in all the treatments, and its root yield was slightly lower than that of RP and FP, the latter both were very close. Therefore, it is suggested that RS should be adopted to achieve sustained high yield while maintaining a high SOC level.

A general procedure for establishing composite quality evaluation indices based on key quality attributes of traditional Chinese medicine

Licorice, a medicinal herb and food flavor ingredient, has been widely used in traditional Chinese medicine (TCM) for the past 4000 years. In this study, we propose a new quality evaluation approach for licorice quality control based on the key quality attributes commonly used in TCM. The high quality of TCM formulations is ensured by verifying the genuine origin and implementing good agricultural and collection practices for each medicinal herb. In our study, the genuine production area, the harvest season, and the number of growth years were considered the key quality attributes of TCM. To ensure the representativeness of our analysis, we obtained a total of 158 licorice sample batches that differed in the number of growth years, the location of the production areas, and the season for harvesting. Initially, the 158 sample batches were subjected to ultra-high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS). A preliminary screen identified 11 licorice compounds related to the three key quality attributes of TCM . An analysis by ultra-high-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UHPLC-TQ-MS/MS) verified the presence of 34 compounds in all licorice samples. These 34 compounds included the 11 compounds related to the three key quality attributes of the samples, along with other bioactive components identified in previous studies. After using UHPLC-TQ-MS/MS to assess the signal peak intensities of the 34 compounds, we selected 17 licorice compounds to establish sample content evaluation indices, which were determined by high-performance liquid chromatography at four different wavelengths in all 158 licorice sample batches. Finally, the screen identified nine compounds that were closely associated with the quality attributes of licorice based on principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA). Our results suggested that liquiritin and eight other compounds could be used as quality control indicators of licorice, which provided a foundation to establish the TCM quality composite evaluation index (TCM QCEI). In summary, this research concept can serve as a reference for research on quality markers and the evaluation of TCM.

Metabolite Profiling and Transcriptome Analysis Explains Difference in Accumulation of Bioactive Constituents in Licorice (Glycyrrhiza uralensis) Under Salt Stress

Salinity stress significantly affects the contents of bioactive constituents in licorice Glycyrrhiza uralensis. To elucidate the molecular mechanism underlying the difference in the accumulation of these constituents under sodium chloride (NaCl, salt) stress, licorice seedlings were treated with NaCl and then subjected to an integrated transcriptomic and metabolite profiling analysis. The transcriptomic analysis results identified 3,664 differentially expressed genes (DEGs) including transcription factor family MYB and basic helix-loop-helix (bHLH). Most DEGs were involved in flavonoid and terpenoid biosynthesis pathways. In addition, 121 compounds including a triterpenoid and five classes of flavonoids (isoflavone, flavone, flavanone, isoflavan, and chalcone) were identified, and their relative levels were compared between the stressed and control groups using data from the ultrafast liquid chromatography (UFLC)-triple quadrupole-time of flight-tandem mass spectrometry (TOF-MS/MS) analysis. Putative biosynthesis networks of the flavonoids and triterpenoids were created and combined with structural DEGs such as phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase [4CL], cinnamate 4-hydroxylase [C4H], chalcone synthase [CHS], chalcone-flavanone isomerase [CHI], and flavonoid-3',5' hydroxylase (F3',5'H) for flavonoids, and CYP88D6 and CYP72A154 for glycyrrhizin biosynthesis. Notably, significant upregulation of UDP-glycosyltransferase genes (UGT) in salt-stressed licorice indicated that postmodification of glycosyltransferase may participate in downstream biosynthesis of flavonoid glycosides and triterpenoid saponins. Accordingly, the expression trend of the DEGs is positively correlated with the accumulation of glycosides. Our study findings indicate that key DEGs and crucial UGT genes co-regulate flavonoid and saponin biosynthesis in licorice under salt stress.

Association analysis and molecular tagging of phytochemicals in the endangered medicinal plant licorice (Glycyrrhiza glabra L.)

Licorice (Glycyrrhiza glabra L.) is a medicinal plant species valued in many countries in Asia and Europe for its phytochemical characteristics. Licorice biodiversity is becoming threatened nowadays in Iran due to increasing demand and a drastic decline of its natural habitats. Therefore, licorice domestication would be necessary in the near future, and molecular breeding would help to introduce genotypes suitable for cultivation. The present study was carried out with 170 individual licorice plants sampled in the wild in 59 localizations in 21 provinces of Iran. The association of 436 polymorphic AFLP markers, produced by 15 primer combinations (EcoRI/MseI), with six phenotypic phytochemical traits was studied. The AMOVA analysis show gene diversity among and within localizations. The population structure analysis identified two main sub-populations with significant genetic variation. Significant associations were identified between three markers (E3/M40-4, E34/M4-12 and E12/M31-15) and glycyrrhizin concentration, and between four markers (E11/M34-12, E11/M34-15, E9/M7-29, and E9/M7-30) and phenolic compounds contents. Markers detected can be useful in the domestication of licorice as well as in breeding programs. Licorice sampled in four localizations (KBA1, KBA2, SKh2 and Fa1) were found to be superior in terms of glycyrrhizin and antioxidants content, and therefore they can be considered as elite genotypes which could be included in the domestication process.

Comparative Proteomic Analysis Reveals the Molecular Mechanisms Underlying the Accumulation Difference of Bioactive Constituents in Glycyrrhiza uralensis Fisch under Salt Stress

Licorice (Glycyrrhiza uralensis Fisch) possesses a substantial share of the global markets for its unique sweet flavor and diverse pharmacological compounds. Cultivated licorice is widely distributed in northwest regions of China, covered with land with a broad range of salinities. A preliminary study indicated that suitable salt stress significantly increased the content of bioactive constituents in licorice. However, the molecular mechanisms underlying the influence of salinity on the accumulation of these constituents remain unclear, which hinders quality breeding of cultivated licorice. In our study, flavonoid-related structural genes were obtained, and most of them, such as phenylalanine ammonia-lyases, cinnamate 4-hydroxylases, 4-coumarate: CoA ligases, chalcone synthases, chalcone-flavanone isomerase, and flavonol synthase, showed high levels after salt treatment. In the biosynthesis of glycyrrhizin, three key enzymes (bAS, CYP88D6, and CYP72A154) were identified as differentially expressed proteins and remarkably upregulated in the salt-stressed group. Combining these results with the contents of 14 bioactive constituents, we also found that the expression patterns of those structural proteins were logically consistent with changes in bioactive constituent profiles. Thus, we believe that suitable salt stress increased the accumulation of bioactive constituents in licorice by upregulating proteins involved in the related biosynthesis pathways. This work provided valuable proteomic information for unraveling the molecular mechanism of flavonoid and glycyrrhizin metabolism and offered fundamental resources for quality breeding in licorice.

Dynamic Variations in Multiple Bioactive Constituents under Salt Stress Provide Insight into Quality Formation of Licorice

The demand for licorice and its natural product derivatives in domestic and foreign market is considerably huge. The core production areas of licorice are covered with salinity and drought land in northwestern China. Studies have shown that suitable environmental stress can promote the accumulation of glycyrrhizin and liquiritin to improve its quality as medicinal materials. However, there are few reports on other bioactive constituents of licorice, not to mention their dynamic accumulation under stressed conditions. To explore the quality formation of licorice from the perspective of salt influence, a reliable method based on ultra-fast liquid chromatography tandem triple quadrupole mass spectrometry (UFLC–MS/MS) was established for simultaneous determination of sixteen bioactive constituents, including triterpenoids, flavonoids, chalcones and their glycosides. Physiological experiments were performed to investigate salt tolerance of licorice under different salinity treatments. The expressions of crucial genes (bAS and CHS), key enzymes of triterpenoid and flavonoid synthesis, were also tested by qRT-PCR. Our study found that 50 mM NaCl treatment (low stress) was the most favorable to promote the accumulation of bioactive constituents in the long term, without harming the plants. Flavonoid accumulation of non-stressed and low-stressed groups became different in the initial synthesis stage, and glycosyltransferases may have great influence on their downstream synthesis. Furthermore, bAS and CHS also showed higher levels in low-stressed licorice at harvest time. This work provides valuable information on dynamic variations in multiple bioactive constituents in licorice treated by salt and insight into its quality formation under stressed conditions.

Effect of seedling grade standard on improving the quality of licorice (Glycyrrhiza uralensis F.): changes in the seven bioactive components and root biomass during two-year growth

Licorice cultivated is one of the most popular herbal medicines, while its quality is unstable. The aim of present study is to investigate the effect of licorice seedling grade standard on improving its quality. One-year-old Glycyrrhiza uralensis seedlings were classified into three grades 1, 2, and 3 by weight per plant. The major root biomass indexes (root fresh weight, root dry weight and taproot diameter) and contents of 7 bioactive components (glycyrrhizin, liquiritin, liquiritin apioside, liquiritigenin, isoliquiritin, isoliquiritin apioside, and isoliquiritigenin) varied in different grades seedlings. Further, the contents of 7 investigated compounds of 3-year-old licorice produced by grade 1 seedlings were 1.5-2 times as much as those produced by grade 2 and 3. Additionally, the contents of liquiritin apioside and isoliquiritin apioside were positively correlated with licorice root biomass. These results indicated that establishing licorice seedling grade standard is an effective way to improve and control its quality.

Utilization of the Ability to Induce Activation of the Nuclear Factor (Erythroid-derived 2)-like Factor 2 (Nrf2) to Assess Potential Cancer Chemopreventive Activity of Liquorice Samples

INTRODUCTION

Nuclear factor (erythroid-derived 2)-like factor 2 (Nrf2) is a transcription factor that regulates expression of many detoxification enzymes. Nrf2-antioxidant responsive element (Nrf2-ARE) signalling pathway can be a target for cancer chemoprevention. Glycyrrhiza glabra, common name, 'liquorice', is used as a sweetening and flavouring agent, and traditionally, to treat various ailments, and implicated to chemoprevention. However, its chemopreventive property has not yet been scientifically substantiated.

OBJECTIVE

To assess the ability of liquorice root samples to induce Nrf2 activation correlating to their potential chemopreventive property.

METHODS

The ability of nine methanolic extracts of liquorice root samples, collected from various geographical origins, to induce Nrf2 activation was determined by the luciferase reporter assay using the ARE-reporter cell line, AREc32. The antioxidant properties were determined by the 2,2-diphenyl-1-picryhydrazyl (DPPH) and the ferric-reducing antioxidant power (FRAP) assays.

RESULTS

All extracts exhibited free-radical-scavenging property (RC50  = 136.39-635.66 µg/mL). The reducing capacity of ferrous ion was 214.46-465.59 μM Fe(II)/g. Nrf2 activation indicated that all extracts induced expression of ARE-driven luciferase activity with a maximum induction of 2.3 fold relative to control. These activities varied for samples from one geographical location to another.

CONCLUSIONS

The present findings add to the existing knowledge of cancer chemoprevention by plant-derived extracts or purified phytochemicals, particularly the potential use of liquorice for this purpose. Copyright © 2016 John Wiley & Sons, Ltd.

Metabolite Profiling and Classification of DNA-Authenticated Licorice Botanicals

Raw licorice roots represent heterogeneous materials obtained from mainly three Glycyrrhiza species. G. glabra, G. uralensis, and G. inflata exhibit marked metabolite differences in terms of flavanones (Fs), chalcones (Cs), and other phenolic constituents. The principal objective of this work was to develop complementary chemometric models for the metabolite profiling, classification, and quality control of authenticated licorice. A total of 51 commercial and macroscopically verified samples were DNA authenticated. Principal component analysis and canonical discriminant analysis were performed on (1)H NMR spectra and area under the curve values obtained from UHPLC-UV chromatograms, respectively. The developed chemometric models enable the identification and classification of Glycyrrhiza species according to their composition in major Fs, Cs, and species specific phenolic compounds. Further key outcomes demonstrated that DNA authentication combined with chemometric analyses enabled the characterization of mixtures, hybrids, and species outliers. This study provides a new foundation for the botanical and chemical authentication, classification, and metabolomic characterization of crude licorice botanicals and derived materials. Collectively, the proposed methods offer a comprehensive approach for the quality control of licorice as one of the most widely used botanical dietary supplements.