Characterization of Non-Anthocyanic Flavonoids in Some Hybrid Red Grape Extracts Potentially Interesting for Industrial Uses

Antitrypanosomal, Antitopoisomerase-I, and Cytotoxic Biological Evaluation of Some African Plants Belonging to Crassulaceae; Chemical Profiling of Extract Using UHPLC/QTOF-MS/MS

In our continuous study for some African plants as a source for antitrypanosomally and cytotoxic active drugs, nine different plants belonging to the Crassulaceae family have been selected for the present study. Sedum sieboldii leaves extract showed an antitrypanosomal activity against Trypanosoma brucei with an IC₅₀ value of 8.5 µg/mL. In addition, they have cytotoxic activities against (HCT-116), (HEPG-2) and (MCF-7), with IC₅₀ values of 28.18 ± 0.24, 22.05 ± 0.66, and 26.47 ± 0.85 µg/mL, respectively. Furthermore, the extract displayed inhibition against Topoisomerase-1 with an IC₅₀ value of 1.31 µg/mL. It showed the highest phenolics and flavonoids content among the other plants' extracts. In order to identify the secondary metabolites which may be responsible for such activities, profiling of the polar secondary metabolites of S. sieboldii extract via Ultra-Performance Liquid Chromatography coupled to High-Resolution QTOF-MS operated in negative and positive ionization modes, which revealed the presence of 46 metabolites, including flavonoids, phenolic acids, anthocyanidins, coumarin, and other metabolites.

Autofluorescence-Based Investigation of Spatial Distribution of Phenolic Compounds in Soybeans Using Confocal Laser Microscopy and a High-Resolution Mass Spectrometric Approach

In this research, we present a detailed comparative analysis of the bioactive substances of soybean varieties k-11538 (Russia), k-11559 (Russia), k-569 (China), k-5367 (China), k-5373 (China), k-5586 (Sweden), and Primorskaya-86 (Russia) using an LSM 800 confocal laser microscope and an amaZon ion trap SL mass spectrometer. Laser microscopy made it possible to clarify in detail the spatial arrangement of the polyphenolic content of soybeans. Our results revealed that the phenolics of soybean are spatially located mainly in the seed coat and the outer layer of the cotyledon. High-performance liquid chromatography (HPLC) was used in combination with an amaZon SL BRUKER DALTONIKS ion trap (tandem mass spectrometry) to identify target analytes in soybean extracts. The results of initial studies revealed the presence of 63 compounds, and 45 of the target analytes were identified as polyphenolic compounds.

Allelopathic Potential of Mangroves from the Red River Estuary against the Rice Weed Echinochloa crus-galli and Variation in Their Leaf Metabolome

Mangroves are the only forests located at the sea–land interface in tropical and subtropical regions. They are key elements of tropical coastal ecosystems, providing numerous ecosystem services. Among them is the production of specialized metabolites by mangroves and their potential use in agriculture to limit weed growth in cultures. We explored the in vitro allelopathic potential of eight mangrove species’ aqueous leaf extracts (Avicennia marina, Kandelia obovata, Bruguiera gymnorhiza, Sonneratia apetala, Sonneratia caseolaris, Aegiceras corniculatum, Lumnitzera racemosa and Rhizophora stylosa) on the germination and growth of Echinochloa crus-galli, a weed species associated with rice, Oryza sativa. Leaf methanolic extracts of mangrove species were also studied via UHPLC-ESI/qToF to compare their metabolite fingerprints. Our results highlight that A. corniculatum and S. apetala negatively affected E. crus-galli development with a stimulating effect or no effect on O. sativa. Phytochemical investigations of A. corniculatum allowed us to putatively annotate three flavonoids and two saponins. For S. apetala, three flavonoids, a tannin and two unusual sulfated ellagic acid derivatives were found. Some of these compounds are described for the first time in these species. Overall, A. corniculatum and S. apetala leaves are proposed as promising natural alternatives against E. crus-galli and should be further assessed under field conditions.

Based on Multi-Activity Integrated Strategy to Screening, Characterization and Quantification of Bioactive Compounds from Red Wine

According to French Paradox, red wine was famous for the potential effects on coronary heart disease (CHD), but the specific compounds against CHD were unclear. Therefore, screening and characterization of bioactive compounds from red wine was extremely necessary. In this paper, the multi-activity integrated strategy was developed and validated to screen, identify and quantify active compounds from red wine by using ultra high performance liquid chromatography-fraction collector (UHPLC-FC), ultra fast liquid chromatography-quadrupole-time-of-flight/mass spectrometry (UFLC-Q-TOF/MS) and bioactive analysis. UHPLC-FC was employed to separate and collect the components from red wine, which was further identified by UFLC-Q-TOF/MS to acquire their structural information. Furthermore, the active fractions were tested for antioxidant activity, inhibitory activity against thrombin and lipase activities in vitro by the activity screening kit. As the results, there were 37 fractions had antioxidant activity, 22 fractions had thrombin inhibitory activity and 28 fractions had lipase inhibitory activity. Finally, 77 active components from red wine were screened and 12 ingredients out of them were selected for quantification based on the integration of multi-activity. Collectively, the multi-activity integrated strategy was helpful for the rapid and effective discovery of bioactive components, which provided reference for exploring the health care function of food.

AGSE: A Novel Grape Seed Extract Enriched for PP2A Activating Flavonoids That Combats Oxidative Stress and Promotes Skin Health

Environmental stimuli attack the skin daily resulting in the generation of reactive oxygen species (ROS) and inflammation. One pathway that regulates oxidative stress in skin involves Protein Phosphatase 2A (PP2A), a phosphatase which has been previously linked to Alzheimer’s Disease and aging. Oxidative stress decreases PP2A methylation in normal human dermal fibroblasts (NHDFs). Thus, we hypothesize agents that increase PP2A methylation and activity will promote skin health and combat aging. To discover novel inhibitors of PP2A demethylation activity, we screened a library of 32 natural botanical extracts. We discovered Grape Seed Extract (GSE), which has previously been reported to have several benefits for skin, to be the most potent PP2A demethylating extract. Via several fractionation and extraction steps we developed a novel grape seed extract called Activated Grape Seed Extract (AGSE), which is enriched for PP2A activating flavonoids that increase potency in preventing PP2A demethylation when compared to commercial GSE. We then determined that 1% AGSE and 1% commercial GSE exhibit distinct gene expression profiles when topically applied to a 3D human skin model. To begin to characterize AGSE’s activity, we investigated its antioxidant potential and demonstrate it reduces ROS levels in NHDFs and cell-free assays equal to or better than Vitamin C and E. Moreover, AGSE shows anti-inflammatory properties, dose-dependently inhibiting UVA, UVB and chemical-induced inflammation. These results demonstrate AGSE is a novel, multi-functional extract that modulates methylation levels of PP2A and supports the hypothesis of PP2A as a master regulator for oxidative stress signaling and aging in skin.

Phytochemical Analysis of Phenolics, Sterols, and Terpenes in Colored Wheat Grains by Liquid Chromatography with Tandem Mass Spectrometry

The colored grain of wheat (Triticum aestivum L.) contains a large number of polyphenolic compounds that are biologically active ingredients. The purpose of this work was a comparative metabolomic study of extracts from anthocyaninless (control), blue, and deep purple (referred to here as black) grains of seven genetically related wheat lines developed for the grain anthocyanin pigmentation trait. To identify target analytes in ethanol extracts, high-performance liquid chromatography was used in combination with Bruker Daltonics ion trap mass spectrometry. The results showed the presence of 125 biologically active compounds of a phenolic (85) and nonphenolic (40) nature in the grains of T. aestivum (seven lines). Among them, a number of phenolic compounds affiliated with anthocyanins, coumarins, dihydrochalcones, flavan-3-ols, flavanone, flavones, flavonols, hydroxybenzoic acids, hydroxycinnamic acids, isoflavone, lignans, other phenolic acids, stilbenes, and nonphenolic compounds affiliated with alkaloids, carboxylic acids, carotenoids, diterpenoids, essential amino acids, triterpenoids, sterols, nonessential amino acids, phytohormones, purines, and thromboxane receptor antagonists were found in T. aestivum grains for the first time. A comparative analysis of the diversity of the compounds revealed that the lines do not differ from each other in the proportion of phenolic (53.3% to 70.3% of the total number of identified compounds) and nonphenolic compounds (46.7% to 29.7%), but diversity of the compounds was significantly lower in grains of the control line. Even though the lines are genetically closely related and possess similar chemical profiles, some line-specific individual compounds were identified that constitute unique chemical fingerprints and allow to distinguish each line from the six others. Finally, the influence of the genotype on the chemical profiles of the wheat grains is discussed.

Antioxidant Activity and Polyphenols Characterization of Four Monovarietal Grape Pomaces from Salento (Apulia, Italy)

The wine industry annually produces millions of tons of by-products rich in polyphenolic compounds that can be reused as secondary raw material in the food, cosmetic and pharmaceutical industries. The purpose of this work was to describe the presence of nutraceutical compounds and to evaluate the antioxidant activity of pomaces from three Apulian (South Italy, Italy) grape varieties (Negroamaro, Malvasia di Lecce and Primitivo) and to compare them with one of the most cultivated wines in Europe (Cabernet Sauvignon). The main classes of polyphenolic substances were characterized via high performance liquid chromatography/diode array detector/mass spectrometer time of flight (HPLC/DAD/TOF) and the antioxidant activity was evaluated with three different methods. The four investigated grape marcs have shown different polyphenols and antioxidant activities. Primitivo marc showed the higher antioxidant activity due to the excellent level of polyphenols, followed by the Negroamaro cultivar. In addition, marcs from traditional Apulian vines showed higher antioxidant activities than Cabernet Sauvignon because of an elevated level of active polyphenolic substances such as catechin, epicatechin, quercetin and its derivatives.

Evaluation of the antioxidant capacity, volatile composition and phenolic content of hybrid Vitis vinifera L. varieties sweet sapphire and sweet surprise

Bioactive compounds were extracted using two different extraction solvents (acetone and water) from pulp and whole grape berries derived from hybrid Vitis vinifera L. varieties Sweet sapphire (SP) and Sweet surprise (SU) and were characterised based on a comprehensive metabolomic approach by chromatography coupled with mass spectrometry (UPLC-QTOF-MSE and GC-FID/MS). GC-FID/MS analysis was performed with two different extraction methods (solvent extraction method and solid-phase extraction). Anthocyanins were characterised and quantified by HPLC-UV. The antioxidant potential was assessed by different assays. SP acetone extract from grape skin had the highest mean to DPPH, FRAP, ORAC and phenolic content SP samples, also showed higher anthocyanin content. Globally, 87 phenolic compounds were identified. The relative quantification by UPLC-MS^E showed flavonoids the most abundant class. Forty two compounds were found in the volatile fraction of SU, while only thirty one volatile compounds were found in the SP samples.

Impact of Environmental Conditions on Growth and the Phenolic Profile of Achillea atrata L

Achillea atrata L. is a traditionally used medicinal plant. With its pronounced antimicrobial potential, this alpine Achillea species may also be used in modern phytotherapy to treat MRSA infections and prevent dermal infections, such as acne vulgaris. For the present study, A. atrata was cultivated in its natural habitat in Switzerland as well as in Germany to elucidate the potential of standardizing plant material derived from this species for pharmaceutical production. Phytochemical characterization of phenolic constituents by HPLC-DAD-MSn revealed that environmental conditions have only a minor impact on the phenolic profile. Metabolic differences between cultivated and wild plants grown in the same environment suggested the possible existence of genetically derived chemotypes. In total, 28 substances were identified, with marked differences in the occurrence of phenolic compounds observed between flowers and leaves. Moreover, to the best of our knowledge, 7 phenolic compounds have been reported for the first time in A. atrata in the present study. The quantitation of individual constituents revealed their contents to depend on environmental factors and to reach their maximum at increasing altitudes. The results here presented may help to select and cultivate A. atrata plant material with defined and constant compound profiles, which is of particular importance for potential pharmaceutical use.

Comprehensive polyphenolic profiling in promising resistant grapevine hybrids including 17 novel breeds in northern Italy

BACKGROUND

A promising way to overcome the susceptibility of Vitis vinifera L. to fungal diseases is the integration of genetic resistance by the interspecific crossing between V. vinifera varieties and resistant species. However, the products of such hybrids are still not accepted by customers, particularly due to their organoleptic characteristics, not least influenced by their polyphenolic profile.

RESULTS

A total of 58 resistant breeding lines, 41 from international programs and 17 new progeny individuals, were grown in one untreated vineyard to exclude any variances by climatic and pedologic conditions or vineyard practice. A total of 60 polyphenols (including acids, anthocyanins, flavonols, flavan‐3‐ols, and stilbenoids) were determined in grapevine berries by ultrahigh‐performance liquid chromatography–mass spectrometry in two consecutive years. The overall profiles were rather consistent (variation P > 0.05) within the two harvests, with the exceptions of epicatechin and caftaric acid. Anthocyanin diglucosides were found in ten of the red breeding lines, malvidin‐3,5‐O‐diglucoside being predominant in nine of them. Total polyphenol content of the unknown progeny individuals and international breeding lines was comparable, with the exception of significantly increased amounts of gallic acid and some flavonoids.

CONCLUSION

The comprehensive study reported herein of the polyphenolic profile of hybrids from international breeding programs, but also of new breeds from private initiatives, all cultivated in the same vineyard, will support the selection of promising candidates for further breeding programs to overcome impairment due to undesired sensory characteristics of new highly resistant varieties.

Grapevine as a Rich Source of Polyphenolic Compounds

Grapes are rich in primary and secondary metabolites. Among the secondary metabolites, polyphenolic compounds are the most abundant in grape berries. Besides their important impacts on grape and wine quality, this class of compounds has beneficial effects on human health. Due to their antioxidant activity, polyphenols and phenolic acids can act as anti-inflammatory and anticancerogenic agents, and can modulate the immune system. In grape berries, polyphenols and phenolic acids can be located in the pericarp and seeds, but distribution differs considerably among these tissues. Although some classes of polyphenols and phenolic acids are under strict genetic control, the final content is highly influenced by environmental factors, such as climate, soil, vineyard, and management. This review aims to present the main classes of polyphenolic compounds and phenolic acids in different berry tissues and grape varieties and special emphasis on their beneficial effect on human health.

Phytochemical characterization of different yarrow species (Achillea sp.) and investigations into their antimicrobial activity

Various Achillea species are rich in bioactive compounds and are important medicinal plants in phytotherapy. In the present study, Achillea millefolium L., Achillea moschata Wulfen, and Achillea atrata L. were compared with respect to their phenolic profile and antibacterial activity against gram-positive bacteria strains (Staphylococcus, Propionibacterium). Particular focus was given to A. atrata, which has hardly been studied so far. Based on the metabolite profile, A. atrata exhibited more similarities to A. moschata than to A. millefolium. The former two only differed in the occurrence of four compounds. The flavonols syringetin-3-O-glucoside and mearnsetin-hexoside, not reported for an Achillea species before, have been detected in A. atrata and A. moschata. All Achillea species reduced growth of the tested bacteria. A. atrata demonstrated highest activity against Propionibacterium acnes and Staphylococcus epidermidis, both being involved in the pathogenesis of acne vulgaris. Furthermore, A. atrata has a pronounced anti-methicillin-resistant Staphylococcus aureus potential. Bioassay-guided fractionation revealed that only the most polar fraction of A. moschata displayed antimicrobial activity, which was attributed to phenolics such as apigenin, centaureidin, and nevadensin, being present in high amounts in A. atrata. Thus, this alpine species shows promising antimicrobial activity and might be a potential source for developing novel dermal/topical drugs.

Thiol precursors in Vitis mould-tolerant hybrid varieties

BACKGROUND

Over recent years, a new wave of disease-tolerant to mildew varieties has flooded the viticulture sector, for reasons of human safety and economic expediency. These hybrid grape cultivars are selected mainly on the basis of their intrinsic capability to counter the attack of the main fungal diseases that affect grape production, such as downy mildew and powdery mildew. However, their organoleptic and oenological characteristics have not yet been studied in depth for purposes of both juice and wine production, due to the high number of newly proposed germplasms and the lack of information about their adaptability to different environments. This work examines the thiol aroma precursors concentration in 64 red and white disease-tolerant hybrid varieties in the vine germplasm collections of Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria-Viticulture and Enology Research Center and Fondazione Edmund Mach, both from the north-east of Italy.

RESULTS

All cultivars showed the presence of 3-mercaptohexan-1-ol (3MH) precursors, ranging from 4.4 to 1141 μg kg^-1 for 3-S-glutathionyl hexan-1-ol (GSH-3MH), and from 0.3 to 136 μg kg^-1 for 3-S-cysteinyl 3-hexan-1-ol. The concentration of GSH-3MH exceeded 600 μg kg^-1 in eight varieties, with values comparable to those of the richest Vitis vinifera reported so far. On average, red grapes showed higher concentrations of 3MH precursors than white ones did. Only two hybrids had 4-mercapto-4-methylpentan-2-one (4MMP) precursors over the limit of quantification, albeit with a much higher concentration than those normally reported in Sauvignon Blanc.

CONCLUSION

This is the first detailed survey of 3MH and 4MMP precursors carried out taking into account a considerable number of hybrid grape varieties. The results show that some of these varieties could be interesting for the production of tropical juices or tropical-aromatic wines and soft drinks, through the enzymatic liberation of thiol aromas, as well as for the production of aromatizing tannins to be used in the food industry. © 2020 Society of Chemical Industry.

Metabolite Profiling of Aquilaria malaccensis Leaf Extract Using Liquid Chromatography-Q-TOF-Mass Spectrometry and Investigation of Its Potential Antilipoxygenase Activity In-Vitro

The Aquilaria malaccensis species of the genus Aquilaria is an abundant source of agarwood resin and many bioactive phytochemicals. Recent data regarding the chemical constituents and biological activities of Aquilaria leaves led us to attempt to qualitatively profile the metabolites of Aquilaria malaccensis leaves from a healthy, noninoculated tree through phytochemical screening, GC-MS, and LC/Q-TOF-MS. The present work is also the first to report the antilipoxygenase activity of A. malaccensis leaves from healthy noninoculated tree and investigate its toxicity on oral mucosal cells. A total of 53 compounds were tentatively identified in the extract, some of which have been described in literature as exhibiting anti-inflammatory activity. A number of compounds were identified for the first time in the extract of A. malaccensis leaf, including quercetin, quercetin-O-hexoside, kaempferol-O-dirhamnoside, isorhamnetin-O-hexoside, syringetin-O-hexoside, myricetin, tetrahydroxyflavanone, hesperetin, sissotrin, and lupeol. The antilipoxygenase assay was used to determine the lipoxygenase (LOX) inhibitory potential of the extract, while a WST-1 assay was conducted to investigate the effect of the extract on oral epithelial cells (OEC). The extract implied moderate anti-LOX activity with IC50 value of 71.6 µg/mL. Meanwhile, the cell viability of OEC ranged between 92.55% (10 µg/mL)–76.06% ± (100 µg/mL) upon treatment, indicating some potential toxicity risks. The results attained encourage future studies of the isolation of bioactive compounds from Aquilaria malaccensis leaves, as well as further investigation on the anti-inflammatory mechanisms and toxicity associated with their use.

New technological approaches for recovering bioactive food constituents from sweet cherry (Prunus avium L.) stems

INTRODUCTION

In recent years, an increasing interest in biological properties of sweet cherry (Prunus avium L.) stems has resulted in increased attention for advanced extraction techniques and their optimisation.

OBJECTIVES

In the present study chemical profiles of P. avium stems extracts obtained by selected emerging technologies, such as pressurised liquid extraction (PLE) and supercritical fluid extraction (SFE), under different experimental conditions were compared.

MATERIAL AND METHODS

All SFEs were carried out at 40°C in a dynamic mode with different solvent combinations (CO₂ plus ethanol at 7 and 15%) and pressures (150 and 300 bar). The PLE experiments were performed in a static mode for all tested combinations of extraction solvent (ethanol-water from 0% to 100%) at temperatures ranging from 40 to 200°C. A complete analytical characterisation of cherry stem extracts was performed by high-performance liquid chromatography coupled to electrospray ionisation quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS).

RESULTS

PLE showed to be more efficient than SFE removing a wide variety of compounds with different polarities being phenols the most abundant, whereas SFE resulted in a higher amount of fatty acids and derivatives. Chemical characterisation of the extracts was carried out by HPLC-ESI-QTOF-MS yielding in total 42 identified compounds, among which 22 compounds were identified in P. avium stems for the first time.

CONCLUSION

These results point out the possibility of sweet cherry stem extracts to be incorporated in formulations manufactured by food and pharmaceutical industry. Also, these new thermal and high-pressure industrial technologies proved to be promising candidates in the valorisation of sweet cherry by-product.

Metabolomic and transcriptomic changes underlying cold and anaerobic stresses after storage of table grapes

The currently accepted paradigm is that fruits and vegetables should be consumed fresh and that their quality deteriorates during storage; however, there are indications that some metabolic properties can, in fact, be improved. We examined the effects of low temperature and high-CO₂ conditions on table grapes, Vitis vinifera L. cv. 'Superior Seedless'. Berries were sampled at harvest (T0) and after low-temperature storage for 6 weeks under either normal atmosphere conditions (TC) or under an O₂ level of 5 kPa and elevated CO₂ levels of 5, 10 or 15 kPa (T5, T10, T15). Accumulation of 10 stilbenes, including E-ε-viniferin, E-miyabenol C and piceatannol, significantly increased under TC treatment as compared to T0 or T15. Sensory analysis demonstrated that elevated CO₂ elicited dose-dependent off-flavor accumulation. These changes were accompanied by an accumulation of 12 volatile metabolites, e.g., ethyl acetate and diacetyl, that imparted disagreeable flavors to fresh fruit. Transcriptome analysis revealed enrichment of genes involved in pyruvate metabolism and the phenylpropanoid pathway. One of the transcription factors induced at low temperature but not under high CO₂ was VvMYB14, which regulates stilbene biosynthesis. Our findings reveal the potential to alter the levels of targeted metabolites in stored produce through understanding the effects of postharvest treatments.

Procyanidin trimer C1 reactivates latent HIV as a triple combination therapy with kansui and JQ1

Although anti-retroviral therapies have greatly extended the lives of HIV infected individuals, current treatments are unable to completely eliminate virally infected cells. A number of latency reversing agents have been proposed for use in a "shock and kill" strategy to reactivate latent HIV, thus making it vulnerable to killing mechanisms. Procyanidin trimer C1 (PC1) is a flavonoid found in multiple plant sources including grape, apple, and cacao, which has antioxidant and anti-inflammatory properties. We determined that PC1 reactivates latent HIV in cell line and primary cell models of HIV, through activation of the MAPK pathway. Notably, PC1 reactivates latent HIV without increasing surface markers of T cell activation. Combining several therapeutics, which activate HIV transcription through different mechanisms, is the most efficient approach to clinically reactivate latent reservoirs. We utilized PC1 (MAPK agonist), kansui (PKC agonist), and JQ1 (BET bromodomain inhibitor) in a triple combination approach to reactivate latent HIV in cell line and primary cell models of HIV latency. When used in combination, low concentrations which fail to reactivate HIV as single treatments, are effective. Thus, several mechanisms, using distinct activation pathways, act together to reactivate latent HIV.

LC-QTOF characterization of non-anthocyanic flavonoids in four Tunisian fig varieties

Flavonoids are compounds characterized by antioxidant activity, and their intake in the human diet is considered useful for health and nutrition. Non-anthocyanic flavonoids in 4 different types of Tunisian figs belonging to the smyrna-type Ficus carica varieties known as Kholi, Tchich Asal, Himri, and Bidhi were studied by liquid chromatography/high-resolution mass spectrometry UHPLC-QqTOF. Twenty-two compounds belonging to the classes of flavanones (naringenin and eriodictyol), flavones (3 apigenin and 5 luteolin derivatives), and flavonols (2 kaempferol and 7 quercetin derivatives) were identified. Three O-methoxy flavonols (tamarixetin, syringetin, and isorhamnetin-3-O-glucoside) were found in figs for the first time. Total content of non-anthocyanic flavonoids found in dark varieties (between 410 and 830 mg/kg) show that these F. carica are fruits qualitatively and quantitatively rich of dietary polyphenols.

Natural Products and HIV/AIDS

The study of natural products in biomedical research is not a modern concept. Many of the most successful medical therapeutics are derived from natural products, including those studied in the field of HIV/AIDS. Biomedical research has a rich history of discovery based on screens of medicinal herbs and traditional medicine practices. Compounds derived from natural products, which repress HIV and those that activate latent HIV, have been reported. It is important to remember the tradition in medical research to derive therapies based on these natural products and to overcome the negative perception of natural products as an "alternative medicine."

Characterization of UGT716A1 as a Multi-substrate UDP:Flavonoid Glucosyltransferase Gene in Ginkgo biloba

Ginkgo biloba L., a "living fossil" and medicinal plant, is a well-known rich source of bioactive flavonoids. The molecular mechanism underlying the biosynthesis of flavonoid glucosides, the predominant flavonoids in G. biloba, remains unclear. To better understand flavonoid glucosylation in G. biloba, we generated a transcriptomic dataset of G. biloba leaf tissue by high-throughput RNA sequencing. We identified 25 putative UDP-glycosyltransferase (UGT) unigenes that are potentially involved in the flavonoid glycosylation. Among them, we successfully isolated and expressed eight UGT genes in Escherichia coli, and found that recombinant UGT716A1 protein was active toward broad range of flavonoid/phenylpropanoid substrates. In particular, we discovered the first recombinant UGT protein, UGT716A1 from G. biloba, possessing unique activity toward flavanol gallates that have been extensively documented to have significant bioactivity relating to human health. UGT716A1 expression level paralleled the flavonoid distribution pattern in G. biloba. Ectopic over-expression of UGT716A1 in Arabidopsis thaliana led to increased accumulation of several flavonol glucosides. Identification and comparison of the in vitro enzymatic activity of UGT716A1 homologs revealed a UGT from the primitive land species Physcomitrella patens also showed broader substrate spectrum than those from higher plants A. thaliana, Vitis vinifera, and Medicago truncatula. The characterization of UGT716A1 from G. biloba bridges a gap in the evolutionary history of UGTs in gymnosperms. We also discuss the implication of UGT716A1 for biosynthesis, evolution, and bioengineering of diverse glucosylated flavonoids.