Flavones and flavone synthases

Molecular and Structural Characterization of a Chalcone di-C-Methyltransferase RdCMT from Rhododendron dauricum and Its Application in De Novo Biosynthesis of Farrerol in Pichia pastoris

Methylation plays a crucial role in drug design and optimization. While numerous methyltransferases have been characterized from plants, C-methyltransferases, particularly those targeting phenolic skeletons, are rare. In this study, we identified a novel di-C-methyltransferase RdCMT from the medicinal plant Rhododendron dauricum. RdCMT catalyzes a sequential two-step 3'-C/5'-C-methylation of naringenin chalcone, leading to the biosynthesis of farrerol. RdCMT exhibited a strict substrate specificity for chalcones. Through combinatorial catalysis, a series of C-methylated flavonoids were synthesized. Moreover, farrerol was synthesized de novo in Nicotiana benthamiana and Pichia pastoris with yields of 0.4 mg/g (dry weight) and 149.0 mg/L, respectively. The structure of RdCMT was determined using cryo-electron microscopy (cryo-EM), revealing that residues R328 and G296 significantly influence the substrate specificity of RdCMT. This work not only introduces a potent biocatalyst for the preparation of C-methylated flavonoids but also offers insights into the catalytic mechanisms of C-methyltransferases.

Effects of Apigenin and Luteolin on Myzus persicae (Hemiptera: Aphididae) Probing Behavior

Apigenin and luteolin are products of the phenylpropanoid pathway, where apigenin serves as a substrate for the synthesis of luteolin. Apigenin and luteolin are highly bioactive flavones; therefore, in search of prospective biopesticides, the receptiveness of the polyphagous green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) to apigenin and luteolin was studied. The flavones were applied as 0.1% ethanolic solutions to the host plant leaf surface, and aphid probing and feeding activities were monitored using the Electrical Penetration Graph (EPG) technique. The structural difference between apigenin and luteolin, which was the number of hydroxyl groups in the molecule, had an impact on the activity of these flavones. On apigenin-treated plants, the duration of the first probe was three times as short as on the control and five times as short as on the luteolin-treated plants; the duration of the time to the first ingestion phase within the successful probe was shorter than on the control and luteolin-treated plants; the mean duration of xylem sap ingestion bouts and the proportion of xylem phase in all probing activities were the highest; and the duration of salivation before phloem sap ingestion was the longest. Aphids' response to luteolin-treated plants was less distinct as compared to apigenin-treated plants.

Two Caffeoyl-CoA O-methyltransferase-like enzyme are involved in the biosynthesis of polymethoxyflavones in Citrus reticulata 'Chachiensis'

Polymethoxyflavones (PMFs) are abundant in citrus plants and exhibit remarkable biological activities in the inhibition of the occurrence and development of various tumours. O-methyltransferase (OMTs)-mediated methylation plays a crucial role in the biosynthesis of PMFs. However, the OMTs catalyzing the methylation of hydroxyflavonoids in citrus have not been fully identified. In this study, we identified two novel CCoAOMT-like enzymes in Citrus reticulata 'Chachiensis', designated CrcCCoAOMT7-1 and CrcCCoAOMT7-2. The transient overexpression and virus-induced gene silencing experiments further confirmed the essential role of CrcCCoAOMT7-1/7-2 in the regulation of PMF synthesis in citrus. Furthermore, in vitro functional analysis showed that CrcCCoAOMT7-1 preferentially catalyzes flavones, while CrcCCoAOMT7-2 exhibits a preference for flavanones and quercetin (flavonol). The two enzymes methylate the 3'-, 4'-, 3-, 6-, 8-OH sites and the 3'-, 4'-, 6-, 7-, 8-OH sites with hydroxyflavonoids, respectively, covering nearly all methylation sites during the biosynthesis of PMFs. Functional diversification of CCoAOMTs expended our understanding of PMFs biosynthesis modes in citrus. This study enriches the PMF biosynthetic pathway in citrus and lays the foundation for the selection and breeding of high-quality Citrus reticulata 'Chachiensis' mandarins, as well as the synthesis of natural anticancer PMFs through genetic engineering.

Metabolic division engineering of Escherichia coli consortia for de novo biosynthesis of flavonoids and flavonoid glycosides

Heterologous biosynthesis of natural products with long biosynthetic pathways in microorganisms often suffers from diverse problems, such as enzyme promiscuity and metabolic burden. Flavonoids and their glycosides are important phytochemicals in the diet of human beings, with various health benefits and biological activities. Despite previous efforts and achievements, efficient microbial production of plant-derived flavonoid compounds with long pathways remains challenging. Herein, we applied metabolic division engineering of Escherichia coli consortia to overcome these limitations. By establishing new biosynthetic pathways, rationally adjusting metabolic node intermediates, and engineering different auxotrophic and orthogonal carbon sources for hosts, we established stable two- and three-bacteria co-culture systems to efficiently de novo produce 12 flavonoids (61.15-325.31 mg/L) and 36 corresponding flavonoid glycosides (1.31-191.79 mg/L). Furthermore, the co-culture system was rapidly extended in a plug-and-play manner to produce isoflavonoids, dihydrochalcones, and their glycosides. This study successfully alleviates metabolic burden and overcomes enzyme promiscuity, and provides significant insights that could guide the biosynthesis of other complex secondary metabolites.

Antioxidants: a comprehensive review

Antioxidants had a growing interest owing to their protective roles in food and pharmaceutical products against oxidative deterioration and in the body and against oxidative stress-mediated pathological processes. Screening of antioxidant properties of plants and plant derived compounds requires appropriate methods, which address the mechanism of antioxidant activity and focus on the kinetics of the reactions including the antioxidants. Many studies have been conducted with evaluating antioxidant activity of various samples of research interest using by different methods in food and human health. These methods were classified methods described and discussed in this review. Methods based on inhibited autoxidation are the most suited for termination-enhancing antioxidants and, for chain-breaking antioxidants while different specific studies are needed for preventive antioxidants. For this purpose, the most commonly methods used in vitro determination of antioxidant capacity of food and pharmaceutical constituents are examined and also a selection of chemical testing methods is critically reviewed and highlighting. In addition, their advantages, disadvantages, limitations and usefulness were discussed and investigated for pure molecules and raw plant extracts. The effect and influence of the reaction medium on performance of antioxidants is also addressed. Hence, this overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceuticals, and dietary supplement industries. Also, the most important advantages and shortcomings of each method were detected and highlighted. The underlying chemical principles of these methods have been explained and thoroughly analyzed. The chemical principles of methods of 1,1-diphenyl-2-picrylhydrazyl (DPPH•) radical scavenging, 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical (ABTS·+) scavenging, ferric ions (Fe3+) reducing assay, ferric reducing antioxidant power (FRAP) assay, cupric ions (Cu2+) reducing power assay (Cuprac), Folin-Ciocalteu reducing capacity (FCR assay), superoxide radical anion (O2·-), hydroxyl radical (OH·) scavenging, peroxyl radical (ROO·) removing, hydrogen peroxide (H2O2) decomposing, singlet oxygen (1O2) quenching assay, nitric oxide radical (NO·) scavenging assay and chemiluminescence assay are overviewed and critically discussed. Also, the general antioxidant aspects of the main food and pharmaceutical components were discussed through several methods currently used for detecting antioxidant properties of these components. This review consists of two main sections. The first section is devoted to the main components in food and their pharmaceutical applications. The second general section includes definitions of the main antioxidant methods commonly used for determining the antioxidant activity of components. In addition, some chemical, mechanistic, and kinetic properties, as well as technical details of the above mentioned methods, are provided. The general antioxidant aspects of main food components have been discussed through various methods currently used to detect the antioxidant properties of these components.

Biochemical evaluation of molecular parts for flavonoid production using plant synthetic biology

Among organisms on Earth, plants have the unique ability to produce a wide variety of biomolecules using soil nutrients, air, and solar energy. Therefore, plants are regarded as the most productive and cost-efficient bioreactors among living organisms. Flavonoids, a major group of secondary metabolites exclusively produced in plants, play crucial roles in plant physiology and have various effects on human health. Flavonoids are used in diverse industries such as the pharmaceutical, nutraceutical, and cosmetics industries. These compounds are typically extracted from specific plants that naturally produce large amounts of the target flavonoid for commercial production. However, with the increasing demand for flavonoids, efforts have been made to enhance flavonoid production using synthetic biology for sustainable production in microbes or plants. Synthetic biology has been utilized for plant metabolic engineering to reconstitute the biosynthetic pathways of target flavonoids at the whole-pathway level, thereby enhancing flavonoid production. For the most efficient flavonoid production using plant synthetic biology, first of all, optimized molecular parts and enzymes must be identified and selected. The best modules to produce the precursors and final target flavonoids can then be constructed using these optimized parts. In this review, we summarize the enzyme kinetics of natural and engineered molecular parts derived from different plant species and provide insight into the selection of molecular parts, design of devices, and reconstitution of pathways based on enzyme performance for sustainable flavonoid production using plant synthetic biology.

Therapeutic potential of flavonoids in gastrointestinal cancer: Focus on signaling pathways and improvement strategies (Review)

Flavonoids are a group of polyphenolic compounds distributed in vegetables, fruits and other plants, which have considerable antioxidant, anti‑tumor and anti‑inflammatory activities. Several types of gastrointestinal (GI) cancer are the most common malignant tumors in the world. A large number of studies have shown that flavonoids have inhibitory effects on cancer, and they are recognized as a class of potential anti‑tumor drugs. Therefore, the present review investigated the molecular mechanisms of flavonoids in the treatment of different types of GI cancer and summarized the drug delivery systems commonly used to improve their bioavailability. First, the classification of flavonoids and the therapeutic effects of various flavonoids on human diseases were briefly introduced. Then, to clarify the mechanism of action of flavonoids on different types of GI cancer in the human body, the metabolic process of flavonoids in the human body and the associated signaling pathways causing five common types of GI cancer were discussed, as well as the corresponding therapeutic targets of flavonoids. Finally, in clinical settings, flavonoids have poor water solubility, low permeability and inferior stability, which lead to low absorption efficiency in vivo. Therefore, the three most widely used drug delivery systems were summarized. Suggestions for improving the bioavailability of flavonoids and the focus of the next stage of research were also put forward.

Unraveling the hydroxylation and methylation mechanism in polymethoxylated flavones biosynthesis in Dracocephalum moldavica

Dracocephalum moldavica, which belongs to the Lamiaceae family, is an important medicinal plant rich in polymethoxylated flavones (PMFs). PMFs have multi-methoxy groups on the central flavone skeleton. Hydroxylation and methylation are important modifications in the biosynthesis of PMFs, but the corresponding mechanism and related enzymes have not yet been elucidated in D. moldavica. In this study, we analyzed the transcriptome database of D. moldavica and identified three flavonoid hydroxylases (DmFH1/2/3) and four flavonoid O-methyltransferases (DmOMT1/2/3/4) related to the biosynthesis of PMFs. DmFH1 was characterized as a novel F6/8/3'H and has broad substrate specificity for flavones and flavanones. It catalyzes the formation of 7-methylscutellarein and isoscutellarein, which are the key intermediates in PMF biosynthesis. DmOMT4 and DmOMT1 sequentially catalyze the two-step methylation of scutellarein to generate circimaritin, while DmOMT3 has high specificity for 4'-OH of flavonoids. Notably, it catalyzes the conversion of circimaritin into salvigenin, which is an important polymethoxylated flavone. In addition, through heterologous expression of DmFH1 and DmOMT1 in Nicotiana benthamiana, diversified polyhydroxylated and polymethylated metabolites, including 7-methylscutellarein and circimaritin were achieved. Our work uncovers the key hydroxylation and the complex metabolic network of methylation processes in the biosynthesis of PMFs in D. moldavica, and the screened candidate genes can be exploited in synthetic biology research on PMFs.

Efficient synthesis and evaluation of therapeutic potential of fluorine containing 2-arylchromen-4-ones

A large series of 2-arylchromen-4-ones containing from 1 to 3 fluorine atoms or a trifluoromethyl group in the structure was synthesized by condensation of fluorinated 2-hydroxyacetophenones with benzaldehydes in an alkaline medium and subsequent oxidative cyclization of the resulting 2'-hydroxychalcones by action of I2 in DMSO. The cytotoxicity of the obtained compounds was studied in glioblastoma cell line, SNB19, and in a monkey-derived normal kidney epithelium cell line, Vero. In addition, antiglycation activity of the obtained compounds was evaluated. The inhibitory activity of some fluorinated 2-arylchromen-4-ones against acetylcholinesterase, butyrylcholinesterase and carboxylesterase as well their primary antioxidant activity in ABTS and FRAP tests were investigated. Screening of the synthesized compounds for their inhibitory activity against influenza A virus A/Puerto Rico/8/34 (H1N1) in the MDCK cell culture revealed that fluorinated compounds 32, 31 and 39 showed manifest antiviral effects (with IS = 57, 38 and 25 correspondingly) that makes this series of new biologically attractive fluorinated heterocycles promising for further development and in-depth study.

Natural Products in Cyperus Species (Cyperaceae): Phytochemistry, Pharmacological Activities, and Biosynthesis

The review provides an update on the traditional uses, geographical distribution, pharmacological activities, biosynthesis, and mechanisms of action of potent natural products derived from Cyperus species. Cyperus species are widely distributed in the tropical and subtropical regions across the globe. Cyperus is the second-largest genus in this family with about 950 species. Since 1964, a total of about 403 natural products have been isolated from 43 Cyperus species, including terpenoids (51.61%), flavonoids (17.37%), stilbenoids (6.45%), quinones (5.71%), aromatics (7.69%), coumarins (5.21%), and other compounds (5.96%). The isolated compounds displayed anticancer, antiviral, antidiabetic, antimicrobial, antidepressant, and other activities. Terpenoids and flavonoids are the most abundant class of natural products that have been isolated from Cyperus species. The biosynthesis of some terpenoids and flavonoids has been provided in the paper. Natural products isolated from Cyperus species have demonstrated interesting in vitro activities that warrant further scientific investigations.

The parsley genome assembly and DNA methylome shed light on apigenin biosynthesis in the Apiaceae

Parsley [Petroselinum crispum (Mill.)] is a medicinal and edible vegetable of the Apiaceae family that is rich in apigenin. The Apiaceae family is well known for its diverse secondary metabolites. As a high-quality reference genome is lacking for parsley, the evolution and apigenin biosynthesis in Apiaceae have remained unexplored. Here, we report the chromosome-level genome sequence of parsley, consisting of 1.85 Gb that mainly arose from the expansion of long terminal repeats. Whole-genome bisulfite sequencing revealed a significantly higher number of hypermethylated differentially expressed genes in leaf blades and petioles than in root tissues. Moreover, we identified and characterized chalcone isomerase (CHI) genes, encoding key enzymes involved in apigenin biosynthesis in parsley. We also established that the APETALA2 family transcription factor Pcrispum_6.2855 (PcAP2) binds to the (Pcrispum_11.4764) PcCHI promoter and promotes apigenin accumulation. In conclusion, our work presents a multiomics data resource for understanding apigenin biosynthesis and its transcriptional regulation in parsley, in addition to shedding light on the evolution of parsley within the Apiaceae.

Thymbra spicata extract and arbuscular mycorrhizae improved the morphophysiological traits, biochemical properties, and essential oil content and composition of Rosemary (Rosmarinus officinalis L.) under salinity stress

BACKGROUND

Enhancing the content of essential oils and valuable secondary metabolites is a primary goal for medicinal plant breeders. In this study, the effects of Thymbra spicata extract at concentrations of 0% (C), 10% (TS1), and 20% (TS2), along with mycorrhizal fungus (MF) biofertilizer at a rate of 50 g/2.5 kg of soil, were evaluated on the growth, photosynthetic pigments, relative water content (RWC), proline, protein, malondialdehyde (MDA), catalase (CAT), phenylalanine ammonia-lyase (PAL), and essential oil content and composition of Rosmarinus officinalis L. under varying salinity stress levels of 0 mM (S0), 100 mM (S1), and 200 mM (S2) NaCl. The experiment was conducted as a factorial study within a completely randomized design, with three replications.

RESULTS

As salinity stress increased, the yield and growth characteristics of the plants declined. However, the applied treatments effectively mitigated the negative effects of salinity. The highest chlorophyll a, b, and total chlorophyll contents were observed in the TS2 + MF treatment under nonsaline conditions. Under S2 salinity stress, carotenoid and anthocyanin contents increased by 38.29% and 11.11%, respectively, with the use of TS2 + MF. Under S1 stress conditions, the proline and soluble sugar content increased by 268% and 44%, respectively, in the MF treatment. Essential oil content was enhanced by 80.43% with the TS2 + MF treatment under S1 stress. Essential oil analysis showed significant increases in camphene (9.71%), β-pinene (43.75%), α-phellandrene (13.3%), geranyl acetate (156%), cineole (21.39%), and β-linalool (5.12%) in the TS2 + MF treatment compared to the control under S1 stress conditions.

CONCLUSIONS

Among all the treatments, the combined application of TS2 and MF proved to be the most effective in enhancing the morphophysiological and biochemical characteristics of rosemary plants. This treatment not only boosted the production of essential oils and secondary metabolites but also mitigated the detrimental effects of salinity stress. Therefore, it is recommended as a beneficial agricultural practice for improving the productivity and quality of rosemary plants under salinity stress.

Critical review on the intervention effects of flavonoids from cereal grains and food legumes on lipid metabolism

Obesity, often caused by disorders of lipid metabolism, is a global health concern. Flavonoids from staple grains and legumes are expected as a safer and more cost-effective alternative for the future development of dietary flavonoid-based anti-obesity dietary supplements or drugs. This review systematically summarized their content variation, metabolism in the human body, effects and molecular mechanisms on lipid metabolism. These flavonoids intervene in lipid metabolism by inhibiting lipogenesis, promoting lipolysis, enhancing energy metabolism, reducing appetite, suppressing inflammation, enhancing insulin sensitivity, and improving the composition of the gut microbial. Fermentation and sprouting techniques enhance flavonoid content and these beneficial effects. The multidirectional intervention of lipid metabolism is mainly through regulating AMPK signaling pathway. This study provides potential improvement for challenges of application, including addressing high extraction costs and improving bioavailability, ensuring safety, filling clinical study gaps, and investigating potential synergistic effects between flavonoids in grains and legumes, and other components.

Chemistry, biosynthesis, and theranostics of antioxidant flavonoids and polyphenolics of genus Rhododendron: an overview

The genus Rhododendron is an ancient and most widely distributed genus of the family Ericaceae consisting of evergreen plant species that have been utilized as traditional medicine since a very long time for the treatment of various ailments including pain, asthma, inflammation, cold, and acute bronchitis. The chemistry of polyphenolics isolated from a number of species of the genus Rhododendron has been investigated. During the currently designed study, an in-depth study on the phytochemistry, natural distribution, biosynthesis, and pharmacological properties including their potential capability as free radical scavengers has been conducted. This work provides structural characteristics of phenolic compounds isolated from the species of Rhododendron with remarkable antioxidant potential. In addition, biosynthesis and theranostic study have also been encompassed with the aims to furnish a wide platform of valuable information for designing of new drug entities. The detailed information including names, structural features, origins, classification, biosynthetic pathways, theranostics, and pharmacological effects of about 171 phenolics and flavonoids isolated from the 36 plant species of the genus Rhododendron with the antioxidant potential has been covered in this manuscript. This study demonstrated that species of Rhododendron genus have excellent antioxidant activities and great potential as a source for natural health products. This comprehensive review might serve as a foundation for more investigation into the Rhododendron genus.

Chemical Biology Meets Metabolomics: The Response of Barley Seedlings to 3,5-Dichloroanthranilic Acid, a Resistance Inducer

Advances in combinatorial synthesis and high-throughput screening methods have led to renewed interest in synthetic plant immunity activators as well as priming agents. 3,5-Dichloroanthranilic acid (3,5-DCAA) is a derivative of anthranilic acid that has shown potency in activating defence mechanisms in Arabidopsis and barley. Chemical biology, which is the interface of chemistry and biology, can make use of metabolomic approaches and tools to better understand molecular mechanisms operating in complex biological systems. Here we report on the untargeted metabolomic profiling of barley seedlings treated with 3,5-DCAA to gain deeper insights into the mechanism of action of this resistance inducer. Histochemical analysis revealed the production of reactive oxygen species in the leaves upon 3,5-DCAA infiltration. Subsequently, methanolic extracts from different time periods (12, 24, and 36 h post-treatment) were analysed by ultra-high-performance liquid chromatography hyphenated to a high-resolution mass spectrometer. Both unsupervised and supervised chemometric methods were used to reveal hidden patterns and highlight metabolite variables associated with the treatment. Based on the metabolites identified, both the phenylpropanoid and octadecanoid pathways appear to be main routes activated by 3,5-DCAA. Different classes of responsive metabolites were annotated with flavonoids, more specifically flavones, which were the most dominant. Given the limited understanding of this inducer, this study offers a metabolomic analysis of the response triggered by its foliar application in barley. This additional insight could help make informed decisions for the development of more effective strategies for crop protection and improvement, ultimately contributing to crop resilience and agricultural sustainability.

Antioxidative and Anticancer Potential of Luteolin: A Comprehensive Approach Against Wide Range of Human Malignancies

Luteolin is widely distributed phytochemical, a flavonoid, in kingdom plantae. Luteolin with potential antioxidant activity prevent ROS-induced damages and reduce oxidative stress which is mainly responsible in pathogenesis of many diseases. Several chemo preventive activities and therapeutic benefits are associated with luteolin. Luteolin prevents cancer via modulation of numerous pathways, that is, by inactivating proteins; such as procaspase-9, CDC2 and cyclin B or upregulation of caspase-9 and caspase-3, cytochrome C, cyclin A, CDK2, and APAF-1, in turn inducing cell cycle arrest as well as apoptosis. It also enhances phosphorylation of p53 and expression level of p53-targeted downstream gene. By Increasing BAX protein expression; decreasing VEGF and Bcl-2 expression it can initiate cell cycle arrest and apoptosis. Luteolin can stimulate mitochondrial-modulated functions to cause cellular death. It can also reduce expression levels of p-Akt, p-EGFR, p-Erk1/2, and p-STAT3. Luteolin plays positive role against cardiovascular disorders by improving cardiac function, decreasing the release of inflammatory cytokines and cardiac enzymes, prevention of cardiac fibrosis and hypertrophy; enhances level of CTGF, TGFβ1, ANP, Nox2, Nox4 gene expressions. Meanwhile suppresses TGFβ1 expression and phosphorylation of JNK. Luteolin helps fight diabetes via inhibition of alpha-glucosidase and ChE activity. It can reduce activity levels of catalase, superoxide dismutase, and GS4. It can improve blood glucose, insulin, HOMA-IR, and HbA1c levels. This review is an attempt to elaborate molecular targets of luteolin and its role in modulating irregularities in cellular pathways to overcome severe outcomes during diseases including cancer, cardiovascular disorders, diabetes, obesity, inflammation, Alzheimer's disease, Parkinson's disease, hepatic disorders, renal disorders, brain injury, and asthma. As luteolin has enormous therapeutic benefits, it could be a potential candidate in future drug development strategies.

Antifungal and antibiofilm activities of flavonoids against Candida albicans: Focus on 3,2'-dihydroxyflavone as a potential therapeutic agent

Effective management of microbial biofilms holds significance within food and medical environments. Candida albicans, an opportunistic fungus, forms mucosal biofilms closely linked to candidiasis and drug-resistant infections due to their drug tolerance. Morphologic change from yeast to filamentous cells is a key virulence factor and a prerequisite for biofilm development. This study investigated the anti-fungal and antibiofilm activities of 20 flavonoids against C. albicans. With their known antioxidant capabilities, flavonoids hold promise in combating infections associated with biofilms. Among them, flavone and its derivatives exhibited moderate antifungal activity, 3,2'-dihydroxyflavone (3,2'-DHF) at 1 μg/mL exhibited strong antibiofilm activity (MIC 50 μg/mL). In addition, 3,2'-DHF dramatically inhibited cell aggregation and germ tube/hyphae formation. Transcriptomic analyses revealed that flavone and 3,2'-DHF behaved differently, as 3,2'-DHF downregulated the expressions of germ tube/hyphae-forming and biofilm-related genes (ECE1, HWP1, TEC1, and UME6) but upregulated the biofilm/hyphal regulators (CHK1, IFD6, UCF1, and YWP1). Tests evaluating toxicity with plant and nematode models revealed that flavone and 3,2'-DHF exhibited mild toxicity. Current results indicate that hydroxylated flavone derivatives can enhance anti-fungal and antibiofilm activities and provide a source of potential anti-fungal agents against drug-resistant C. albicans.

Fluorinated 2-arylchroman-4-ones and their derivatives: synthesis, structure and antiviral activity

A number of new biologically interesting fluorinated 2-arylchroman-4-ones and their 3-arylidene derivatives were synthesized based on the p-toluenesulfonic acid-catalyzed one-pot reaction of 2-hydroxyacetophenones with benzaldehydes. It was found that obtained (E)-3-arylidene-2-aryl-chroman-4-ones reacted with malononitrile under base conditions to form 4,5-diaryl-4H,5H-pyrano[3,2-c]chromenes. The structures of the synthesized fluorinated compounds were confirmed by 1H, 19F, and 13C NMR spectral data, and for some representatives of heterocycles also using NOESY spectra and X-ray diffraction analysis. A large series of obtained flavanone derivatives as well as products of their modification (35 examples) containing from 1 to 12 fluorine atoms in the structure was tested in vitro for cytotoxicity in MDCK cell line and for antiviral activity against influenza A virus. Among the studied heterocycles 6,8-difluoro-2-(4-(trifluoromethyl)phenyl)chroman-4-one (IC50 = 6 μM, SI = 150) exhibited the greatest activity against influenza A/Puerto Rico/8/34 (H1N1) virus. Moreover, this compound appeared active against phylogenetically distinct influenza viruses, A(H5N2) and influenza B (SI's of 53 and 42, correspondingly). The data obtained suggest that the fluorinated derivatives of 2-arylchroman-4-ones are prospective scaffolds for further development of potent anti-influenza antivirals.

Fungal communities are more sensitive to mildew than bacterial communities during tobacco storage processes

Mildew poses a significant threat to tobacco production; however, there is limited information on the structure of the abundant and rare microbial subcommunities in moldy tobacco leaves. In this study, we employed high-throughput sequencing technology to discern the disparities in the composition, diversity, and co-occurrence patterns of abundant and rare fungal and bacterial subcommunities between moldy and normal tobacco leaves collected from Guizhou, Shanghai, and Jilin provinces, China. Furthermore, we explored the correlation between microorganisms and metabolites by integrating the metabolic profiles of moldy and normal tobacco leaves. The results showed that the fungi are more sensitive to mildew than bacteria, and that the fungal abundant taxa exhibit greater resistance and environmental adaptability than the rare taxa. The loss of rare taxa results in irreversible changes in the diversity, richness, and composition of the fungal community. Moreover, rare fungal taxa and abundant bacterial taxa played crucial roles in maintaining the stability and functionality of the tobacco microecosystem. In moldy tobacco, however, the disappearance of rare taxa as key nodes resulted in reduced connectivity and stability within the fungal network. In addition, metabolomic analysis showed that the contents of indoles, pyridines, polyketones, phenols, and peptides were significantly enriched in the moldy tobacco leaves, while the contents of amino acids, carbohydrates, lipids, and other compounds were significantly reduced in these leaves. Most metabolites showed negative correlations with Dothideomycetes, Alphaproteobacteria, and Gammaproteobacteria, but showed positive correlations with Eurotiales and Bacilli. This study has demonstrated that abundant fungal taxa are the predominant biological agents responsible for tobacco mildew, while bacteria may indirectly contribute to this process through the production and degradation of metabolites. KEY POINTS: • Fungi exhibited greater sensitivity to mildew of tobacco leaf compared to bacteria • Rare fungal taxa underwent significant damage during the mildew process • Mildew may damage the defense system of the tobacco leaf microecosystem.

Validating the nutraceutical and neuroprotective pharmacodynamics of flavones

Neurodegenerative disorders are generally characterized by progressive neuronal loss and cognitive decline, with underlying mechanisms involving oxidative stress, protein aggregation, neuroinflammation, and synaptic dysfunction. Currently, the available treatment options only improve the symptoms of the disease but do not stop disease progression; neurodegeneration. This underscores the urgent need for novel therapeutic strategies targeting multiple neurodegenerative pathways alongside the conventional therapeutic strategies available. Emerging evidence demonstrates that flavones a subgroup of flavonoids found abundantly in various dietary sources, have surfaced as promising candidates for neuroprotection due to their multifaceted pharmacological properties. Flavones possess the potency to modulate these pathophysiological processes through their antioxidant, anti-inflammatory, and neurotrophic activities. Additionally, flavones have been shown to interact with various cellular targets, including receptors and enzymes, to confer neuroprotection. Though there are ample evidence available, the nutraceutical and neuroprotective pharmacodynamics of flavones have not been very well established. Hence, the current review aims to explores the therapeutic potential of flavones as nutraceuticals with neuroprotective effects, focusing on their ability to modulate key pathways implicated in neurodegenerative diseases. The current article also aims to actuate supplementary research into flavones as potential agents for alleviating neurodegeneration and improving patient outcomes in neurodegenerative disorders globally.

Leaf pigmentation in Cannabis sativa: Characterization of anthocyanin biosynthesis in colorful Cannabis varieties

Cannabis plants produce a spectrum of secondary metabolites, encompassing cannabinoids and more than 300 non-cannabinoid compounds. Among these, anthocyanins have important functions in plants and also have well documented health benefits. Anthocyanins are largely responsible for the red/purple color phenotypes in plants. Although some well-known Cannabis varieties display a wide range of red/purple pigmentation, the genetic underpinnings of anthocyanin biosynthesis have not been well characterized in Cannabis. This study unveils the genetic diversity of anthocyanin biosynthesis genes found in Cannabis, and we characterize the diversity of anthocyanins and related phenolics found in four differently pigmented Cannabis varieties. Our investigation revealed that the genes 4CL, CHS, F3H, F3'H, FLS, DFR, ANS, and OMT exhibited the strongest correlation with anthocyanin accumulation in Cannabis leaves. The results of this study enhance our understanding of the anthocyanin biosynthetic pathway and shed light on the molecular mechanisms governing Cannabis leaf pigmentation.

Evolution and Domestication of a Novel Biosynthetic Gene Cluster Contributing to the Flavonoid Metabolism and High-Altitude Adaptability of Plants in the Fagopyrum Genus

The diversity of secondary metabolites is an important means for plants to cope with the complex and ever-changing terrestrial environment. Plant biosynthetic gene clusters (BGCs) are crucial for the biosynthesis of secondary metabolites. The domestication and evolution of BGCs and how they affect plant secondary metabolites biosynthesis and environmental adaptation are still not fully understood. Buckwheat exhibits strong resistance and abundant secondary metabolites, especially flavonoids, allowing it to thrive in harsh environments. A non-canonical BGC named UFGT3 cluster is identified, which comprises a phosphorylase kinase (PAK), two transcription factors (MADS1/2), and a glycosyltransferase (UFGT3), forming a complete molecular regulatory module involved in flavonoid biosynthesis. This cluster is selected during Tartary buckwheat domestication and is widely present in species of the Fagopyrum genus. In wild relatives of cultivated buckwheat, a gene encoding anthocyanin glycosyltransferase (AGT), which glycosylates pelargonidin into pelargonidin-3-O-glucoside, is found inserted into this cluster. The pelargonidin-3-O-glucoside can help plants resist UV stress, endowing wild relatives with stronger high-altitude adaptability. This study provides a new research paradigm for the evolutionary dynamics of plant BGCs, and offers new perspectives for exploring the mechanism of plant ecological adaptability driven by environmental stress through the synthesis of secondary metabolites.

Acacetin, a Natural Flavone with Potential in Improving Liver Disease Based on Its Anti-Inflammation, Anti-Cancer, Anti-Infection and Other Effects

Liver disease is a global public problem, and the cost of its therapy is a large financial burden to governments. It is well known that drug therapy plays a critical role in the treatment of liver disease. However, present drugs are far from meeting clinical needs. Lots of efforts have been made to find novel agents to treat liver disease in the past several decades. Acacetin is a dihydroxy and monomethoxy flavone, named 5,7-dihydroxy-4'-methoxyflavone, which can be found in diverse plants. It has been reported that acacetin exhibits multiple pharmacological activities, including anti-cancer, anti-inflammation, anti-virus, anti-obesity, and anti-oxidation. These studies indicate the therapeutic potential of acacetin in liver disease. This review discussed the comprehensive information on the pathogenesis of liver disease (cirrhosis, viral hepatitis, drug-induced liver injury, and hepatocellular carcinoma), then introduced the biological source, structural features, and pharmacological properties of acacetin, and the possible application in preventing liver disease along with the pharmacokinetic and toxicity of acacetin, and future research directions. We systemically summarized the latest research progress on the potential therapeutic effect of acacetin on liver disease and existing problems. Based on the present published information, the natural flavone acacetin is an anticipated candidate agent for the treatment of liver disease.

Screening of Lipid-Reducing Activity and Cytotoxicity of the Exometabolome from Cyanobacteria

Cyanobacteria are rich producers of secondary metabolites, excreting some of these to the culture media. However, the exometabolome of cyanobacteria has been poorly studied, and few studies have dwelled on its characterization and bioactivity assessment. In this work, exometabolomes of 56 cyanobacterial strains were characterized by HR-ESI-LC-MS/MS. Cytotoxicity was assessed on two carcinoma cell lines, HepG2 and HCT116, while the reduction in lipids was tested in zebrafish larvae and in a steatosis model with fatty acid-overloaded human liver cells. The exometabolome analysis using GNPS revealed many complex clusters of unique compounds in several strains, with no identifications in public databases. Three strains reduced viability in HCT116 cells, namely Tolypotrichaceae BACA0428 (30.45%), Aphanizomenonaceae BACA0025 (40.84%), and Microchaetaceae BACA0110 (46.61%). Lipid reduction in zebrafish larvae was only observed by exposure to Dulcicalothrix sp. BACA0344 (60%). The feature-based molecular network shows that this bioactivity was highly correlated with two flavanones, a compound class described in the literature to have lipid reduction activity. The exometabolome characterization of cyanobacteria strains revealed a high chemodiversity, which supports it as a source for novel bioactive compounds, despite most of the time being overlooked.

Characterization of key genes in anthocyanin and flavonoid biosynthesis during floral development in Rosa canina L

This study investigates the transition of Rosa canina L. petals from pink to white, driven by genetic and biochemical factors. It characterizes the expression of ten key genes involved in anthocyanin and flavonoid biosynthesis across five developmental stages, correlating gene expression with flavonoid and anthocyanin concentrations and colorimetric changes. Initially, the petals exhibit a rich flavonoid profile, dominated by Rutin and Kaempferol derivatives. The peak anthocyanin concentration, corresponding to the deepest color saturation, occurs in the subsequent stage. Advanced chromatographic analyses identify key flavonoids persisting into the final white petal stage. Notably, the ANS gene shows a dramatic 137.82-fold increase in expression at the final stage, indicating its crucial role in petal color maturation despite the absence of visible pigmentation. The study provides a comprehensive characterization of the genetic and biochemical mechanisms underlying petal pigmentation, suggesting that reduced anthocyanin synthesis and increased flavonol concentration led to white petals. It also highlights the roles of other genes such as PAL, CCD1, FLS, CHI, CHS, UFGT, F3H, DFR, and RhMYB1, indicating that post-translational modifications and other regulatory mechanisms may influence anthocyanin stability and degradation.

Characterization of the 2ODD genes of DOXC subfamily and its members involved in flavonoids biosynthesis in Scutellaria baicalensis

BACKGROUND

2-oxoglutarate-dependent dioxygenase (2ODD) superfamily is the second largest enzyme family in the plant genome and plays diverse roles in secondary metabolic pathways. The medicinal plant Scutellaria baicalensis Georgi contains various flavonoids, which have the potential to treat coronavirus disease 2019 (COVID-19), such as baicalein and myricetin. Flavone synthase I (FNSI) and flavanone 3-hydroxylase (F3H) from the 2ODDs of DOXC subfamily have been reported to participate in flavonoids biosynthesis. It is certainly interesting to study the 2ODD members involved in the biosynthesis of flavonoids in S. baicalensis.

RESULTS

We provided a genome-wide analysis of the 2ODDs of DOXC subfamily in S. baicalensis, a total of 88 2ODD genes were identified, 82 of which were grouped into 25 distinct clades based on phylogenetic analysis of At2ODDs. We then performed a functional analysis of Sb2ODDs involved in the biosynthesis of flavones and dihydroflavonols. Sb2ODD1 and Sb2ODD2 from DOXC38 clade exhibit the activity of FNSI (Flavone synthase I), which exclusively converts pinocembrin to chrysin. Sb2ODD1 has significantly higher transcription levels in the root. While Sb2ODD7 from DOXC28 clade exhibits high expression in flowers, it encodes a F3H (flavanone 3-hydroxylase). This enzyme is responsible for catalyzing the conversion of both naringenin and pinocembrin into dihydrokaempferol and pinobanksin, kinetic analysis showed that Sb2ODD7 exhibited high catalytic efficiency towards naringenin.

CONCLUSIONS

Our experiment suggests that Sb2ODD1 may serve as a supplementary factor to SbFNSII-2 and play a role in flavone biosynthesis specifically in the roots of S. baicalensis. Sb2ODD7 is mainly responsible for dihydrokaempferol biosynthesis in flowers, which can be further directed into the metabolic pathways of flavonols and anthocyanins.

Antibacterial activity of natural flavones against bovine mastitis pathogens: in vitro, SAR analysis, and computational study

Bovine mastitis is a worldwide disease affecting dairy cattle and causes major economic losses in the dairy industry. Recently, the emergence of microbial resistance to the current antibiotics complicates the treatment protocol which necessitates antibiotic stewardship and further research to find new active compounds. Recently, phytobiotics have gained interest in being used as an alternative to antibiotics in the poultry industry as an antibiotic stewardship intervention. This study evaluated the in vitro antibacterial activity of 16 flavonoids against bovine mastitis pathogens. Two flavones: 2-(4-methoxyphenyl)chromen-4-one (1) and 2-(3-hydroxyphenyl)chromen-4-one (4) showed inhibition of the growth of Klebsiella oxytoca with MIC values range (25-50 µg mL- 1) followed by a structure-activity relationship (SAR) study indicating that the presence of a hydroxyl group at C-3` or methoxy at C-4` increases the activity against Klebsiella oxytoca while the presence of hydroxyl group at C-7 decreases the activity. Furthermore, a structure-based drug development approach was applied using several in silico tools to understand the interactions of active flavones at the active site of the DNA gyrase protein. Compound (4) showed a higher docking score than quercetin (standard) which is known to have antibacterial activity by inhibiting the DNA gyrase. In addition, the structure-based pharmacophores of compound (4) and quercetin showed similar pharmacophoric features and interactions with DNA gyrase. Based on our findings, compounds (1) and (4) are promising for further study as potential anti-microbial phytochemicals that can have a role in controlling bovine mastitis as well as to investigate their mechanism of action further.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-024-00253-w.

Surface modification prepared porous copper oxide/(Cu-S)n metal-organic framework/reduced graphene oxide hierarchical structure for highly selective electrochemical quercetin detection

Electrochemical alkalization of (Cu-S)n metal-organic framework (MOF) and graphene oxide ((Cu-S)n MOF/GO) composite yields a new CuO/(Cu-S)n MOF/RGO (reduced GO) composite with porous morphology on screen printed carbon electrode (SPCE) which facilitated the electron transfer properties in electrochemical quercetin (QUE) detection. A selective QUE detection ability has been demonstrated by the constructed electrochemical sensor (CuO/(Cu-S)n MOF/RGO/SPCE), which also has a broad dynamic range of 0.5 to 115 µM in pH 3 by differential pulse voltammetry. The detection limit is 0.083 µM (S/N = 3). In this study, it was  observed that the real samples contained 0.34 mg mL-1 and 27.7 µg g-1 QUE in wine and onion, respectively.

Developments in the stereoselective synthesis of benzopyran, benzopyrone and flavonoid based natural product analogues using C-glycosides as an intrinsic chiral synthon

Stereoselective synthesis is essential for propelling mainstream academia toward a relentless pursuit of novel and cutting-edge strategies for constructing molecules with unparalleled precision. Naturally derived benzopyrans, benzopyrones, and flavonoids are an essentially prominent group of oxa-heterocycles, highly significant targets in medicinal chemistry owing to their extensive abundance in biologically active natural products and pharmaceuticals. The molecular complexity and stereoselectivity induced by heterocycles embedded with C-glycosides have attracted considerable interest and emerged as a fascinating area of research for synthetic organic chemists. This present article emphasizes the existing growths in the strategies involving the diastereoselective synthesis of C-glycosylated benzopyrans, benzopyrones, and flavonoids using naturally acquired glycones as chiral synthons.

Identification of crucial inflammaging related risk factors in multiple sclerosis

Background

Multiple sclerosis (MS) is an immune-mediated disease characterized by inflammatory demyelinating lesions in the central nervous system. Studies have shown that the inflammation is vital to both the onset and progression of MS, where aging plays a key role in it. However, the potential mechanisms on how aging-related inflammation (inflammaging) promotes MS have not been fully understood. Therefore, there is an urgent need to integrate the underlying mechanisms between inflammaging and MS, where meaningful prediction models are needed.

Methods

First, both aging and disease models were developed using machine learning methods, respectively. Then, an integrated inflammaging model was used to identify relative risk factors, by identifying essential "aging-inflammation-disease" triples. Finally, a series of bioinformatics analyses (including network analysis, enrichment analysis, sensitivity analysis, and pan-cancer analysis) were further used to explore the potential mechanisms between inflammaging and MS.

Results

A series of risk factors were identified, such as the protein homeostasis, cellular homeostasis, neurodevelopment and energy metabolism. The inflammaging indices were further validated in different cancer types. Therefore, various risk factors were integrated, and even both the theories of inflammaging and immunosenescence were further confirmed.

Conclusion

In conclusion, our study systematically investigated the potential relationships between inflammaging and MS through a series of computational approaches, and could present a novel thought for other aging-related diseases.

Neofunctionalization of an OMT cluster dominates polymethoxyflavone biosynthesis associated with the domestication of citrus

Polymethoxyflavones (PMFs) are a class of abundant specialized metabolites with remarkable anticancer properties in citrus. Multiple methoxy groups in PMFs are derived from methylation modification catalyzed by a series of hydroxylases and O-methyltransferases (OMTs). However, the specific OMTs that catalyze the systematic O-methylation of hydroxyflavones remain largely unknown. Here, we report that PMFs are highly accumulated in wild mandarins and mandarin-derived accessions, while undetectable in early-diverging citrus species and related species. Our results demonstrated that three homologous genes, CreOMT3, CreOMT4, and CreOMT5, are crucial for PMF biosynthesis in citrus, and their encoded methyltransferases exhibit multisite O-methylation activities for hydroxyflavones, producing seven PMFs in vitro and in vivo. Comparative genomic and syntenic analyses indicated that the tandem CreOMT3, CreOMT4, and CreOMT5 may be duplicated from CreOMT6 and contributes to the genetic basis of PMF biosynthesis in the mandarin group through neofunctionalization. We also demonstrated that N17 in CreOMT4 is an essential amino acid residue for C3-, C5-, C6-, and C3'-O-methylation activity and provided a rationale for the functional deficiency of OMT6 to produce PMFs in early-diverging citrus and some domesticated citrus species. A 1,041-bp deletion in the CreOMT4 promoter, which is found in most modern cultivated mandarins, has reduced the PMF content relative to that in wild and early-admixture mandarins. This study provides a framework for reconstructing PMF biosynthetic pathways, which may facilitate the breeding of citrus fruits with enhanced health benefits.

Untargeted metabolomics for lifestyle biomarker discovery in human hair

There is a risk of crimes remaining unsolved when no matching DNA profiles or fingermarks are found. If this is the case, forensic investigations are faced with a significant shortage of evidence and information regarding the unknown perpetrator and/or victim as well as any missing persons. However, a rather commonly found biological trace encountered at crime scenes is human hair. As hair acts as a biochemical reservoir, it may contain valuable information regarding one's characteristics and habits. This study aimed to build an analytical method capable of determining a marker set of relevant metabolites in hair, eventually building up a profile of its donor. To find potential markers, an untargeted metabolomics approach was developed to select and identify statistically significant features. For that purpose, a total of 68 hair samples were collected at several hairdresser shops in varying neighbourhoods. Compound extraction was achieved via methanolic incubation overnight and analysis performed using a high-resolution mass spectrometry (HRMS) Orbitrap Q Exactive Focus. The acquired data was uploaded and statistically evaluated using two free online software/libraries, where a total of eight compounds have given a match on both tools. Their presumptive identity was confirmed using reference standards and consequently added to a dynamic target donor profiling list. These results show the potential of using untargeted metabolomics for the search for lifestyle biomarkers capable of differentiating individuals. Such tools are of paramount importance in a forensic setting with little or no evidence available and no clear tactical leads.

Genomic insights into the evolution of flavonoid biosynthesis and O-methyltransferase and glucosyltransferase in Chrysanthemum indicum

Flavonoids are a class of secondary metabolites widely distributed in plants. Regiospecific modification by methylation and glycosylation determines flavonoid diversity. A rare flavone glycoside, diosmin (luteolin-4'-methoxyl-7-O-glucosyl-rhamnoside), occurs in Chrysanthemum indicum. How Chrysanthemum plants evolve new biosynthetic capacities remains elusive. Here, we assemble a 3.11-Gb high-quality C. indicum genome with a contig N50 value of 4.39 Mb and annotate 50,606 protein-coding genes. One (CiCOMT10) of the tandemly repeated O-methyltransferase genes undergoes neofunctionalization, preferentially transferring the methyl group to the 4'-hydroxyl group of luteolin with ortho-substituents to form diosmetin. In addition, CiUGT11 (UGT88B3) specifically glucosylates 7-OH group of diosmetin. Next, we construct a one-pot cascade biocatalyst system by combining CiCOMT10, CiUGT11, and our previously identified rhamnosyltransferase, effectively producing diosmin with over 80% conversion from luteolin. This study clarifies the role of transferases in flavonoid diversity and provides important gene elements essential for producing rare flavone.

Co-expressed network analysis based on 289 transcriptome samples reveals methyl jasmonate-mediated gene regulatory mechanism of flavonoid compounds in Dendrobium catenatum

Flavonoids are momentous bioactive ingredients in orchid plant Dendrobium catenatum (D. catenatum), which are bioactive compounds with great medical and commercial potential. However, the accurate dissection of flavonoids profiling and their accumulation mechanism are largely unknown. In this study, methyl jasmonate (MeJA) treatment was used to investigate the change of flavonoids content and transcripts in two D. catenatum clones (A6 and B1). We identified 40 flavonoids using liquid chromatograph mass spectrometer (LC-MS). By weighted gene co-expressed network analysis (WGCNA) of flavonoids content and transcript expression of MeJA-treated samples, 37 hub genes were identified. Among them, DcCHIL, DcFLS, and DcDFR were highly correlation with two key transcription factors DcWRKY3/4 by correlation analysis of large-scale transcriptome data and above hub genes expression. Furthermore, transient overexpression of DcWRKY3/4 in tobacco leaves significantly increased the content of flavonoids. This study identified flavonoid profiling and built a new approach to mine regulatory mechanism of flavonoids in D. catenatum. These valuable flavonoids and gene resources will be key for understanding and harnessing natural flavonoids products in pharmaceuticals and foods industry of D. catenatum.

Exploring the Evolvability of Plant Specialized Metabolism: Uniqueness Out Of Uniformity and Uniqueness Behind Uniformity

The huge structural diversity exhibited by plant specialized metabolites has primarily been considered to result from the catalytic specificity of their biosynthetic enzymes. Accordingly, enzyme gene multiplication and functional differentiation through spontaneous mutations have been established as the molecular mechanisms that drive metabolic evolution. Nevertheless, how plants have assembled and maintained such metabolic enzyme genes and the typical clusters that are observed in plant genomes, as well as why identical specialized metabolites often exist in phylogenetically remote lineages, is currently only poorly explained by a concept known as convergent evolution. Here, we compile recent knowledge on the co-presence of metabolic modules that are common in the plant kingdom but have evolved under specific historical and contextual constraints defined by the physicochemical properties of each plant specialized metabolite and the genetic presets of the biosynthetic genes. Furthermore, we discuss a common manner to generate uncommon metabolites (uniqueness out of uniformity) and an uncommon manner to generate common metabolites (uniqueness behind uniformity). This review describes the emerging aspects of the evolvability of plant specialized metabolism that underlie the vast structural diversity of plant specialized metabolites in nature.

Unveiling the flavone-solubilizing effects of α-glucosyl rutin and hesperidin: probing structural differences through NMR and SAXS analyses

Flavonoids often exhibit broad bioactivity but low solubility and bioavailability, limiting their practical applications. The transglycosylated materials α-glucosyl rutin (Rutin-G) and α-glucosyl hesperidin (Hsp-G) are known to enhance the dissolution of hydrophobic compounds, such as flavonoids and other polyphenols. In this study, the effects of these materials on flavone solubilization were investigated by probing their interactions with flavone in aqueous solutions. Rutin-G and Hsp-G prepared via solvent evaporation and spray-drying methods were evaluated for their ability to dissolve flavones. Rutin-G had a stronger flavone-solubilizing effect than Hsp-G in both types of composite particles. The origin of this difference in behavior was elucidated by small-angle X-ray scattering (SAXS) and nuclear magnetic resonance analyses. The different self-association structures of Rutin-G and Hsp-G were supported by SAXS analysis, which proved that Rutin-G formed polydisperse aggregates, whereas Hsp-G formed core-shell micelles. The observation of nuclear Overhauser effects (NOEs) between flavone and α-glucosyl materials suggested the existence of intermolecular hydrophobic interactions. However, flavone interacted with different regions of Rutin-G and Hsp-G. In particular, NOE correlations were observed between the protons of flavone and the α-glucosyl protons of Rutin-G. The different molecular association states of Rutin-G or Hsp-G could be responsible for their different effects on the solubility of flavone. A better understanding of the mechanism of flavone solubility enhancement via association with α-glucosyl materials would permit the application of α-glucosyl materials to the solubilization of other hydrophobic compounds including polyphenols such as flavonoids.

Inhibitory effect of γ-ray-modified hydroxymethylated baicalins on NO production

Baicalin, a glucuronic flavone, is the major active component in the medicinal plant Scutellaria baicalensis. Herein, baicalin was irradiated by γ-rays to afford four unusual flavanones, baicalinols A (2), B (3), and C (4) and peroxybaicaleinol (5), and two known flavones, oroxylin A (6) and baicalein (7). The structures of the hydroxymethylated products were elucidated using nuclear magnetic resonance spectroscopy and mass spectrometry, and their absolute configuration was established using electronic circular dichroism spectroscopy. Novel hydroxymethylated flavanones 2 and 3 suppressed both nitric oxide (NO) production and the expression of inducible NO synthase and showed significantly higher anti-inflammatory activities in lipopolysaccharide-stimulated macrophages than the parent compound. These newly generated hydroxymethylated flavanones can be potentially used for treating inflammatory diseases.

Comparative transcriptome analysis and flavonoid profiling of floral mutants reveals CmMYB11 regulating flavonoid biosynthesis in chrysanthemum

Flavonoids, of which the major groups are flavones, flavonols, and anthocyanins, confer a variety of colors on plants. Bud sports with variation of floral colors occur occasionally during chrysanthemum cultivation. Although it has been reported that methylation at the promoter of CmMYB6 was related to anthocyanin contents, the regulatory networks of flavonoid biosynthesis still remain largely unknown in mutation of chrysanthemum. We compared phenotypes, pigment composition and transcriptomes in two chrysanthemum cultivars, 'Anastasia Dark Green' and 'Anastasia Pink', and regenerated bud sports of these cultivars with altered floral colors. Increased anthocyanins turned the 'Anastasia Dark Green' mutant red, while decreased anthocyanins turned the 'Anastasia Pink' mutant white. Moreover, total flavonoids were reduced in both mutants. Multiple flavonoid biosynthetic genes and regulatory genes encoding MYBs and bHLHs transcription factors were differentially expressed in pairwise comparisons of transcriptomes in 'Anastasia Dark Green' or 'Anastasia Pink' and their mutants at different flowering stages. Among these regulatory genes, the expression patterns of CmMYB6 and CmbHLH2 correlated to changes of anthocyanin contents, and down-regulation of CmMYB11 correlated to decreased total flavonoid contents in two mutants. CmMYB11 was shown to directly activate the promoter activities of CmCHS2, CmCHI, CmDFR, CmANS, CmFNS, and CmFLS. Furthermore, overexpression of CmMYB11 increased both flavonols and anthocyanins in tobacco petals. Our work provides new insights into regulatory networks involved in flavonoid biosynthesis and coloration in chrysanthemum.

Selectfluor-mediated tandem cyclization of enaminones with diselenides toward the synthesis of 3-selenylated chromones

A practical and metal-free approach for the regioselective selenation of chromones employing Selectfluor reagent under mild conditions is described. The developed method is suitable for a wide substrate scope and affords 3-selenylated chromones in good to excellent yield with high selectivity. An ionic mechanism is proposed for this transformation. Furthermore, the application of potassium thiocyanate with enaminones for the synthesis of thiocyano chromones in this transformation is also successful.

Functional characterization of two flavone synthase II members in citrus

Polymethoxylated flavones (PMFs), the main form of flavones in citrus, are derived from the flavone branch of the flavonoid biosynthesis pathway. Flavone synthases (FNSs) are enzymes that catalyze the synthesis of flavones from flavanones. However, the FNS in citrus has not been characterized yet. Here, we identified two type II FNSs, designated CitFNSII-1 and CitFNSII-2, based on phylogenetics and transcriptome analysis. Both recombinant CitFNSII-1 and CitFNSII-2 proteins directly converted naringenin, pinocembrin, and liquiritigenin to the corresponding flavones in yeast. In addition, transient overexpression of CitFNSII-1 and CitFNSII-2, respectively, in citrus peel significantly enhanced the accumulation of total PMFs, while virus-induced CitFNSII-1 and CitFNSII-2 genes silencing simultaneously significantly reduced the expression levels of both genes and total PMF content in citrus seedlings. CitFNSII-1 and CitFNSII-2 presented distinct expression patterns in different cultivars as well as different developmental stages. Methyl salicylate (MeSA) treatment reduced the CitFNSII-2 expression as well as the PMFs content in the peel of Citrus sinensis fruit but did not affect the CitFNSII-1 expression. These results indicated that both CitFNSII-1 and CitFNSII-2 participated in the flavone biosynthesis in citrus while the regulatory mechanism governing their expression might be specific. Our findings improved the understanding of the PMFs biosynthesis pathway in citrus and laid the foundation for further investigation on flavone synthesis regulation.

A Polyphenol Oxidase Catalyzes Aurone Synthesis in Marchantia polymorpha

Aurones constitute one of the major classes of flavonoids, with a characteristic furanone structure that acts as the C-ring of flavonoids. Members of various enzyme families are involved in aurone biosynthesis in different higher plants, suggesting that during evolution plants acquired the ability to biosynthesize aurones independently and convergently. Bryophytes also produce aurones, but the biosynthetic pathways and enzymes involved have not been determined. The present study describes the identification and characterization of a polyphenol oxidase (PPO) that acts as an aureusidin synthase (MpAS1) in the model liverwort, Marchantia polymorpha. Crude enzyme assays using an M. polymorpha line overexpressing MpMYB14 with high accumulation of aureusidin showed that aureusidin was biosynthesized from naringenin chalcone and converted to riccionidin A. This activity was inhibited by N-phenylthiourea, an inhibitor specific to enzymes of the PPO family. Of the six PPOs highly induced in the line overexpressing MpMyb14, one, MpAS1, was found to biosynthesize aureusidin from naringenin chalcone when expressed in Saccharomyces cerevisiae. MpAS1 also recognized eriodictyol chalcone, isoliquiritigenin and butein, showing the highest activity for eriodictyol chalcone. Members of the PPO family in M. polymorpha evolved independently from PPOs in higher plants, indicating that aureusidin synthases evolved in parallel in land plants.

Functional characterization of nine critical genes encoding rate-limiting enzymes in the flavonoid biosynthesis of the medicinal herb Grona styracifolia

Grona styracifolia is a photophilous legume that contains abundant flavonoids with multiple pharmacological activities, which is used to cure urethral and biliary calculus in China for thousands of years. The authentication of the rate-limiting enzymes involved in the flavonoids biosynthesis pathway enabled a better understanding of the molecular aspect of quality formation and modulation of this medicinal herb. In this study, the chemical distribution characteristics and content of flavonoids in different tissues of Grona styracifolia were analyzed using ultraperormance liquid chromatography coupled with Q-TOF mass spectrometry and showed that active flavonoids were primarily synthesized and stored in the leaves. Subsequently, RNA sequencing (RNA-seq)-based transcriptome profiling of the different tissues revealed that the flavonoids biosynthesis in the leaves was the most active. Meanwhile, 27 full-length transcripts inferred encoding vital enzymes involved in the flavonoids biosynthesis were preliminarily excavated. Finally, four CHSs, four CHIs, and one FNSII were successfully characterized by heterologous expression, which involved in three rate-limiting steps of the flavonoid biosynthetic pathway. In conclusion, these results laid a foundation for further investigation of the molecular mechanism of the biosynthesis and modulation of active flavonoids in Grona styracifolia.

Dietary Polyphenols as a Protection against Cognitive Decline: Evidence from Animal Experiments; Mechanisms and Limitations

Emerging evidence suggests that cognitive impairments may result from various factors, such as neuroinflammation, oxidative stress, mitochondrial damage, impaired neurogenesis, synaptic plasticity, blood-brain barrier (BBB) disruption, amyloid β protein (Aβ) deposition, and gut dysbiosis. Meanwhile, dietary polyphenol intake in a recommended dosage has been suggested to reverse cognitive dysfunction via various pathways. However, excessive intake of polyphenols could trigger unwanted adverse effects. Thus, this review aims to outline possible causes of cognitive impairments and how polyphenols alleviate memory loss via various pathways based on in vivo experimental studies. Thus, to identify potentially relevant articles, the keywords (1) nutritional polyphenol intervention NOT medicine AND neuron growth OR (2) dietary polyphenol AND neurogenesis AND memory impairment OR (3) polyphenol AND neuron regeneration AND memory deterioration (Boolean operators) were used in the Nature, PubMed, Scopus, and Wiley online libraries. Based on the inclusion and exclusion criteria, 36 research papers were selected to be further reviewed. The outcome of all the studies included supports the statement of appropriate dosage by taking into consideration gender differences, underlying conditions, lifestyle, and causative factors for cognitive decline, which will significantly boost memory power. Therefore, this review recapitulates the possible causes of cognitive decline, the mechanism of polyphenols involving various signaling pathways in modulating the memory, gut dysbiosis, endogenous antioxidants, bioavailability, dosage, and safety efficacy of polyphenols. Hence, this review is expected to provide a basic understanding of therapeutic development for cognitive impairments in the future.

Advances in the study of the function and mechanism of the action of flavonoids in plants under environmental stresses

MAIN CONCLUSION

This review summarizes the anti-stress effects of flavonoids in plants and highlights its role in the regulation of polar auxin transport and free radical scavenging mechanism. As secondary metabolites widely present in plants, flavonoids play a vital function in plant growth, but also in resistance to stresses. This review introduces the classification, structure and synthetic pathways of flavonoids. The effects of flavonoids in plant stress resistance were enumerated, and the mechanism of flavonoids in plant stress resistance was discussed in detail. It is clarified that plants under stress accumulate flavonoids by regulating the expression of flavonoid synthase genes. It was also determined that the synthesized flavonoids are transported in plants through three pathways: membrane transport proteins, vesicles, and bound to glutathione S-transferase (GST). At the same time, the paper explores that flavonoids regulate polar auxin transport (PAT) by acting on the auxin export carrier PIN-FORMED (PIN) in the form of ATP-binding cassette subfamily B/P-glycoprotein (ABCB/PGP) transporter, which can help plants to respond in a more dominant form to stress. We have demonstrated that the number and location of hydroxyl groups in the structure of flavonoids can determine their free radical scavenging ability and also elucidated the mechanism by which flavonoids exert free radical removal in cells. We also identified flavonoids as signaling molecules to promote rhizobial nodulation and colonization of arbuscular mycorrhizal fungi (AMF) to enhance plant-microbial symbiosis in defense to stresses. Given all this knowledge, we can foresee that the in-depth study of flavonoids will be an essential way to reveal plant tolerance and enhance plant stress resistance.

Molecular phylogenetic study of flavonoids in medicinal plants: a case study family Apiaceae

The current study examined the phylogenetic pattern of medicinal species of the family Apiaceae based on flavonoid groups production, as well as the overall mechanism of the key genes involved in flavonol and flavone production. Thirteen species of the family Apiaceae were used, including Eryngium campestre from the subfamily Saniculoideae, as well as Cuminum cyminum, Carum carvi, Coriandrum sativum, Apium graveolens, Petroselinum crispum, Pimpinella anisum, Anethum graveolens, Foeniculum vulgare, Daucus carota, Ammi majus, Torilis arvensis, and Deverra tortuosa from the subfamily Apioideae. The seeds were cultivated, and the leaves were collected to estimate flavonoids and their groups, physiological factors, transcription levels of flavonol and flavone production-related genes. The phylogenetic relationship between the studied species was established using the L-ribosomal 16 (rpl16) chloroplast gene. The results revealed that the studied species were divided into two patterns: six plant species, E. campestre, C. carvi, C. sativum, P. anisum, An. graveolens, and D. carota, contained low content of flavonoids, while the other seven species had high content. This pattern of flavonoids production coincided with the phylogenetic relationships between the studied species. In contrast, the phylogeny of the flavonol and flavone synthase genes was incompatible with the quantitative production of their products. The study concluded that the increment in the production of flavonol depends on the high expression of chalcone synthase, chalcone isomerase, flavanone 3 hydroxylase, flavonol synthase, the increase of Abscisic acid, sucrose, and phenyl ammonia lyase, while flavone mainly depends on evolution and on the high expression of the flavone synthase gene.

Transcriptomic Analysis on the Peel of UV-B-Exposed Peach Fruit Reveals an Upregulation of Phenolic- and UVR8-Related Pathways

UV-B treatment deeply influences plant physiology and biochemistry, especially by activating the expression of responsive genes involved in UV-B acclimation through a UV-B-specific perception mechanism. Although the UV-B-related molecular responses have been widely studied in Arabidopsis, relatively few research reports deepen the knowledge on the influence of post-harvest UV-B treatment on fruit. In this work, a transcriptomic approach is adopted to investigate the transcriptional modifications occurring in the peel of UV-B-treated peach (Prunus persica L., cv Fairtime) fruit after harvest. Our analysis reveals a higher gene regulation after 1 h from the irradiation (88% of the differentially expressed genes-DEGs), compared to 3 h recovery. The overexpression of genes encoding phenylalanine ammonia-lyase (PAL), chalcone syntase (CHS), chalcone isomerase (CHI), and flavonol synthase (FLS) revealed a strong activation of the phenylpropanoid pathway, resulting in the later increase in the concentration of specific flavonoid classes, e.g., anthocyanins, flavones, dihydroflavonols, and flavanones, 36 h after the treatment. Upregulation of UVR8-related genes (HY5, COP1, and RUP) suggests that UV-B-triggered activation of the UVR8 pathway occurs also in post-harvest peach fruit. In addition, a regulation of genes involved in the cell-wall dismantling process (PME) is observed. In conclusion, post-harvest UV-B exposure deeply affects the transcriptome of the peach peel, promoting the activation of genes implicated in the biosynthesis of phenolics, likely via UVR8. Thus, our results might pave the way to a possible use of post-harvest UV-B treatments to enhance the content of health-promoting compounds in peach fruits and extending the knowledge of the UVR8 gene network.

Modulation of the Dipole Potential of Model Lipid Membranes with Phytochemicals: Molecular Mechanisms, Structure-Activity Relationships, and Implications in Reconstituted Ion Channels

Phytochemicals, such as flavonoids, stilbenoids, alkaloids, terpenoids, and related compounds, have a wide range of useful pharmacological properties which cannot be ascribed to binding to a single peptide or protein target alone. Due to the relatively high lipophilicity of phytochemicals, the lipid membrane is thought to mediate their effects via changes in the properties of the lipid matrix, in particular, by modulating the transmembrane distribution of the electrical potential and, consequently, the formation and functioning of the ion channels reconstituted in the lipid bilayers. Therefore, biophysical studies on the interactions between plant metabolites and model lipid membranes are still of interest. This review represents an attempt to provide a critical analysis of a variety of studies on altering membranes and ion channels with phytochemicals via disturbing the potential drop at the membrane-aqueous solution interface. Critical structural motifs and functioning groups in the molecules of plant polyphenols (alkaloids and saponins are identified) and the possible mechanisms of dipole potential modulation with phytochemicals are discussed.

The Classification, Molecular Structure and Biological Biosynthesis of Flavonoids, and Their Roles in Biotic and Abiotic Stresses

With the climate constantly changing, plants suffer more frequently from various abiotic and biotic stresses. However, they have evolved biosynthetic machinery to survive in stressful environmental conditions. Flavonoids are involved in a variety of biological activities in plants, which can protect plants from different biotic (plant-parasitic nematodes, fungi and bacteria) and abiotic stresses (salt stress, drought stress, UV, higher and lower temperatures). Flavonoids contain several subgroups, including anthocyanidins, flavonols, flavones, flavanols, flavanones, chalcones, dihydrochalcones and dihydroflavonols, which are widely distributed in various plants. As the pathway of flavonoid biosynthesis has been well studied, many researchers have applied transgenic technologies in order to explore the molecular mechanism of genes associated with flavonoid biosynthesis; as such, many transgenic plants have shown a higher stress tolerance through the regulation of flavonoid content. In the present review, the classification, molecular structure and biological biosynthesis of flavonoids were summarized, and the roles of flavonoids under various forms of biotic and abiotic stress in plants were also included. In addition, the effect of applying genes associated with flavonoid biosynthesis on the enhancement of plant tolerance under various biotic and abiotic stresses was also discussed.

Discovery of a Unique Flavonoid Biosynthesis Mechanism in Fungi by Genome Mining

Flavonoids are important plant natural products with variable structures and bioactivities. All known plant flavonoids are generated under the catalysis of a type III polyketide synthase (PKS) followed by a chalcone isomerase (CHI) and a flavone synthase (FNS). In this study, the biosynthetic gene cluster of chlorflavonin, a fungal flavonoid with acetolactate synthase inhibitory activity, was discovered using a self-resistance-gene-directed strategy. A novel flavonoid biosynthetic pathway in fungi was revealed. A core nonribosomal peptide synthetase-polyketide synthase (NRPS-PKS) is responsible for the generation of the key precursor chalcone. Then, a new type of CHI catalyzes the conversion of a chalcone into a flavanone by a histidine-mediated oxa-Michael addition mechanism. Finally, the desaturation of flavanone to flavone is catalyzed by a new type of FNS, a flavin mononucleotide (FMN)-dependent oxidoreductase.

Discovery of Flavone Derivatives Containing Carboxamide Fragments as Novel Antiviral Agents

Plant virus diseases seriously affect the yield and quality of agricultural products, and their prevention and control are difficult. It is urgent to develop new and efficient antiviral agents. In this work, a series of flavone derivatives containing carboxamide fragments were designed, synthesized, and systematically evaluated for their antiviral activities against tobacco mosaic virus (TMV) on the basis of a structural-diversity-derivation strategy. All the target compounds were characterized by 1H-NMR, 13C-NMR, and HRMS techniques. Most of these derivatives displayed excellent in vivo antiviral activities against TMV, especially 4m (inactivation inhibitory effect, 58%; curative inhibitory effect, 57%; and protection inhibitory effect, 59%), which displayed similar activity to ningnanmycin (inactivation inhibitory effect, 61%; curative inhibitory effect, 57%; and protection inhibitory effect, 58%) at 500 μg mL-1; thus, it emerged as a new lead compound for antiviral research against TMV. Antiviral mechanism research by molecular docking demonstrated that compounds 4m, 5a, and 6b could interact with TMV CP and disturb virus assembly.