Identification and characterization of a rhamnosyltransferase involved in rutin biosynthesis in Fagopyrum esculentum (common buckwheat)

Rhamnosyltransferases: Biochemical activities, potential biotechnology for production of natural products and their applications

Rhamnosyltransferase is an enzyme that catalyzes the transfer of rhamnose moieties from an activated donor molecule, typically nucleotide diphosphate-rhamnose (NDP-rhamnose), to a wide range of acceptor molecules, including proteins, lipids, saccharides, glycoproteins, glycans, and glycolipids. This enzymatic process, known as rhamnosylation, plays a fundamental role in the biosynthesis of critical biomolecules, such as components of the cell wall, plasma membrane channels, receptors, antigens, signaling molecules, antibiotics, and other secondary metabolites. Due to its essential involvement in both primary and secondary metabolic pathways, rhamnosyltransferase is indispensable for various biological processes and exhibits significant potential for applications in human health and industrial biotechnology. In recent years, this enzyme has garnered substantial attention from the scientific community, owing to its unique biochemical properties and its utility in diverse sectors, including medicine, food technology, and cosmetics. This review aims to synthesize recent advancements in the study of rhamnosyltransferase, with a focus on its catalytic mechanisms, biological significance, and emerging applications in biotechnological innovation.

Identification and Functional Characterization of Two UDP-Glycosyltransferases Involved in Narcissoside Biosynthesis in Anoectochilus roxburghii

Flavonoid rutinosides, a group of bioactive compounds in Anoectochilus roxburghii, contribute greatly to the plant's beneficial effects on human health. However, the glycosylation mechanism of flavonoid rutinosides in A. roxburghii remains unclear. In this study, two efficient and selective glycosyltransferases, AUTG25 and AUTG23, involved in the biosynthesis of narcissoside, a major flavonoid rutinoside in A. roxburghii, were identified through transcriptome analysis and functional validation. AUTG25 could regioselectively catalyze 3-O-glucosylation of isorhamnetin to produce isorhamnetin 3-O-glucoside, while AUTG23 could further catalyze 6"-O-rhamnosylation to generate narcissoside. Both AUTG25 and AUTG23 exhibited high positional and sugar donor selectivities in the catalytic reaction. Homology modeling and site-directed mutagenesis showed that H20, E83, E385, and F143 in AUTG25 and E280, E89, D188, W327, D369, and Y191 in AUTG23 may be critical for their catalytic functions. Transient expression in Nicotiana benthamiana finally confirmed that AUTG25 possesses flavonol-3-O-glucosyltransferase activity and AUTG23 has flavonol-3-O-glucoside (1→6) rhamnosyltransferase activity. This study clarified and provided candidate UDP-dependent glycosyltransferase genes for narcissoside biosynthesis in A. roxburghii.

Possible lessons of a model experiment: To what extent can UV activate the production of leaf phenolics in indoor plant cultivation?

Tobacco (Nicotiana tabacum L.) plants were grown outdoors (N°46.07, E°18.18) under either natural or UV-deprived sunlight for 25 days in the summer. High PAR resulted in high polyphenol content, which was selectively affected by solar UV-A and UV-B irradiation. Solar UV-A irradiation increased anthocyanins, but not flavonoids, in the epidermis, and this additional protection resulted in higher photochemical yields and lower NPQ. The simultaneous presence of UV-B overrode the effects of UV-A, increased epidermal flavonoids, and decreased anthocyanins. Leaves grown in full sunlight had the same photochemical yields of NPQ as those grown under a UV-excluding filter. A combination of these effects can falsely dismiss the effects of UV-B on outdoor photosynthesis. Phenolic acid content, corresponding to approximately 80% of phenolic compounds, did not depend on solar UV, and total flavonoids increased under full solar UV irradiation, but not under UV-A only. The polyphenol content in outdoor leaves also served as a reference point for an indoor experiment, which showed that even a short, 4-day exposure of low PAR grown plants to UV from an artificial source increased the amount of some, although not all, components close to or even above outdoor levels. In indoor leaves, a selective increase in quercetin glycosides (to 62-85% of outdoor levels) supports both enzymatic and non-enzymatic antioxidant functions, and the increase in crypto- and neochlorogenic acids (to 76% and 117% of outdoor levels, respectively) suggests a redistribution among biosynthesis pathways. These results demonstrate the potential and efficiency of cultivation systems without sunlight.

Spatial-resolved metabolome imaging of petals for Forsythia viridissima and Jasminum nudiflorum using online extraction (OLE) coupled to LC-Qtof-MS

MS imaging (MSI) is a powerful technique for investigating the spatial distribution of metabolites in complex biological samples. However, due to the absence of liquid chromatography (LC) separation in routine MSI analysis, matrix effect is obvious and isomers identification remains challenging. To overcome these shortcomings of classical MSI tools (e.g., DESI-MSI and MALDI-MSI) for isomer differentiation and insufficient datapoints for quantification, online extraction-liquid chromatogram-hybrid triple quadrupole-time-of-flight mass spectrometry (OLE-LC-Qtof-MS) platform has been developed for spatial metabolome. As a proof-of-concept, two species flowers namely Forsythia viridissima (FV) and Jasminum nudiflorum (JN) that bloom in early spring were collected, dried, and cut into small pieces (1.0 mm × 1.0 mm). All pieces successively underwent OLE-LC-Qtof-MS measurements. As a result, 46 and 41 metabolites were observed and identified from FV and JN petals, respectively. Particularly, each compound corresponded to a chromatographic peak and isomeric differentiation was achieved amongst a set of chlorogenic acid derivatives. The peak areas of high intensity metabolites were aligned and combined within either species. The datasets were individually converted into heatmaps for all compounds, 87 ones in total, and each grid of any heatmap was assigned to the original location in the petal. Then, the spatial-resolved distribution style of each compound crossing the petal was reflected by the re-organized heatmap bearing the petal shape. As expected, regio-specific occurrence and accumulation were observed for several compounds, particularly among the chlorogenic acid isomers. Above all, OLE-LC-Qtof-MS is an alternative tool for spatial-resolved metabolome attributing to the advantages of isomeric separation and reliable quantification.

CRISPR/Cas9 targeted editing of UDP-rhamnose: Rhamnosyltransferase gene decreases its functions in acteoside biosynthesis and pest resistance in Rehmarmia glutinosa

UDP-rhamnose: rhamnosyltransferases (URTs)in Rehmarmia glutinosa (RgURT1-RgURT4)may catalyze two key downstream steps of acteoside biosynthesis. Moreover, they were identified from Rehmarmia glutinosa and preliminarily characterized, but their bioinformatics analysis and functions remain to be further explored. The present study mainly focused on investigating their bioinformatics function prediction, genotype-dependent expression, and roles for acteoside biosynthesis and pest resistance with CRISPR/Cas9 technology.Some key findings were as follows:they had a low identity but a typical PSPG box of rhamnosyltransferases, belonging to Glycosyltansferase-GTB type superfamily; They could be expressed depending on genotype,but RgURT4 expression is the highest; Based on RgURT4, two sgRNAs were designed and cloned into pBWA(V)HS-zmpl vector to construct a pBWA(V)HS-Cas9-RgURT vector. It was transferred to Rehmarmia glutinosa using Agrobacterium-mediated transformation so that hygromycin-resistant R. glutinosa plants were obtained. Sequencing indicated that CRISPR/Cas9 targeted editing resulted in base replacements in RgURT4,while its expression was decreased among these edited plants; A few of them had yellower leaves with white dots, lower acteoside and a little higher decaffeoylacteoside than WTs; Tetranychus cinnbarinus among them was observed by stereomicroscope. The results demonstrated that CRISPR/Cas9-mediated RgURT4 editing reduced the acteoside content and pest resistance but decaffeoylacteoside content of Rehmarmia glutinosa. This study will contribute to the function analyses of rhamnosyltransferases gene and downstream steps of acteoside biosynthesis as well as its CRISPR-Cas9-based molecular breeding.

Regulatory Module FtMYB5/6-FtGBF1-FtUFGT163 Promotes Rutin Biosynthesis in Tartary Buckwheat

Tartary buckwheat is highly valued for its abundant rutin (quercetin 3-O-rutinoside). As a flavonoid glycoside, rutin is synthesized with the crucial involvement of UDP-dependent glycosyltransferases (UGTs). However, the functions and transcriptional regulation of the UGT-encoded genes remain poorly understood. This study identified a key gene, FtUFGT163, potentially encoding flavonol 3-O-glucoside (1 → 6) rhamnosyltransferase in Tartary buckwheat through omics analysis and molecular docking methods. The recombinant FtUFGT163 expressed in Escherichia coli demonstrated the capacity to glycosylate isoquercetin into rutin. Overexpression of FtUFGT163 significantly enhanced the rutin content in Tartary buckwheat. Further investigation identified a novel bZIP transcription factor, FtGBF1, that enhances FtUFGT163 expression by binding to the G-box element within its promoter, thereby augmenting rutin biosynthesis. Additional molecular biology experiments indicated that the specific positive regulator of rutin, FtMYB5/6, could directly activate the FtGBF1 promoter. Collectively, this study elucidates a novel regulatory module, termed "FtMYB5/6-FtGBF1-FtUFGT163", which effectively coordinates the biosynthesis of rutin in Tartary buckwheat, offering insights into the genetic enhancement of nutraceutical components in crops.

Systematic analysis of the UDP-glucosyltransferase family: discovery of a member involved in rutin biosynthesis in Solanum melongena

Eggplant (Solanum melongena) is an economically important crop and rich in various nutrients, among which rutin that has positive effects on human health is found in eggplant. Glycosylation mediated by UDP-glycosyltransferases (UGTs) is a key step in rutin biosynthesis. However, the UGT gene has not been reported in eggplant to date. Herein, 195 putative UGT genes were identified in eggplant by genome-wide analysis, and they were divided into 17 subgroups (Group A-P and Group R) according to the phylogenetic evolutionary tree. The members of Groups A, B, D, E and L were related to flavonol biosynthesis, and rutin was the typical flavonol. The expression profile showed that the transcriptional levels of SmUGT genes in Clusters 7-10 were closely related to those of rutin biosynthetic pathway genes. Notably, SmUGT89B2 was classified into Cluster 7 and Group B; its expression was consistent with rutin accumulation in different tissues and different leaf stages of eggplant. SmUGT89B2 was located in the nucleus and cell membrane. Virus-induced gene silencing (VIGS) and transient overexpression assays showed that SmUGT89B2 can promote rutin accumulation in eggplant. These findings provide new insights into the UGT genes in eggplant, indicating that SmUGT89B2 is likely to encode the final enzyme in rutin biosynthesis.

Functional characterization of two efficient glycosyltransferases catalysing the formation of rutin from Sophora japonica L

Two efficient and selective glycosyltransferases were identified from Sophora japonica L. Sj3GT could regio-selectively catalyse 3-O-glucosylation of quercetin to produce isoquercitrin, and Sj6''RhaT could further catalyse its 6''-O-rhamnosylation to generate rutin. It is particularly noteworthy that Sj6''RhaT shows high sugar donor selectivity towards UDP-rhamnose.

Development and chromosomal characterization of interspecific hybrids between common buckwheat (Fagopyrum esculentum) and a related perennial species (F. cymosum)

Common buckwheat (Fagopyrum esculentum) is an annual self-incompatible plant that is widely grown. The genus Fagopyrum comprises more than 20 species, including F. cymosum, a perennial that, unlike common buckwheat, is highly resistant to excess water. In this study, we developed interspecific hybrids between F. esculentum and F. cymosum via embryo rescue, to improve undesirable traits of common buckwheat, such as low tolerance to excess water. The interspecific hybrids were confirmed by genomic in situ hybridization (GISH). We also developed DNA markers to confirm the identity of the hybrids and if genes derived from each genome were inherited by the next generation. Observations of pollen indicated that the interspecific hybrids were essentially sterile. Unpaired chromosomes and abnormal segregation during meiosis were likely responsible for the pollen sterility of the hybrids. These findings could facilitate buckwheat breeding to produce lines that can withstand harsh environments with wild or related species in the genus Fagopyrum.

Flavonoid Metabolism in Tetrastigma hemsleyanum Diels et Gilg Based on Metabolome Analysis and Transcriptome Sequencing

Tetrastigma hemsleyanum Diels et Gilg, known as a "plant antibiotic", possesses several attractive properties including anti-inflammatory, anti-tumor, and antioxidant effects, with its efficacy being attributed to flavonoids. However, the flavonoid biosynthesis of T. hemsleyanum has rarely been studied. In this study, we investigated the flavonoid metabolism of T. hemsleyanum through metabolome analysis and transcriptome sequencing. The metabolomic results showed differences in the flavonoids of the leaves and root tubers of T. hemsleyanum. A total of 22 flavonoids was detected, and the concentrations of most flavonoids in the leaves were higher than those in the root tubers. Transcriptome analysis revealed that differentially expressed genes (DEGs) in the leaves and root tubers were enriched in photosynthesis-antenna proteins. Pearson correlation analysis indicated that the expression levels of chalcone isomerase (CHI) and UDP-glycose flavonoid glycosyltransferase (UFGT) were highly correlated with the concentrations of most flavonoids. Further, this study found that the photosynthesis-antenna proteins essentially contributed to the difference in the flavonoids in T. hemsleyanum. The gene expressions and concentrations of the total flavonoids of leaves and root tubers in Hangzhou, Jinhua, Lishui, and Taizhou in Zhejiang Province, China, showed that CHI (CL6715.Contig1_All, Unigene19431_All, CL921.Contig4_All) and UFGT (CL11556.Contig3_All, CL11775.Contig1_All) were the potential key genes of accumulation of most flavonoids in T. hemsleyanum.

Rhamnosyltransferases involved in the biosynthesis of flavone rutinosides in Chrysanthemum species

Linarin (acacetin-7-O-rutinoside), isorhoifolin (apigenin-7-O-rutinoside), and diosmin (diosmetin-7-O-rutinoside) are chemically and structurally similar flavone rutinoside (FR) compounds found in Chrysanthemum L. (Anthemideae, Asteraceae) plants. However, their biosynthetic pathways remain largely unknown. In this study, we cloned and compared FRs and genes encoding rhamnosyltransferases (RhaTs) among eight accessions of Chrysanthemum polyploids. We also biochemically characterized RhaTs of Chrysanthemum plants and Citrus (Citrus sinensis and Citrus maxima). RhaTs from these two genera are substrate-promiscuous enzymes catalyzing the rhamnosylation of flavones, flavanones, and flavonols. Substrate specificity analysis revealed that Chrysanthemum 1,6RhaTs preferred flavone glucosides (e.g. acacetin-7-O-glucoside), whereas Cs1,6RhaT preferred flavanone glucosides. The nonsynonymous substitutions of RhaTs found in some cytotypes of diploids resulted in the loss of catalytic function. Phylogenetic analysis and specialized pathways responsible for the biosynthesis of major flavonoids in Chrysanthemum and Citrus revealed that rhamnosylation activity might share a common evolutionary origin. Overexpression of RhaT in hairy roots resulted in 13-, 2-, and 5-fold increases in linarin, isorhoifolin, and diosmin contents, respectively, indicating that RhaT is mainly involved in the biosynthesis of linarin. Our findings not only suggest that the substrate promiscuity of RhaTs contributes to the diversity of FRs in Chrysanthemum species but also shed light on the evolution of flavone and flavanone rutinosides in distant taxa.

Visualizing the spatial distribution of functional metabolites in Forsythia suspensa at different harvest stages by MALDI mass spectrometry imaging

As a traditional Chinese medicine, Forsythia suspensa (F. suspensa) has attracted much attention due to its significant pharmacological activity. Revealing the spatial distribution of metabolites during F. suspensa development is important for understanding its biosynthesis rules and improving the quality of medicinal materials. However, there is currently a lack of information on the spatial distribution of F. suspensa metabolites. In this work, the spatial distribution and growth metabolism patterns of important metabolites of F. suspensa were studied for the first time using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Using 2,5-dimethylnaphthalene (DAN) as the matrix and detecting in negative ion mode, the spatial distribution and growth patterns of 11 metabolites obtained from longitudinal sections of F. suspensa included pinoresinol, phillygenin, forsythoside A, forsythoside E, rutin, caffeic acid, malic acid, citric acid, stearic acid, oleic acid, and linoleic acid. These results showed the mesocarp and endosperm tissues of F. suspensa were important for storing important functional metabolites. Changes in mesocarp and endosperm growth and development tissues caused large changes in the content of important functional metabolites in F. suspensa. These results provide a basis for understanding the spatial distribution of metabolites in F. suspensa tissues and the significant changes that occur during growth and development, exploring the mechanism of important synthesis of metabolites, regulating the harvest of F. suspensa, and improving the quality of medicinal herbs.

Phenolic compounds in common buckwheat sprouts: composition, isolation, analysis and bioactivities

Phenolic compounds in common buckwheat sprouts (CBSs) have gained research interest because of their multiple health benefits. Phenolic acids, flavanones, flavonols, flavan-3-ols, and anthocyanins are important bioactive components of CBS that exhibit biological activities, including anti-inflammatory, antioxidant, anti-proliferative, and immunomodulatory effects. The isolation and quantitative and qualitative analyses of these phenolic compounds require effective and appropriate extraction and analytical methods. The most recent analytical method developed for determining the phenolic profile is HPLC coupled with a UV-visible detector and/or MS. This review highlights the extraction, purification, analysis, and bioactive properties of phenolic compounds from CBS described in the literature.

Unravelling the consecutive glycosylation and methylation of flavonols in peach in response to UV-B irradiation

Flavonol glycosides are bioactive compounds important for plant defence and human nutrition. Glycosylation and methylation play an important role in enriching the diversity of flavonols in response to the environment. Peach flowers and fruit are rich in flavonol diglycosides such as isorhamnetin 3-O-rutinoside (I3Rut), kaempferol 3-O-rutinoside and quercetin 3-O-rutinoside, and flavonol monoglycosides such as I 3-O-glucoside and Q 3-O-galactoside. UV-B irradiation of fruit significantly induced accumulation of all these flavonol glycosides. Candidate biosynthetic genes induced by UV-B were identified by genome homology searches and the in vitro catalytic activities of purified recombinant proteins determined. PpUGT78T3 and PpUGT78A2 were identified as flavonol 3-O-glucosyltransferase and 3-O-galactosyltransferase, respectively. PpUGT91AK6 was identified as flavonol 1,6-rhamnosyl trasferase catalysing the formation of flavonol rutinosides and PpFOMT1 was identified as a flavonol O-methyltransferase that methylated Q at the 3'-OH-OH to form isorhamnetin derivatives. Transient expression in Nicotiana benthamiana confirmed the specificity of PpUGT78T3 as a flavonol 3-O-glucosyltransferase, PpUGT78A2 as a 3-O-galactosyltransferase, PpUGT91AK6 as a 1,6-rhamnosyltrasferase and PpFOMT1 as an O-methyltransferase. This study provides new insights into the mechanisms of glycosylation and methylation of flavonols, especially the formation of flavonol diglycosides such as I3Rut, and will also be useful for future potential metabolic engineering of complex flavonols.

Creating diverse glycosides of 2'-hydroxyflavone through microbial glycosylation

Four new 2'-hydroxyflavone glycosides, namely hydroxyflavone-2'-O-β-D-glucuronide (1), hydroxyflavone-2'-O-α-L-rhamnoside (2), hydroxyflavone-2'-O-β-D-glucoside (3), and hydroxyflavone-2'-O-4"-O-methyl-β-D-glucoside (4), were biosynthesized through microbial glycosylation using Streptomyces coeruleorubidus NRRL B-2569, Streptomyces toxytricini NRRL 15443, Escherichia coli BL21(DE3)/pWZ8, and Beauveria bassiana ATCC 7159, respectively. Compounds 1-4 were structurally characterized through extensive analysis of 1D and 2D NMR spectroscopic data. The water solubility of glycosylated products 1-4 were enhanced by 7 to 15 times compared to the substrate 2'-hydroxyflavone. Moreover, antioxidant assays revealed that compounds 1 and 2 exhibited stronger 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity than the substrate, decreasing the logIC₅₀ by 68.7% and 80.7%, respectively. Therefore, this research provides several effective biocatalysts that can be used for structural modification of flavonoids for enhanced water solubility and biological activities.

FtUGT79A15 is responsible for rutinosylation in flavonoid diglycoside biosynthesis in Fagopyrum tataricum

Tartary buckwheat shows health benefits with its high antioxidant activity and abundant flavonoid content. However, glycosylated flavonoid accumulation patterns and their molecular basis remain unidentified in Tartary buckwheat. Here, our metabolomics analysis revealed that F3'H branching was the major flavonoid metabolic flux in Tartary buckwheat. Interestingly, metabolome results also showed that the most abundant flavonoids were mainly in the glycosylated form, including flavonoid glycosides and flavonoid diglycosides in Tartary buckwheat. However, the flavonoid glycosides glycosyltransferase (GGT) gene catalyzing the second glycosylation step of flavonoid diglycoside has not been discovered yet in Tartary buckwheat. Thus, we explored GGT genes in the transcriptome-metabolome correlation network and confirmed that FtUGT79A15 showed the rhamnosyltransferase activity to catalyze quercetin 3-O-glucoside to rutin invitro and inplanta. Overall, FtUGT79A15 was identified to involve in the flavonoid diglycoside biosynthesis pathway in Tartary buckwheat.

Food Containing Bioactive Flavonoids and Other Phenolic or Sulfur Phytochemicals With Antiviral Effect: Can We Design a Promising Diet Against COVID-19?

Since in late 2019, when the coronavirus 2 (SARS-CoV-2) pathogen of coronavirus disease 2019 (COVID-19) started to spread all over the world, causing the awful global pandemic we are still experiencing, an impressive number of biologists, infectious disease scientists, virologists, pharmacologists, molecular biologists, immunologists, and other researchers working in laboratories of all the advanced countries focused their research on the setting up of biotechnological tools, namely vaccines and monoclonal antibodies, as well as of rational design of drugs for therapeutic approaches. While vaccines have been quickly obtained, no satisfactory anti-Covid-19 preventive, or therapeutic approach has so far been discovered and approved. However, among the possible ways to achieve the goal of COVID-19 prevention or mitigation, there is one route, i.e., the diet, which until now has had little consideration. In fact, in the edible parts of plants supplying our food, there are a fair number of secondary metabolites mainly belonging to the large class of the flavonoids, endowed with antiviral or other health beneficial activities such as immunostimulating or anti-inflammatory action that could play a role in contributing to some extent to prevent or alleviate the viral infection and/or counteract the development of SARS induced by the novel coronavirus. In this review, a number of bioactive phytochemicals, in particular flavonoids, proven to be capable of providing some degree of protection against COVID-19, are browsed, illustrating their beneficial properties and mechanisms of action as well as their distribution in cultivated plant species which supply food for the human diet. Furthermore, room is also given to information regarding the amount in food, the resistance to cooking processes and, as a very important feature, the degree of bioavailability of these compounds. Concluding, remarks and perspectives for future studies aimed at increasing and improving knowledge and the possibility of using this natural complementary therapy to counteract COVID-19 and other viral pathologies are discussed.

Arachis hypogaea resveratrol synthase 3 alters the expression pattern of UDP-glycosyltransferase genes in developing rice seeds

The resveratrol-producing rice (Oryza sativa L.) inbred lines, Iksan 515 (I.515) and Iksan 526 (I.526), developed by the expression of the groundnut (Arachis hypogaea) resveratrol synthase 3 (AhRS3) gene in the japonica rice cultivar Dongjin, accumulated both resveratrol and its glucoside, piceid, in seeds. Here, we investigated the effect of the AhRS3 transgene on the expression of endogenous piceid biosynthesis genes (UGTs) in the developing seeds of the resveratrol-producing rice inbred lines. Ultra-performance liquid chromatography (UPLC) analysis revealed that I.526 accumulates significantly higher resveratrol and piceid in seeds than those in I.515 seeds and, in I.526 seeds, the biosynthesis of resveratrol and piceid reached peak levels at 41 days after heading (DAH) and 20 DAH, respectively. Furthermore, RNA-seq analysis showed that the expression patterns of UGT genes differed significantly between the 20 DAH seeds of I.526 and those of Dongjin. Quantitative real-time PCR (RT-qPCR) analyses confirmed the data from RNA-seq analysis in seeds of Dongjin, I.515 and I.526, respectively, at 9 DAH, and in seeds of Dongjin and I.526, respectively, at 20 DAH. A total of 245 UGTs, classified into 31 UGT families, showed differential expression between Dongjin and I.526 seeds at 20 DAH. Of these, 43 UGTs showed more than 2-fold higher expression in I.526 seeds than in Dongjin seeds. In addition, the expression of resveratrol biosynthesis genes (PAL, C4H and 4CL) was also differentially expressed between Dongjin and I.526 developing seeds. Collectively, these data suggest that AhRS3 altered the expression pattern of UGT genes, and PAL, C4H and 4CL in developing rice seeds.

Genome-wide transcriptome variation landscape in Ruta chalepensis organs revealed potential genes responsible for rutin biosynthesis

Ruta chalepensis L., most commonly known as 'fringed rue,' is an excellent and valuable bioactive plant that produces a range of complex flavonoids, of which rutin is the major compound present in this plant of great pharmaceutical and medicinal significance. The present study is a pioneering attempt to examine the changes in the transcriptomic landscape of leaf, stem, and root tissues and correlate this with rutin quantity in each tissue in order to identify the candidate genes responsible for rutin biosynthesis and to increase genomic resources in fringed rue. Comparative transcriptome sequencing of leaves, stems and roots were performed using the NovaSeq 6000 platform. The de novo transcriptome assembly generated 254,685 transcripts representing 154,018 genes with GC content of 42.60 % and N50 of 2280 bp. Searching assembled transcripts against UniRef90 and SwissProt databases annotated 79.7 % of them as protein coding. The leaf tissues had the highest rutin content followed by stems and roots. Several differentially expressed genes and transcripts relating to rutin biosynthesis were identified in leaves comparing with roots or stems comparing with roots. All the genes known to be involved in rutin biosynthesis showed up-regulation in leaves as compared with roots. These results were confirmed by gene ontology (GO) and pathway enrichment analyses. Up-regulated genes in leaves as compared with roots enriched GO terms with relation to rutin biosynthesis e.g. action of flavonol synthase, biosynthetic mechanism of malonyl-CoA, and action of monooxygenase. Phylogenetic analysis of the rhamnosyltransferase (RT) gene showed that it was highly homologues with RT sequence from Citrus species and all were located in the same clade. This transcriptomic dataset will serve as an important public resource for future genomics and transcriptomic studies in R. chalepensis and will act as a benchmark for the identification and genetic modification of genes involved in the biosynthesis of secondary metabolites.

Characterizing glycosyltransferases by a combination of sequencing platforms applied to the leaf tissues of Stevia rebaudiana

Background

Stevia rebaudiana (Bertoni) is considered one of the most valuable plants because of the steviol glycosides (SGs) that can be extracted from its leaves. Glycosyltransferases (GTs), which can transfer sugar moieties from activated sugar donors onto saccharide and nonsaccharide acceptors, are widely distributed in the genome of S. rebaudiana and play important roles in the synthesis of steviol glycosides.

Results

Six stevia genotypes with significantly different concentrations of SGs were obtained by induction through various mutagenic methods, and the contents of seven glycosides (stevioboside, Reb B, ST, Reb A, Reb F, Reb D and Reb M) in their leaves were considerably different. Then, NGS and single-molecule real-time (SMRT) sequencing were combined to analyse leaf tissue from these six different genotypes to generate a full-length transcriptome of S. rebaudiana. Two phylogenetic trees of glycosyltransferases (SrUGTs) were constructed by the neighbour-joining method and successfully predicted the functions of SrUGTs involved in SG biosynthesis. With further insight into glycosyltransferases (SrUGTs) involved in SG biosynthesis, the weighted gene co-expression network analysis (WGCNA) method was used to characterize the relationships between SrUGTs and SGs, and forty-four potential SrUGTs were finally obtained, including SrUGT85C2, SrUGT74G1, SrUGT76G1 and SrUGT91D2, which have already been reported to be involved in the glucosylation of steviol glycosides, illustrating the reliability of our results.

Conclusion

Combined with the results obtained by previous studies and those of this work, we systematically characterized glycosyltransferases in S. rebaudiana and forty-four candidate SrUGTs involved in the glycosylation of steviol glucosides were obtained. Moreover, the full-length transcriptome obtained in this study will provide valuable support for further research investigating S. rebaudiana.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07195-5.

Identification and tissue-specific expression of rutin biosynthetic pathway genes in Capparis spinosa elicited with salicylic acid and methyl jasmonate

Capparis spinosa is an edible medicinal plant which is considered as an excellent source of rutin. Rutin is a glycoside of the flavonoid quercetin that has been reported to have a beneficial role in controlling various diseases such as hypertension, arteriosclerosis, diabetes, and obesity. In this study, the partial cDNA of four genes involved in the rutin biosynthetic pathway including 4-coumaroyl CoA ligase (4CL), flavonoid 3′-hydroxylase (F3′H), flavonol synthase (FLS) and flavonol-3-O-glucoside L-rhamnosyltransferase (RT) were identified in C.spinosa plants for the first time. The protein sequences of these genes shared high similarity with the same proteins in other plant species. Subsequently, the expression patterns of these genes as well as rutin accumulation in C.spinosa leaves treated with different concentrations of salicylic acid (SA) and methyl jasmonate (MeJA) and also in different tissues of Caper plants treated with 100 mgL⁻¹ SA and 150 μM MeJA were evaluated. The expression of all four genes was clearly up-regulated and rutin contents increased in response to MeJA and SA treatments after 24 h. The highest rutin contents (5.30 mgg⁻¹ DW and 13.27 mgg⁻¹ DW), as well as the highest expression levels of all four genes, were obtained using 100 mgL⁻¹ SA and 150 μM MeJA, respectively. Among the different tissues, the highest rutin content was observed in young leaves treated with 150 μM MeJA, which corresponded to the expression of related genes, especially RT, as a key gene in the rutin biosynthetic pathway. These results suggest that rutin content in various tissues of C. spinosa can be enhanced to a significant extent by MeJA and SA treatments and the gene expression patterns of rutin-biosynthesis-related genes are regulated by these elicitors.

Anticancer Activity of Rutin and Its Combination with Ionic Liquids on Renal Cells

The renal cell carcinoma (RCC) is the most common type of kidney cancer. Identifying novel and more effective therapies, while minimizing toxicity, continues to be fundamental in curtailing RCC. Rutin, a bioflavonoid widely found in nature, has shown promising anticancer properties, but with limited applicability due to its poor water solubility and pharmacokinetics. Thus, the potential anticancer effects of rutin toward a human renal cancer cell line (786-O), while considering its safety in Vero kidney cells, was assessed, as well as the applicability of ionic liquids (ILs) to improve drug delivery. Rutin (up to 50 µM) did not show relevant cytotoxic effects in Vero cells. However, in 786-O cells, a significant decrease in cell viability was already observed at 50 µM. Moreover, exposure to rutin caused a significant increase in the sub-G1 population of 786-O cells, reinforcing the possible anticancer activity of this biomolecule. Two choline-amino acid ILs, at non-toxic concentrations, enhanced rutin’s solubility/loading while allowing the maintenance of rutin’s anticancer effects. Globally, our findings suggest that rutin may have a beneficial impact against RCC and that its combination with ILs ensures that this poorly soluble drug is successfully incorporated into ILs–nanoparticles hybrid systems, allowing controlled drug delivery.

Stabilization of dhurrin biosynthetic enzymes from Sorghum bicolor using a natural deep eutectic solvent

In recent years, ionic liquids and deep eutectic solvents (DESs) have gained increasing attention due to their ability to extract and solubilize metabolites and biopolymers in quantities far beyond their solubility in oil and water. The hypothesis that naturally occurring metabolites are able to form a natural deep eutectic solvent (NADES), thereby constituting a third intracellular phase in addition to the aqueous and lipid phases, has prompted researchers to study the role of NADES in living systems. As an excellent solvent for specialized metabolites, formation of NADES in response to dehydration of plant cells could provide an appropriate environment for the functional storage of enzymes during drought. Using the enzymes catalyzing the biosynthesis of the defense compound dhurrin as an experimental model system, we demonstrate that enzymes involved in this pathway exhibit increased stability in NADES compared with aqueous buffer solutions, and that enzyme activity is restored upon rehydration. Inspired by nature, application of NADES provides a biotechnological approach for long-term storage of entire biosynthetic pathways including membrane-anchored enzymes.

The light-induced transcription factor FtMYB116 promotes accumulation of rutin in Fagopyrum tataricum

Tartary buckwheat (Fagopyrum tataricum) not only provides a supplement to primary grain crops in China but also has high medicinal value, by virtue of its rich content of flavonoids possessing antioxidant, anti-inflammatory, and anticancer properties. Light is an important environmental factor that can regulate the synthesis of plant secondary metabolites. In this study, we treated tartary buckwheat seedlings with different wavelengths of light and found that red and blue light could increase the content of flavonoids and the expression of genes involved in flavonoid synthesis pathways. Through coexpression analysis, we identified a new MYB transcription factor (FtMYB116) that can be induced by red and blue light. Yeast one-hybrid assays and an electrophoretic mobility shift assay showed that FtMYB116 binds directly to the promoter region of flavonoid-3'-hydroxylase (F3'H), and a transient luciferase activity assay indicated that FtMYB116 can induce F3'H expression. After transforming FtMYB116 into the hairy roots of tartary buckwheat, we observed significant increases in the content of rutin and quercetin. Collectively, our results indicate that red and blue light promote an increase in flavonoid content in tartary buckwheat seedlings; we also identified a new MYB transcription factor, FtMYB116, that promotes the accumulation of rutin via direct activation of F3'H expression.