Characterization of a heat responsive UDP: Flavonoid glucosyltransferase gene in tea plant (Camellia sinensis)

First Clarification of the Involvement of Glycosyltransferase MdUGT73CG22 in the Detoxification Metabolism of Nicosulfuron in Apple

Nicosulfuron, an acetolactate synthase (ALS) inhibitor herbicide, is a broad-spectrum and highly effective post-emergence herbicide. Glycosyltransferases (GTs) are widely found in organisms and transfer sugar molecules from donors to acceptors to form glycosides or sugar esters, thereby altering the physicochemical properties of the acceptor molecule, such as participating in detoxification. In this study, nine glycosyltransferases in group D of the apple glycosyltransferase family I were predicted to possibly be involved in the detoxification metabolism of ALS-inhibiting herbicides based on gene chip data published online. In order to confirm this, we analysed whether the expression of the nine glycosyltransferase genes in group D was induced by the previously reported ALS-inhibiting herbicides by real-time PCR (polymerase chain reaction). It was found that the ALS-inhibiting herbicide nicosulfuron significantly increased the expression of the MdUGT73CG22 gene in group D. Further investigation of the mechanism of action revealed that the apple glycosyltransferase MdUGT73CG22 glycosylated and modified nicosulfuron both in vivo and ex vivo to form nicosulfuron glycosides, which were involved in detoxification metabolism. In conclusion, a new glycosyltransferase, MdUGT73CG22, was identified for the first time in this study, which can glycosylate modifications of the ALS-inhibiting herbicide nicosulfuron and may be involved in the detoxification process in plants, which can help to further improve the knowledge of the non-targeted mechanism of herbicides.

Untargeted metabolomics in Anectocillus roxburghii with habitat heterogeneity and the key abiotic factors affecting its active ingredients

Introduction

Anoectochilus roxburghii is a rare, endangered herb with diverse pharmacological properties. Understanding the main metabolite types and characteristics of wild A. roxburghii is important for efficiently utilizing resources and examining quality according to origin.

Methods

Samples were collected from the main production areas across five regions in Fujian Province, China. An untargeted metabolomics analysis was performed on the entire plants to explore their metabolic profiles. We utilized UPLC-MS/MS to specifically quantify eight targeted flavonoids in these samples. Subsequently, correlation analysis was conducted to investigate the relationships between the flavonoids content and both the biological characteristics and geographical features.

Results

A comprehensive analysis identified a total of 3,170 differential metabolites, with terpenoids and flavonoids being the most prevalent classes. A region-specific metabolite analysis revealed that the Yongchun (YC) region showed the highest diversity of unique metabolites, including tangeretin and oleanolic acid. Conversely, the Youxi (YX) region was found to have the smallest number of unique metabolites, with only one distinct compound identified. Further investigation through KEGG pathway enrichment analysis highlighted a significant enrichment in pathways related to flavonoid biosynthesis. Further examination of the flavonoid category showed that flavonols were the most differentially abundant. We quantified eight specific flavonoids, finding that, on average, the YX region exhibited higher levels of these compounds. Correlation analysis highlighted a significant association between flavonoids and habitat, especially temperature and humidity.

Discussion

Untargeted metabolomics via LC-MS was suitable for identifying region-specific metabolites and their influence via habitat heterogeneity. The results of this study serve as a new theoretical reference for unique markers exclusively present in a specific sample group.

CsMYB67 participates in the flavonoid biosynthesis of summer tea leaves

Flavonoids are important compounds in tea leaves imparting bitter and astringent taste, which also play key roles in tea plants responding to environmental stress. Our previous study showed that the expression level of CsMYB67 was positively correlated with the accumulation of flavonoids in tea leaves as exposed to sunlight. Here, we newly reported the function of CsMYB67 in regulating flavonoid biosynthesis in tea leaves. CsMYB67 was localized in the nucleus and responded to temperature. The results of transient expression assays showed the co-transformation of CsMYB67 and CsTTG1 promoted the transcription of CsANS promoter in the tobacco system. CsTTG1 was bound to the promoter of CsANS based on the results of yeast one-hybrid (Y1H) and transient expression assays, while CsMYB67 enhanced the transcription of CsANS through protein interaction with CsTTG1 according to the results of yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC). Thus, CsMYB67-CsTTG1 module enhanced the anthocyanin biosynthesis through up-regulating the transcription of CsANS. Besides, CsMYB67 also enhanced the transcription of CsFLS and CsUFGT through forming transcription factor complexes. The function of CsMYB67 on flavonoid biosynthesis in tea leaves was validated by gene suppression assay. As CsMYB67 was suppressed, the transcriptional level of CsFLS was greatly reduced, leading to a significant increase in the contents of total catechins and total anthocyanidins. Hence, CsMYB67 plays an important role in regulating the downstream pathway of flavonoid biosynthesis in summer tea leaves.

Glycosylation of Secondary Metabolites: A Multifunctional UDP-Glycosyltransferase, CsUGT74Y1, Promotes the Growth of Plants

Camellia sinensis contains numerous glycosylated secondary metabolites that provide various benefits to plants and humans. However, the genes that catalyze the glycosylation of multitype metabolites in tea plants remain unclear. Here, 180 uridine diphosphate-dependent glycosyltransferases that may be involved in the biosynthesis of glycosylated secondary metabolites were identified from the National Center for Biotechnology Information public databases. Subsequently, CsUGT74Y1 was screened through phylogenetic analysis and gene expression profiling. Compositional and induced expression analyses revealed that CsUGT74Y1 was highly expressed in tea tender shoots and was induced under biotic and abiotic stress conditions. In vitro enzymatic assays revealed that rCsUGT74Y1 encoded a multifunctional UGT that catalyzed the glycosylation of flavonoids, phenolic acids, lignins, and auxins. Furthermore, CsUGT74Y1-overexpressing Arabidopsis thaliana exhibited enhanced growth and accumulation of flavonol and auxin glucosides. Our findings provide insights into identifying specific UGTs and demonstrate that CsUGT74Y1 is a multifunctional UGT that promotes plant development.

Biochemical Characterization of Parsley Glycosyltransferases Involved in the Biosynthesis of a Flavonoid Glycoside, Apiin

The flavonoid glycoside apiin (apigenin 7-O-[β-D-apiosyl-(1→2)-β-D-glucoside]) is abundant in apiaceous and asteraceous plants, including celery and parsley. Although several enzymes involved in apiin biosynthesis have been identified in celery, many of the enzymes in parsley (Petroselinum crispum) have not been identified. In this study, we identified parsley genes encoding the glucosyltransferase, PcGlcT, and the apiosyltransferase, PcApiT, that catalyze the glycosylation steps of apiin biosynthesis. Their substrate specificities showed that they were involved in the biosynthesis of some flavonoid 7-O-apiosylglucosides, including apiin. The expression profiles of PcGlcT and PcApiT were closely correlated with the accumulation of flavonoid 7-O-apiosylglucosides in parsley organs and developmental stages. These findings support the idea that PcGlcT and PcApiT are involved in the biosynthesis of flavonoid 7-O-apiosylglucosides in parsley. The identification of these genes will elucidate the physiological significance of apiin and the development of apiin production methods.

Pour some sugar on me: The diverse functions of phenylpropanoid glycosylation

The phenylpropanoid metabolism is the source of a vast array of specialized metabolites that play diverse functions in plant growth and development and contribute to all aspects of plant interactions with their surrounding environment. These compounds protect plants from damaging ultraviolet radiation and reactive oxygen species, provide mechanical support for the plants to stand upright, and mediate plant-plant and plant-microorganism communications. The enormous metabolic diversity of phenylpropanoids is further expanded by chemical modifications known as "decorative reactions", including hydroxylation, methylation, glycosylation, and acylation. Among these modifications, glycosylation is the major driving force of phenylpropanoid structural diversification, also contributing to the expansion of their properties. Phenylpropanoid glycosylation is catalyzed by regioselective uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs), whereas glycosyl hydrolases known as β-glucosidases are the major players in deglycosylation. In this article, we review how the glycosylation process affects key physicochemical properties of phenylpropanoids, such as molecular stability and solubility, as well as metabolite compartmentalization/storage and biological activity/toxicity. We also summarize the recent knowledge on the functional implications of glycosylation of different classes of phenylpropanoid compounds. A balance of glycosylation/deglycosylation might represent an essential molecular mechanism to regulate phenylpropanoid homeostasis, allowing plants to dynamically respond to diverse environmental signals.

Integrated multi-omic analysis reveals the cytokinin and sucrose metabolism-mediated regulation of flavone glycoside biosynthesis by MeJA exposure in Ficus pandurata Hance

Ficus pandurata Hance (FPH) holds a rich history as a traditional Chinese botanical remedy, utilized both as a culinary condiment and a medicinal intervention for diverse ailments. This study focuses on enhancing FPH's therapeutic potential by subjecting it to exogenous methyl jasmonate (MeJA) treatment, a strategy aimed at elevating the levels of active constituents to align with clinical and commercial requirements. Employing metabolomics, the impact of MeJA treatment on the lipid and flavonoid profiles of FPH leaves was investigated, revealing a marked increase in flavone glycosides, a subset of flavonoids. Investigation into the regulatory mechanism governing flavone glycoside biosynthesis uncovered elevated expression of structural genes associated with flavonoid production in response to MeJA exposure. Global endogenous hormone analysis pinpointed the selective activation of JA and cytokinin biosynthesis following MeJA treatment. Through a comprehensive integration of transcriptomic and metabolomic data, the cooperative stimulation of glucosyltransferase activity, alongside the JA and cytokinin signaling pathways, orchestrated by MeJA were explored. Furthermore, genes linked to sucrose metabolism exhibited heightened expression, concomitant with a noteworthy surge in antioxidant activity subsequent to MeJA treatment. These findings validate the augmentation of FPH leaf antioxidant capacity through MeJA intervention, while also offering profound insights into the regulatory role of MeJA in flavone glycoside biosynthesis, mediated by the interplay between cytokinin and sucrose metabolism pathways.

The apiosyltransferase celery UGT94AX1 catalyzes the biosynthesis of the flavone glycoside apiin

Apiose is a unique branched-chain pentose found in plant glycosides and a key component of the cell wall polysaccharide pectin and other specialized metabolites. More than 1,200 plant-specialized metabolites contain apiose residues, represented by apiin, a distinctive flavone glycoside found in celery (Apium graveolens) and parsley (Petroselinum crispum) in the family Apiaceae. The physiological functions of apiin remain obscure, partly due to our lack of knowledge on apiosyltransferase during apiin biosynthesis. Here, we identified UGT94AX1 as an A. graveolens apiosyltransferase (AgApiT) responsible for catalyzing the last sugar modification step in apiin biosynthesis. AgApiT showed strict substrate specificity for the sugar donor, UDP-apiose, and moderate specificity for acceptor substrates, thereby producing various apiose-containing flavone glycosides in celery. Homology modeling of AgApiT with UDP-apiose, followed by site-directed mutagenesis experiments, identified unique Ile139, Phe140, and Leu356 residues in AgApiT, which are seemingly crucial for the recognition of UDP-apiose in the sugar donor pocket. Sequence comparison and molecular phylogenetic analysis of celery glycosyltransferases suggested that AgApiT is the sole apiosyltransferase-encoding gene in the celery genome. Identification of this plant apiosyltransferase gene will enhance our understanding of the physioecological functions of apiose and apiose-containing compounds.

Artificial warming affects sugar signals and flavonoid accumulation to improve female willows' growth faster than males

Increasing global warming is severely affecting tree growth and development. However, research on the sex-specific responses of dioecious trees to warming is scarce. Here, male and female Salix paraplesia were selected for artificial warming (an increase of 4 °C relative to ambient temperature) to investigate the effects on morphological, physiological, biochemical and molecular responses. The results showed that warming significantly promoted the growth of female and male S. paraplesia, but females grew faster than males. Warming affected photosynthesis, chloroplast structures, peroxidase activity, proline, flavonoids, nonstructural carbohydrates (NSCs) and phenolic contents in both sexes. Interestingly, warming increased flavonoid accumulation in female roots and male leaves but inhibited it in female leaves and male roots. The transcriptome and proteome results indicated that differentially expressed genes and proteins were significantly enriched in sucrose and starch metabolism and flavonoid biosynthesis pathways. The integrative analysis of transcriptomic, proteomic, biochemical and physiological data revealed that warming changed the expression of SpAMY, SpBGL, SpEGLC and SpAGPase genes, resulting in the reduction of NSCs and starch and the activation of sugar signaling, particularly SpSnRK1s, in female roots and male leaves. These sugar signals subsequently altered the expression of SpHCTs, SpLAR and SpDFR in the flavonoid biosynthetic pathway, ultimately leading to the differential accumulation of flavonoids in female and male S. paraplesia. Therefore, warming causes sexually differential responses of S. paraplesia, with females performing better than males.

Genome-wide identification of UDP-glycosyltransferases in the tea plant (Camellia sinensis) and their biochemical and physiological functions

Tea (Camellia sinensis) has been an immensely important commercially grown crop for decades. This is due to the presence of essential nutrients and plant secondary metabolites that exhibit beneficial health effects. UDP-glycosyltransferases (UGTs) play an important role in the diversity of such secondary metabolites by catalysing the transfer of an activated sugar donor to acceptor molecules, and thereby creating a huge variety of glycoconjugates. Only in recent years, thanks to the sequencing of the tea plant genome, have there been increased efforts to characterise the UGTs in C. sinensis to gain an understanding of their physiological role and biotechnological potential. Based on the conserved plant secondary product glycosyltransferase (PSPG) motif and the catalytically active histidine in the active site, UGTs of family 1 in C. sinensis are identified here, and shown to cluster into 21 groups in a phylogenetic tree. Building on this, our current understanding of recently characterised C. sinensis UGTs (CsUGTs) is highlighted and a discussion on future perspectives made.

Flavonoids Are Intra- and Inter-Kingdom Modulator Signals

Flavonoids are a broad class of secondary metabolites with multifaceted functionalities for plant homeostasis and are involved in facing both biotic and abiotic stresses to sustain plant growth and health. Furthermore, they were discovered as mediators of plant networking with the surrounding environment, showing a surprising ability to perform as signaling compounds for a multitrophic inter-kingdom level of communication that influences the plant host at the phytobiome scale. Flavonoids orchestrate plant-neighboring plant allelopathic interactions, recruit beneficial bacteria and mycorrhizal fungi, counteract pathogen outbreak, influence soil microbiome and affect plant physiology to improve its resilience to fluctuating environmental conditions. This review focuses on the diversified spectrum of flavonoid functions in plants under a variety of stresses in the modulation of plant morphogenesis in response to environmental clues, as well as their role as inter-kingdom signaling molecules with micro- and macroorganisms. Regarding the latter, the review addresses flavonoids as key phytochemicals in the human diet, considering their abundance in fruits and edible plants. Recent evidence highlights their role as nutraceuticals, probiotics and as promising new drugs for the treatment of several pathologies.

Tea (Camellia sinensis): A Review of Nutritional Composition, Potential Applications, and Omics Research

Tea (Camelliasinensis) is the world’s most widely consumed non-alcoholic beverage with essential economic and health benefits since it is an excellent source of polyphenols, catechins, amino acids, flavonoids, carotenoids, vitamins, and polysaccharides. The aim of this review is to summarize the main secondary metabolites in tea plants, and the content and distribution of these compounds in six different types of tea and different organs of tea plant were further investigated. The application of these secondary metabolites on food processing, cosmetics industry, and pharmaceutical industry was reviewed in this study. With the rapid advancements in biotechnology and sequencing technology, omics analyses, including genome, transcriptome, and metabolome, were widely used to detect the main secondary metabolites and their molecular regulatory mechanisms in tea plants. Numerous functional genes and regulatory factors have been discovered, studied, and applied to improve tea plants. Research advances, including secondary metabolites, applications, omics research, and functional gene mining, are comprehensively reviewed here. Further exploration and application trends are briefly described. This review provides a reference for basic and applied research on tea plants.

Two UDP-Glycosyltransferases Catalyze the Biosynthesis of Bitter Flavonoid 7-O-Neohesperidoside through Sequential Glycosylation in Tea Plants

Flavonoid glycosides are typical bitter and astringent tasting compounds that contribute to the taste of tea beverages. However, the genes that contribute to the biosynthesis of bitter compounds (e.g., flavanone 7-O-neohesperidoside) in tea plants have yet to be identified. In this study, we identified 194 UDP-glycosyltransferases (UGTs) from the tea transcriptome database. Among them, two genes, CsUGT75L12 and CsUGT79B28, encoding flavonoid 7-O-glycosyltransferase and 7-O-glucoside(1→2)rhamnosyltransferase, respectively, were identified from Camellia sinensis. In vitro, the purified recombinant enzyme rCsUGT75L12 specifically transports the glucose unit from UDP-glucose to the 7-OH position of the flavonoid to produce the respective 7-O-glucoside. rCsUGT79B28 regiospecifically transfers a rhamnose unit from UDP-rhamnose to the 2″-OH position of flavonoid 7-O-glucosides to produce flavonoid 7-O-di-glycosides. Additionally, the expression profiles of the two CsUGTs were correlated with the accumulation patterns of 7-O-glucoside and 7-O-neohesperidoside, respectively, in tea plants. These results indicated that the two CsUGTs are involved in the biosynthesis of bitter flavonoid 7-O-neohesperidoside through the sequential glucosylation and rhamnosylation of flavonoids in C. sinensis. Taken together, our findings provided not only molecular insights into flavonoid di-glycoside metabolism in tea plants but also crucial molecular markers for controlling the bitterness and astringent taste of tea.

Metabolomics profile responses to changing environments in a common bean (Phaseolus vulgaris L.) germplasm collection

Metabolomics is one of the most powerful -omics to assist plant breeding. Despite the recognized genetic diversity in Portuguese common bean germplasm, details on its metabolomics profiles are still missing. Aiming to promote their use and to understand the environment's effect in bean metabolomics profiles, 107 Portuguese common bean accessions, cropped under contrasting environments, were analyzed using spectrophotometric, untargeted and targeted mass spectrometry approaches. Although genotype was the most relevant factor on bean metabolomics profile, a clear genotype × environment interaction was also detected. Multivariate analysis highlighted, on the heat-stress environment, the existence of higher levels of salicylic acid, and lower levels of triterpene saponins. Three clusters were defined within each environment. White accessions presented the lowest content and the colored ones the highest levels of prenol lipids and flavonoids. Sources of interesting metabolomics profiles are now identified for bean breeding, focusing either on local or on broad adaptation.

Screening the Key Region of Sunlight Regulating the Flavonoid Profiles of Young Shoots in Tea Plants (Camellia sinensis L.) Based on a Field Experiment

Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes.

Phenolic, Carotenoid and Saccharide Compositions of Vietnamese Camellia sinensis Teas and Herbal Teas

Tea (Camellia sinensis) and herbal tea have been recognized as rich sources of bioactive constituents with the ability to exert antioxidant actions. The aims of this study were to analyze phenolic, carotenoid and saccharide contents in a set of Vietnamese tea and herbal tea and compare the results with those of green and black teas marketed in the U.S. In total, 27 phenolics, six carotenoids and chlorophylls, and three saccharides were quantitatively identified. Catechins, quercetin glycosides and chlorogenic acid were the predominating phenolics in the teas, with the concentrations following the order: jasmine/green teas > oolong tea > black tea. Lutein was the dominant carotenoid in the teas and its concentrations were generally found to be higher in the jasmine and green teas than in the oolong and black teas. The study showed that the green teas originating in Vietnam had much higher levels of phenolics and carotenoids than their counterparts stemming from another country. The application of partial least squares discriminant analysis (PLS-DA) as a chemometric tool was able to differentiate phenolic profiles between methanolic extracts and tea infusions. Through principal component analysis (PCA), the similarities and dissimilarities among the jasmine, green, oolong, black teas and herbal teas were depicted.

Molecular regulation of anthocyanin discoloration under water stress and high solar irradiance in pluckable shoots of purple tea cultivar

During water-deficit stress, antioxidant enzymes use anthocyanin molecules as co-substrates to scavenge for reactive oxygen species leading to reduced anthocyanin content and ultimately loss of purple leaf pigmentation in tea. Anthocyanins are an important class of flavonoids responsible for liquor color and market acceptability of processed tea from the anthocyanin-rich purple tea cultivar 'TRFK 306'. However, the color in pluckable shoots fade and turn green during the dry and hot season, before rapidly reverting back to purple when weather is favorably wet and cool/cold. Our study revealed that loss of purple leaf pigmentation correlated well with reduced precipitation, high soil water-deficit, increased intensity and duration of sunlight and temperature. Richly purple pigmented leaves harvested during the cool, wet conditions recorded significantly higher anthocyanin content compared to faded samples harvested during the dry season. Similarly, individual anthocyanins were affected by seasonal changes with malvidin being the most abundant. Comparative transcriptomics of two RNA-seq libraries, dry/discolored and wet/colored seasons, revealed depression of most metabolic processes related to anthocyanin accumulation in dry conditions. Specifically, transcripts encoding pathway regulators, MYB-bHLH-WD40 (MBW) complex, were repressed possibly contributing to the suppression of late biosynthetic genes of the pathway. Further, suppression of anthocyanin transport genes could be linked to reduced accumulation of anthocyanin in the vacuole during the dry season. However, slight increase in expression of some transporter and reactive oxygen species (ROS) antioxidant genes in the discolored leaf suggests non-enzymatic degradation of anthocyanin, ultimately leading to loss of purple color during the dry season. Based on increased expression of ROS antioxidant genes (especially catalase and superoxide dismutase) in the discolored leaf, we speculate that anthocyanins are used as co-substrates by antioxidant enzymes to scavenge for ROS (especially hydrogen peroxide) that escape from organelles, leading to reduced anthocyanins and loss of pigmentation during the dry season.

Effects of Light Intensity and Spectral Composition on the Transcriptome Profiles of Leaves in Shade Grown Tea Plants (Camellia sinensis L.) and Regulatory Network of Flavonoid Biosynthesis

Black net shade treatment attenuates flavonoid biosynthesis in tea plants, while the effect of light quality is still unclear. We investigated the flavonoid and transcriptome profiles of tea leaves under different light conditions, using black nets with different shade percentages, blue, yellow and red nets to alter the light intensity and light spectral composition in the fields. Flavonol glycosides are more sensitive to light intensity than catechins, with a reduction percentage of total flavonol glycosides up to 79.6% compared with 38.7% of total catechins under shade treatment. A total of 29,292 unigenes were identified, and the KEGG result indicated that flavonoid biosynthesis was regulated by both light intensity and light spectral composition while phytohormone signal transduction was modulated under blue net shade treatment. PAL, CHS, and F3H were transcriptionally downregulated with light intensity. Co-expression analysis showed the expressions of key transcription factors MYB12, MYB86, C1, MYB4, KTN80.4, and light signal perception and signaling genes (UVR8, HY5) had correlations with the contents of certain flavonoids (p < 0.05). The level of abscisic acid in tea leaves was elevated under shade treatment, with a negative correlation with TFG content (p < 0.05). This work provides a potential route of changing light intensity and spectral composition in the field to alter the compositions of flavor substances in tea leaves and regulate plant growth, which is instructive to the production of summer/autumn tea and matcha.

Structure-function relationship of terpenoid glycosyltransferases from plants

Covering: up to 2021Terpenoids are physiologically active substances that are of great importance to humans. Their physicochemical properties are modified by glycosylation, in terms of polarity, volatility, solubility and reactivity, and their bioactivities are altered accordingly. Significant scientific progress has been made in the functional study of glycosylated terpenes and numerous plant enzymes involved in regio- and enantioselective glycosylation have been characterized, a reaction that remains chemically challenging. Crucial clues to the mechanism of terpenoid glycosylation were recently provided by the first crystal structures of a diterpene glycosyltransferase UGT76G1. Here, we review biochemically characterized terpenoid glycosyltransferases, compare their functions and primary structures, discuss their acceptor and donor substrate tolerance and product specificity, and elaborate features of the 3D structures of the first terpenoid glycosyltransferases from plants.

Integration of Metabolome and Transcriptome Reveals the Relationship of Benzenoid-Phenylpropanoid Pigment and Aroma in Purple Tea Flowers

Tea (Camellia sinensis) flowers are normally white, even though the leaves could be purple. We previously discovered a specific variety with purple leaves and flowers. In the face of such a phenomenon, researchers usually focus on the mechanism of color formation but ignore the change of aroma. The purple tea flowers contain more anthocyanins, which belong to flavonoids. Meanwhile, phenylalanine (Phe), derived from the shikimate pathway, is a precursor for both flavonoids and volatile benzenoid-phenylpropanoids (BPs). Thus, it is not clear whether the BP aroma was attenuated for the appearance of purple color. In this study, we integrated metabolome and transcriptome of petals of two tea varieties, namely, Zijuan (ZJ) with white flowers and Baitang (BT) with purple flowers, to reveal the relationship between color (anthocyanins) and aroma (volatile BPs). The results indicated that in purple petals, the upstream shikimate pathway promoted for 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHPS) was elevated. Among the increased anthocyanins, delphinidin-3-O-glucoside (DpG) was extremely higher; volatile BPs, including benzyl aldehyde, benzyl alcohol, acetophenone (AP), 1-phenylethanol, and 2-phenylethanol, were also enhanced, and AP was largely elevated. The structural genes related to the biosynthesis of volatile BPs were induced, while the whole flavonoid biosynthesis pathway was downregulated, except for the genes flavonoid 3'-hydroxylase (F3'H) and flavonoid 3',5'-hydroxylase (F3'5'H), which were highly expressed to shift the carbon flux to delphinidin, which was then conjugated to glucoside by increased bronze-1 (BZ1) (UDP-glucose: flavonoid 3-O-glucosyltransferase) to form DpG. Transcription factors (TFs) highly related to AP and DpG were selected to investigate their correlation with the differentially expressed structural genes. TFs, such as MYB, AP2/ERF, bZIP, TCP, and GATA, were dramatically expressed and focused on the regulation of genes in the upstream synthesis of Phe (DAHPS; arogenate dehydratase/prephenate dehydratase) and the synthesis of AP (phenylacetaldehyde reductase; short-chain dehydrogenase/reductase), Dp (F3'H; F3'5'H), and DpG (BZ1), but inhibited the formation of flavones (flavonol synthase) and catechins (leucoanthocyanidin reductase). These results discovered an unexpected promotion of volatile BPs in purple tea flowers and extended our understanding of the relationship between the BP-type color and aroma in the tea plant.

Transcriptomic and Translatomic Analyses Reveal Insights into the Developmental Regulation of Secondary Metabolism in the Young Shoots of Tea Plants (Camellia sinensis L.)

Accumulation of secondary metabolites in the young shoots of tea plants is developmentally modulated, especially flavonoids. Here, we investigate the developmental regulation mechanism of secondary metabolism in the developing leaves of tea plants using an integrated multiomic approach. For the pair of Leaf2/Bud, the correlation coefficient of the fold change of mRNA and RPFs abundances involved in flavonoid biosynthesis was 0.9359, being higher than that of RPFs and protein (R² = 0.6941). These correlations were higher than the corresponding correlation coefficients for secondary metabolisms and genome-wide scale. Metabolomic analysis demonstrates that the developmental modulations of the structural genes for flavonoid biosynthesis-related pathways align with the concentration changes of catechin and flavonol glycoside groups. Relatively high translational efficiency (TE > 2) was observed in the four flavonoid structural genes (chalcone isomerase, dihydroflavonol 4-reductase, anthocyanidin synthase, and flavonol synthase). In addition, we originally provided the information on identified small open reading frames (small ORFs) and main ORFs in tea leaves and elaborated that the presence of upstream ORFs may have a repressive effect on the translation of downstream ORFs. Our data suggest that transcriptional regulation coordinates with translational regulation and may contribute to the elevation of translational efficiencies for the structural genes involved in the flavonoid biosynthesis pathways during tea leaf development.

Flavonols regulate root hair development by modulating accumulation of reactive oxygen species in the root epidermis

Reactive oxygen species (ROS) are signaling molecules produced by tissue-specific respiratory burst oxidase homolog (RBOH) enzymes to drive development. In Arabidopsis thaliana, ROS produced by RBOHC was previously reported to drive root hair elongation. We identified a specific role for one ROS, H₂O₂, in driving root hair initiation and demonstrated that localized synthesis of flavonol antioxidants control the level of H₂O₂ and root hair formation. Root hairs form from trichoblast cells that express RBOHC and have elevated H₂O₂ compared with adjacent atrichoblast cells that do not form root hairs. The flavonol-deficient tt4 mutant has elevated ROS in trichoblasts and elevated frequency of root hair formation compared with the wild type. The increases in ROS and root hairs in tt4 are reversed by genetic or chemical complementation. Auxin-induced root hair initiation and ROS accumulation were reduced in an rbohc mutant and increased in tt4, consistent with flavonols modulating ROS and auxin transport. These results support a model in which localized synthesis of RBOHC and flavonol antioxidants establish patterns of ROS accumulation that drive root hair formation.

Effects of Different Drying Methods on Untargeted Phenolic Metabolites, and Antioxidant Activity in Chinese Cabbage (Brassica rapa L. subsp. chinensis) and Nightshade (Solanum retroflexum Dun.)

Chinese cabbage (Brassica rapa L. subsp. chinensis) and Nightshade (Solanum retroflexum are popular traditional leafy vegetables consumed predominantly by rural Africans. Sun drying is adopted as a traditional method of postharvest preservation to store theses leaves during off seasons. The influence of different types of postharvest processing treatments, such as conventional oven drying, solar cabinet drying, sun drying and freeze drying, on the changes on colour properties and antioxidant components were investigated. Freeze-drying retained the ascorbic acid content, antioxidant activities, total chlorophyll content, green colour by reducing the colour difference (∆E). With regard to Chinese cabbage and Nightshade leaves, sun and microwave drying respectively had the most negative impact on all the identified phenolic compounds. The OPLS-DA and the UPLC–QTOF/MS and chemometric approach showed kaempferol-3-O-sophoroside, kaempferol-3-sophorotrioside-7-glucoside and hydroxyoctadecenedioic acid as the markers responsible for the separation of sun-dried samples from the other drying treatments in Chinese cabbage. Sinapoyl malate was not detected in sun-dried samples. Caffeoylmalic acid was identified as the marker compound to separate the other drying treatments from the microwave dried samples of Nightshade leaves. Trihydroxyoctadecadiene derivative and hydroxyoctadecanedioic acid were detected in microwaved samples. Due to the cost effectiveness, solar dryer cabinet treatment was recommended for drying both vegetables. The proximate analysis of solar dried functional powder of Chinese cabbage and Nightshade vegetables demonstrated higher contents of protein and dietary fibre.