Cloning of beta-primeverosidase from tea leaves, a key enzyme in tea aroma formation

Another inner truth of shaking: Water migration and transformation-advanced physicochemical alterations in tea leaves

Shaking, essential in oolong tea production, is becoming an innovative method to impart floral fragrance. Research on shaking primarily concentrates on biological underpinnings, including modifications in gene expression and stress-triggered enzymatic catalysis, and consequent physicochemical properties. Water phase and distribution, reshaped by shaking and affected the biological and physicochemical alterations of tea leaves, is always ignored. This work utilized TEM, LF-NMR, UPLC-QqQ-MS, and GC-TOF-MS to explore physicochemical alterations during shaking. Results revealed shaking induced stomatal opening, water migration from stems to leaf veins, and a reduction in free water, transformed into bound water. Mechanical stimulation disrupted cell microstructures, including vacuoles, chloroplasts, and cell walls, releasing precursors and enzyme substrates. Shaking triggered intracellular physicochemical reactions that decreased polyphenols, amino acids, chlorophyll, and carotenoids, while increasing organic acids and sugars. Also catalyzed the synthesis of aromatic compounds like (E)-nerolidol, β-ionone epoxide, and α-farnesene, shaping the floral-fruity aroma and mellow taste of tea.

Gene isolation and enzymatic characterization of UDP-glycosyltransferases of terpene glucoside biosynthesis involved in linalyl-glycoside accumulation in Coffea arabica

Terpenes, one of the secondary metabolites produced by plants, have diverse physiological functions. They are volatile compounds with physiological bioactivities (e.g., insect repellent, attracting enemies, and interacting with other plants). Terpenoids are also essential for flavor and aroma in plant-derived foods. In coffee, its aroma decides the value of coffee beans. Linalool, one of the volatile terpene compounds, is dominant in the coffee aroma. Coffee, with its good flavor and aroma, has high demand worldwide. Because terpenoids generally accumulate as glycosides in plant cells, glycosylation is catalyzed by UDP-glycosyltransferases (UGTs). Two linalyl-diglycosides have been identified: terpenoids reflected as necessary for coffee flavor. However, these UGTs and their action mechanisms are unknown in the Coffea genus. To obtain knowledge of terpene UGTs and elucidate the mechanism of terpene glycosylation in coffee, this study isolated terpene UGT genes and analyzed their functions. In silico screening based on the sequence of UGT85K11, which catalyzes terpene glycosylation from Camellia sinensis, was performed to obtain sequence information on five candidate UGT genes (CaUGT4, CaUGT5, CaUGT10, CaUGT15, and CaUGT20). These genes were isolated by reverse transcription-polymerase chain reaction, and the recombinant enzymes were produced with the Escherichia coli expression system. In functional analysis using radioisotopes, CaUGT4 showed critical activity against linalool, which had a higher affinity for its substrate than that of UGT85A84 from Osmanthus fragrans. Liquid chromatography-tandem mass spectrometry also revealed that CaUGT4 mainly produces linalyl glucoside. In this study, the first linalyl UGT was isolated from coffee. These findings can be used to elucidate the fundamental mechanism of the chemical defense in plants and apply aroma precursors for the plant-derived food industry in the future.

Genome-wide identification of glycoside hydrolase family 1 members reveals GeBGL1 and GeBGL9 for degrading gastrodin in Gastrodia elata

KEY MESSAGE

We revealed the intrinsic transformation molecular mechanism of gastrodin by two β-d-glucosidases (GeBGL1 and GeBGL9) during the processing of Gastrodia elata. Gastrodia elata is a plant resource with medicinal and edible functions, and its active ingredient is gastrodin. However, the intrinsic transformation molecular mechanism of gastrodin in G. elata has not been verified. We speculated that β-d-glucosidase (BGL) may be the key enzymes hydrolyzing gastrodin. Here, we identified 11 GeBGL genes in the G. elata genome. These genes were unevenly distributed on seven chromosomes. These GeBGL proteins possessed motifs necessary for catalysis, namely, TF(I/M/L)N(T)E(Q)P and I(V/L)T(H/S)ENG(S). These GeBGLs were divided into five subgroups together with homologous genes from Arabidopsis thaliana, rice, and maize. Quantitative real-time PCR analysis showed GeBGL genes expression was tissue-specific. Gene cloning results showed two mutation sites in the GeBGL1 gene compared with the reference genome. And, the GeBGL4 gene has two indel fragments, which resulted in premature termination of translation and seemed to turn into a pseudogene. Furthermore, protein expression and enzyme activity results proved that GeBGL1 and GeBGL9 have the activity of hydrolyzing gastrodin into 4-hydroxybenzyl alcohol. This study revealed the function of β-d-glucosidase in degrading active compounds during the G. elata processing for medicinal purposes. These results offer a theoretical foundation for elevating the standard and enhancing the quality of G. elata production.

Pruned tea biomass plays a significant role in functional food production: A review on characterization and comprehensive utilization of abandon-plucked fresh tea leaves

Tea is the second largest nonalcoholic beverage in the world due to its characteristic flavor and well-known functional properties in vitro and in vivo. Global tea production reaches 6.397 million tons in 2022 and continues to rise. Fresh tea leaves are mainly harvested in spring, whereas thousands of tons are discarded in summer and autumn. Herein, pruned tea biomass refers to abandon-plucked leaves being pruned in the non-plucking period, especially in summer and autumn. At present, no relevant concluding remarks have been made on this undervalued biomass. This review summarizes the seasonal differences of intrinsic metabolites and pays special attention to the most critical bioactive and flavor compounds, including polyphenols, theanine, and caffeine. Additionally, meaningful and profound methods to transform abandon-plucked fresh tea leaves into high-value products are reviewed. In summer and autumn, tea plants accumulate much more phenols than in spring, especially epigallocatechin gallate (galloyl catechin), anthocyanins (catechin derivatives), and proanthocyanidins (polymerized catechins). Vigorous carbon metabolism induced by high light intensity and temperature in summer and autumn also accumulates carbohydrates, such as soluble sugars and cellulose. The characteristics of abandon-plucked tea leaves make them not ideal raw materials for tea, but suitable for novel tea products like beverages and food ingredients using traditional or hybrid technologies such as enzymatic transformation, microbial fermentation, formula screening, and extraction, with the abundant polyphenols in summer and autumn tea serving as prominent flavor and bioactive contributors.

Selenosugar, selenopolysaccharide, and putative selenoflavonoid in plants

Selenium (Se) is a naturally occurring essential micronutrient that is required for human health. Selenium supports cellular antioxidant defense and possesses bioeffects such as anti-inflammation, anti-cancer, anti-diabetic, and cardiovascular and liver protective effects arising from Se-enhanced cellular antioxidant activity. Past studies on Se have focused on elucidating Se speciation in foods, biofortification strategies to produce Se-enriched foods to address Se deficiency in the population, and the biochemical activities of Se in health. The bioavailability and toxicity of Se are closely correlated to its chemical forms and may exhibit varying effects on body physiology. Selenium exists in inorganic and organic forms, in which inorganic Se such as sodium selenite and sodium selenate is more widely available. However, it is a challenge for safe and effective supplementation considering inorganic Se low bioavailability and high cytotoxicity. Organic Se, by contrast, exhibits higher bioavailability and lower toxicity and has a more diverse composition and structure. Organic Se exists as selenoamino acids and selenoproteins, but recent research has provided evidence that it also exists as selenosugars, selenopolysaccharides, and possibly as selenoflavonoids. Different food categories contain various Se compounds, and their Se profiles vary significantly. Therefore, it is necessary to delineate Se speciation in foods to understand their impact on health. This comprehensive review documents our knowledge of the recent uncovering of the existence of selenosugars and selenopolysaccharides and the putative evidence for selenoflavonoids. The bioavailability and bioactivities of these food-derived organic Se compounds are highlighted, in addition to their composition, structural features, and structure-activity relationships.

A β-Primeverosidase-like Enzyme in Soybean [Glycine max (L.) Merr] Hypocotyls: Specificity toward 1-Octen-3-yl and 3-Octanyl β-Primeverosides

A novel β-primeverosidase-like enzyme, originating from the hypocotyl of soybeans, was isolated and characterized. This enzyme, with an estimated molecular weight of 44 kDa, was identified as a monomer and exhibited peak activity at 55 °C and pH 5.5. It demonstrated a specific and efficient hydrolysis of 1-octen-3-yl β-primeveroside (1-octen-3-yl prim) and 3-octanyl β-primeveroside (3-octanyl prim) but did not act on glucopyranosides. Mn2+ significantly enhanced its activity, while Zn2+, Cu2+, and Hg2+ exerted inhibitory effects. Kinetic analysis revealed a higher hydrolytic capacity toward 1-octen-3-yl prim. Partial amino acid sequences were determined and the N-terminal amino acid sequence was determined to be AIVAYAL ALSKRAIAAQ. The binding energy and binding free energy between the β-primeverosidase enzyme and its substrates were observed to be higher than that of β-glucosidase, thus validating its superior hydrolysis efficiency. Hydrogen bonds and hydrophobic interactions were the main types of interactions between β-primeverosidase enzyme and 1-octen-3-yl prim and 3-octanyl prim, involving amino acid residues such as GLU-470, TRP-463, GLU-416, TRP-471, GLN-53, and GLN-477 (hydrogen bonds) and PHE-389, TYR-345, LEU-216, and TYR-275 (hydrophobic interactions). This study contributes to the application of a β-primeverosidase-like enzyme in improving the release efficiency of glycosidically conjugated flavor substances.

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.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

Rutinosidase and other diglycosidases: Rising stars in biotechnology

Diglycosidases are a special class of glycosidases (EC 3.2.1) that catalyze the separation of intact disaccharide moieties from the aglycone part. The main diglycosidase representatives comprise rutinosidases that cleave rutinose (α-l-Rha-(1-6)-β-d-Glc) from rutin or other rutinosides, and (iso)primeverosidases processing (iso)primeverosides (d-Xyl-(1-6)-β-d-Glc), but other activities are known. Notably, some diglycosidases may be ranked as monoglucosidases with enlarged substrate specificity. Diglycosidases are found in various microorganisms and plants. Diglycosidases are used in the food industry for aroma enhancement and flavor modification. Besides their hydrolytic activity, they also possess pronounced synthetic (transglycosylating) capabilities. Recently, they have been demonstrated to glycosylate various substrates in a high yield, including peculiar species like inorganic azide or carboxylic acids, which is a unique feature in biocatalysis. Rhamnose-containing compounds such as rutinose are currently receiving increased attention due to their proven activity in anti-cancer and dermatological experimental studies. This review demonstrates the vast and yet underrated biotechnological potential of diglycosidases from various sources (plant, microbial), and reveals perspectives on the use of these catalysts as well as of their products in biotechnology.

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.

Spectroscopic studies on a natural biomarker for the identification of origin and quality of tea extracts for the development of a portable and field deployable prototype

Even in the era of smart technologies and IoT enabled devices, tea testing technique continues to be a person specific subjective task. In this study, we have employed optical spectroscopy-based detection technique for the quantitative validation of tea quality. In this regard, we have employed the external quantum yield of quercetin at 450 nm (λ_ex = 360 nm), which is an enzymatic product generated by the activity of β-glucosidase on rutin, a naturally occurring metabolite responsible for tea-flavour (quality). We have found that a specific point in a graph representing Optical Density and external Quantum Yield as independent and dependent variables respectively of an aqueous tea extract objectively indicates a specific variety of the tea. A variety of tea samples from various geographical origin have been analysed with the developed technique and found to be useful for the tea quality assessment. The principal component analysis distinctly showed the tea samples originated from Nepal and Darjeeling having similar external quantum yield, while the tea samples from Assam region had a lower external quantum yield. Furthermore, we have employed experimental and computational biology techniques for the detection of adulteration and health benefit of the tea extracts. In order to assure the portability/field use, we have also developed a prototype which confirms the results obtained in the laboratory. We are of the opinion that the simple user interface and almost zero maintenance cost of the device will make it useful and attractive with minimally trained manpower at low resource setting.

Chemical and Quality Analysis of Beauty Tea Processed from Fresh Leaves of Tieguanyin Variety with Different Puncturing Degrees

Beauty tea with special flavor can be affected by the degree of leafhopper puncturing. The present research adopted widely targeted metabolomics to analyze the characteristic metabolites of fresh tea leaves and beauty tea with different degrees of leafhopper puncturing. Low-puncturing beauty tea (LPBT) exhibited a superior quality. Altogether, 95 and 65 differential metabolites, including tea polyphenols, saccharides, and lipids, were identified from fresh leaves and beauty tea, respectively. The partial least squares regression (PLSR) analysis results showed that isomaltulose, theaflavic acid, and ellagic acid, may be the characteristic metabolites that form the different taste outlines of beauty tea. Based on odor activity values (OAVs) and partial least squares discriminant analysis (PLS-DA), dihydrolinalool and cis-linalool oxide were identified as characteristic volatile components, which may be essential for the formation of the different aroma characteristic of beauty tea. The results provide a theoretical basis for selecting raw materials, performing quality research, and developing beauty tea industrially.

Acuminosylation of Tyrosol by a Commercial Diglycosidase

A commercial glycosidase mixture obtained from Penicillium multicolor (Aromase H2) was found to comprise a specific diglycosidase activity, β-acuminosidase, alongside undetectable levels of β-apiosidase. The enzyme was tested in the transglycosylation of tyrosol using 4-nitrophenyl β-acuminoside as the diglycosyl donor. The reaction was not chemoselective, providing a mixture of Osmanthuside H and its counterpart regioisomer 4-(2-hydroxyethyl)phenyl β-acuminoside in 58% yield. Aromase H2 is therefore the first commercial β-acuminosidase which is also able to glycosylate phenolic acceptors.

Identification of a tomato UDP-arabinosyltransferase for airborne volatile reception

Volatiles from herbivore-infested plants function as a chemical warning of future herbivory for neighboring plants. (Z)-3-Hexenol emitted from tomato plants infested by common cutworms is taken up by uninfested plants and converted to (Z)-3-hexenyl β-vicianoside (HexVic). Here we show that a wild tomato species (Solanum pennellii) shows limited HexVic accumulation compared to a domesticated tomato species (Solanum lycopersicum) after (Z)-3-hexenol exposure. Common cutworms grow better on an introgression line containing an S. pennellii chromosome 11 segment that impairs HexVic accumulation, suggesting that (Z)-3-hexenol diglycosylation is involved in the defense of tomato against herbivory. We finally reveal that HexVic accumulation is genetically associated with a uridine diphosphate-glycosyltransferase (UGT) gene cluster that harbors UGT91R1 on chromosome 11. Biochemical and transgenic analyses of UGT91R1 show that it preferentially catalyzes (Z)-3-hexenyl β-D-glucopyranoside arabinosylation to produce HexVic in planta.

Application of Aroma Precursors in Food Plant Raw Materials: Biotechnological Aspect

The article is devoted to the analysis of the main factors accompanying the use of aroma precursors, in particular, of a lipid nature, in food raw materials. The prerequisites for the impact on the precursors of aroma with the help of plant enzymes are given. The purpose of the article is to analyze the biotechnological aspect, which is based on enzymatic reactions with aroma precursors and enzymes of plant origin. Features of the mechanism of action of lipid precursors are highlighted, their diversity causing various characteristic reactions is analyzed, and possible end products of reactions with certain odors are noted. The attention is paid to the issue of the status of the naturalness of flavor precursors in food products, which varies in different countries. A scheme of factors influencing the formation of aroma from lipid precursors has been developed. The influence of pigments of carotenoid nature on the aroma is considered, namely: examples of instantaneous change of watermelon aroma to pumpkin one due to isomerization of carotenoids are given. The main factors of enzymatic formation of aroma from precursors of polyunsaturated fatty acids for their effective use by creating micromicelles are summarized. A way to overcome the barrier of interaction between lipid precursors of a hydrophobic nature and hydrophilic enzymes has been substantiated. It is proposed to accelerate enzymatic reactions under in vitro conditions and use the vacuum effect to overcome the barrier between enzymes and precursors. To explain the effect of vacuum in a system with enzymes, ideas about disjoining pressure and the reasonable expediency of its use are considered. A schematic process flow diagram for the restoration of aroma lost during the technological processing of raw materials is given; it demonstrates the factors for ensuring interfacial activation conditions for enzymes and aroma precursors.

United States tea: A synopsis of ongoing tea research and solutions to United States tea production issues

Tea is a steeped beverage made from the leaves of Camellia sinensis. Globally, this healthy, caffeine-containing drink is one of the most widely consumed beverages. At least 50 countries produce tea and most of the production information and tea research is derived from international sources. Here, we discuss information related to tea production, genetics, and chemistry as well as production issues that affect or are likely to affect emerging tea production and research in the United States. With this review, we relay current knowledge on tea production, threats to tea production, and solutions to production problems to inform this emerging market in the United States.

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.

Apiose-Relevant Glycosidases

Apiose is a branched pentose naturally occurring either as a component of the plant cell wall polysaccharides or as a sugar moiety present in numerous plant secondary metabolites such as flavonoid and phenylethanoid glycosides, substrates in plant defense systems or as glycosylated aroma precursors. The enzymes catalyzing hydrolysis of such apiosylated substances (mainly glycosidases specific towards apiose or acuminose) have promising applications not only in hydrolysis (flavor development), but potentially also in the synthesis of apiosides and apioglucosides with pharmaceutical relevance. This review summarizes the actual knowledge of glycosidases recognizing apiose and their potential application in biocatalysis.

Integrated metabolic phenotypes and gene expression profiles revealed the effect of spreading on aroma volatiles formation in postharvest leaves of green tea

Spreading is an indispensable process in the aroma formation of premium green tea. In this study, volatile metabolomics and transcriptomics were performed for three tea plant cultivars to investigate the mechanism of changes occurring in volatile compounds during green tea spreading. The content of primary aroma compounds significantly increased after spreading, the Wickremasinghe-Yamanishi ratio decreased and the Owuor's flavor index increased with the extension of spreading time, and the degree of aroma production was genotype-dependent. Volatile terpenes and fatty acid-derived volatiles were the principal aroma volatiles that accumulated during the spreading of green tea, and the trends of their changes were consistent with the expression pattern of related synthesis pathway genes, indicating that they were primarily derived from de novo synthesis rather than glycoside hydrolysis. Two co-expression networks that were highly correlated with variations in the volatile component contents during the spreading process were identified via WGCNA. Our results provide insights into spreading that can be considered to improve the quality of green tea.

VqBGH40a isolated from Chinese wild Vitis quinquangularis degrades trans-piceid and enhances trans-resveratrol

Resveratrol (3,5,4'-trihydroxy-stilbene) is a phytoalexin that can prevent plants from pathogen attacks. Piceid is the glycosylation product of resveratrol and the main storage form of stilbenes in grapevines. Here, we reported the function of a β-glycoside hydrolase gene, VqBGH40a, from the Chinese wild grapevine Vitis quinquangularis accession Danfeng-2 in the regulation of plant resistance to powdery mildew (Uncinula necator). VqBGH40a belonging to β-glycoside hydrolase family 1 encoded 506 amino acids and was located on the cytomembrane. Its optimal induction condition was 28 or 30℃, for 4 h, with 0.1 mM IPTG in a prokaryotic expression system. Enzyme activity detection showed that purified VqBGH40a could hydrolyze trans-piceid to form trans-resveratrol in vitro. VqBGH40a was transiently overexpressed in Danfeng-2 leaves and then artificially inoculated with powdery mildew showed that VqBGH40a protein could hydrolyze trans-piceid in vivo. Additionally, a comparative family analysis between VqBGH40a and 38 VviBGHs was performed. Overall, these results demonstrate that VqBGH40a can hydrolyze trans-piceid, enhance trans-resveratrol content, and participate in the defense mechanism of grapevine against powdery mildew.

Tissue-Dependent Variation Profiles of Tea Quality-Related Metabolites in New Shoots of Tea Accessions

Several metabolites define tea quality in new tea shoots composed of leaf and stem. To improve tea quality for breeding, it is important to understand the tissue-dependent genetic mechanisms and metabolic network responsible for the profile of tea quality-related metabolites. We analyzed the volatiles and specialized metabolites as the tea quality-related metabolites in leaves and stems of new shoots in 30 tea accessions to understand the tissue variation and network between tea quality-related metabolites. Our results provided the tissue-dependent variation network in the tea quality-related metabolites, including volatiles in new leaves and stems in tea accessions. Each volatile content in tea accessions showed the coefficient of variation ranging from 58.7 to 221.9% and 54.2 to 318.3% in new leaves and new stems, respectively. The accumulation pattern of tea quality-related metabolites in new leaves and stems varied depending on the accession. When comparing tea genetic populations, the profile of tea quality-related metabolites of new leaves, but not new stems, was the key to distinguishing tea genetic populations by chemical indicators. We described the network between tea quality-related metabolites, especially the dense network in new leaves. These results also will provide the key information for metabolic engineering and the selection of breeding materials in tea plants based on the tea quality-related metabolites and aid in understanding their molecular mechanisms and network of metabolic variation.

How does tea (Camellia sinensis) produce specialized metabolites which determine its unique quality and function: a review

Tea (Camellia sinensis) is both a plant and a foodstuff. Many bioactive compounds, which are present in the final tea product and related to its quality or functional properties, are produced during the tea manufacturing process. However, the characteristic secondary metabolites, which give tea its unique qualities and are beneficial to human health, are produced mainly in the leaves during the process of plant growth. Therefore, it is important to understand how tea leaves produce these specialized metabolites. In this review, we first compare the common metabolites and specialized metabolites in tea, coffee, cocoa, and grape and discuss the occurrence of characteristic secondary metabolites in tea. Progress in research into the formation of these characteristic secondary metabolites in tea is summarized, including establishing a biological database and genetic transformation system, and the biosynthesis of characteristic secondary metabolites. Finally, speculation on future research into the characteristic secondary metabolites of tea is provided from the viewpoints of the origin, resources, cultivation, and processing of tea. This review provides an important reference for future research on the specialized metabolites of tea in terms of its characteristics.

Multiple-genotypes transcriptional analysis revealed candidates genes and nucleotide variants for improvement of quality characteristics in tea (Camellia sinensis (L.) O. Kuntze)

Tea quality is a polygenic trait that exhibits tremendous genetic variability due to accumulation of array of secondary metabolites. To elucidate global molecular insights controlling quality attributes, metabolite profiling and transcriptome sequencing of twelve diverse tea cultivars was performed in tea shoots harvested during quality season. RP-HPLC-DAD analysis of quality parameters revealed significant difference in catechins, theanine and caffeine contents. Transcriptome sequencing resulted into 50,107 non-redundant transcripts with functional annotations of 81.6% (40,847) of the transcripts. Interestingly, 2872 differentially expressed transcripts exhibited significant enrichment in 38 pathways (FDR ≤ 0.05) including secondary metabolism, amino acid and carbon metabolism. Thirty-eight key candidates reportedly involved in biosynthesis of fatty acid derived volatiles, volatile terpenes, glycoside hydrolysis and key quality related pathways (flavonoid, caffeine and theanine-biosynthesis) were highly expressed in catechins-rich tea cultivars. Furthermore, enrichment of candidates involved in flavonoid biosynthesis, transcriptional regulation, volatile terpene and biosynthesis of fatty acid derived volatile in Protein-Protein Interactome network revealed well-coordinated regulation of quality characteristics in tea. Additionally, ascertainment of 23,649 non-synonymous SNPs and validation of candidate SNPs present in quality related genes suggests their potential utility in genome-wide mapping and marker development for expediting breeding of elite compound-rich tea cultivars.

Uncovering reasons for differential accumulation of linalool in tea cultivars with different leaf area

It is generally proposed that tea cultivars with larger leaves contain more linalool, an important tea aroma contributor, than ones with smaller leaves. The objective of this study was to confirm the trait and explore the involved reason. Investigation on ten tea cultivars with different leaf areas demonstrated a significant positive correlation between linalool content and leaf area (R² = 0.739, p = 0.010). Analysis of metabolite and gene expression level showed that the transform ability of linalool into linalool oxides was the key factor. Feeding experiments that supplied tea leaves of different leaf areas with [²H₃]linalool under different light conditions revealed that the larger tea leaves receive more light and are less capable of transformation of linalool to linalool oxides, thus leading to linalool accumulation. This information will advance understanding of the variation of linalool content in tea varieties and will provide assistance in breeding and screening of high-linalool tea cultivars.

Induction of priming by cold stress via inducible volatile cues in neighboring tea plants

Plants have evolved sophisticated defense mechanisms to overcome their sessile nature. However, if and how volatiles from cold-stressed plants can trigger interplant communication is still unknown. Here, we provide the first evidence for interplant communication via inducible volatiles in cold stress. The volatiles, including nerolidol, geraniol, linalool, and methyl salicylate, emitted from cold-stressed tea plants play key role(s) in priming cold tolerance of their neighbors via a C-repeat-binding factors-dependent pathway. The knowledge will help us to understand how plants respond to volatile cues in cold stress and agricultural ecosystems.

Similarities and Differences of Photosynthesis Establishment Related mRNAs and Novel lncRNAs in Early Seedlings (Coleoptile/Cotyledon vs. True Leaf) of Rice and Arabidopsis

Photosynthesis uses sunlight and carbon dioxide to produce biomass that is vital to all life on earth. In seed plants, leaf is the main organ for photosynthesis and production of organic nutrients. The seeds are mobilized to fuel post-germination seedling growth until seedling photosynthesis can be efficiently established. However, the photosynthesis and metabolism in the early growth and development have not been studied systematically and are still largely unknown. In this study, we used two model plants, rice (Oryza sativa L.; monocotyledonous) and Arabidopsis (Arabidopsis thaliana; dicotyledonous) to determine the similarities and differences in photosynthesis in cotyledons and true leaves during the early developmental stages. The photosynthesis-related genes and proteins, and chloroplast functions were determined through RNA-seq, real-time PCR, western blotting and chlorophyll fluorescence analysis. We found that in rice, the photosynthesis established gradually from coleoptile (cpt), incomplete leaf (icl) to first complete leaf (fcl); whereas, in Arabidopsis, photosynthesis well-developed in cotyledon, and the photosynthesis-related genes and proteins expressed comparably in cotyledon (cot), first true leaf (ftl) and second true leaf (stl). Additionally, we attempted to establish an mRNA-lncRNA signature to explore the similarities and differences in photosynthesis establishment between the two species, and found that DEGs, including encoding mRNAs and novel lncRNAs, related to photosynthesis in three stages have considerable differences between rice and Arabidopsis. Further GO and KEGG analysis systematically revealed the similarities and differences of expression styles of photosystem subunits and assembly factors, and starch and sucrose metabolisms between cotyledons and true leaves in the two species. Our results help to elucidate the gene functions of mRNA-lncRNA signatures.

Transrutinosylation of tyrosol by flower buds of Sophora japonica

Dried flower buds of Japanese sophora (Sophora japonica) comprising rutinosidase activity were tested in rutinosylation of tyrosol via transglycosylation process from rutin. Optimal conditions for transrutinosylation of tyrosol were 49 mM rutin and 290 mM tyrosol, giving maximum conversion up to 66.4% and 24% yield of isolated and purified rutinoside. The rutinosylation proceeded exclusively on the primary hydroxyl of tyrosol, thus forming rhamnosylated derivative of salidroside. This strict regioselectivity differentiates the sophora biocatalyst from microbial rutinosidases.

Exploring plant metabolic genomics: chemical diversity, metabolic complexity in the biosynthesis and transport of specialized metabolites with the tea plant as a model

The diversity and complexity of secondary metabolites in tea plants contribute substantially to the popularity of tea, by determining tea flavors and their numerous health benefits. The most significant characteristics of tea plants are that they concentrate the complex plant secondary metabolites into one leaf: flavonoids, alkaloids, theanine, volatiles, and saponins. Many fundamental questions regarding tea plant secondary metabolism remain unanswered. This includes how tea plants accumulate high levels of monomeric galloylated catechins, unlike the polymerized flavan-3-ols in most other plants, as well as how they are evolved to selectively synthesize theanine and caffeine, and how tea plants properly transport and store these cytotoxic products and then reuse them in defense. Tea plants coordinate many metabolic pathways that simultaneously take place in young tea leaves in response to both developmental and environmental cues. With the available genome sequences of tea plants and high-throughput metabolomic tools as great platforms, it is of particular interest to launch metabolic genomics studies using tea plants as a model system. Plant metabolic genomics are to investigate all aspects of plant secondary metabolism at the genetic, genome, and molecular levels. This includes plant domestication and adaptation, divergence and convergence of secondary metaboloic pathways. The biosynthesis, transport, storage, and transcriptional regulation mechanisms of all metabolites are of core interest in the plant as a whole. This review highlights relevant contexts of metabolic genomics, outstanding questions, and strategies for answering them, with aim to guide future research for genetic improvement of nutrition quality for healthier plant foods.

Tea plant genomics: achievements, challenges and perspectives

Tea is among the world's most widely consumed non-alcoholic beverages and possesses enormous economic, health, and cultural values. It is produced from the cured leaves of tea plants, which are important evergreen crops globally cultivated in over 50 countries. Along with recent innovations and advances in biotechnologies, great progress in tea plant genomics and genetics has been achieved, which has facilitated our understanding of the molecular mechanisms of tea quality and the evolution of the tea plant genome. In this review, we briefly summarize the achievements of the past two decades, which primarily include diverse genome and transcriptome sequencing projects, gene discovery and regulation studies, investigation of the epigenetics and noncoding RNAs, origin and domestication, phylogenetics and germplasm utilization of tea plant as well as newly developed tools/platforms. We also present perspectives and possible challenges for future functional genomic studies that will contribute to the acceleration of breeding programs in tea plants.

Purification and characterization of theobromine synthase in a Theobromine-Enriched wild tea plant (Camellia gymnogyna Chang) from Dayao Mountain, China

Camellia gymnogyna Chang (CgC), a wild tea plant, was discovered on Dayao Mountain, China. However, research regarding this tea plant is limited. Our study found that CgC contains theobromine, caffeine, and theacrine, among which theobromine content was the highest (14.37-39.72 mg/g). In addition, theobromine synthase (TS) was partially purified from CgC leaves, up to 35.87-fold, with consecutive chromatography, and its molecular weight was found to be approximately 62 kDa. The optimum reaction time, pH, and temperature for theobromine synthase from 7-methylxanthine was found to be 6 h, 4, and 45 °C, respectively. TS expression at both mRNA and protein stages was higher in the first than in the fourth leaf (P < 0.05). Subcellular localization of TS indicated that it was localized in the nucleus. These results indicate that CgC can be of scientific value and could lead to efficient utilization of this rare wild tea germplasm.

The flavonoid degrading fungus Acremonium sp. DSM 24697 produces two diglycosidases with different specificities

AbstractDiglycosidases hydrolyze the heterosidic linkage of diglycoconjugates, releasing the disaccharide and the aglycone. Usually, these enzymes do not hydrolyze or present only low activities towards monoglycosylated compounds. The flavonoid degrading fungus Acremonium sp. DSM 24697 produced two diglycosidases, which were termed 6-O-α-rhamnosyl-β-glucosidase I and II (αRβG I and II) because of their function of releasing the disaccharide rutinose (6-O-α-L-rhamnosyl-β-D-glucose) from the diglycoconjugates hesperidin or rutin. In this work, the genome of Acremonium sp. DSM 24697 was sequenced and assembled with a size of ~ 27 Mb. The genes encoding αRβG I and II were expressed in Pichia pastoris KM71 and the protein products were purified with apparent molecular masses of 42 and 82 kDa, respectively. A phylogenetic analysis showed that αRβG I grouped in glycoside hydrolase family 5, subfamily 23 (GH5), together with other fungal diglycosidases whose substrate specificities had been reported to be different from αRβG I. On the other hand, αRβG II grouped in glycoside hydrolase family 3 (GH3) and thus is the first GH3 member that hydrolyzes the heterosidic linkage of rutinosylated compounds. The substrate scopes of the enzymes were different: αRβG I showed exclusive specificity toward 7-O-β-rutinosyl flavonoids, whereas αRβG II hydrolyzed both 7-O-β-rutinosyl- and 3-O-β-rutinosyl- flavonoids. None of the enzymes displayed activity toward 7-O-β-neohesperidosyl- flavonoids. The recombinant enzymes also exhibited transglycosylation activities, transferring rutinose from hesperidin or rutin onto various alcoholic acceptors. The different substrate scopes of αRβG I and II may be part of an optimized strategy of the original microorganism to utilize different carbon sources.

Cloning and molecular characterization of rutin degrading enzyme from tartary buckwheat (Fagopyrum tataricum Gaertn.)

Rutin and quercetin, abundant in tartary buckwheat, have physiological and pharmacological functions and play roles in abiotic stress tolerance in plant. Rutin degrading enzymes (RDE) are the key enzymes for rutin metabolism. However, the RDE coding sequence information has not been available. In this study, a 1515-bp coding sequence of RDE was cloned from tartary buckwheat (named FtRDE) using 5' and 3' RACE, based on the FtRDE protein sequence. The recombinant RDE (rRDE) expressed in P.pastoris with glycosylation modification degraded rutin into quercetin and the Glu171 and Glu382 were indispensable residues for catalytic activity. FtRDE was highly expressed in seed filling stage and response to ABA and MeJA, confirmed by qRT-PCR and FtRDE promoter activity analysis in mesophyll protoplast. This study provided a new approach for the large-scale preparation of RDE by heterologous expression and production of quercetin by hydrolyzing rutin, and could be helpful for understanding the FtRDE function under stress conditions.

β-Glucosidase from tartary buckwheat immobilization on bifunctionalized nano-magnetic iron oxide and its application in tea soup for aroma and flavonoid aglycone enhancement

β-Glucosidase (BG) was immobilized on the surface of bifunctionalized nano-magnetic iron oxide with silica and amine groups (Fe₃O₄@SiO₂-NH₂). The aroma and flavonoid aglycone enhancement effect of BG in tea soup was investigated. The immobilized BG-synthesized nanocomposite morphology and structure were characterized by using different analytical techniques, including Fourier transform infrared spectroscopy and scanning electron microscopy. The immobilized BG showed enhanced pH and temperature endurance at an optimum pH of 5.0 and temperature of 65 °C. After seven cycles of reuse, immobilized BG showed 51.8% initial activity. Immobilized-BG treatment in green tea and black tea soup elevated the aroma content by approximately 16% and 48%, respectively. In addition, flavonoid aglycones, such as myricetin, kaempferol, and quercetin, in green tea and black tea soup increased by approximately 65- and 5-fold, respectively. These results suggested that immobilized BG showed excellent potential in the enhancement of aroma and effectively hydrolyzed the flavonoid glycosides to release flavonoid aglycones in tea soup. Hence, this study provides a green and sustainable approach for the tea industry to efficiently enhance tea soup properties.

Advances in research on functional genes of tea plant

Tea plant (Camellia sinensis) is an important leaf-type woody crop used to produce non-alcoholic beverages all over the world. Tea is one of the oldest and most popular non-alcoholic beverages in the world, and long-term tea drinking has numerous healthful for humans due to many of the important secondary metabolites, such as polyphenols and theanine. Theanine and polyphenols are also closely related to tea flavor and tea aroma, which is usually as the standard for judging tea quality. The growth of tea plants and quality of teas are susceptible to adversity abiotic and biotic stresses, such as low temperatures and pests. Consequently, this review focus on the research progress of key genes related to the stress resistance and material metabolism of tea plants in recent years. We aim at comprehensively understanding the growth and metabolism of tea plants and their relationship with the external environment, so as to provide an in-depth and broad theoretical support for the breeding of excellent tea plant varieties.

Elucidation of ( Z)-3-Hexenyl-β-glucopyranoside Enhancement Mechanism under Stresses from the Oolong Tea Manufacturing Process

The enzymatic hydrolysis of glycosidically bound volatiles (GBVs) plays an important role in tea aroma formation during the tea manufacturing process. However, during the enzyme-active manufacturing process of oolong tea, most GBVs showed no reduction, while ( Z)-3-hexenyl-β-glucopyranoside significantly enhanced at the turnover stage. This study aimed to determine the reason for this increase in ( Z)-3-hexenyl-β-glucopyranoside. Continuous wounding stress in the turnover stage did not enhance the expression level of glycosyltransferase 1 ( CsGT1), while it induced a significant increase in the ( Z)-3-hexenol content ( p ≤ 0.05). Furthermore, observing the cell structures of tea leaves exposed to continuous wounding and subcellular localizations of CsGTs suggested that the interaction of ( Z)-3-hexenol (substrate) and CsGT1 (enzyme) was available. In conclusion, both continuous wounding and subcellular localizations led to a ( Z)-3-hexenyl-β-glucopyranoside enhancement mechanism during the oolong tea's turnover stage. These results advance our understanding of GBV formation during the tea manufacturing process and their relationship with the stress from the tea manufacturing process. In addition, the information will help us further evaluate contribution of GBVs to enzymatic formation of oolong tea aroma compounds.

Reaction mechanism of β-apiosidase from Aspergillus aculeatus

Apiosidases are glycosidases relevant for aroma development during fermentation of wines and black tea. Reaction mechanism of apiosidase from Aspergillus aculeatus in commercial glycanase Viscozyme L was studied by ¹H NMR technique. Study of hydrolysis of 4-nitrophenyl β-D-apiofuranoside revealed that this reaction proceeds with inversion of hydroxyl group in the anomeric center, which confirms inverting mechanism of the enzyme and its inability to catalyze transapiosylation in syntheses of apiosides.

Variation patterns in the content of glycosides during green tea manufacturing by a modification-specific metabolomics approach: Enzymatic reaction promoting an increase in the glycosidically bound volatiles at the pan firing stage

The glycosides are presumed to influence the quality of green tea but the molecular mechanism behind remains unclear. To elucidate the contribution of glycosides to the flavor formation of green tea, changes of both glycosidically bound non-volatiles (GBNVs) and glycosidically bound volatiles (GBVs) during the manufacturing of green tea were investigated using a modification-specific metabolomics method. A total of 64 glycosides (47 GBNVs and 17 GBVs) were identified and their contents mainly changed during the pan firing and drying stages of green tea manufacturing. Notably, the contents of GBVs significantly increased by 1.12-4.46-fold during pan firing. Correlation analysis showed that the GBVs contents were negatively related to the contents of volatiles and glucose. Model experiments revealed that enzymatic synthesis contributed to the increase in the content of GBVs during the pan firing. This comprehensive study on the glycosides changes revealed the molecular bases for GBVs increments during the pan firing.

Identification of key aromatic compounds in Congou black tea by partial least-square regression with variable importance of projection scores and gas chromatography-mass spectrometry/gas chromatography-olfactometry

BACKGROUND

Gas chromatography-olfactometry (GC-O) is the most frequently used method to estimate the sensory contribution of single odorant, but disregards the interactions between volatiles. In order to select the key volatiles responsible for the aroma attributes of Congou black tea (Camellia sinensis), instrumental, sensory and multivariate statistical approaches were applied.

RESULTS

Using sensory analysis, nine panellists developed eight descriptors: floral, sweet, fruity, green, roasted, oil, spicy, and off-odour. Linalool, (E)-furan linalool oxide, (Z)-pyran linalool oxide, methyl salicylate, β-myrcene, and phenylethyl alcohol, which were identified from the most representative samples by the GC-O procedure, were the essential aroma-active compounds in the formation of basic Congou black tea aroma. In addition, 136 volatiles were identified by gas chromatography-mass spectrometry (GC-MS), among which 55 compounds were determined as the key factors for six sensory attributes by partial least-square regression (PLSR) with variable importance of projection scores.

CONCLUSION

Our results demonstrated that headspace solid-phase microextraction/GC-MS/GC-O was a fast approach for isolation and quantification aroma-active compounds. The PLSR method was also considered to be a useful tool in selecting important variables for sensory attributes. These two strategies, which allowed us to comprehensively evaluate the sensorial contribution of a single volatile from different perspectives, can be applied to related products for comprehensive quality control. © 2018 Society of Chemical Industry.

Differential Accumulation of Aroma Compounds in Normal Green and Albino-Induced Yellow Tea (Camellia sinensis) Leaves

Tea (Camellia sinensis) cultivars with green leaves are the most widely used for making tea. Recently, tea mutants with white or yellow young shoots have attracted increasing interest as raw materials for making "high-quality" tea products. Albino teas are generallycharacterized as having metabolites of relatively high amino acid content and lower catechin content. However, little is known about aroma compounds in albino tea leaves. Herein, we compared original normal leaves (green) and light-sensitive albino leaves (yellow) of cv. Yinghong No. 9. GC-MS was employed to analyze endogenous tea aroma compounds and related precursors. Quantitative real time PCR was used to measure expression levels of genes involved in biosyntheses of tea aromas.The total contents of most endogenous free tea aromas, including aroma fatty acid derivatives, aroma terpenes, and aroma phenylpropanoids/benzenoids, and their glycosidically bound aroma compounds, were lower in yellow leaves than in green leaves. The content of the key precursor geranyl diphosphate (GDP) and expression levels of key synthetic genes involved in the formation of linalool, a major aroma compound in cv. Yinghong No. 9, were investigated. Linalool content was lower in albino-induced yellow leaves, which was due to the lower GDP content compared with normal green leaves.

Attractive but Toxic: Emerging Roles of Glycosidically Bound Volatiles and Glycosyltransferases Involved in Their Formation

Plants emit an overabundance of volatile compounds, which act in their producers either as appreciated attractants to lure beneficial animals or as repellent toxins to deter pests in a species-specific and concentration-dependent manner. Plants have evolved solutions to provide sufficient volatiles without poisoning themselves. Uridine-diphosphate sugar-dependent glycosyltransferases (UGTs) acting on volatiles is one important part of this sophisticated system, which balances the levels of bioactive metabolites and prepares them for cellular and long-distance transport and storage but enables the remobilization of disarmed toxins for the benefit of plant protection. This review provides an overview of the research history of glycosidically bound volatiles (GBVs), a relatively new group of plant secondary metabolites, and discusses the role of UGTs in the production of GBVs for plant protection.

Understanding the biosyntheses and stress response mechanisms of aroma compounds in tea (Camellia sinensis) to safely and effectively improve tea aroma

Metabolite formation is a biochemical and physiological feature of plants developed as an environmental response during the evolutionary process. These metabolites help defend plants against environmental stresses, but are also important quality components in crops. Utilizing the stress response to improve natural quality components in plants has attracted increasing research interest. Tea, which is processed by the tender shoots or leaves of tea plant (Camellia sinensis (L.) O. Kuntze), is the second most popular beverage worldwide after water. Aroma is an important factor affecting tea character and quality. The defense responses of tea leaves against various stresses during preharvest (tea growth process) and postharvest (tea manufacturing) processing can result in aroma formation. Herein, we summarize recent investigations into the biosyntheses of several characteristic aroma compounds prevalent in teas and derived from volatile fatty acid derivatives, terpenes, and phenylpropanoids/benzenoids. Several key aroma synthetic genes from tea leaves have been isolated, cloned, sequenced, and functionally characterized. Biotic stress (such as tea green leafhopper attack) and abiotic stress (such as light, temperature, and wounding) could enhance the expression of aroma synthetic genes, resulting in the abundant accumulation of characteristic aroma compounds in tea leaves. Understanding the specific relationships between characteristic aroma compounds and stresses is key to improving tea quality safely and effectively.

An alternative pathway for the formation of aromatic aroma compounds derived from l-phenylalanine via phenylpyruvic acid in tea (Camellia sinensis (L.) O. Kuntze) leaves

Aromatic aroma compounds contribute to flavor of tea (Camellia sinensis (L.) O. Kuntze) and they are mostly derived from l-phenylalanine via trans-cinnamic acid or directly from l-phenylalanine. The objective of this study was to investigate whether an alternative pathway derived from l-phenylalanine via phenylpyruvic acid is involved in formation of aroma compounds in tea. Enzyme reaction with phenylpyruvic acid showed that benzaldehyde, benzyl alcohol, and methyl benzoate were derived from phenylpyruvic acid in tea leaves. Feeding experiments using [²H₈]l-phenylalanine indicated that phenylpyruvic acid was derived from l-phenylalanine in a reaction catalyzed by aromatic amino acid aminotransferases (AAATs). CsAAAT1 showed higher catalytic efficiency towards l-phenylalanine (p ≤ 0.001) while CsAAAT2 showed higher catalytic efficiency towards l-tyrosine (p ≤ 0.001). Both CsAAATs were localized in the cytoplasm of leaf cells. In conclusion, an alternative pathway for the formation of aromatic aroma compounds derived from l-phenylalanine via phenylpyruvic acid occurred in tea leaves.