Functional analysis of flavonoid 3',5'-hydroxylase from tea plant (Camellia sinensis): critical role in the accumulation of catechins

Zinc Treatment of Tea Plants Improves the Synthesis of Trihydroxylated Catechins via Regulation of the Zinc-Sensitive Protein CsHIPP3

The tea plant (Camellia sinensis [L.] O. Kussntze) is a global economic crop. Zinc treatment of tea plants can enhance catechin biosynthesis. However, the underlying molecular mechanism behind catechin formation through zinc regulation remains unclear. This study identified a zinc-responsive protein, C. sinensis heavy metal-associated isoprenylated plant protein 3 (CsHIPP3), from zinc-treated tea seedlings. CsHIPP3 expression was positively correlated with trihydroxylated catechin (TRIC) content. CsF3'5'H1 is a crucial regulator of the TRIC synthesis pathway. The interaction between CsHIPP3 and CsF3'5'H1 was assessed using bimolecular fluorescence complementation, firefly luciferase complementation imaging, and pulldown experiments. CsHIPP3 knockdown using virus-induced gene silencing technology decreased the content of each component of TRICs. Compared with the control, the relative catechin content was reduced by 40.12-55.39%. Co-overexpression of CsHIPP3 and CsF3'5'H1 significantly elevated the TRIC content in tea leaves and calli. Moreover, the TRIC content in transient co-overexpression leaves was 1.44-fold higher than that of the control group, and tea callus was 50.83% higher in transient co-overexpression than in the wild type. Thus, zinc-regulated TRIC synthesis in a zinc-rich environment was mediated by binding CsHIPP3 with CsF3'5'H1 to promote TRIC synthesis and accumulation.

Integrated analysis of multiple metabolome and transcriptome revealed the accumulation of flavonoids and associated molecular regulation mechanisms in Rubus chingii Hu at different developmental stages

The traditional Chinese herb Rubus chingii Hu (R. chingii) is widely used in clinical practice due to its beneficial effects. Flavonoids are the important class of pharmacological substances in R. chingii, however, the molecular mechanism underlying the differences in active flavonoid contents in R. chingii at different developmental stages remain poorly understood. In this experiment, we selected four developmental stages (GG, GY, YR, RR) of R. chingii as the research material. We studied the untargeted and targeted metabolic profiles of flavonoids in different periods of R. chingii, combining full-length and comparative transcriptome analyses. Functional analyses were conducted on genes implicated in flavonoid differences. GG and RR displayed relatively higher and lower contents of flavonols, flavones, flavanols, flavanones, and isoflavonoid, respectively. RNA-seq analyses showed structural genes such as RcPAL, RcC4H, Rc4CL, RcCHS, RcCHI, RcF3H, RcF3'H, and RcFLS in flavonoid biosynthesis pathway were upregulated in GG, which were essential for the accumulation flavanones, flavones, and flavonols (effective components). qRT-PCR analyses investigated that six structural genes RcCHI, RcF3H, 2 RcCHS, and 2 Rc4CL, two TFs RcMYB308 and RcMYB123 had a consistent expression pattern with which in transcriptome. Also, an interaction network showed that the RcMYB308 could positively regulate Ka3R, Qu, Qu3G, AS, Hy, Ti through RcF3H. Furthermore, Subcellular localization analysis revealed that RcMYB308 was localization to the nucleus. In tobacco, RcMYB308 was overexpressed, resulting in higher flavonoids, RcF3H, RcF3'H, RcCHI, and RcFLS. RcMYB308 upregulated RcF3H in dual-luciferase assays. These results provide new insights for further understanding the molecular mechanism regulating flavonol biosynthesis in R. chingii fruit, and also provide a potential MYB regulator for molecular breeding of R. chingii.

Heterologous Expression of Platycodon grandiflorus PgF3'5'H Modifies Flower Color Pigmentation in Tobacco

Flavonoid-3',5'-hydroxylase (F3'5'H) is the key enzyme for the biosynthesis of delphinidin-based anthocyanins, which are generally required for purple or blue flowers. Previously, we isolated a full-length cDNA of PgF3'5'H from Platycodon grandiflorus, which shared the highest homology with Campanula medium F3'5'H. In this study, PgF3'5'H was subcloned into a plant over-expression vector and transformed into tobacco via Agrobacterium tumefaciens to investigate its catalytic function. Positive transgenic tobacco T0 plants were obtained by hygromycin resistance screening and PCR detection. PgF3'5'H showed a higher expression level in all PgF3'5'H transgenic tobacco plants than in control plants. Under the drive of the cauliflower mosaic virus (CaMV) 35S promoter, the over-expressed PgF3'5'H produced dihydromyricetin (DHM) and some new anthocyanin pigments (including delphinidin, petunidin, peonidin, and malvidin derivatives), and increased dihydrokaempferol (DHK), taxifolin, tridactyl, cyanidin derivatives, and pelargonidin derivatives in PgF3'5'H transgenic tobacco plants by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis, resulting in a dramatic color alteration from light pink to magenta. These results indicate that PgF3'5'H products have F3'5'H enzyme activity. In addition, PgF3'5'H transfer alters flavonoid pigment synthesis and accumulation in tobacco. Thus, PgF3'5'H may be considered a candidate gene for gene engineering to enhance anthocyanin accumulation and the molecular breeding project for blue flowers.

Genome-based identification of the CYP75 gene family in Orchidaceae and its expression patterns in Cymbidium goeringii

With a great diversity of species, Orchidaceae stands out as an essential component of plant biodiversity, making it a primary resource for studying angiosperms evolution and genomics. This study focuses on 13 published orchid genomes to identify and analyze the CYP75 gene family belonging to the cytochrome P450 superfamily, which is closely related to flavonoid biosynthetic enzymes and pigment regulation. We found 72 CYP75s in the 13 orchid genomes and further classified them into two classes: CYP75A and CYP75B subfamily, the former synthesizes blue anthocyanins, while the latter is involved in the production of red anthocyanins. Furthermore, the amount of CYP75Bs (53/72) greatly exceeds the amount of CYP75As (19/72) in orchids. Our findings suggest that CYP75B genes have a more important evolutionary role, as red plants are more common in nature than blue plants. We also discovered unique conserved motifs in each subfamily that serve as specific recognition features (motif 19 belong to CYP75A; motif 17 belong to CYP75B). Two diverse-colored varieties of C. goeringii were selected for qRT-PCR experiments. The expression of CgCYP75B1 was significantly higher in the purple-red variant compared to the yellow-green variant, while CgCYP75A1 showed no significant difference. Based on transcriptomic expression analysis, CYP75Bs are more highly expressed than CYP75As in floral organs, especially in colorful petals and lips. These results provide valuable information for future studies on CYP75s in orchids and other angiosperms.

Genome of Phyllanthus emblica: the medicinal plant Amla with super antioxidant properties

Phyllanthus emblica or Indian gooseberry, commonly known as amla, is an important medicinal horticultural plant used in traditional and modern medicines. It bears stone fruits with immense antioxidant properties due to being one of the richest natural sources of vitamin C and numerous flavonoids. This study presents the first genome sequencing of this species performed using 10x Genomics and Oxford Nanopore Technology. The draft genome assembly was 519 Mbp in size and consisted of 4,384 contigs, N50 of 597 Kbp, 98.4% BUSCO score, and 37,858 coding sequences. This study also reports the genome-wide phylogeny of this species with 26 other plant species that resolved the phylogenetic position of P. emblica. The presence of three ascorbate biosynthesis pathways including L-galactose, galacturonate, and myo-inositol pathways was confirmed in this genome. A comprehensive comparative evolutionary genomic analysis including gene family expansion/contraction and identification of multiple signatures of adaptive evolution provided evolutionary insights into ascorbate and flavonoid biosynthesis pathways and stone fruit formation through lignin biosynthesis. The availability of this genome will be beneficial for its horticultural, medicinal, dietary, and cosmetic applications and will also help in comparative genomics analysis studies.

CYCLOIDEA-like genes control floral symmetry, floral orientation, and nectar guide patterning

Actinomorphic flowers usually orient vertically (relative to the horizon) and possess symmetric nectar guides, while zygomorphic flowers often face horizontally and have asymmetric nectar guides, indicating that floral symmetry, floral orientation, and nectar guide patterning are correlated. The origin of floral zygomorphy is dependent on the dorsoventrally asymmetric expression of CYCLOIDEA (CYC)-like genes. However, how horizontal orientation and asymmetric nectar guides are achieved remains poorly understood. Here, we selected Chirita pumila (Gesneriaceae) as a model plant to explore the molecular bases for these traits. By analyzing gene expression patterns, protein-DNA and protein-protein interactions, and encoded protein functions, we identified multiple roles and functional divergence of 2 CYC-like genes, i.e. CpCYC1 and CpCYC2, in controlling floral symmetry, floral orientation, and nectar guide patterning. CpCYC1 positively regulates its own expression, whereas CpCYC2 does not regulate itself. In addition, CpCYC2 upregulates CpCYC1, while CpCYC1 downregulates CpCYC2. This asymmetric auto-regulation and cross-regulation mechanism might explain the high expression levels of only 1 of these genes. We show that CpCYC1 and CpCYC2 determine asymmetric nectar guide formation, likely by directly repressing the flavonoid synthesis-related gene CpF3'5'H. We further suggest that CYC-like genes play multiple conserved roles in Gesneriaceae. These findings shed light on the repeated origins of zygomorphic flowers in angiosperms.

High light triggers flavonoid and polysaccharide synthesis through DoHY5-dependent signaling in Dendrobium officinale

Dendrobium officinale is edible and has medicinal and ornamental functions. Polysaccharides and flavonoids, including anthocyanins, are important components of D. officinale that largely determine the nutritional quality and consumer appeal. There is a need to study the molecular mechanisms regulating anthocyanin and polysaccharide biosynthesis to enhance D. officinale quality and its market value. Here, we report that high light (HL) induced the accumulation of polysaccharides, particularly mannose, as well as anthocyanin accumulation, resulting in red stems. Metabolome and transcriptome analyses revealed that most of the flavonoids showed large changes in abundance, and flavonoid and polysaccharide biosynthesis was significantly activated under HL treatment. Interestingly, DoHY5 expression was also highly induced. Biochemical analyses demonstrated that DoHY5 directly binds to the promoters of DoF3H1 (involved in anthocyanin biosynthesis), DoGMPP2, and DoPMT28 (involved in polysaccharide biosynthesis) to activate their expression, thereby promoting anthocyanin and polysaccharide accumulation in D. officinale stems. DoHY5 silencing decreased flavonoid- and polysaccharide-related gene expression and reduced anthocyanin and polysaccharide accumulation, whereas DoHY5 overexpression had the opposite effects. Notably, naturally occurring red-stemmed D. officinale plants similarly have high levels of anthocyanin and polysaccharide accumulation and biosynthesis gene expression. Our results reveal a previously undiscovered role of DoHY5 in co-regulating anthocyanin and polysaccharide biosynthesis under HL conditions, improving our understanding of the mechanisms regulating stem color and determining nutritional quality in D. officinale. Collectively, our results propose a robust and simple strategy for significantly increasing anthocyanin and polysaccharide levels and subsequently improving the nutritional quality of D. officinale.

Fine mapping of the flavonoid 3',5'-hydroxylase gene controlling anthocyanin biosynthesis in pepper anthers and stems

Pepper (Capsicum annuum L) is one of the most important vegetables grown worldwide. Nevertheless, the key structural and regulatory genes involved in anthocyanin accumulation in pepper have not been well understood or fine mapped yet. In this study, F1, F2, BC1P1, and BC1P2 pepper populations were analyzed and these populations were derived from a cross between line 14-Z4, which has yellow anthers and green stems, and line 14-Z5, which has purple anthers and stems. The results showed that the yellow anthers and green stems were determined by a single recessive locus called to as ayw. While, using preliminary and fine mapping techniques, ayw locus was located between markers aywSNP120 and aywSNP124, with physical distance of 0.2 Mb. The CA11g18550 gene was identified as promising candidate for the ayw locus, as it co-segregated with the yellow anthers and green stems phenotypes. CA11g18550 encodes a homolog of the F3'5'H (flavonoid 3',5'-hydroxylase) anthocyanin synthesis structure gene. The missense mutation of CA11g18550 possibly resulted in a loss-of-function. The expression analysis showed that CA11g18550 was significantly expressed in the stems, leaves, anthers and petals in 14-Z5, and it's silencing caused the stems changing from purple to green. This study provides a theoretical basis for using yellow anthers and green stems in pepper breeding and helps to advance the understanding of anthocyanin synthesis.

Integrated physiological, metabolite and proteomic analysis reveal the glyphosate stress response mechanism in tea plant (Camellia sinensis)

Glyphosate residues can tremendously impact the physiological mechanisms of tea plants, thus threatening tea security and human health. Herein, integrated physiological, metabolite, and proteomic analyses were performed to reveal the glyphosate stress response mechanism in tea plant. After exposure to glyphosate (≥1.25 kg ae/ha), the leaf ultrastructure was damaged, and chlorophyll content and relative fluorescence intensity decreased significantly. The characteristic metabolites catechins and theanine decreased significantly, and the 18 volatile compounds content varied significantly under glyphosate treatments. Subsequently, tandem mass tags (TMT)-based quantitative proteomics was employed to identify the differentially expressed proteins (DEPs) and to validate their biological functions at the proteome level. A total of 6287 proteins were identified and 326 DEPs were screened. These DEPs were mainly catalytic, binding, transporter and antioxidant active proteins, involved in photosynthesis and chlorophyll biosynthesis, phenylpropanoid and flavonoid biosynthesis, sugar and energy metabolism, amino acid metabolism, and stress/defense/detoxification pathway, etc. A total of 22 DEPs were validated by parallel reaction monitoring (PRM), demonstrating that the protein abundances were consistent between TMT and PRM data. These findings contribute to our understanding of the damage of glyphosate to tea leaves and molecular mechanism underlying the response of tea plants to glyphosate.

Integrated Transcriptomic and Metabolomic Analyses Reveal the Effects of Grafting on Special Metabolites of Acanthopanax senticosus Leaves

Acanthopanax senticosus (A. senticosus) is a member of Acanthopanax Miq. and is used in traditional Chinese medicine, and it has been found that grafting technology can be used to alter plant metabolite composition and transcriptome characteristics. In this study, shoots of A. senticosus were grafted onto the rootstocks of the vigorous Acanthopanax sessiliflorus (A. sessiliflorus) to improve its varietal characteristics. In order to investigate the changes in metabolites and transcriptional patterns in grafted A. senticosus leaves (GSCL), fresh leaves were collected from 2-year-old grafted A. senticosus scions, while self-rooted seedling A. senticosus leaves (SCL) were used as controls to analyse the transcriptome and metabolome. Metabolic profiles and gene expression patterns were further identified and correlated in special metabolite target pathways. The content of chlorogenic acid and triterpenoids in the GSCL was higher than in the control, while the quercetin content was lower. All these metabolic changes were associated with changes in the expression pattern of transcripts. Our results revealed the transcriptome and metabolome characteristics of GSCL. This may help to improve leaf quality in A. senticosus cultivation, suggesting that it is feasible to improve the medicinal quality of GSCL through asexual propagation, but the long-term effects need further investigation. In conclusion, this dataset provides a useful resource for future studies on the effects of grafting on medicinal plants.

Engineering medicinal plant-derived CYPs: a promising strategy for production of high-valued secondary metabolites

Cytochorme P450s (CYPs) play a critical role in the catalysis of secondary metabolite biosynthetic pathways. For their commercial use, various strategies for metabolic pathway engineering using CYP as a potential target have been explored. Plants produce a vast diversity of secondary metabolites which are being used to treat various ailments and diseases. Some of these metabolites are difficult to obtain in large quantities limiting their industrial use. Cytochrome P450 enzymes (CYPs) are important catalysts in the biosynthesis of highly valued secondary metabolites, and are found in all domains of life. With the development of high-throughput sequencing and high-resolution mass spectrometry, new biosynthetic pathways and associated CYPs are being identified. In this review, we present CYPs identified from medicinal plants as a potential game changer in the metabolic engineering of secondary metabolic pathways. We present the achievements made so far in enhancing the production of important bioactivities through pathway engineering, giving some popular examples. At last, current challenges and possible strategies to overcome the limitations associated with CYP engineering to enhance the biosynthesis of target secondary metabolites are also highlighted.

Proanthocyanidin biosynthesis in the developing wheat seed coat investigated by chemical and RNA-Seq analysis

The composition of proanthocyanidins in the testa (seed coat) of bread wheat was analyzed by thiolysis of PA oligomers from developing grain and found to consist of (+)-catechin monomers, with a small amount of (+)-gallocatechin. The average chain length of soluble PA stayed relatively constant between 10 and 20 days post-anthesis, whereas that of unextractable PA increased over the same period, suggesting that increases in chain length might account for the insolubility of PAs from mature wheat grain. We carried out RNA-Seq followed by differential expression analysis from dissected tissues of developing grain from red- and white-grained near-isogenic lines differing in the presence of an active R gene that encodes a MYB transcription factor involved in control of PA biosynthesis. In addition to genes already identified encoding chalcone synthase, chalcone isomerase, flavanone 3-hydroxylase, and dihydroxyflavonoid 4-reductase, we showed that wheat genes encoding phenylalanine ammonia lyase, flavonoid 3',5'-hydroxylase, leucoanthocyanidin reductase, and a glutathione S-transferase (the orthologue of maize Bronze-2) were more highly expressed in the red NIL. We also identified candidate orthologues of other catalytic and regulatory components of flavonoid biosynthesis in wheat.

Identification of Seven Key Structural Genes in the Anthocyanin Biosynthesis Pathway in Sepals of Hydrangea macrophylla

Under specific cultivation conditions, the sepal color of Hydrangea macrophylla (H. macrophylla) changes from red to blue due to the complexation of aluminum ions (Al3+), delphinidin 3-glucoside, and copigments. However, this phenomenon cannot occur in all cultivars despite the presence of sufficient Al3+ and copigments. To explore the mechanism of sepal bluing in H. macrophylla, there is an urgent need to study the molecular regulation of the anthocyanin biosynthesis pathway. However, the key structural genes, other than CHS, regulating anthocyanin biosynthesis in the sepals of H. macrophylla have not been identified. In this study, based on full-length transcriptome data from H.macrophylla ‘Bailmer’, the key structural genes regulating anthocyanin biosynthesis in the sepals of H. macrophylla were isolated and investigated. Ultimately, seven key structural genes, HmCHS1, HmCHI, HmF3H1, HmF3′H1, HmF3′5′H, HmDFR2, and HmANS3, were demonstrated to show high expression levels in colored sepals. The expression levels of these seven genes increased gradually with the development of sepals and were highest in the full-bloom stage. The trend of gene expression was consistent with the trend of anthocyanin contents. It was concluded that the seven selected genes were involved in anthocyanin biosynthesis in the sepals of H. macrophylla. The full-length sequence data have been deposited into the NCBI Sequence Read Archive (SRA) with accession number PRJNA849710. This study lays a good foundation for the further elucidation of the molecular mechanism of sepal coloration in H. macrophylla.

Decoding the formation of diverse petal colors of Lagerstroemia indica by integrating the data from transcriptome and metabolome

Lagerstroemia indica has great economic value due to its ecological, medicinal, and ornamental properties. Because its bloom color is one of the most essential characteristics, research into its color development is a hot topic. In this study, five representative colored cultivars were chosen, each representing a different color, such as white, red, pink, violet, and purple. Fully bloomed flowers were used to detect flavonoids in the petals. Anthocyanin is the main factor for the color formation of L. indica. 14 anthocyanins were discovered among the 299 flavonoids. Among 14 anthocyanins, malvidin-3,5-di-O-glucoside varied greatly among four colored samples and is the main contributor to color diversity. Transcriptome sequencing revealed that compared to white flowers, Anthocyanin pathway genes appear to be more active in colored samples. Analyzing the correlation network between metabolites and differential expressed genes, 53 key structural genes, and 24 TFs were detected that may play an essential role in the formation of color in L. indica flowers. Among these, the differential expression of F3'5'H and F3'H between all samples are contributors to color diversity. These findings lay the foundation for discovering the molecular mechanism of L. indica flower color diversity.

Deciphering genome-wide transcriptomic changes in grapevines heavily infested by spotted lanternflies

The spotted lanternfly, a newly invasive insect in the U.S. that is a great concern for the grapevine industry, produces damage on its host plants through aggressive feeding, using a piercing and sucking method to feed on the phloem of plants. In the eastern US, adult SLF can invade vineyards through fruit ripening until the end of the growing season; however, it is still unclear how prolonged late-season SLF feeding can affect the health of grapevines, as well as the host responses to this extensive damage. Thus, we have performed a comprehensive genome-wide transcriptome analysis in grapevines heavily infested by the spotted lanternfly, as it occurs in Pennsylvania vineyards, and compared it to other relevant transcriptomes in grapes with different degrees to susceptibility to similar pests. Among a variety of plant responses, we highlight here a subset of relevant biological pathways that distinguish or are common to the spotted lanternfly and other phloem feeders in grapevine. The molecular interaction between spotted lanternfly and the vine begins with activation of signal transduction cascades mediated mainly by protein kinase genes. It also induces the expression of transcription factors in the nucleus, of other signaling molecules like phytohormones and secondary metabolites, and their downstream target genes responsible for defense and physiological functions, such as detoxification and photosynthesis. Grapevine responses furthermore include the activation of genes for cell wall strengthening via biosynthesis of major structural components. With this study, we hope to provide the regulatory network to explain effects that the invasive spotted lanternfly has on grapevine health with the goal to improve its susceptibility.

Transcriptional Comparison of New Hybrid Progenies and Clone-Cultivars of Tea (Camellia sinensis L.) Associated to Catechins Content

Heterosis or hybrid vigor is the improved performance of a desirable quality in hybrid progeny. Hybridization between high-productive Assam type and high-quality Chinese type clone-cultivar is expected to develop elite tea plant progenies with high quality and productivity. Comparative transcriptomics analyses of leaves from the F1 hybrids and their parental clone-cultivars were conducted to explore molecular mechanisms related to catechin content using a high-throughput next-generation RNA-seq strategy and high-performance liquid chromatography (HPLC). The content of EGCG (epigallocatechin gallate) and C (catechin) was higher in ‘Kiara-8’ × ‘Sukoi’, ‘Tambi-2’ × ‘Suka Ati’, and ‘Tambi-2’ × ‘TRI-2025’ than the other hybrid and clone-cultivars. KEGG (Kyoto Encyclopedia of Genes and Genomes) and GO (Gene Ontology) analysis found that most pathways associated with catechins content were enriched. Significant differentially expressed genes (DEGs) mainly associated with phenylpropanoid, flavonoid, drug metabolism-cytochrome P450, and transcription factor (MYB, bHLH, LOB, and C2H2) pathways appeared to be responsible for the high accumulation of secondary metabolites in ‘Kiara-8’ × ‘Sukoi’, ‘Tambi-2’ × ‘Suka Ati’, and ‘Tambi-2’ × ‘TRI-2025’ as were detected in EGCG and catechin content. Several structural genes related to the above pathways have been obtained, which will be used as candidate genes in the screening of breeding materials.

Transcriptome and Metabolome Analyses of Codonopsis convolvulacea Kurz Tuber, Stem, and Leaf Reveal the Presence of Important Metabolites and Key Pathways Controlling Their Biosynthesis

Codonopsisconvolvulacea Kurz. var. vinciflora (Kom.) L.T. Shen is a member of Campanulaceae, which is used in traditional Chinese medicine. However, apart from a few Codonopsis species, no detailed knowledge is available on the metabolite composition and respective transcriptome signatures. We performed a combined transcriptome and metabolome analysis of the tuber, stem, and leaf of C. convolvulacea and found 1,144 metabolites and 231,840 unigenes in three experimental groups. The analysis revealed considerable variations in the three tissues. Tubers were rich in amino acids and derivatives, flavonoids, and organic acids, whereas the stems and leaves were rich in alkaloids and flavonoids, respectively. Transcriptome sequencing revealed candidate genes being involved in flavonoid, tryptophan, and alkaloid biosyntheses. In particular, we indicated that the variation in the isoflavone content is linked to the expressions of CHI, CYP73A, C3′H, F3H, CYP75B1, anthocyanidin synthase, and FLS. In a similar way, the levels of indole, L-tyrosine, and tryptamine were also consistent with the expressions of TDC/DDCs in the respective tissues. In addition, the expression levels of ASP5, ARO8, GOT, and AOC3 indicated that L-tryptophan is being converted to downstream metabolites. Overall, our datasets present a useful resource for future research on the uses of this medicinal plant and put forward many research questions.

Molecular and biochemical characterization of two 4-coumarate: CoA ligase genes in tea plant (Camellia sinensis)

Two 4-coumarate: CoA ligase genes in tea plant involved in phenylpropanoids biosynthesis and response to environmental stresses. Tea plant is rich in flavonoids benefiting human health. Lignin is essential for tea plant growth. Both flavonoids and lignin defend plants from stresses. The biosynthesis of lignin and flavonoids shares a key intermediate, 4-coumaroyl-CoA, which is formed from 4-coumaric acid catalyzed by 4-coumaric acid: CoA ligase (4CL). Herein, we report two 4CL paralogs from tea plant, Cs4CL1 and Cs4CL2, which are a member of class I and II of this gene family, respectively. Cs4CL1 was mainly expressed in roots and stems, while Cs4CL2 was mainly expressed in leaves. The promoter of Cs4CL1 had AC, nine types of light sensitive (LSE), four types of stress-inducible (SIE), and two types of meristem-specific elements (MSE). The promoter of Cs4CL2 also had AC and nine types of LSEs, but only had two types of SIEs and did not have MSEs. In addition, the LSEs varied in the two promoters. Based on the different features of regulatory elements, three stress treatments were tested to understand their expression responses to different conditions. The resulting data indicated that the expression of Cs4CL1 was sensitive to mechanical wounding, while the expression of Cs4CL2 was UV-B-inducible. Enzymatic assays showed that both recombinant Cs4CL1 and Cs4CL2 transformed 4-coumaric acid (CM), ferulic acid (FR), and caffeic acid (CF) to their corresponding CoA ethers. Kinetic analysis indicated that the recombinant Cs4CL1 preferred to catalyze CF, while the recombinant Cs4CL2 favored to catalyze CM. The overexpression of both Cs4CL1 and Cs4CL2 increased the levels of chlorogenic acid and total lignin in transgenic tobacco seedlings. In addition, the overexpression of Cs4CL2 consistently increased the levels of three flavonoid compounds. These findings indicate the differences of Cs4CL1 and Cs4CL2 in the phenylpropanoid metabolism.

Tea and Citrus maxima complex induces apoptosis of human liver cancer cells via PI3K/AKT/mTOR pathway in vitro

Objective

In this study, black tea and Citrus maxima (BT-CM), yellow tea and C. maxima (YT-CM), green tea and C. maxima (GT-CM) as subjects, the active ingredient content and antioxidant activity of three tea and C. maxima (T-CM) were analyzed. The effects of three T-CMs on apoptosis of liver cells in vitro and its mechanism were further explored.

Methods

National standard method and HPLC were used for active ingredient analysis. MTT, cell flow cytometry and Western blot were used to analyze the effects of three T-CMs on cell proliferation, apoptosis, and its underlying molecular mechanism.

Results

The content of tea polyphenols, free amino acids, ratio of polyphenols and amino acids, ester catechins, non-ester catechins and caffeine in YT-CM and GT-CM was significantly higher than that of BT-CM. The in vitro antioxidant capacity of YT-CM and GT-CM was also significantly stronger than that of BT-CM. Three T-CMs had the effects of inhibiting proliferation, arresting cell cycle and inducing apoptosis in HepG2 and Bel7402 cells, especially YT-CM and GT-CM. Western blot analysis showed three T-CMs activated PI3K/AKT/mTOR signaling pathway and regulated the expression levels of apoptosis-related proteins Bax, Bcl-2 and Caspase-3/9. YT-CM and GT-CM had better ability to change the signal pathway than BT-CM.

Conclusion

In short, T-CMs, which combined different degrees of fermentation tea with C. maxima, were rich in nutrients and biologically active substances. T-CMs, especially YT-CM and GT-CM, are healthy drinks that help to prevent and treat liver cancer.

O-methylated flavonol as a multi-kinase inhibitor of leukemogenic kinases exhibits a potential treatment for acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous disease with poor overall survival characterized by various genetic changes. The continuous activation of oncogenic pathways leads to the development of drug resistance and limits current therapeutic efficacy. Therefore, a multi-targeting inhibitor may overcome drug resistance observed in AML treatment. Recently, groups of flavonoids, such as flavones and flavonols, have been shown to inhibit a variety of kinase activities, which provides potential opportunities for further anticancer applications.

PURPOSE

In this study, we evaluated the anticancer effects of flavonoid compounds collected from our in-house library and investigated their potential anticancer mechanisms by targeting multiple kinases for inhibition in AML cells.

METHODS

The cytotoxic effect of the compounds was detected by cell viability assays. The kinase inhibitory activity of the selected compound was detected by kinase-based and cell-based assays. The binding conformation and interactions were investigated by molecular docking analysis. Flow cytometry was used to evaluate the cell cycle distribution and cell apoptosis. The protein and gene expression were estimated by western blotting and qPCR, respectively.

RESULTS

In this study, an O-methylated flavonol (compound 11) was found to possess remarkable cytotoxic activity against AML cells compared to treatment in other cancer cell lines. The compound was demonstrated to act against multiple kinases, which play critical roles in survival signaling in AML, including FLT3, MNK2, RSK, DYRK2 and JAK2 with IC₅₀ values of 1 - 2 μM. Compared to our previous flavonoid compounds, which only showed inhibitions against MNKs or FLT3, compound 11 exhibited multiple kinase inhibitory abilities. Moreover, compound 11 showed effectiveness in inhibiting internal tandem duplications of FLT3 (FLT3-ITDs), which accounts for 25% of AML cases. The interactions between compound 11 and targeted kinases were investigated by molecular docking analysis. Mechanically, compound 11 caused dose-dependent accumulation of leukemic cells at the G₀/G₁ phase and followed by the cells undergoing apoptosis.

CONCLUSION

O-methylated flavonol, compound 11, can target multiple kinases, which may provide potential opportunities for the development of novel therapeutics for drug-resistant AMLs. This work provides a good starting point for further compound optimization.

An Integrated Metabolome and Transcriptome Analysis Reveal the Regulation Mechanisms of Flavonoid Biosynthesis in a Purple Tea Plant Cultivar

Purple tea plant cultivars, enrich with flavonoids and anthocyanins, are valuable materials for manufacturing tea with unique color and flavor. Researchers found that 'Zijuan' leaves changed from purple to green mainly caused by the decreased flavonoids and anthocyanins concentrations. The mechanism of flavonoids and anthocyanin biosynthesis has been studied in many purple tea plant cultivars and the key genes which regulated the biosynthesis of flavonoid and anthocyanins in different purple tea plant cultivars were quite different. Also, the molecular regulation mechanism underlying the flavonoids and anthocyanins biosynthesis during leaves development and color changes is less-thoroughly understood. In this study, an integrative analysis of transcriptome and metabolome was performed on the purple leaves and green leaves of 'Zijuan' tea plant to reveal the regulatory networks correlated to flavonoid biosynthesis and to identify key regulatory genes. Our results indicated that the 'Zijuan' new shoots leaves were purple might be due to the copigmentation of quercetin and kaempferol derivatives. In 'Zijuan' tea plant cultivar, flavonoids metabolites concentrations in purple leaves and green leaves were significantly influenced by the genes involved in flavonoid biosynthesis, transcriptional regulation, transport, and hormone response. Transcription factors including NAC008, MYB23, and bHLH96 and transporters such as ABC transporter I might be responsible for the flavonoid and anthocyanins accumulation in purple leaves. This study provides a new insight into the metabolism and molecular mechanisms underlying flavonoid and anthocyanin biosynthesis in tea plant.

Genome-wide transcriptome analysis and characterization of the cytochrome P450 flavonoid biosynthesis genes in pigeon pea (Cajanus cajan)

226 CcCYP450 genes were identified at the genomic level and were classified into 45 clades based on phylogenetic analysis. CcCYP75B165 gene was found that might play important roles in the biosynthesis of flavonoids in pigeon pea, and was significantly induced by methyl jasmonate (MeJA). The cytochrome P450 mono-oxygenase (CYP450) superfamily plays a key role in the flavonoid biosynthesis pathway and resists different kinds of stresses. Several CYP450 genes have been identified to be involved in the biosynthesis of crop protection agents. However, the CcCYP450 genes from pigeon pea have not been identified. Here, 226 CcCYP450 genes were identified at the genomic level by analysing the gene structure, distribution on chromosomes, gene duplication, and conserved motifs and were classified into 45 clades based on phylogenetic analysis. RNA-seq analysis revealed clear details of CcCYP450 genes that varied with time of MeJA (methyl jasmonate) induction. Among them, six CcCYP450 subfamily genes were found that might play important roles in the biosynthesis of flavonoids in pigeon pea. The overexpression of CcCYP75B165 in pigeon pea significantly induced the accumulation of genistin and downregulated the contents of cajaninstilbene acid, apigenin, isovitexin, and genistein and the expression of flavonoid synthase genes. This study provides theoretical guidance and plant genetic resources for cultivating new pigeon pea varieties with high flavonoid contents and exploring the molecular mechanisms of the biosynthesis of flavonoids under MeJA treatment.

Anthocyanin regulatory networks in Solanum tuberosum L. leaves elucidated via integrated metabolomics, transcriptomics, and StAN1 overexpression

BACKGROUND

Anthocyanins, which account for color variation and remove reactive oxygen species, are widely synthesized in plant tissues and organs. Using targeted metabolomics and nanopore full-length transcriptomics, including differential gene expression analysis, we aimed to reveal potato leaf anthocyanin biosynthetic pathways in different colored potato varieties.

RESULTS

Metabolomics analysis revealed 17 anthocyanins. Their levels varied significantly between the different colored varieties, explaining the leaf color differences. The leaves of the Purple Rose2 (PurpleR2) variety contained more petunidin 3-O-glucoside and malvidin 3-O-glucoside than the leaves of other varieties, whereas leaves of Red Rose3 (RedR3) contained more pelargonidin 3-O-glucoside than the leaves of other varieties. In total, 114 genes with significantly different expression were identified in the leaves of the three potato varieties. These included structural anthocyanin synthesis-regulating genes such as F3H, CHS, CHI, DFR, and anthocyanidin synthase and transcription factors belonging to multiple families such as C3H, MYB, ERF, NAC, bHLH, and WRKY. We selected an MYB family transcription factor to construct overexpression tobacco plants; overexpression of this factor promoted anthocyanin accumulation, turning the leaves purple and increasing their malvidin 3-o-glucoside and petunidin 3-o-glucoside content.

CONCLUSIONS

This study elucidates the effects of anthocyanin-related metabolites on potato leaves and identifies anthocyanin metabolic network candidate genes.

Sugar signal mediates flavonoid biosynthesis in tea leaves

Sugar metabolism and flavonoid biosynthesis vary with the development of tea leaves. In order to understand the regulatory mechanisms underlying the associations between them, a comprehensive transcriptomic analysis of naturally growing tea leaves at different stages of maturity was carried out. Based on weighted gene coexpression network analysis, the key gene modules (Modules 2 and 3) related to the varying relationship between sugar metabolism and flavonoid biosynthesis as well as the corresponding hub genes were obtained. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis showed that the transcription factors (TFs) in Modules 2 and 3 were mainly enriched in the pathway of plant hormone signal transduction. An in vitro study showed that the transcriptional levels of ERF1B-like TF for hexokinase inhibitor and sucrose treatments were upregulated, being respectively 28.1- and 30.2-fold higher than in the control, suggesting that ERF1B-like TFs participate in the sugar-induced regulation of flavonoid biosynthesis. The results of yeast one-hybrid and dual-luciferase assays demonstrated that CsF3'H, encoding flavonoid 3'-hydroxylase, was the target flavonoid biosynthetic gene for CsERF1B-like TF. Our study identified the potential key regulators participating in the metabolism of sugars and flavonoids, providing new insights into the crosstalk between sugar metabolism and flavonoid biosynthesis in tea plants.

Tea and its phytochemicals: Hidden health benefits & modulation of signaling cascade by phytochemicals

Tea, one of the most widely consumed beverages, is prepared from the leaves of the Camellia sinensis. The promising health recompenses of tea have been linked to its different phenolic components, which have diverse biological characteristics. Tea also contains several flavonoids, alkaloids, phenolic, theanine, etc., which are associated with anti-oxidant characteristics and a variety of health benefits. It can also lower the pervasiveness of neurological disorders as well as prevent different types of cancer, metabolic syndromes, cardiovascular diseases, urinary stone, obesity, type 2 diabetes. Keeping in mind that tea helps to improve health and prevents many diseases, its consumption has been regarded as a "health-promoting habit" and current medical investigators have established the scientific basis for this concept over time. The current review provides new updated information and perspectives on the tea phytochemicals and their overall health benefits based on molecular processes, experimental studies, and clinical trials.

Modular Approach to Benzofurans, 2H-Chromenes and Benzoxepines via Claisen Rearrangement and Ring-Closing Metathesis: Access to Phenylpropanoids

Benzofurans, 2 H -chromenes and benzoxepines are key structural elements present in several natural products and pharmaceuticals. Here, we describe an easy-to-execute strategy for the synthesis of benzofurans, 2 H -chromenes and benzoxepines, by employing Claisen rearrangement and ring-closing metathesis as key steps. A variety of phenols were converted into useful oxacycles in good to excellent yields. The ring-closing metathesis approach has been used to produce phenylpropanoid natural products. Examples described here include, the naturally occurring benzofurans such as 7-methoxywutaifuranal, 7-methoxywutaifuranol, 7-methoxywutaifuranate and the O -prenylated natural products like boropinic acid, boropinols A and C.

Hydroxylation decoration patterns of flavonoids in horticultural crops: chemistry, bioactivity and biosynthesis

Flavonoids are the most widespread polyphenolic compounds and are important dietary constituents present in horticultural crops such as fruits, vegetables, and tea. Natural flavonoids are responsible for important quality traits, such as food colors and beneficial dietary antioxidants and numerous investigations have shown that intake of flavonoids can reduce the incidence of various non-communicable diseases (NCDs). Analysis of the thousands of flavonoids reported so far has shown that different hydroxylation modifications affect their chemical properties and nutritional values. These diverse flavonoids can be classified based on different hydroxylation patterns in the B, C, A rings and multiple structure-activity analyses have shown that hydroxylation decoration at specific positions markedly enhances their bioactivities. This review focuses on current knowledge concerning hydroxylation of flavonoids catalyzed by several different types of hydroxylase enzymes. Flavonoid 3'-hydroxylase (F3'H) and flavonoid 3'5'-hydroxylase (F3'5'H) are important enzymes for the hydroxylation of the B ring of flavonoids. Flavanone 3-hydroxylase (F3H) is key for the hydroxylation of the C ring, while flavone 6-hydroxylase (F6H) and flavone 8-hydroxylase (F8H) are key enzymes for hydroxylation of the A ring. These key hydroxylases in the flavonoid biosynthesis pathway are promising targets for the future bioengineering of plants and mass production of flavonoids with designated hydroxylation patterns of high nutritional importance. In addition, hydroxylation in key places on the ring may help render flavonoids ready for degradation, the catabolic turnover of which may open the door for new lines of inquiry.

Transcriptome sequencing and flavonoid metabolism analysis in the leaves of three different cultivars of Acer truncatum

Young and mature leaves of three Acer truncatum varieties with different leaf colors were examined. Transcriptome sequencing and flavonoid metabolism were used to analyze the differential gene expression associated with different leaf colors and growth stages and the relationships between gene expression and flavonoid and anthocyanin contents to improve ornamental value and develop flavonoid-rich A. truncatum. Kyoto Encyclopedia of Genes and Genomes database annotation of differentially expressed genes indicated that the following genes were related to flavonoid synthesis: phenylpropanoid biosynthesis genes (PAL, C4H, 4CL and CHS), flavonoid biosynthesis genes (E2.1.1.104, CHI, FLS, F3'5'H and ANR), anthocyanin biosynthesis genes (ANS, DFR, HCT, BZ1, GT1, and UGT79B1), isoflavonoid biosynthesis genes (HIDH and CYP81E17), and their transcriptional regulator (MYB). A total of 234 types of flavonoids were detected. The types and contents of anthocyanins in the red-leaf varieties 'Hong Jingling' and 'Caidie Fanfei' were significantly higher than those in the green leaf cultivar 'Lv Baoshi', especially morning glory 3-O-glucoside, delphinidin 3-O-glucoside, and pelargonium-3-O-glucoside, which were not detected in 'Lv Baoshi'. Combined omics analysis showed that downregulated expression of C4H, CHS and F3'5'H and upregulated expression of FLS reduced the supply of raw materials for anthocyanin synthesis, and downstream ANR upregulation converted anthocyanins to procyanidins, increasing the total flavonoid content. F3'5'H expression was downregulated in the leaves of each variety with development, resulting in the accumulation of catechins and the gradual greening of the leaves. F3'5'H was significantly depleted in the young leaves of 'Hong Jingling' and 'Caidie Fanfei' compared with the young leaves of 'Lv Baoshi', while ANS and BZ1 were enriched significantly. It is concluded that F3'5'H, BZ1, and ANS are the key genes needed for breeding red A. truncatum and that ANR is the key gene needed for breeding varieties with a high flavonoids contens. These results may facilitate genetic modification or selection for further improvement of the ornamental qualities and flavonoid content of A. truncatum.

Isolation and Functional Characterization of Multiple NADPH-Cytochrome P450 Reductase Genes from Camellia sinensis in View of Catechin Biosynthesis

Catechins are critical constituents for the sensory quality and health-promoting benefits of tea. Cytochrome P450 monooxygenases are required for catechin biosynthesis and are dependent on NADPH-cytochrome P450 reductases (CPRs) to provide reducing equivalents for their activities. However, CPRs have not been identified in tea, and their relationship to catechin accumulation also remains unknown. Thus, three CsCPR genes were identified in this study, all of which had five CPR-related conserved domains and were targeted to the endoplasmic reticulum. These three recombinant CsCPR proteins could reduce cytochrome c using NADPH as an electron donor. Heterologous co-expression in yeast demonstrated that all the three CsCPRs could support the enzyme activities of CsC4H and CsF3'H. Correlation analysis indicated that the expression level of CsCPR1 (or CsCPR2 or CsCPR3) was positively correlated with 3',4',5'-catechin (or total catechins) content. Our results indicate that the CsCPRs are involved in the biosynthesis of catechins in tea leaves.

The expansion and diversity of the CYP75 gene family in Vitaceae

The CYP75 gene family plays an important role in flavonoid biosynthesis in plants. Little is known about the evolution of the gene family within the grape family. Here, we extracted the CYP75 genes from transcriptome data of 15 grape species and 36 representative genomes from other plants to explore the evolutionary history of the CYP75 gene family in Vitaceae. The structure of the CYP75 protein sequences is highly conserved with the variation mainly occurring in the N terminal and the middle region. The evolutionary analyses suggested classifying the CYP75 gene family into three groups in Vitaceae, namely Vitaceae A1, Vitaceae A2 and Vitaceae B. The Vitaceae A1 and A2 belong to the CYP75A subfamily and the Vitaceae B belongs to the CYP75B subfamily. Within the Vitaceae A1, most Vitaceae taxa present only one copy of the CYP75A protein sequence except for Vitis vinifera with a high number of sequences, which might have originated through recent gene duplications after its split from the other species. Vitaceae A2 contain only CYP75A sequences from Vitaceae sister to one from Camellia sinensis, probably representing a relict lineage. The CYP75B proteins were found to be dominated in Vitaceae and other angiosperms. Our results provide important insights into understanding the evolutionary history of the CYP75 gene family in Vitaceae and other angiosperms.

Elucidation of myricetin biosynthesis in Morella rubra of the Myricaceae

Flavonols are health-promoting bioactive compounds important for plant defense and human nutrition. Quercetin (Q) and kaempferol (K) biosynthesis have been studied extensively while little is known about myricetin (M) biosynthesis. The roles of flavonol synthases (FLSs) and flavonoid 3',5'-hydroxylase (F3'5'H) in M biosynthesis in Morella rubra, a member of the Myricaceae rich in M-based flavonols, were investigated. The level of MrFLS transcripts alone did not correlate well with the accumulation of M-based flavonols. However, combined transcript data for MrFLS1 and MrF3'5'H showed a good correlation with the accumulation of M-based flavonols in different tissues of M. rubra. Recombinant MrFLS1 and MrFLS2 proteins showed strong activity with dihydroquercetin (DHQ), dihydrokaempferol (DHK), and dihydromyricetin (DHM) as substrates, while recombinant MrF3'5'H protein preferred converting K to M, amongst a range of substrates. Tobacco (Nicotiana tabacum) overexpressing 35S::MrFLSs produced elevated levels of K-based and Q-based flavonols without affecting M-based flavonol levels, while tobacco overexpressing 35S::MrF3'5'H accumulated significantly higher levels of M-based flavonols. We conclude that M accumulation in M. rubra is affected by gene expression and enzyme specificity of FLS and F3'5'H as well as substrate availability. In the metabolic grid of flavonol biosynthesis, the strong activity of MrF3'5'H with K as substrate additionally promotes metabolic flux towards M in M. rubra.

Metabolomics and Transcriptomics Provide Insights into Anthocyanin Biosynthesis in the Developing Grains of Purple Wheat (Triticum aestivum L.)

Purple wheat is thought to have beneficial effects on humans owing to its high anthocyanin content. However, a systematic understanding of the anthocyanin biosynthesis process in developing wheat grain is lacking. Here, the dynamic changes in anthocyanin components and transcripts in the grain of purple wheat ZNM168 at five developmental stages (10, 15, 20, 25, and 30 DAF) were characterized. Compared with other anthocyanins, four components, cyanidin 3-O-rutinoside, cyanidin 3-O-glucoside, cyanidin 3,5-O-diglucoside, and malvidin 3-O-glucoside, were significantly accumulated with grain development. In particular, the considerable accumulation of cyanidin 3-O-rutinoside indicated that it was the pivotal pigment for the purple grain. Transcriptome analysis revealed that the nine differentially expressed genes related to anthocyanin biosynthesis belonged to the BZ1 group, the homologous enzyme encoded by the maize Bronze-1 locus, which may primarily serve to glucosylate anthocyanidins. By constructing a gene coexpression network based on weighted gene coexpression network analysis, the TaBZ1 UniGene (TraesCS1D02G019200) was predicted as a core gene in anthocyanin biosynthesis. In addition, correlation analysis between the metabolites and transcripts suggested that TraesCS2A01G527700 (TaCHS) and TraesCS6B01G006200 (TaANS) were considered critical structural genes in the anthocyanin biosynthesis pathway. This study provides insights to exploit genes pinpointed as genetic engineering targets, thereby breeding anthocyanin-enriched wheat.

Identification of Oil Palm's Consistently Upregulated Genes during Early Infections of Ganoderma boninense via RNA-Seq Technology and Real-Time Quantitative PCR

Basal stem rot (BSR) disease caused by pathogenic fungus Ganoderma boninense is a significant concern in the oil palm industry. G. boninense infection in oil palm induces defense-related genes. To understand oil palm defense mechanisms in response to fungal invasion, we analyzed differentially expressed genes (DEGs) derived from RNA-sequencing (RNA-seq) transcriptomic libraries of oil palm roots infected with G. boninense. A total of 126 DEGs were detected from the transcriptomic libraries of G. boninense-infected root tissues at different infection stages. Functional annotation via pathway enrichment analyses revealed that the DEGs were involved in the defense response against the pathogen. The expression of the selected DEGs was further confirmed using real-time quantitative PCR (qPCR) on independent oil palm seedlings and mature palm samples. Seven putative defense-related DEGs consistently showed upregulation in seedlings and mature plants during G. boninense infection. These seven genes might potentially be developed as biomarkers for the early detection of BSR in oil palm.

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.

Poplar MYB117 promotes anthocyanin synthesis and enhances flavonoid B-ring hydroxylation by up-regulating the flavonoid 3',5'-hydroxylase gene

Flavonoids, such as anthocyanins, proanthocyanidins, and flavonols, are widespread plant secondary metabolites and important for plant adaptation to diverse abiotic and biotic stresses. Flavonoids can be variously hydroxylated and decorated; their biological activity is partly dependent on the degree of hydroxylation of the B-ring. Flavonoid biosynthesis is regulated by MYB transcription factors, which have been identified and characterized in a diversity of plants. Here we characterize a new MYB activator, MYB117, in hybrid poplar (Populus tremula×tremuloides). When overexpressed in transgenic poplar plants, MYB117 enhanced anthocyanin accumulation in all tissues. Transcriptome analysis of MYB117-overexpressing poplars confirmed the up-regulation of flavonoid and anthocyanin biosynthesis genes, as well as two flavonoid 3',5'-hydroxylase (F3'5'H) genes. We also identified up-regulated cytochrome b5 genes, required for full activity of F3'5'H . Phytochemical analysis demonstrated a corresponding increase in B-ring hydroxylation of anthocyanins, proanthocyanidins, and flavonols in these transgenics. Similarly, overexpression of F3'5'H1 directly in hybrid poplar also resulted in increased B-ring hydroxylation, but without affecting overall flavonoid content. However, the overexpression of the cytochrome b5 gene in F3'5'H1-overexpressing plants did not further increase B-ring hydroxylation. Our data indicate that MYB117 regulates the biosynthesis of anthocyanins in poplar, but also enhances B-ring hydroxylation by up-regulating F3'5'H1.

Metabolomics reveals the influences of smoke-water and karrikinolide on the biosynthesis of flavonoids and terpenoids in Salvia miltiorrhiza

Metabolomics was used to study the influences of smoke-water (SW) and karrikinolide (KAR1) on the biosynthesis of flavonoids and terpenoids in Salvia miltiorrhiza Bunge. The results showed that a total of 178 and 199 differential metabolites were obtained in SW and KAR1, respectively, compared to the control. The differential metabolites were assigned to the corresponding metabolic pathways. The results indicated that some metabolic pathways in treatments of SW and KAR1 overlapped, suggesting that treatments of SW and KAR1 showed similar effects on the metabolic mechanism of S. miltiorrhiza. To obtain a clear overview of changes in metabolic regulation, TCA cycle, glycolytic pathway, biosynthesis of flavonoids and terpenoids and amino acids metabolism pathway were mapped into a network. We found that treatments with SW and KAR1 could significantly promote the biosynthesis of flavonoids and terpenoids in S. miltiorrhiza. This study could help us better understand the influences of SW and KAR1 on secondary metabolites and their underlying mechanism.

Transcriptome Profiling During Muscadine Berry Development Reveals the Dynamic of Polyphenols Metabolism

Muscadine grapes accumulate higher amounts of bioactive phenolics compared with other grape species. To identify the molecular events associated with polyphenolic accumulation that influence antioxidant capacity, two contrasting muscadine genotypes (C5 and C6) with varied phenolic/flavonoid content and antioxidant activity were investigated via RNA-sequencing during berry development. The results showed that berry development is concomitant with transcriptome profile changes, which was more pronounced at the véraison (V) stage. Despite that the downregulation pattern of gene expression dominated the upregulation through berry development, the C5 genotype maintained higher expression levels. Comparative transcript profiling allowed the identification of 94 differentially expressed genes with potential relevance in regulating fruit secondary metabolism, including 18 transcription factors and 76 structural genes. The genes underlying the critical enzymes in the modification reactions of polyphenolics biosynthetic pathway, including hydroxylation, methylation, and glycosylation were more pronounced during the immature stages of prevéraison (PrV), V, and postvéraison (PoV) in the C5 genotype, resulting in more accumulation of biologically active phenolic/flavonoid derivatives. The results suggested that muscadine grapes, as in bunch grapes (Vitis sp.); possess a similar mechanism that organizes polyphenolics accumulation; however, the set of total flavonoids (TFs) and structural genes coordinating the pathway varies between the two species.

Functional characterization of three flavonol synthase genes from Camellia sinensis: Roles in flavonol accumulation

Flavonol derivatives are a group of flavonoids benefiting human health. Their abundant presence in tea is associated with astringent taste. To date, mechanism pertaining to the biosynthesis of flavonols in tea plants remains unknown. In this study, we used bioinformatic analysis mining the tea genome and obtained three cDNAs that were annotated to encode flavonol synthases (FLS). Three cDNAs, namely CsFLSa, b, and c, were heterogenously expressed in E. coli to induce recombinant proteins, which were further used to incubate with three substrates, dihydrokampferol (DHK), dihydroquercetin (DHQ), and dihydromyricetin (DHM). The resulting data showed that three rCsFLSs preferred to catalyze (DHK). Overexpression of each cDNA in tobacco led to the increase of kampferol and the reduction of anthocyanins in flowers. Further metabolic profiling of flavan-3-ols in young tea shoots characterized that kaempferol derivatives were the most abundant, followed by quercetin and then myricetin derivatives. Taken together, these data characterized the key step committed to the biosynthesis of flavonols in tea leaves. Moreover, these data enhance understanding the metabolic accumulation relevance between flavonols and other main flavonoids such as flavan-3-ols in tea leaves.

Overexpression of GbF3'5'H1 Provides a Potential to Improve the Content of Epicatechin and Gallocatechin

The flavonoids in Ginkgo biloba L. (ginkgo) have important medicinal uses due to their antioxidant, antitumor, and blood circulation-promoting effects. However, the genetic mechanisms underlying flavonoid biosynthesis in ginkgo remain elusive. Flavonoid 3′, 5′-hydroxylase (F3′5′H) is an important enzyme in flavonoid synthesis. We detected a novel differentially expressed GbF3′5′H1 gene homologous to the F3′5′H enzyme involved in the flavonoid synthesis pathway through transcriptome sequencing. In this study, we characterized this gene, performed an expression analysis, and heterologously overexpressed GbF3′5′H1 in Populus. Our results showed that GbF3′5′H1 is abundant in the leaf and highly expressed during April. We also found four metabolites closely related to flavonoid biosynthesis. Importantly, the contents of 4′,5-dihydroxy-7-glucosyloxyflavanone, epicatechin, and gallocatechin were significantly higher in transgenic plants than in nontransgenic plants. Our findings revealed that the GbF3′5′H1 gene functions in the biosynthesis of flavonoid-related metabolites, suggesting that GbF3′5′H1 represents a prime candidate for future studies (e.g., gene-editing) aiming to optimize ginkgo flavonoid production, especially that of flavan-3-ols.

Proanthocyanidin Biosynthesis-a Matter of Protection

Proanthocyanidins are the second most abundant plant phenolic polymer, but, despite intensive investigation, several aspects of their biosynthesis and functions remain unclear.

Inheritance and quantitative trait loci analyses of the anthocyanins and catechins of Camellia sinensis cultivar 'Ziyan' with dark-purple leaves

Owing to the potential health benefits, anthocyanin-rich teas (Camellia sinensis) have attracted interest over the past decade. Previously, we developed the cultivar 'Ziyan,' which has dark-purple leaves because of the accumulation of a high amount of anthocyanins. In this study, we performed a genetic analysis of this anthocyanin-rich tea cultivar and 176 of its naturally pollinated offspring. For two consecutive years, we quantified the anthocyanins and catechins of 'Ziyan' and the offspring population. While >60% of the offspring accumulated less than half of the amount of anthocyanins of 'Ziyan,' 17 (2018) and 15 (2019) individuals exceeded 'Ziyan' in anthocyanin content. A negative correlation between anthocyanin and total catechin content (r = -0.59, P < 0.001) was observed. The population was genotyped with 131 SSR markers spanning all linkage groups of the C. sinensis genome. Kruskal-Wallis tests identified 10 markers significantly associated with anthocyanins, catechins and their ratios in both years. Quantitative trait locus (QTL) analyses using the interval mapping method detected 13 QTLs, suggesting the dark-purple trait of 'Ziyan' is because of the pyramiding of anthocyanin-promoting alleles on at least five linkage groups. Two genetic loci reversely related to anthocyanin and total catechin contents were identified. This study provides valuable information for genetic improvement of purple tea cultivars and for fine-mapping related genes.

Genome assembly of wild tea tree DASZ reveals pedigree and selection history of tea varieties

Wild teas are valuable genetic resources for studying domestication and breeding. Here we report the assembly of a high-quality chromosome-scale reference genome for an ancient tea tree. The further RNA sequencing of 217 diverse tea accessions clarifies the pedigree of tea cultivars and reveals key contributors in the breeding of Chinese tea. Candidate genes associated with flavonoid biosynthesis are identified by genome-wide association study. Specifically, diverse allelic function of CsANR, CsF3'5'H and CsMYB5 is verified by transient overexpression and enzymatic assays, providing comprehensive insights into the biosynthesis of catechins, the most important bioactive compounds in tea plants. The inconspicuous differentiation between ancient trees and cultivars at both genetic and metabolic levels implies that tea may not have undergone long-term artificial directional selection in terms of flavor-related metabolites. These genomic resources provide evolutionary insight into tea plants and lay the foundation for better understanding the biosynthesis of beneficial natural compounds.

Stacking triple genes increased proanthocyanidins level in Arabidopsis thaliana

Anthocyanins and proanthocyanidins are two important plant secondary metabolites, and they contribute to plant survival and human health. In particular, proanthocyanidins could also prevent ruminants from the damage of pasture bloat. However, the improvement of proanthocyanidins content remain unsatisfied. In this study, we attempted to improve proanthocyanidins level by gene stacking in Arabidopsis thaliana as prove-of-concept. Two proanthocyanidin pathway genes from tea plant, CsF3’5’H and CsANR2, were co-expressed in the wild type and PAP1 over-expression Arabidopsis. Over-expression of CsF3’5’H slightly affected anthocyanins level in leaves and proanthocyanidins in mature seed when expressed alone in the pap1-D line. Over-expression of CsANR2 led to an obvious decrease in anthocyanins in leaves of both wild type and pap1-D lines, but increase in proanthocyanidin level in mature seeds. Over-expression of CsANR2 in pap1-D lines lead to production of DMACA-reactive soluble proanthocyanidins in leaves, but not in wild type or pap1-D lines. Anthocyanins level was decreased in the leaves of CsF3’5’H, CsANR2 and pap1-D co-expression lines, but proanthocyanidins were increased remarkably in both leaves and mature seeds in the co-expression line. It is concluded that co-expression of CsANR2 and PAP1 in Arabidopsis produce soluble proanthocyanidins in leaves, and co-expression of CsF3’5’H, CsANR2 and PAP1 lead to a significant increase in proanthocyanidins in mature seeds. The transcript levels of endogenous CHS, DFR, ANS and ANR genes in Arabidopsis were up-regulated in the triple genes co-expression line. Based on these studies, it is possible to develop new plant germplasm with improved proanthocyanidins by co-expressing of multiple genes.

Comparison of Metabolome and Transcriptome of Flavonoid Biosynthesis Pathway in a Purple-Leaf Tea Germplasm Jinmingzao and a Green-Leaf Tea Germplasm Huangdan reveals Their Relationship with Genetic Mechanisms of Color Formation

Purple-leaf tea is a phenotype with unique color because of its high anthocyanin content. The special flavor of purple-leaf tea is highly different from that of green-leaf tea, and its main ingredient is also of economic value. To probe the genetic mechanism of the phenotypic characteristics of tea leaf color, we conducted widely targeted metabolic and transcriptomic profiling. The metabolites in the flavonoid biosynthetic pathway of purple- and green-leaf tea were compared, and results showed that phenolic compounds, including phenolic acids, flavonoids, and tannins, accumulated in purple-leaf tea. The high expression of genes related to flavonoid biosynthesis (e.g., PAL and LAR) exhibits the specific expression of biosynthesis and the accumulation of these metabolites. Our result also shows that two CsUFGTs were positively related to the accumulation of anthocyanin. Moreover, genes encoding transcription factors that regulate flavonoids were identified by coexpression analysis. These results may help to identify the metabolic factors that influence leaf color differentiation and provide reference for future research on leaf color biology and the genetic improvement of tea.

The style and substance of plant flavonoid decoration; towards defining both structure and function

Over 8000 different flavonoids have been described and a considerable number of new flavonoid structures are being elucidated every year. The advent of metabolomics alongside the development of phytochemical genetics - wherein the genetic basis underlying the regulation of the levels of plant metabolites is determined - has provided a massive boost to such efforts. That said our understanding of the individual function(s) of the vast majority of the metabolites that constitute this important class of phytochemicals remains unknown. Here we review what is known concerning the major decorative modifications of flavonoids in plants, namely hydroxylation, glycosylation, methylation and acylation. Our major focus is with regard to the in planta function of these modified compounds, however, we also highlight the demonstrated bioactive roles which they possess. We additionally performed a comprehensive survey of the flavonoids listed in the KNApSAcK database in order to assess the frequency of occurrence of each type of flavonoid modification. We conclude that whilst considerable research has been carried out regarding the biological roles of flavonoids most studies to date have merely provided information on the compound class or sub-classes thereof as a whole with too little currently known on the specific role of individual metabolites. We, therefore, finally suggest a framework based on currently available tools by which the relative importance of the individual compounds can be assessed under various biological conditions in order to fill this knowledge-gap.

Production of the secondary metabolite catechin by in vitro cultures of Camellia sinensis L

Background Catechin is one of the secondary metabolites in Camellia sinensis L. that is alternatively produced through in vitro cultures. The in vitro culture product is possibly improved by optimizing the culture medium with the addition of growth regulators and precursors. The purpose of this study was to confirm the success of the secondary catechin metabolite production through the in vitro culture of C. sinensis L in a relatively short time. Methods The secondary catechin metabolite product is obtained in about 40 days. The study was conducted by (1) leaf cutting for inoculation in Murashige and Skoog media with 1 μg/mL of 2,4-dichlorophenoxyacetic acid growth regulator; (2) the inoculation of callus multiplication on the same medium as a partially modified inoculation media condition with the addition of 1 μg/mL of 6-benzylaminopurine (BAP) and 2 μg/mL of 2,4-dichlorophenoxyacetic acid at concentration; (3) callus multiplication developed on a new medium containing phenylalanine precursors (300 μg/mL); (4) testing growth by harvesting the callus and weighing the wet weight of its biomass and (5) identification of the callus qualitatively and quantitatively by using high-performance liquid chromatography (HPLC). Results The level of secondary catechin metabolite produced was 2.54 μg/mL and 12.13 μg/mL in solid and suspension media, respectively. Conclusions It is concluded that the method is effective and efficient in producing catechin product from C. sinensis L.

Exploration of the Substrate Diversity of Leucoanthocyanidin Reductases

Proanthocyanidins (PAs) are mainly composed of epicatechin (EC) or catechin (C) subunits. C-type catechins (C and GC) are generally considered to be catalyzed by leucocyanidin reductase (LAR). In this study, we re-evaluated the function of LAR. LcLAR1 was isolated from Lotus corniculatus, which is rich in C-type catechins. Overexpression of LcLAR1 in tobacco resulted in a significantly increased content of EC and EC-glucoside. Overexpression of LcLAR1 in Arabidopsis thaliana promoted the accumulation of soluble PAs, including EC, PA dimers, and PA trimers. However, in the transgenic ans mutant overexpressing LcLAR1, the contents of C and C-glucoside were increased. In addition, overexpression of LcLAR1 in L. corniculatus resulted in a significant increase of C levels. Taken together, the products of LcLAR1 depended on the substrates, which revealed the substrate diversity of LcLAR1. Our study provides new insights into the flavonoid pathway, especially the role of LAR.

Transcriptomic Analysis Reveals the Molecular Adaptation of Three Major Secondary Metabolic Pathways to Multiple Macronutrient Starvation in Tea (Camellia sinensis)

Tea (Camellia sinensis (L.) O. Kuntze) is a widely consumed beverage. Lack of macronutrients is a major cause of tea yield and quality losses. Though the effects of macronutrient starvation on tea metabolism have been studied, little is known about their molecular mechanisms. Hence, we investigated changes in the gene expression of tea plants under nitrogen (N), phosphate (P), and potassium (K) deficient conditions by RNA-sequencing. A total of 9103 differentially expressed genes (DEG) were identified. Function enrichment analysis showed that many biological processes and pathways were common to N, P, and K starvation. In particular, cis-element analysis of promoter of genes uncovered that members of the WRKY, MYB, bHLH, NF-Y, NAC, Trihelix, and GATA families were more likely to regulate genes involved in catechins, l-theanine, and caffeine biosynthetic pathways. Our results provide a comprehensive insight into the mechanisms of responses to N, P, and K starvation, and a global basis for the improvement of tea quality and molecular breeding.