Analysis of stereochemistry and biosynthesis of epicatechin in tea plants by chiral phase high performance liquid chromatography

Comprehensive studies of the serine carboxypeptidase-like (SCPL) gene family in Carya cathayensis revealed the roles of SCPL4 in epigallocatechin-3-gallate (EGCG) synthesis and drought tolerance

Hickory (Carya cathayensis) nuts are rich in epigallocatechin-3-gallate (EGCG) with multiple health functions. EGCG also regulates plant growth, development and stress responses. However, research on the synthesis mechanism of EGCG and its function in hickory is currently limited. Herein, 44 serine carboxypeptidase-like (SCPL) members were identified from the hickory genome and classified into three major categories: SCPL-I, SCPL-II, and SCPL-III. In the CcSCPLs-IA branch, CcSCPL3/4/5/8/9/11/13 showed differential expression patterns in various tissues, especially with relatively high expression levels in plant roots, female flowers and seed coat. These proteins have a catalytic triad composed of serine (Ser), aspartic acid (Asp) and histidine (His). Ser-His in the triad and arginine (Arg) mediated the docking of CcSCPL3/4/5/11 with 1-O-galloyl-β-d-glucose (βG) and epigallocatechin (EGC), whereas the Asp of the triad did not. CcSCPL4 was further confirmed to promote the synthesis of EGCG in tobacco leaves. CcSCPL4 may function as monomer and be mainly localized within cellular structures outside the nucleus. Notably, the expression level of CcSCPL4 significantly changed after drought, cold, and salt stress, with the highest expression level under drought stress. Meanwhile CcSCPL4 over-expression could enhance the drought resistance of Saccharomyces cerevisiae and Arabidopsis. This study elucidates key enzymes for EGCG synthesis and their role in drought resistance, providing insights into the EGCG synthesis pathway and molecular breeding of hickory in future.

Effects of Microbial Proteins on Qingzhuan Tea Sensory Quality during Pile Fermentation

To determine the effects of microbial proteins on Qingzhuan tea sensory quality during tea pile fermentation, tea leaf metabolomic and microorganism proteomic analyses were performed. In total, 1835 differential metabolites and 443 differentially expressed proteins of the microorganisms were identified. Correlation analysis between metabolomics and proteomics data revealed that the levels of microbial proteins EG II and CBH I cellulase may play important roles in cell wall construction and permeability, which were crucial for the interaction between tea leaves and microorganisms. Microbial proteins heat shock proteins (HSP), alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and CuAO related to detoxification and stress responses showed a positive correlation with tea theanine, glutamine, γ-aminobutyric acid, glutamic acid, catechin, (-)-gallocatechin gallate, and (-)-catechin gallate, suggesting their effects on tea characteristic compound accumulation, thus affecting Qingzhuan tea sensory quality.

Research progress of proanthocyanidins and anthocyanidins

Proanthocyanidins (PA) are polyphenol compounds that are widely distributed in the bark, fruit core, skin, or seeds of various plants. Anthocyanidins are water-soluble natural pigments widely found in plants. They are all flavonoids, a major coloring substance in plants and fruits. In recent years, research into PA and anthocyanins has become increasingly popular because of their excellent anti-oxidation, scavenging of reactive oxygen free radicals and other physical and chemical activities, and their anti-cancer, vision protection, aging prevention, skin beauty pharmacological, and nutraceutical effects. Especially, recent systematic reviews and meta-analyses indicate their value, safety, and efficacy in the prevention, adjuvant therapy, and management of cardiometabolic disease. Here, we summarize their research progress from the aspects of chemical structure, biosynthetic pathways, distribution, extraction and separation, coloration, efficacy, and potential. The comparison between them might provide a reference for their development and efficient utilization. However, more large-sample-size randomized controlled trials and high-quality studies are needed to firmly establish their clinical efficacy.

Metabolomic analysis reveals the quality characteristics of Yi Gong tea leaves at different harvesting periods

To obtain a theoretical reference for understanding the changes in metabolites of Yigong tea leaves during different harvesting periods and to determine the optimal harvesting period, we performed a metabolome comparison using UPLC-Q-Exactive MS on Yigong tea leaves from different harvesting periods. The results indicated that a total of 41 metabolites were significantly altered during the growth of Yi Gong tea leaves. These involved 7 amino acids and their derivatives, 16 flavonols and flavonol glycosides, 4 organic acids, 3 catechins, 3 carbohydrates, 7 fatty acid esters, 1 terpene, and 3 substances from others. In particular, the levels of arginine and glutamine were higher in early-harvested tea leaves than in late-harvested tea leaves; the levels of flavonoids and flavonols were higher in late-harvested tea leaves. Metabolic pathway analysis revealed that the caffeine metabolism and the flavonoid biosynthesis perform key roles in Yigong tea leaves from different harvesting periods. PRACTICAL APPLICATIONS: At present, the application of metabolomics in tea research is focused on the study of pesticide residues, processing processes, environmental stresses, and regional differences. This study is to focus on the effect of the tea harvesting period on tea quality through metabolomics. Through metabolomics, we can better determine the optimal tea harvesting period, and this study can improve the quality of this tea product and may be able to bring some favourable favorable contributions contribution to the local tea marketing in the future.

Transcriptome and Metabolome Analysis of the Synthesis Pathways of Allelochemicals in Eupatorium adenophorum

Eupatorium adenophorum (Crofton weed) is an invasive weed in more than 30 countries. It inhibits the growth of surrounding plants by releasing allelochemicals during its invasion. However, the synthetic pathways and molecular mechanisms of its allelochemicals have been rarely reported. In this study, the related genes and pathways of allelochemicals in E. adenophorum were analyzed. Transcriptome analysis showed that differentially expressed genes (DEGs) were mainly enriched in the phenylpropanoid biosynthetic pathway and flavonoid biosynthetic pathway. Thirty-three DEGs involved in the synthesis of allelochemicals were identified, and 30 DEGs showed significant differences in blades and stems. Six allelochemicals were identified from blades and stems by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Correlation analysis of genes and metabolites showed a strong correlation between the five genes and allelochemicals. In addition, this study supplemented the biosynthetic pathway of Eupatorium adenophorum B (HHO). It was found that acyclic sesquiterpene synthase (NES), δ-cadinene synthase (TPS), and cytochrome P450 (P450) were involved in the synthesis of HHO. These findings provide a dynamic spectrum consisting of allelochemical metabolism and a coexpression network of allelochemical synthesis genes in E. adenophorum.

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.

Evolutionary and functional characterization of leucoanthocyanidin reductases from Camellia sinensis

MAIN CONCLUSION

LARs promoted the biosynthesis of catechin monomers and inhibited their polymerization. The accumulation of catechin monomers and polymers was increased by up-regulating the expression of NtLAR and NtANR s in CsMYB5b transgenic tobacco. Tea is rich in polyphenolic compounds, and catechins are the major polyphenols in tea. The biosynthesis of polyphenols is closely related to the expression of the leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) genes. In this paper, an evolutionary analysis and functional characterization of three CsLARs were performed. The phylogenetic tree showed that plant LARs could be grouped into three, including gymnosperms, monocotyledons and dicotyledons (clusters I and II). The eighth amino acid residue in a conserved LAR-specific motif is changeable due to a transversion (G → T) and transition (G → C) that occur in the corresponding codon. Therefore, plant LARs can be classified as G-type, A-type and S-type LARs due to this variable amino acid residue. Although (2R, 3S)-trans-flavan-3-ols were the products of recombinant CsLARs proteins expressed in Escherichia coli, both (2R, 3S)-trans and (2R, 3R)-cis-flavan-3-ols were detected in tobacco overexpressing CsLARs. However, a butanol/HCl hydrolysis assay indicated that overexpression of the CsLARs caused a decrease in polymerized catechins. A hybridization experiment with CsLARc + AtPAP1 also showed that no polymers other than epicatechin, catechin and glycoside were detected, although the accumulation of anthocyanins was markedly decreased. CsMYB5b promoted the biosynthesis of both flavan-3-ols and proanthocyanidins (PAs). Therefore, LARs promoted the biosynthesis of catechin monomers and inhibited their polymerization. The accumulation of catechin monomers and polymers was increased by up-regulating the expression of the NtLAR and NtANRs in CsMYB5b transgenic tobacco.

Metabolic Characterization of the Anthocyanidin Reductase Pathway Involved in the Biosynthesis of Flavan-3-ols in Elite Shuchazao Tea (Camellia sinensis) Cultivar in the Field

Anthocyanidin reductase (ANR) is a key enzyme in the ANR biosynthetic pathway of flavan-3-ols and proanthocyanidins (PAs) in plants. Herein, we report characterization of the ANR pathway of flavan-3-ols in Shuchazao tea (Camellia sinesis), which is an elite and widely grown cultivar in China and is rich in flavan-3-ols providing with high nutritional value to human health. In our study, metabolic profiling was preformed to identify two conjugates and four aglycones of flavan-3-ols: (-)-epigallocatechin-gallate [(-)-EGCG], (-)-epicatechin-gallate [(-)-ECG], (-)-epigallocatechin [(-)-EGC], (-)-epicatechin [(-)-EC], (+)-catechin [(+)-Ca], and (+)-gallocatechin [(+)-GC], of which (-)-EGCG, (-)-ECG, (-)-EGC, and (-)-EC accounted for 70-85% of total flavan-3-ols in different tissues. Crude ANR enzyme was extracted from young leaves. Enzymatic assays showed that crude ANR extracts catalyzed cyanidin and delphinidin to (-)-EC and (-)-Ca and (-)-EGC and (-)-GC, respectively, in which (-)-EC and (-)-EGC were major products. Moreover, two ANR cDNAs were cloned from leaves, namely CssANRa and CssANRb. His-Tag fused recombinant CssANRa and CssANRb converted cyanidin and delphinidin to (-)-EC and (-)-Ca and (-)-EGC and (-)-GC, respectively. In addition, (+)-EC was observed from the catalysis of recombinant CssANRa and CssANRb. Further overexpression of the two genes in tobacco led to the formation of PAs in flowers and the reduction of anthocyanins. Taken together, these data indicate that the majority of leaf flavan-3-ols in Shuchazao's leaves were produced from the ANR pathway.