Transcription factor CsDOF regulates glutamine metabolism in tea plants (Camellia sinensis)

Chromatin accessibility mediated transcriptome changes contribute to flavor substance alterations and jasmonic acid hyperaccumulation during oolong tea withering process

During the oolong tea withering process, abiotic stresses induce significant changes in the content of various flavor substances and jasmonic acid (JA). However, the changes in chromatin accessibility during withering and their potential impact remain poorly understood. By integrating ATAC-seq, RNA-seq, metabolite, and hormone assays, we characterized the withering treatment-induced changes in chromatin accessibility, gene expression levels, important metabolite contents, and JA and JA-ILE contents. Additionally, we analyzed the effects of chromatin accessibility alterations on gene expression changes, content changes of important flavor substances, and JA hyperaccumulation. Our analysis identified a total of 3451 open- and 13 426 close-differentially accessible chromatin regions (DACRs) under withering treatment. Our findings indicate that close-DACRs-mediated down-regulated differentially expressed genes (DEGs) resulted in the reduced accumulation of multiple catechins during withering, whereas open-DACRs-mediated up-regulated DEGs contributed to the increased accumulation of important terpenoids, JA, JA-ILE and short-chain C5/C6 volatiles. We further highlighted important DACRs-mediated DEGs associated with the synthesis of catechins, terpenoids, JA and JA and short-chain C5/C6 volatiles and confirmed the broad effect of close-DACRs on catechin synthesis involving almost all enzymes in the pathway during withering. Importantly, we identified a novel MYB transcription factor (CsMYB83) regulating catechin synthesis and verified the binding of CsMYB83 in the promoter-DACRs regions of key catechin synthesis genes using DAP-seq. Overall, our results not only revealed a landscape of chromatin alters-mediated transcription, flavor substance and hormone changes under oolong tea withering, but also provided target genes for flavor improvement breeding in tea plant.

The R2R3-MYB transcription factor CsMYB42 regulates theanine biosynthesis in albino tea leaves

Theanine is a unique secondary metabolite in tea plants and contributes to the umami taste and health benefits of tea. However, theanine biosynthesis in tea plants is not fully understood, and its mechanism of transcriptional regulation remains poorly reported. Theanine content was significantly correlated with the expression of theanine biosynthesis-related gene CsGS1c and transcription factor CsMYB42 in different leaf positions and picking times, but there was no significant correlation in different tissues of albino tea plant 'Anjibaicha'. This suggests that CsMYB42 may regulate CsGS1c to synthesize theanine in albino tea leaves, and the regulation is tissue specific. CsMYB42 is a nuclear-localized R2R3-MYB transcription factor gene with transcriptional activation activity. Yeast one-hybrid assay and electrophoretic mobility shift assay confirmed the direct binding of CsMYB42 to the promoter of CsGS1c. Luciferase assay showed that CsMYB42 activates the CsGS1c expression. Furthermore, the inhibition of CsMYB42 using an antisense oligonucleotide in tea leaves decreased CsGS1c expression and theanine content. These results indicate that CsMYB42 plays a crucial role in activating the expression of CsGS1c and may be involved in the biosynthesis of theanine in albino tea leaves. This study provides fresh insights into the tissue-specific regulation of theanine biosynthesis, which laid a foundation for breeding high-theanine tea plants.

5mC DNA methylation modification-mediated regulation in tissue functional differentiation and important flavor substance synthesis of tea plant (Camellia sinensis L.)

In plants, 5mC DNA methylation is an important and conserved epistatic mark involving genomic stability, gene transcriptional regulation, developmental regulation, abiotic stress response, metabolite synthesis, etc. However, the roles of 5mC DNA methylation modification (5mC methylation) in tea plant growth and development (in pre-harvest processing) and flavor substance synthesis in pre- and post-harvest processing are unknown. We therefore conducted a comprehensive methylation analysis of four key pre-harvest tissues (root, leaf, flower, and fruit) and two processed leaves during oolong tea post-harvest processing. We found that differential 5mC methylation among four key tissues is closely related to tissue functional differentiation and that genes expressed tissue-specifically, responsible for tissue-specific functions, maintain relatively low 5mC methylation levels relative to non-tissue-specifically expressed genes. Importantly, hypomethylation modifications of CsAlaDC and TS/GS genes in roots provided the molecular basis for the dominant synthesis of theanine in roots. In addition, integration of 5mC DNA methylationomics, metabolomics, and transcriptomics of post-harvest leaves revealed that content changes in flavor metabolites during oolong tea processing were closely associated with transcription level changes in corresponding metabolite synthesis genes, and changes in transcript levels of these important synthesis genes were strictly regulated by 5mC methylation. We further report that some key genes during processing are regulated by 5mC methylation, which can effectively explain the content changes of important aroma metabolites, including α-farnesene, nerolidol, lipids, and taste substances such as catechins. Our results not only highlight the key roles of 5mC methylation in important flavor substance synthesis in pre- and post-harvest processing, but also provide epimutation-related gene targets for future improvement of tea quality or breeding of whole-tissue high-theanine varieties.

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.

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.

The association of HpDof1.7 and HpDof5.4 with soluble sugar accumulation in pitaya fruit by transcriptionally activating sugar metabolic genes

Soluble sugar is one of the important factors affecting fruit flavor and quality. Here, we report the identification of two Dof (DNA-binding with one finger) transcription factors termed HpDof1.7 and HpDof5.4, and their roles in influencing sugar accumulation in pitayas. HpDof1.7 and HpDof5.4 shared a similar expression pattern with sugar metabolism-related genes HpSuSy1 and HpINV2, and sugar transporter genes HpTMT2 and HpSWEET14 during pitayas maturation, and their expression pattern was also consistent with the accumulation of glucose and fructose, which were the predominant sugars in pitayas. HpDof1.7 and HpDof5.4 were both typical nucleus-localized proteins with trans-activation ability. Gel mobility shift assay revealed that HpDof1.7 and HpDof5.4 were bound to promoters of HpSuSy1, HpINV2, HpTMT2 and HpSWEET14. Finally, transient expression assays in tobacco leaves showed that HpDof1.7 and HpDof5.4 increased the activities of HpSuSy1, HpINV2, HpTMT2 and HpSWEET14 promoters, thus facilitating sugar accumulation by transcriptionally enhancing sugar metabolic pathway genes. Our findings provide a new perspective on the regulatory mechanisms of Dof transcription factors in sugar accumulation and pitaya fruit quality formation.

Regulation of biosynthesis of the main flavor-contributing metabolites in tea plant (Camellia sinensis): A review

In the process of adapting to the environment, tea plants (Camellia sinensis) endow tea with unique flavor and health functions, which should be attributed to secondary metabolites, including catechins, L-theanine, caffeine and terpene volatiles. Since the content of these flavor-contributing metabolites are mainly determined by the growth of tea plant, it is very important to understand their alteration and regulation mechanisms. In the present work, we first summarize the distribution, change characteristics of the main flavor-contributing metabolites in different cultivars, organs and under environmental stresses of tea plant. Subsequently, we discuss the regulating mechanisms involved in the biosynthesis of these metabolites based on the existing evidence. Finally, we propose the remarks and perspectives on the future study relating flavor-contributing metabolites. This review would contribute to the acceleration of research on the characteristic secondary metabolites and the breeding programs in tea plants.

Two Dof transcription factors promote flavonoid synthesis in kumquat fruit by activating C-glucosyltransferase

Although DNA binding with one finger (Dof) constitutes a crucial plant-specific family of transcription factors (TFs) that plays important roles in a wide range of biological processes, the molecular mechanisms underlying Dof regulation of flavonoid biosynthesis in plants remain largely unknown. Here, we characterized 28 Dof genes (FhDof1-FhDof28) from the 'Hongkong' kumquat (Fortunella hindsii) cultivar genome. Promoter analysis and transcriptome profiling revealed that four FhDofs - FhDof4, FhDof9, FhDof15, and FhDof16 - may be involved in flavonoid biosynthesis through binding to the flavonoid C-glycosyltransferase (FhCGT) promoter. We cloned homologous genes of four FhDofs, designated as FcDof4, FcDof9, FcDof15, FcDof16, and a homologous gene of FhCGT, designated as FcCGT, from the widely cultivated 'HuaPi' kumquat (F. crassifolia). Quantitative reverse transcription-polymerase chain reaction analysis revealed that FcDof4 and FcDof16 were significantly correlated with FcCGT expression during development stages in the 'HuaPi' fruit (Pearson's correlation coefficient > 0.7) and were localized to the nucleus. Results of yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays indicated that the two FcDofs trigger FcCGT expression by specifically binding to its promoters. Moreover, transient overexpression of FcDof4 and FcDof16 enhances the transcription of structural genes in the flavonoid biosynthetic pathway and increases C-glycosylflavonoid content. Our results provide strong evidence that the TFs FcDof4 and FcDof16 promote flavonoid synthesis in kumquat fruit by activating FcCGT expression.

Theanine metabolism and transport in tea plants (Camellia sinensis L.): advances and perspectives

Theanine, a tea plant-specific non-proteinogenic amino acid, is the most abundant free amino acid in tea leaves. It is also one of the most important quality components of tea because it endows the "umami" taste, relaxation-promoting, and many other health benefits of tea infusion. Its content in tea leaves is directly correlated with the quality and price of green tea. Theanine biosynthesis primarily occurs in roots and is transported to new shoots in tea plants. Recently, great advances have been made in theanine metabolism and transport in tea plants. Along with the deciphering of the genomic sequences of tea plants, new genes in theanine metabolic pathway were discovered and functionally characterized. Theanine transporters were identified and were characterized on the affinity for: theanine, substrate specificity, spatiotemporal expression, and the role in theanine root-to-shoot transport. The mechanisms underlying the regulation of theanine accumulation by: cultivars, seasons, nutrients, and environmental factors are also being rapidly uncovered. Transcription factors were identified to be critical regulators of theanine biosynthesis. In this review, we summarize the progresses in theanine: biosynthesis, catabolism, and transport processes. We also discuss the future studies on theanine in tea plants, and application of the knowledge to crops to synthesize theanine to improve the health-promoting quality of non-tea crops.

Ammonium transporter PsAMT1.2 from Populus simonii functions in nitrogen uptake and salt resistance

Ammonium (NH4+) is a primary nitrogen (N) source for many species, and NH4+ uptake is mediated by various transporters. However, the effects of NH4+ transporters on N uptake and metabolism under salt stress remain unclear. In the present study, we investigated the expression characteristics and transport function of PsAMT1.2 in Populus simonii and its role in ammonium uptake and metabolism under salt stress. PsAMT1.2 was localized in the plasma membrane highly expressed in the roots. Heterologous functionality tests demonstrated that PsAMT1.2 mediates NH4+ permeation across the plasma membrane in yeast mutants, restoring growth. A short-term NH4+ uptake experiment showed that PsAMT1.2 is a high-affinity NH4+ transporter with a Km value of 80.603 μM for NH4+. Compared with the wild type (WT, Populus tremula × Populus alba INRA 717-IB4 genotype), PsAMT1.2-overexpressing transgenic poplar grew better, with higher increases in stem height and relative chlorophyll content under both control and salt-stress conditions. PsAMT1.2 overexpression significantly increased the total NH4+ concentration and total N of whole plants under salt stress. The glutamate synthase (GS), glutamine synthetase (GOGAT) and glutamate dehydrogenase (GDH) activities and the total amino acids largely increased in the roots of PsAMT1.2-overexpressing transgenic plants compared with the WT plants under control conditions, suggesting that PsAMT1.2 overexpression promotes NH4+ assimilation and metabolism in poplar roots. Consistent with the increased total amino acid content, GS1.3, GS2 and Fd-GOGAT expression was upregulated in the roots and leaves of the PsAMT1.2-overexpressing transgenic plants compared with the WT plants under salt stress. Collectively, PsAMT1.2 encodes a high-affinity NH4+ transporter crucial to NH4+ uptake and metabolism under salt stress.