Lipidomics analysis unravels changes from flavor precursors in different processing treatments of purple-leaf tea.

BACKGROUND: Lipids are one of the most important bioactive compounds, affecting the character and quality of tea. However, the contribution of lipids to tea productions is still elusive. Here, we systematically identified the lipid profiles of green, oolong, and black teas in purple-leaf tea (Jinmingzao, JMZ) and green-leaf tea (Huangdan, HD), respectively. RESULTS: The lipids analysis showed regular accumulation in tea products with different manufacturing processes, among which the fatty acids, glycerolipids, glycerophospholipids, and sphingolipids contribute to the quality characteristics of tea products, including typical fatty acyl (FA), monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerols (DGDG), and phosphatidylcholine (PC). Compared tea materials with products, levels of fatty acids were up-regulated, while glycerolipids and glycerophospholipids were down-regulated in tea products. FA 18:3, FA 16:0, MGDG 36:6, DGDG 36:6, PC 34:3, and PC 36:6 were the negative contributors to green tea flavor formation of purple-leaf tea. The pathway analysis of significant lipids in materials and products of purple-leaf tea were enriched linolenic acid metabolism pathway and glycerolipid metabolism. CONCLUSION: This study provides insights into the lipid metabolism profiles of different tea leaf colors, and found that fatty acids are essential precursors of black tea flavor formation. © 2021 Society of Chemical Industry.

R2R3-MYB transcription factor family in tea plant (Camellia sinensis): Genome-wide characterization, phylogeny, chromosome location, structure and expression patterns.

MYB transcription factors play essential roles in many biological processes and environmental stimuli. However, the functions of the MYB transcription factor family in tea plants have not been elucidated. Here, a total of 122 CsR2R3-MYB genes were identified from the chromosome level genome of tea plant (Camellia sinensis). The CsR2R3-MYB genes were phylogenetically classified into 25 groups. Results from the structure analysis of the gene, conserved motifs, and chromosomal distribution supported the relative conservation of the R2R3-MYB genes family in the tea plant. Synteny analysis indicated that 122, 34, and 112 CsR2R3-MYB genes were orthologous to Arabidopsis thaliana, Oryza sativa and C. sinensis var. 'huangdan' (HD), respectively. Tissue-specific expression showed that all CsR2R3-MYB genes had different expression patterns in the tea plant tissues, indicating that these genes may perform diverse functions. The expression patterns of representative R2R3-MYB genes and the regulatory network of the main anthocyanin components were analyzed, which suggested that CsMYB17 may played a key role in the regulation of cya-3-O-gal, del-3-O-gal, cya-3-O-glu and pel-3-O-glu. Results from the qRT-PCR validation of selected genes suggested that CsR2R3-MYB genes were induced in response to drought, cold, GA, and ABA treatments. Overall, this study provides comprehensive and systematic information for research on the function of R2R3-MYB genes in tea plants.

Integrated transcriptomics and metabolomics provide novel insight into changes in specialized metabolites in an albino tea cultivar (Camellia sinensis (L.) O. Kuntz).

Tea varieties with specific colours have often been studied by researchers. However, previous studies on the albinism of tea plants have mostly been based on plants with different genetic backgrounds or focused on common components in albino tea leaves, such as amino acids, flavones, and carotenoids. In this study, we conducted widely targeted metabolic and transcriptomic analyses between a wildtype tea genotype (Shuixian, LS) and its albino mutant (Huangjinshuixian, HS). At the molecular level, alteration of gene expression levels in the MEP pathway may have reduced the production of chlorophyll and carotenoids in HS, which could be the main cause of the phenotypic changes in HS. At the metabolite level, a large number of metabolites related to light protection that significantly accumulated in HS, including flavones, anthocyanins, flavonols, flavanones, vitamins and their derivatives, polyphenols, phenolamides. This result, combined with an enzyme activity experiment, suggested that the absence of photosynthetic pigments made the albino tea leaves of HS more vulnerable to UV stress, even under normal light conditions. In addition, except for the common amino acids, we also identified numerous nitrogen-containing compounds, including nucleotides and their derivates, amino acid derivatives, glycerophospholipids, and phenolamides, which implied that significant accumulation of NH4+ in albino tea leaves could not only promote amino acid synthesis but could also activate other specialized metabolic pathways related to nitrogen metabolism. In conclusion, our results provide new information to guide further studies of the extensive metabolic reprogramming events caused by albinism in tea plants.

Exploration of the Effects of Different Blue LED Light Intensities on Flavonoid and Lipid Metabolism in Tea Plants via Transcriptomics and Metabolomics.

Blue light extensively regulates multiple physiological processes and secondary metabolism of plants. Although blue light quantity (fluence rate) is important for plant life, few studies have focused on the effects of different blue light intensity on plant secondary metabolism regulation, including tea plants. Here, we performed transcriptomic and metabolomic analyses of young tea shoots (one bud and two leaves) under three levels of supplemental blue light, including low-intensity blue light (LBL, 50 µmol m-2 s-1), medium-intensity blue light (MBL, 100 µmol m-2 s-1), and high-intensity blue light (HBL, 200 µmol m-2 s-1). The total number of differentially expressed genes (DEGs) in LBL, MBL and HBL was 1, 7 and 1097, respectively, indicating that high-intensity blue light comprehensively affects the transcription of tea plants. These DEGs were primarily annotated to the pathways of photosynthesis, lipid metabolism and flavonoid synthesis. In addition, the most abundant transcription factor (TF) families in DEGs were bHLH and MYB, which have been shown to be widely involved in the regulation of plant flavonoids. The significantly changed metabolites that we detected contained 15 lipids and 6 flavonoid components. Further weighted gene co-expression network analysis (WGCNA) indicated that CsMYB (TEA001045) may be a hub gene for the regulation of lipid and flavonoid metabolism by blue light. Our results may help to establish a foundation for future research investigating the regulation of woody plants by blue light.

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.

Genome-wide and expression pattern analysis of JAZ family involved in stress responses and postharvest processing treatments in Camellia sinensis.

The JASMONATE-ZIM DOMAIN (JAZ) family genes are key repressors in the jasmonic acid signal transduction pathway. Recently, the JAZ gene family has been systematically characterized in many plants. However, this gene family has not been explored in the tea plant. In this study, 13 CsJAZ genes were identified in the tea plant genome. Phylogenetic analysis showed that the JAZ proteins from tea and other plants clustered into 11 sub-groups. The CsJAZ gene transcriptional regulatory network predictive and expression pattern analyses suggest that these genes play vital roles in abiotic stress responses, phytohormone crosstalk and growth and development of the tea plant. In addition, the CsJAZ gene expression profiles were associated with tea postharvest processing. Our work provides a comprehensive understanding of the CsJAZ family and will help elucidate their contributions to tea quality during tea postharvest processing.

Identification of CBF Transcription Factors in Tea Plants and a Survey of Potential CBF Target Genes under Low Temperature.

C-repeat binding factors (CBFs) are key signaling genes that can be rapidly induced by cold and bind to the C-repeat/dehydration-responsive motif (CRT/DRE) in the promoter region of the downstream cold-responsive (COR) genes, which play a vital role in the plant response to low temperature. However, the CBF family in tea plants has not yet been elucidated, and the possible target genes regulated by this family under low temperature are still unclear. In this study, we identified five CsCBF family genes in the tea plant genome and analyzed their phylogenetic tree, conserved domains and motifs, and cis-elements. These results indicate that CsCBF3 may be unique in the CsCBF family. This is further supported by our findings from the low-temperature treatment: all the CsCBF genes except CsCBF3 were significantly induced after treatment at 4 °C. The expression profiles of eight tea plant tissues showed that CsCBFs were mainly expressed in winter mature leaves, roots and fruits. Furthermore, 685 potential target genes were identified by transcriptome data and CRT/DRE element information. These target genes play a functional role under the low temperatures of winter through multiple pathways, including carbohydrate metabolism, lipid metabolism, cell wall modification, circadian rhythm, calcium signaling, transcriptional cascade, and hormone signaling pathways. Our findings will further the understanding of the stress regulatory network of CsCBFs in tea plants.

Transcriptome and Metabolite Profiling Reveal Novel Insights into Volatile Heterosis in the Tea Plant (Camellia Sinensis).

Tea aroma is a key indicator for evaluating tea quality. Although notable success in tea aroma improvement has been achieved with heterosis breeding technology, the molecular basis underlying heterosis remains largely unexplored. Thus, the present report studies the tea plant volatile heterosis using a high-throughput next-generation RNA-seq strategy and gas chromatography-mass spectrometry. Phenotypically, we found higher terpenoid volatile and green leaf volatile contents by gas chromatography-mass spectrometry in the F1 hybrids than in their parental lines. Volatile heterosis was obvious in both F1 hybrids. At the molecular level, the comparative transcriptomics analysis revealed that approximately 41% (9027 of 21,995) of the genes showed non-additive expression, whereas only 7.83% (1723 of 21,995) showed additive expression. Among the non-additive genes, 42.1% showed high parental dominance and 17.6% showed over-dominance. Among different expression genes with high parental dominance and over-dominance expression patterns, KEGG and GO analyses found that plant hormone signal transduction, tea plant physiological process related pathways and most pathways associated with tea tree volatiles were enriched. In addition, we identified multiple genes (CsDXS, CsAATC2, CsSPLA2, etc.) and transcription factors (CsMYB1, CsbHLH79, CsWRKY40, etc.) that played important roles in tea volatile heterosis. Based on transcriptome and metabolite profiling, we conclude that non-additive action plays a major role in tea volatile heterosis. Genes and transcription factors involved in tea volatiles showing over-dominance expression patterns can be considered candidate genes and provide novel clues for breeding high-volatile tea varieties.

Identification, expression, and putative target gene analysis of nuclear factor-Y (NF-Y) transcription factors in tea plant (Camellia sinensis).

MAIN CONCLUSION: Genome-wide identification and characterization of nuclear factor-Y family in tea plants, and their expression profiles and putative targets provide the basis for further elucidation of their biological functions. The nuclear factor-Y (NF-Y) transcription factors (TFs) are crucial regulators of plant growth and physiology. However, the NF-Y TFs in tea plant (Camellia sinensis) have not yet been elucidated, and its biological functions, especially the putative target genes within the genome range, are still unclear. In this study, we identified 35 CsNF-Y encoding genes in the tea plant genome, including 10 CsNF-YAs, 15 CsNF-YBs and 10 CsNF-YCs. Their conserved domains and motifs, phylogeny, duplication event, gene structure, and promoter were subsequently analyzed. Tissue expression analysis revealed that CsNF-Ys exhibited three distinct expression patterns in eight tea tree tissues, among which CsNF-YAs were moderately expressed. Drought and abscisic acid (ABA) treatment indicated that CsNF-YAs may have a greater impact than other subunit members. Furthermore, through the genome-wide investigation of the presence of the CCAAT box, we found that CsNF-Ys may participate in the development of tea plants by regulating target genes of multiple physiological pathways, including photosynthesis, chlorophyll metabolism, fatty acid biosynthesis, and amino acid metabolism pathways. Our findings will contribute to the functional analysis of NF-Y genes in woody plants and the cultivation of high-quality tea plant cultivars.