Differential Metabolic Profiles during the Albescent Stages of 'Anji Baicha' (Camellia sinensis)

In-depth exploration of the genomic diversity in tea varieties based on a newly constructed pangenome of Camellia sinensis

Tea, one of the most widely consumed beverages globally, exhibits remarkable genomic diversity in its underlying flavour and health-related compounds. In this study, we present the construction and analysis of a tea pangenome comprising a total of 11 genomes, with a focus on three newly sequenced genomes comprising the purple-leaved assamica cultivar "Zijuan", the temperature-sensitive sinensis cultivar "Anjibaicha" and the wild accession "L618" whose assemblies exhibited excellent quality scores as they profited from latest sequencing technologies. Our analysis incorporates a detailed investigation of transposon complement across the tea pangenome, revealing shared patterns of transposon distribution among the studied genomes and improved transposon resolution with long read technologies, as shown by long terminal repeat (LTR) Assembly Index analysis. Furthermore, our study encompasses a gene-centric exploration of the pangenome, exploring the genomic landscape of the catechin pathway with our study, providing insights on copy number alterations and gene-centric variants, especially for Anthocyanidin synthases. We constructed a gene-centric pangenome by structurally and functionally annotating all available genomes using an identical pipeline, which both increased gene completeness and allowed for a high functional annotation rate. This improved and consistently annotated gene set will allow for a better comparison between tea genomes. We used this improved pangenome to capture the core and dispensable gene repertoire, elucidating the functional diversity present within the tea species. This pangenome resource might serve as a valuable resource for understanding the fundamental genetic basis of traits such as flavour, stress tolerance, and disease resistance, with implications for tea breeding programmes.

Non-targeted metabolomics reveals the taste variations during Baccaurea ramiflora Lour. fruit maturation

Baccaurea ramiflora Lour. is a new kind of underutilized wild fruit tree; the metabolic reasons for its fruit flavor changes are not yet clear. In this study, the pink flesh of this excellent tasting fruit (BR) was used to reveal the metabolic causes of taste variations through five developmental stages. We identified 154 common differential metabolites of different developmental stages based on non-targeted metabolomics analysis. The accumulation of sugar and fatty acids increased significantly after 73 days, while citric acid decreased significantly. Flesh color accumulation mainly occurred 53 days ago, and vitamin accumulation occurred after 93 days. Interestingly, L-sorbose and 5-hydroxyindole-3-acetic acid were positively correlated with the sugar-acid ratio but negatively correlated with titratable acids. It indicated that L-sorbose and 5-hydroxyindole-3-acetic acid may be taste biomarkers of BR B. ramiflora. The results provided new metabolic lines of evidence for the taste variation during the ripening process of B. ramiflora.

Multi-Omics Research Accelerates the Clarification of the Formation Mechanism and the Influence of Leaf Color Variation in Tea (Camellia sinensis) Plants

Tea is a popular beverage with characteristic functional and flavor qualities, known to be rich in bioactive metabolites such as tea polyphenols and theanine. Recently, tea varieties with variations in leaf color have been widely used in agriculture production due to their potential advantages in terms of tea quality. Numerous studies have used genome, transcriptome, metabolome, proteome, and lipidome methods to uncover the causes of leaf color variations and investigate their impacts on the accumulation of crucial bioactive metabolites in tea plants. Through a comprehensive review of various omics investigations, we note that decreased expression levels of critical genes in the biosynthesis of chlorophyll and carotenoids, activated chlorophyll degradation, and an impaired photosynthetic chain function are related to the chlorina phenotype in tea plants. For purple-leaf tea, increased expression levels of late biosynthetic genes in the flavonoid synthesis pathway and anthocyanin transport genes are the major and common causes of purple coloration. We have also summarized the influence of leaf color variation on amino acid, polyphenol, and lipid contents and put forward possible causes of these metabolic changes. Finally, this review further proposes the research demands in this field in the future.

Topics and trends in fresh tea (Camellia sinensis) leaf research: A comprehensive bibliometric study

Tea plant (Camellia sinensis) is a widely cultivated cash crop and tea is a favorite functional food in the world. Fresh tea leaves (FTLs) play a critical role in bridging the two fields closely related to tea cultivation and tea processing, those are, tea plant biology and tea biochemistry. To provide a comprehensive overview of the development stages, authorship collaboration, research topics, and hotspots and their temporal evolution trends in the field of FTLs research, we conducted a bibliometric analysis, based on 971 publications on FTLs-related research published during 2001-2021 from Web of Science Core Collection. CiteSpace, R package Bibliometrix, and VOSviewer were employed in this research. The results revealed that the development history can be roughly divided into three stages, namely initial stage, slow development stage and rapid development stage. Journal of Agricultural & Food Chemistry published most articles in this field, while Frontiers in Plant Science held the highest total citations and h-index. The most influential country, institution, and author in this field was identified as China, the Chinese Academy of Agricultural Sciences, and Xiaochun Wan, respectively. FTLs-related research can be categorized into three main topics: the regulation mechanism of key genes, the metabolism and features of essential compounds, and tea plants' growth and stress responses. The most concerning hotspots are the application of advanced technologies, essential metabolites, leaf color variants, and effective cultivation treatments. There has been a shift from basic biochemical and enzymatic studies to studies of molecular mechanisms that depend on multi-omics technologies. We also discussed the future development in this field. This study provides a comprehensive summary of the research field, making it easier for researchers to be informed about its development history, status, and trends.

Widely Targeted Metabolomics Analysis Reveals Great Changes in Nonvolatile Metabolites of Oolong Teas during Long-Term Storage

As a semifermented tea, oolong is exceedingly popular worldwide for its elegant, flowery aroma and mellow, rich taste. However, recent marketing trends for old oolong teas and their chemical quality largely remain unexplored. In this study, we applied widely targeted metabolomics using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) combined with multivariate analysis to investigate the chemical change of oolong teas in the aging process. With the increasing of store time, most nongalloylated catechins; tannins, including TFs and proanthocyanidins; flavonols and glycosylated flavonols; amino acids and their derivatives; nucleotides and their derivatives; and lots of alkaloids and phospholipids declined, while most fatty acids and organic acids increased, and galloylated catechins, GA, and caffeine were almost stable. The result also suggested that approximately seven years (but not an infinite extension) was a special period for oolong tea storage, which brings about excellent taste.

Metabolomics, a Powerful Tool for Understanding Plant Abiotic Stress

Metabolomics is a technology that generates large amounts of data and contributes to obtaining wide and integral explanations of the biochemical state of a living organism. Plants are continuously affected by abiotic stresses such as water scarcity, high temperatures and high salinity, and metabolomics has the potential for elucidating the response-to-stress mechanisms and develop resistance strategies in affected cultivars. This review describes the characteristics of each of the stages of metabolomic studies in plants and the role of metabolomics in the characterization of the response of various plant species to abiotic stresses.

Joint Transcriptomic and Metabolic Analysis of Flavonoids in Cyclocarya paliurus Leaves

Flavonoids are a class of commonly occurring natural compounds in the plant kingdom with various biological activities. This study compares the content of flavonoids in Cyclocarya paliurus at different developmental stages to better inform the selection of the optimal picking period. Thus, we analyzed the transcriptome and metabolome of C. paliurus at different developmental stages. The transcriptome analysis revealed 44 genes involved in the biosynthesis of flavonoids in C. paliurus, with 10 differentially expressed genes across the four different developmental stages. The metabolites were separated and identified by a combination of chromatography and mass spectrometry, followed by multi-reaction monitoring mode analysis of triple quadrupole mass spectrometry for complete metabolite quantification. In the flavonoid synthesis pathway, a total of 137 differential flavonoids were detected. The joint transcriptome and metabolome analysis showed that the expression trends in differential metabolites and genes were significantly related. Four MYB transcription factors and two bHLH transcription factors that are closely related to flavonoid biosynthesis were identified. The regulation network of flavonoid biosynthesis in C. paliurus was thus established, providing guidance for follow-up research.

The Response of Volvariella volvacea to Low-Temperature Stress Based on Metabonomics

Low temperature can lead to the autolysis of Volvariella volvacea (V. volvacea), hindering its growth and preservation and severely reducing its yield and quality. This autolysis of V. volvacea at low temperature has been reported, but a metabolomics-based investigation of the underlying mechanisms of the V. volvacea response to low temperature has not been reported. Therefore, this study aimed to explore the changes, levels and expression patterns of V. volvacea metabolites at low temperature. To understand the metabolic differences within V. volvacea, two strains with different levels of low-temperature tolerance were treated in an ice bath at 0°C for 2, 4, 8, and 10 h, while the blank control group was treated for 0 h. Metabonomics analysis was adopted to study the changes in V. volvacea in response to low temperature and the differences between the two different strains. Metabolic curves were analyzed at different time points by high-performance liquid chromatography-mass spectrometry (HPLC-MS). A total of 216 differential metabolites were identified and enriched in 39 metabolic pathways, mainly involving amino acid metabolism, carbohydrate metabolism, the TCA cycle, energy metabolism, etc. In this paper, we report the metabonomic analysis of V. volvacea in response to low temperature and compare the differences in metabolite expression between the low-temperature-resistant strain VH3 and the low-temperature-sensitive strain V23. Finally, the putative low-temperature resistance mechanism of VH3 is revealed at the metabolic level. This study provides a theoretical basis for revealing the regulatory mechanism of low-temperature resistance in V. volvacea and for future molecular breeding efforts.

Transcriptomic analysis reveals mechanism of light-sensitive albinism in tea plant Camellia sinensis 'Huangjinju'

BACKGROUND

Camellia sinensis 'Huangjinju' is an albino tea variety developed recently in China. Young leaves of 'Huangjinju' demonstrate bright yellow when cultivated under natural sunlight, but regreens under reduced light intensity. To elucidate the physiological and molecular mechanisms of this light-sensitive albinism, we compared leaf pigmentation, metabolites, cellular ultrastructure and transcriptome between plants cultured under natural sunlight and shade.

RESULTS

Shading treatment doubled the chlorophyll concentration and regreened albino leaves; carotenoid also increased by 30%. Electron microscopy analyses showed that chloroplast not only increased in number but also in size with a complete set of components. In addition, regreened leaves also had a significantly higher concentration of polyphenols and catechins than albino leaves. At transcriptomic level, a total of 507 genes were differentially expressed in response to light condition changes. The most enriched pathways include light harvest protein complex, response to stimuli, oxidation-reduction process, generation of precursor metabolites and energy response.

CONCLUSION

The integrated strategy in this study allows a mechanistic understanding of leaf albinism in light-sensitive tea plants and suggested the regulation of gene networks involved in pigmentation and protein processing. Results from this study provide valuable information to this area and can benefit the domestication and artificial breeding to develop new albino tea varieties.

Metabolomics analysis of Camellia sinensis with respect to harvesting time

The metabolites of green tea influence its quality and physiological characteristics. Therefore, to further increase the utilization of green tea leaves, it is imperative to understand the distribution and variation of their secondary metabolites with respect to different harvesting times. This study compared the metabolomes of young leaves of 'Anji Baicha' between early spring tea and late spring tea in positive and negative ESI modes using UPLC-ESI-Q-TOF/MS. Potential biomarkers were selected by principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of chemometrics methods. Results showed that the metabolic profiles of young leaves in early and late spring tea were significantly different. The metabolite-related pathways associated with these differences included those involved in biosynthesis of flavonoids, phenylpropanoids, flavone and flavonol, phenylalanine, tyrosine, and tryptophan. In early spring tea leaves, concentrations of amino acids (l-glutamine and l-tryptophan), (S)-(-)-limonene, most of the catechins, and flavonol/flavone glycosides were found to be significantly increased, while proanthocyanidins (proanthocyanidin A1, prodelphinidin A1, and prodelphinidin A₂ 3'-gallate) concentrations were significantly decreased. As a result of the metabolomics analysis of young leaves of green tea plants with respect to different harvesting time, information regarding physiological characteristics and optimal harvesting time was obtained.

Analysis of Young Shoots of 'Anji Baicha' (Camellia sinensis) at Three Developmental Stages Using Nontargeted LC-MS-Based Metabolomics

'Anji Baicha' (Camellia sinensis) is a low-temperature-sensitive tea variety. During the development of young shoots, the leaves of 'Anji Baicha' exhibit periodic albinism. The quality of 'Anji Baicha' is closely related to the color of the fresh leaves, with whiter leaves affording a higher amino acid content and superior sensory quality after processing. However, the metabolic mechanism of its quality formation is still unclear. In this study, we analyzed the metabolomic changes of young shoots of 'Anji Baicha' and screened for metabolic markers that may be involved in the periodic albinism. Positive- and negative-mode UPLC-QTOF-MS was applied to the metabolomic analysis of young leaves of 'Anji Baicha' during three developmental stages (i.e., the pre-albescent, albescent, and regreening stages). The results revealed significant differences in the metabolic profiles of the young leaves at the three stages. The differential metabolites were mainly related to the pathways of flavonoid, phenylpropanoid, and amino acid biosynthesis. The concentrations of several amino acids (primarily l-theanine, l-glutamate, N₂ -acetyl-l-ornithine, l-aspartic acid, d-proline, l-glutamine, l-leucine, and pyroglutamic acid) and 12-OPDA were significantly higher in the albescent stage. In contrast, during the albescent stages, the concentrations of several carbohydrates (d-fructose, β-d-galactopyranose, 3-O-fucopyranosyl-2-acetamido-2-deoxyglucopyranose, galactose-β-1, 4-xylose acetyl-maltose, and 2-fucosyllactose) were significantly lower. Moreover, catechins (mainly epigallocatechin and catechin derivatives), dimeric catechins (primarily proanthocyanidins), and flavonol and flavonol/flavone glycosides (mainly kaempferol, myricetin, quercetin, cyanidin, and delphinidin glycosides) were detected at the highest levels in the regreening or pre-albescent stages. The obtained results enhance the current understanding of the metabolic mechanisms of periodic albinism and quality development formation in 'Anji Baicha'. PRACTICAL APPLICATION: The obtained results not only provide information regarding differential metabolites but also advance the understanding of the mechanism of periodic albinism in 'Anji Baicha' at the metabolite level and open up new possibilities for the genetic improvement of tea cultivars.

Neuroprotective and Anti-Amyloid β Effect and Main Chemical Profiles of White Tea: Comparison Against Green, Oolong and Black Tea

White tea (WT) is one of six tea types originally derived from Fujian Province, China. White tea is known for its health-promoting properties. However, the neuroprotective and anti-aggregatory properties of WT against the hallmark toxic Alzheimer's protein, Aβ have not been investigated. In this study, WT, green tea (GT), oolong tea (OT) and black tea (BT) were manufactured using tea leaves from the cultivar Camellia sinensis (Jin Guanyin). The protective effects of these tea extracts were then studied under oxidative stress conditions via t-bhp and H₂O₂ exposure, in addition to Aβ treatment using a PC-12 cell model. Each tea type failed to rescue PC-12 cells from either t-bhp or H₂O₂-mediated toxicity, however each extract exerted significant protection against Aβ-evoked neurotoxicity. Results of the Thioflavin T Kinetic (ThT) and TEM assay showed that Aβ aggregate formation was inhibited by each tea type. Additionally, TEM also supported the different anti-aggregatory effect of WT by modifying Aβ into an amorphous and punctate aggregate morphology. Higher accumulated precedent or potential neuroprotective compounds in WT, including ECG''3Me, 8-C-ascorbyl-EGCG, GABA and Gln, in addition to flavonol or flavone glycosides detected by using UPLC-QTOF-MS and UPLC-QqQ-MS, may contribute to a favourable anti-aggregative and neuroprotective effect of WT against Aβ.

Dissection of Chemical Composition and Associated Gene Expression in the Pigment-Deficient Tea Cultivar 'Xiaoxueya' Reveals an Albino Phenotype and Metabolite Formation

The tea cultivar 'Xiaoxueya', a temperature-sensitive albino mutant, is a rare tea germplasm because of its highly enriched amino acid content and brisk flavour. In comparison with green leaf tissues of 'Xiaoxueya', albino leaves show significant deficiency in chlorophylls and carotenoids and severely disrupted chloroplasts. Furthermore, the accumulation of quality-related secondary metabolites is altered in 'Xiaoxueya' albino leaf, with significantly increased contents of total amino acids, theanine, and glutamic acid and significantly decreased contents of alkaloids, catechins, and polyphenols. To uncover the molecular mechanisms underlying albinism and quality-related constituent variation in 'Xiaoxueya' leaves, expression profiles of pivotal genes involved in the biosynthetic pathways of pigments, caffeine, theanine, and catechins were investigated by quantitative real-time PCR technology. The results revealed that suppressed expression of the chloroplast-localized 1-deoxy-D-xylulose-5-phosphate synthase genes DXS1 and DXS2 involved in the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway and protochlorophyllide oxidoreductase genes POR1 and POR2 involved in the chlorophyll biosynthetic pathway is responsible for the pigment deficiency in 'Xiaoxueya' albino leaf. Additionally, the low expression of the tea caffeine synthase gene (TCS) involved in caffeine biosynthesis and the chalcone synthase genes CHS1, CHS2, and CHS3, the chalcone isomerase gene CHI, the flavonoid 3',5'-hydroxylase genes F3'5'H1 and F3'5'H2, and the anthocyanidin reductase genes ANR1 and ANR2 involved in the flavonoid pathway is related to the reduction in alkaloid and catechin levels in 'Xiaoxueya' albino leaves.

Metabolomic Analysis of Pollen Grains with Different Germination Abilities from Two Clones of Chinese Fir (Cunninghamia lanceolata (Lamb) Hook)

Pollen grains produce certain metabolites, which can improve or inhibit germination and tube growth. Metabolomic analysis of germinating and growing Chinese fir pollen has not been reported. Therefore, this study aimed to analyse metabolites changes, content and expression in the germinating pollen of Chinese fir. To understand the metabolic differences, two clones from Chinese fir were selected. Metabolomics analyses were performed on three stages (1-, 24- and 48-h) during in vitro pollen germination. The metabolites profiles at different time points were analyzed by using liquid chromatography-mass spectrometry. The results showed that 171 peaks were screened; the corresponding differential metabolites of 121 peaks were classified into nine types of substances. The expression of metabolites showed significant differences across and between clones, and the variation was evident at all germination stages. The expression was obvious at the early stage of germination, which differed clearly from that of the late stage after pollen tube growth. Moreover, the metabolites were mainly enriched in 14 metabolic pathways. Pollen germination and tube growth and metabolites expressions changed per incubation time. Since this work is preliminary, we suggest further investigations to understand the relationship between the differential metabolites and pollen development, and factors affecting pollen germination process.

Discovery of Plant Viruses From Tea Plant (Camellia sinensis (L.) O. Kuntze) by Metagenomic Sequencing

The tea plant (Camellia sinensis (L.) O. Kuntze) is an economically important woody species. In this study, we collected 26 tea plant samples with typical discoloration symptoms from different tea gardens and performed metagenomic analysis based on next-generation sequencing. Homology annotation and PCR sequencing validation finally identified seven kinds of plant viruses from tea plant. Based on abundance distribution analysis, the two most abundant plant viruses were highlighted. Genetic characterization suggested that they are two novel virus species with relatively high homology to Blueberry necrotic ring blotch virus and American plum line pattern virus. We named the newly discovered viruses tea plant necrotic ring blotch virus (TPNRBV) and tea plant line pattern virus (TPLPV). Evolutionary relationship analysis indicated that TPNRBV and TPLPV should be grouped into the Blunervirus and the Ilarvirus genera, respectively. TPLPV might have same genome activation process with known ilarviruses based on sequence analysis. Moreover, specific primers for both viruses detection were designed and validated. The symptoms and ultrastructure of TPNRBV infected leaves were first recorded. Virus detections in the symptomatic and asymptomatic tissues from field plants showing tea plant necrotic ring blotch disease suggest that TPNRBV has a systemic movement feature. In summary, we first identified seven kinds of putative plant viruses by metagenomic analysis and report two novel viruses being latent pathogens to tea plant. The results will advance our understanding of tea plant virology and have significance for the genetic breeding of tea plants in the future.

Comprehensive Dissection of Metabolic Changes in Albino and Green Tea Cultivars

Albino tea cultivars are special mutants of tea plants with white or yellow leaf color. In this study, three albino tea cultivars, including 'Anji Baicha', 'Huangjinya', and 'Baijiguan', and two green tea cultivars, 'Longjing 43' and 'Fuding Dabaicha', were applied to metabolite profiling by gas chromatography-mass spectrometry and ultraperformance liquid chromatography-mass spectrometry. Multivariate analyses revealed significantly different metabolite phenotypes in leaves among albino cultivars and green cultivars. The differential metabolite-related pathways included galactose metabolism, tryptophan metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis. For the young leaves of albino cultivars, the sugar (sorbitol and erythrose) and amino acid (mainly proline, isoleucine, ornithine, aspartic acid, threonine, and valine) concentrations increased, whereas gallocatechin and epigallocatechin gallate concentrations decreased. These results reveal the divergence in metabolic profiling between tea plant cultivars with different leaf colors. With the development of leaves, the concentrations of flavonoids increased largely in the older leaves of albino cultivars.

Metabolite Profiling of 14 Wuyi Rock Tea Cultivars Using UPLC-QTOF MS and UPLC-QqQ MS Combined with Chemometrics

Wuyi Rock tea, well-recognized for rich flavor and long-lasting fragrance, is a premium subcategory of oolong tea mainly produced in Wuyi Mountain and nearby regions of China. The quality of tea is mainly determined by the chemical constituents in the tea leaves. However, this remains underexplored for Wuyi Rock tea cultivars. In this study, we investigated the leaf metabolite profiles of 14 major Wuyi Rock tea cultivars grown in the same producing region using UPLC-QTOF MS and UPLC-QqQ MS with data processing via principal component analysis and cluster analysis. Relative quantitation of 49 major metabolites including flavan-3-ols, proanthocyanidins, flavonol glycosides, flavone glycosides, flavonone glycosides, phenolic acid derivatives, hydrolysable tannins, alkaloids and amino acids revealed clear variations between tea cultivars. In particular, catechins, kaempferol and quercetin derivatives were key metabolites responsible for cultivar discrimination. Information on the varietal differences in the levels of bioactive/functional metabolites, such as methylated catechins, flavonol glycosides and theanine, offers valuable insights to further explore the nutritional values and sensory qualities of Wuyi Rock tea. It also provides potential markers for tea plant fingerprinting and cultivar identification.

Transcriptomic analyses identify albino-associated genes of a novel albino tea germplasm 'Huabai 1'

Albinism in shoots of tea plants is a common phenotypic expression which gives the tea infusion a pleasant umami taste. A novel natural albino mutant tea germplasm containing high amino acids content was found and named as 'Huabai 1'. 'Huabai 1' has white jade tender shoots under low temperature and turns green with increased temperature. In order to understand the molecular mechanism of color change in leaf of 'Huabai 1', transcriptome analysis was performed to identify albino-associated differentially expressed genes (DEGs). A total of 483 DEGs were identified from white shoots of 'Huabai 1' compared to its green shoots. There were 15 DEGs identified to be involved in phenylpropanoid biosynthesis, which account for the majority of characterized DEGs. The metabolites related to phenylpropanoid biosynthesis revealed similar expression pattern of DEGs. Furthermore, metabolic pathways such as ubiquonone, tyrosine, and flavonoid biosynthesis associated with phenylpropanoid biosynthesis could also contribute to the color change in 'Huabai 1' tender shoots. Protein-protein interaction analysis revealed a hub protein NEDD8 (CSA009575) which interacted with many regulated genes in spliceosome, nitrogen metabolism, phenylpropanoid biosynthesis, and other pathways. In conclusion, the findings in this study indicate that the color change of 'Huabai 1' tender shoots is a combined effect of phenylpropanoid biosynthesis pathway and other metabolic pathways including flavonoid biosynthesis in tea plants. Chlorophyll biosynthesis-related genes LHCII and SGR may also play some roles in color change of 'Huabai 1'.

Proteome and Acetyl-Proteome Profiling of Camellia sinensis cv. 'Anjin Baicha' during Periodic Albinism Reveals Alterations in Photosynthetic and Secondary Metabolite Biosynthetic Pathways

Tea leaf color is not only important from an aesthetics standpoint but is also related to tea quality. To investigate the molecular mechanisms that determine tea leaf color, we examined Camellia sinensis cv. 'Anjin Baicha' (an albino tea cultivar) by tandem mass tag isobaric labeling to generate a high-resolution proteome and acetyl-proteome atlas of three leaf developmental stages. We identified a total of 7,637 proteins and quantified 6,256; of these, 3,232 were classified as differentially accumulated proteins (DAPs). We also identified 3,161 lysine acetylation sites in 1,752 proteins and quantified 2,869 in 1,612 proteins. The acetylation levels at 468 sites were significantly altered across the three developmental stages during periodic albinism; the corresponding proteins were associated with a variety of biological processes. Interestingly, a large number of DAPs and acetylated proteins with increased/decreased acetylation were related to photosynthesis and secondary metabolite biosynthetic pathways, suggesting that the accumulation or acetylation level of these proteins regulates periodic albinism in 'Anjin Baicha.' Additionally, overlap between succinylome and acetylome among three 'Anjin Baicha' developmental stages were found. These data provide important insight into the mechanisms of leaf coloration in the tea plant. The mass spectrometry data have been deposited to Proteome X change via the PRIDE partner repository with the data set identifier PXD008134.

Quantitative Succinyl-Proteome Profiling of Camellia sinensis cv. 'Anji Baicha' During Periodic Albinism

Lysine succinylation is a novel dynamic and evolutionarily conserved post-translational modification (PTM) that regulates various biological processes. ‘Anji Baicha’ is an albino tea variety that exhibits temperature-based variability of leaf colour and amino acid concentrations. However, the mechanism underlying albinism in ‘Anji Baicha’ has not been investigated at the level of succinylation. Here, we identify 3530 lysine succinylation sites mapped to 2132 proteins in ‘Anji Baicha’, representing the first extensive data on the lysine succinylome in the tea plant. Eleven conserved succinylation motifs were enriched among the identified succinylated peptides. The protein-protein interaction maps were visualized using Cytoscape software. Comparison across three typical developmental stages of ‘Anji Baicha’ revealed that proteins exhibiting differential succinylation levels were primarily involved in photosynthesis, carbon fixation, biosynthesis of amino acids and porphyrin and chlorophyll metabolism, suggesting that these succinylated proteins are involved in ‘Anji Baicha’ leaf colour variability. These results not only deepen our understanding of the mechanism underlying ‘Anji Baicha’ albinism and the regulatory role of succinylation in the tea plant but also provide new insight into molecular breeding for leaf colour variety.

L-Theanine Content and Related Gene Expression: Novel Insights into Theanine Biosynthesis and Hydrolysis among Different Tea Plant (Camellia sinensis L.) Tissues and Cultivars

L-Theanine content has tissues and cultivars specificity in tea plant (Camellia sinensis L.), the correlations of theanine metabolic related genes expression profiles with theanine contents were explored in this study. L-theanine contents in the bud and 1st leaf, 2nd leaf, 3rd leaf, old leaf, stem, and lateral root were determined by HPLC from three C. sinensis cultivars, namely 'Huangjinya', 'Anjibaicha', and 'Yingshuang', respectively. The theanine contents in leaves and root of 'Huangjinya' were the highest, followed by 'Anjibaicha', and 'Yingshuang'. The theanine contents in the leaves reduced as the leaf mature gradually, and in stem were the least. Seventeen genes encoding enzymes involved in theanine metabolism were identified from GenBank and our tea transcriptome database, including CsTS1, CsTS2, CsGS1, CsGS2, CsGOGAT-Fe, CsGOGAT-NAD(P)H, CsGDH1, CsGDH2, CsALT, CsSAMDC, CsADC, CsCuAO, CsPAO, CsNiR, CsNR, CsGGT1, and CsGGT3. The transcript profiles of those seventeen genes in the different tissues of three tea plant cultivars were analyzed comparatively. Among the different cultivars, the transcript levels of most selected genes in 'Huangjinya' were significantly higher than that in the 'Anjibaicha' and 'Yingshuang'. Among the different tissues, the transcript levels of CsTS2, CsGS1, and CsGDH2 almost showed positive correlation with the theanine contents, while the other genes showed negative correlation with the theanine contents in most cases. The theanine contents showed correlations with related genes expression levels among cultivars and tissues of tea plant, and were determined by the integrated effect of the metabolic related genes.

Biochemical and transcriptomic analyses reveal different metabolite biosynthesis profiles among three color and developmental stages in 'Anji Baicha' (Camellia sinensis)

BACKGROUND

The new shoots of the albino tea cultivar 'Anji Baicha' are yellow or white at low temperatures and turn green as the environmental temperatures increase during the early spring. 'Anji Baicha' metabolite profiles exhibit considerable variability over three color and developmental stages, especially regarding the carotenoid, chlorophyll, and theanine concentrations. Previous studies focused on physiological characteristics, gene expression differences, and variations in metabolite abundances in albino tea plant leaves at specific growth stages. However, the molecular mechanisms regulating metabolite biosynthesis in various color and developmental stages in albino tea leaves have not been fully characterized.

RESULTS

We used RNA-sequencing to analyze 'Anji Baicha' leaves at the yellow-green, albescent, and re-greening stages. The leaf transcriptomes differed considerably among the three stages. Functional classifications based on Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that differentially expressed unigenes were mainly related to metabolic pathways, biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, and carbon fixation in photosynthetic organisms. Chemical analyses revealed higher β-carotene and theanine levels, but lower chlorophyll a levels, in the albescent stage than in the green stage. Furthermore, unigenes involved in carotenoid, chlorophyll, and theanine biosyntheses were identified, and the expression patterns of the differentially expressed unigenes in these biosynthesis pathways were characterized. Through co-expression analyses, we identified the key genes in these pathways. These genes may be responsible for the metabolite biosynthesis differences among the different leaf color and developmental stages of 'Anji Baicha' tea plants.

CONCLUSIONS

Our study presents the results of transcriptomic and biochemical analyses of 'Anji Baicha' tea plants at various stages. The distinct transcriptome profiles for each color and developmental stage enabled us to identify changes to biosynthesis pathways and revealed the contributions of such variations to the albino phenotype of tea plants. Furthermore, comparisons of the transcriptomes and related metabolites helped clarify the molecular regulatory mechanisms underlying the secondary metabolic pathways in different stages.

Isolation and dynamic expression of four genes involving in shikimic acid pathway in Camellia sinensis 'Baicha 1' during periodic albinism

Flavonoids are the main flavor components and functional ingredients in tea, and the shikimic acid pathway is considered as one of the most important pathways in flavonoid biosynthesis, but little was known about the function of regulatory genes in the metabolism phenolic compounds in tea plant (Camellia sinensis), especially related genes in shikimic acid pathway. The dynamic changes of catechin (predominant flavonoid) contents were analyzed in this study, and four genes (CsPPT, CsDAHPS, CsSDH and CsCS) involving in shikimic acid pathway in C. sinensis albino cultivar 'Baicha 1' were cloned and characterized. The full-length cDNA sequences of these genes were obtained using reverse transcription-PCR and rapid amplification of cDNA ends. At the albinistic stage, the amounts of all catechins decreased to the lowest levels, when epigallocatechin gallate was the highest, whereas gallocatechin-3-O-gallate the lowest. Gene expression patterns analyzed by qRT-PCR showed that CsPPT and CsDAHPS were highly expressed in flowers and buds, while CsSDH and CsCS showed high expression levels in buds and leaves. It was also found that the transcript abundance of shikimic acid biosynthetic genes followed a tightly regulated biphasic pattern, and was affected by albinism. The transcript levels of CsPPT and CsDAHPS were decreased at albinistic stage followed elevated expression, whereas CsSDH and CsCS were increased only at re-greening stage. Taken together, these findings suggested that these four genes in C. sinensis may play different roles in shikimic acid biosynthesis and these genes may have divergent functions.