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

Amino acids and flavonoids analysis reveals quality constituents difference among different albino tea resources

Albino tea has attracted increased attention due to its unique flavor. To reveal the difference in key metabolites constituting the important quality of different tea resources, amino acids and flavonoids profiles in three albino resources with different degrees of albinism and one normal green variety were comprehensively investigated. K-means analysis revealed 35 amino acids were significantly enriched in 'Jibai', while 3 and 2 were specifically accumulated in 'Huangjinya' and 'Anjibaicha', respectively. Based on OPLS-DA models, 40, 31 and 45 significantly differential flavonoids were determined in 'Huangjinya', 'Anjibaicha' and 'Jibai' compared to 'Fudingdabaicha', and most were down-regulated. Among them, 10, 5 and 13 differential flavonoids were exclusively found in 'Huangjinya', 'Anjibaicha' and 'Jibai', respectively, which may contribute to unique quality for different resources. The differential flavonoids and amino acids involved in their metabolic pathways were obviously different among four resources, resulting in the difference in tea quality and flavor.

CsNYC1a Mediates Chlorophyll Degradation and Albino Trait Formation in the Arbor-Type Tea Plant Camellia nanchuanica

Albino germplasms are prized tea plant mutants with yellow/white leaves. However, understanding of the albino mechanisms in non-Camellia sinensis tea species remains limited. This study elucidated the albino trait formation in Nanchuan Dachashu (C. nanchuanica), an arbor-type tea species, and its association with tea quality. The yellow-leaved albino individual NH1 exhibited abnormal chloroplast ultrastructure and reduced chlorophyll/carotenoid levels compared to green-leaved NL1. Integrating transcriptomics, metabolomics, yeast one-hybrid, and transgenic approaches identified the chlorophyll b reductase gene CsNYC1a as a key regulator, which was significantly up-regulated in NH1, and its overexpression in Arabidopsis recapitulated the albino phenotype. In yeast, histone CsH1.2 binds to the CsNYC1a promoter. These findings suggest that CsH1.2-CsNYC1a-mediated chlorophyll degradation may be a key mechanism underlying albino formation in Nanchuan Dachashu. In addition, as a germplasm with higher polyphenol-to-amino acid ratio than NL1, NH1 offers more possibilities for breeding and application.

Transcriptomic analysis of hub genes regulating albinism in light- and temperature-sensitive albino tea cultivars 'Zhonghuang 1' and 'Zhonghuang 2'

Albino tea cultivars have high economic value because their young leaves contain enhanced free amino acids that improve the quality and properties of tea. Zhonghuang 1 (ZH1) and Zhonghuang 2 (ZH2) are two such cultivars widely planted in China; however, the environmental factors and molecular mechanisms regulating their yellow-leaf phenotype remain unclear. In this study, we demonstrated that both ZH1 and ZH2 are light- and temperature-sensitive. Under natural sunlight and low-temperature conditions, their young shoots were yellow with decreased chlorophyll and an abnormal chloroplast ultrastructure. Conversely, young shoots were green with increased chlorophyll and a normal chloroplast ultrastructure under shading and high-temperature conditions. RNA-seq analysis was performed for high light and low light conditions, and pairwise comparisons identified genes exhibiting different light responses between albino and green-leaf cultivars, including transcription factors, cytochrome P450 genes, and heat shock proteins. Weighted gene coexpression network analyses of RNA-seq data identified the modules related to chlorophyll differences between cultivars. Genes involved in chloroplast biogenesis and development, light signaling, and JA biosynthesis and signaling were typically downregulated in albino cultivars, accompanied by a decrease in JA-ILE content in ZH2 during the albino period. Furthermore, we identified the hub genes that may regulate the yellow-leaf phenotype of ZH1 and ZH2, including CsGDC1, CsALB4, CsGUN4, and a TPR gene (TEA010575.1), which were related to chloroplast biogenesis. This study provides new insights into the molecular mechanisms underlying leaf color formation in albino tea cultivars.

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.

Integrative transcriptome and whole-genome bisulfite sequencing analyses of a temperature-sensitive albino tea plant cultivar

Green tea made from albino buds and leaves has a strong umami taste and aroma. The cultivar 'Zhonghuang 2' (ZH2, Camellia sinensis) is a natural mutant with young shoots that are yellow in spring and green or yellow-green in summer. However, the mechanism of leaf color change remains unclear. Here, we found that young shoots of ZH2 were yellow at low temperature (LT) and green at high temperature (HT), indicating that ZH2 is a temperature-sensitive cultivar. Transmission electron microscopy analysis showed that the grana in the chloroplasts of young shoots grown at LT were poorly stacked, which caused a lack of photoreactions and chlorophyll. RNA-seq results showed 1279 genes differentially expressed in the young shoots grown at LT compared with those at HT, including genes related to cytochrome synthesis, chloroplast development, photosynthesis, and DNA methylation. A whole-genome bisulfite sequencing assay revealed that the dynamics of DNA methylation levels in the CG, CHG, and CHH contexts decreased under LT, and the change was most obvious in the CHH context. Furthermore, 72 genes showed significant changes in both expression and DNA methylation levels, and most of them were related to cytochrome synthesis, chloroplast development, photosynthesis, transcription factors, and signaling pathways. These results demonstrate that DNA methylation is involved in the LT-regulated albino processes of ZH2. Changes in DNA methylation levels were associated with changes in gene expression levels, affecting the structure and function of chloroplasts, which may have a phenotypic impact on shoot and leaf color.

Magnesium transporter CsMGT10 of tea plants plays a key role in chlorosis leaf vein greening

Magnesium (Mg2+), as the central atom of chlorophyll, is the most abundant divalent cation for plant growth and development in living cells. MRS2/MGT magnesium transporters play important roles in coping with magnesium stress, chloroplast development and photosynthesis. However, the molecular mechanism of MGT influencing tea plant leaf vein color remains unknown. Here, we demonstrate that CsMGT10 may be a potential transporter influencing leaf vein color. CsMGT10 belongs to Clade A member of MRS2/MGT family. CsMGT10 has the highest expression level in leaves of tea plants. And it is mainly expressed in aboveground parts, especially in vascular bundles. Moreover, CsMGT10 localizes to the chloroplast envelope of tea plants with a high affinity to Mg2+. And the GMN motif is required for its magnesium transport function. Ectopic expression of CsMGT10 in Arabidopsis leaf variegation mutant var5-1 can restore green color of chlorosis leaf veins, and the contents of chlorophyll and carotenoid change significantly, proving its essential role in leaf vein greening. Furthermore, the chlorophyll and carotenoid of tea leaves treated with CsMGT10 antisense oligonucleotides also decrease significantly. Our findings indicate that CsMGT10 mainly acts as Mg2+ transporter in chloroplast envelope of leaf veins, which may play a key role in leaf vein greening of tea plants.

Light Intensity Regulates Low-Temperature Adaptability of Tea Plant through ROS Stress and Developmental Programs

Low-temperature stress limits global tea planting areas and production efficiency. Light is another essential ecological factor that acts in conjunction with temperature in the plant life cycle. However, it is unclear whether the differential light environment affects the low temperature adaptability of tea plant (Camellia sect. Thea). In this study, tea plant materials in three groups of light intensity treatments showed differentiated characteristics for low-temperature adaptability. Strong light (ST, 240 μmol·m^-2·s^-1) caused the degradation of chlorophyll and a decrease in peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and polyphenol oxidase (PPO) activities, as well as an increase in soluble sugar, soluble protein, malondialdehyde (MDA), and relative conductivity in tea leaves. In contrast, antioxidant enzyme activities, chlorophyll content, and relative conductivity were highest in weak light (WT, 15 μmol·m^-2·s^-1). Damage was observed in both ST and WT materials relative to moderate light intensity (MT, 160 μmol·m^-2·s^-1) in a frost resistance test. Chlorophyll degradation in strong light was a behavior that prevented photodamage, and the maximum photosynthetic quantum yield of PS II (Fv/Fm) decreased with increasing light intensity. This suggests that the browning that occurs on the leaf surface of ST materials through frost may have been stressed by the previous increase in reactive oxygen species (ROS). Frost intolerance of WT materials is mainly related to delayed tissue development and tenderness holding. Interestingly, transcriptome sequencing revealed that stronger light favors starch biosynthesis, while cellulose biosynthesis is enhanced in weaker light. It showed that light intensity mediated the form of carbon fixation in tea plant, and this was associated with low-temperature adaptability.

Effect of shading on physiological attributes and comparative transcriptome analysis of Camellia sinensis cultivar reveals tolerance mechanisms to low temperatures

Tea is a vital beverage crop all over the world, including in China. Low temperatures restrict its growth, development, and terrestrial distribution, and cold event variability worsens cold damage. However, the physiological and molecular mechanisms of Camellia sinensis under shade in winter remain unclear. In our study, tea leaves were utilized for physiological attributes and transcriptome analysis in November and December in three shading groups and no-shade control plants. When compared to the no-shade control plants, the shading group protected tea leaves from cold damage, increased photochemical efficiency (Fv/Fm) and soil plant analysis development (SPAD), and sustained chlorophyll a, chlorophyll b, chlorophyll, and carotenoid contents by physiological mean. Then, transcriptome analysis revealed 20,807 differentially expressed genes (DEGs) and transcription factors (TFs) in November and December. A comparative study of transcriptome resulted in 3,523 DEGs and many TFs under SD0% vs. SD30%, SD0% vs. SD60%, and SD0% vs. SD75% of shading in November and December. Statistically, 114 DEGs were downregulated and 72 were upregulated under SD0% vs. SD30%. SD0% vs. SD60% resulted in 154 DEGs, with 60 downregulated and 94 upregulated. Similarly, there were 505 DEGs of which 244 were downregulated and 263 were upregulated under SD0% vs. SD75% of shading throughout November. However, 279 DEGs were downregulated and 105 were upregulated under SD0% vs. SD30%. SD0% vs. SD60% resulted in 296 DEGs, with 172 downregulated and 124 upregulated. Finally, 2,173 DEGs were regulated in December, with 1,428 downregulated and 745 upregulated under SD0% vs. SD75%. These indicate that the number of downregulated DEGs in December was higher than the number of upregulated DEGs in November during low temperatures. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of differentially expressed genes were highly regulated in the photosynthesis, plant hormone signal transduction, and mitogen-activated protein kinase (MAPK) signaling pathways. However, qRT-PCR and RNA-seq relative expression of photosynthetic (DEGs) Lhcb2 in both November and December, plant hormone (DEGs) BRI1 and JAZ in November and IAA and ERF1 in December, and key DEGs of MAPK signal transduction FLS2, CHIB, and MPK4 in November and RBOH, MKK4_5, and MEKK1 in December in three shading groups and no-shade control plants responded to tea cold tolerance. The enhanced expression of light-harvesting photosystem I gene Lhca5, light-harvesting photosystem II gene Lhcb2, and mitogen-activated protein kinases MEKK1 and MPK4/6 enhance the cold-tolerance mechanism of C. sinensis. These comprehensive transcriptomic findings are significant for furthering our understanding of the genes and underlying regulatory mechanisms of shade-mediated low-temperature stress tolerance in horticultural crops.

Chemical constituents of green teas processed from albino tea cultivars with white and yellow shoots

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Green teas produced from white (NB) and yellow (HJY) shoots have distinct flavor.

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Concentrations of non-galloylated catechins and amino acids are high in NB teas.

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HJY green teas contain high concentration of galloylated catechins.

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CsTA and CsPDX2.1 (involved in catabolism) are highly expressed in HJY tea shoots.

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Total concentration of volatile compounds is higher in HJY than in NB green teas.

Green tea processed from albino tea varieties often has umami taste and fresh aroma. This study identified green teas made from two types of albino tea cultivar, one having the white shoots (called Naibai, NB) and the other having the yellow shoots (called Huangjinya, HJY). Taste compounds analyses showed that galloylated catechins were highly concentrated in HJY green teas, whereas non-galloylated catechins and amino acids were more abundant in NB green teas. CsTA (involved in the catabolism of galloylated catechins) showed high expression in HJY tea shoots, resulting in gallic acid as a precursor for β-glucogallin biosynthesis being abundant in HJY. CsPDX2.1 (responsible for theanine hydrolyzation) had a lower expression level in NB than HJY shoots. Fatty acid–derived volatiles (FADVs), glycosidically bound volatiles (GBVs) and carotenoid–derived volatiles (CDVs) were highly concentrated in HJY green teas, whereas amino acids–derived volatiles were highly concentrated in NB green teas.

Metabolic and Transcriptomic Profiling Reveals Etiolated Mechanism in Huangyu Tea (Camellia sinensis) Leaves

Leaf color is one of the key factors involved in determining the processing suitability of tea. It relates to differential accumulation of flavor compounds due to the different metabolic mechanisms. In recent years, photosensitive etiolation or albefaction is an interesting direction in tea research field. However, the molecular mechanism of color formation remains unclear since albino or etiolated mutants have different genetic backgrounds. In this study, wide-target metabolomic and transcriptomic analyses were used to reveal the biological mechanism of leaf etiolation for 'Huangyu', a bud mutant of 'Yinghong 9'. The results indicated that the reduction in the content of chlorophyll and the ratio of chlorophyll to carotenoids might be the biochemical reasons for the etiolation of 'Huangyu' tea leaves, while the content of zeaxanthin was significantly higher. The differentially expressed genes (DEGs) involved in chlorophyll and chloroplast biogenesis were the biomolecular reasons for the formation of green or yellow color in tea leaves. In addition, our results also revealed that the changes of DEGs involved in light-induced proteins and circadian rhythm promoted the adaptation of etiolated tea leaves to light stress. Variant colors of tea leaves indicated different directions in metabolic flux and accumulation of flavor compounds.

Effect of Shading on the Morphological, Physiological, and Biochemical Characteristics as Well as the Transcriptome of Matcha Green Tea

High-quality tea leaves are required for matcha production. Shading is one of the key agronomic practices that can increase the quality of green tea. The objectives among matcha tea producers include increasing the ammonia and chlorophyll contents of tea buds, decreasing tea polyphenol contents, and enhancing tea aroma formation. In this study, Fuding white tea plants were cultivated under open-air conditions (control) as well as under 85% (S85) and 95% (S95) shade. The chlorophyll contents were highest for the S85 treatment, followed by the S95 and control treatments. Moreover, shading increased the theanine and caffeine contents, while decreasing the polyphenol (epicatechin and epigallocatechin) contents, thereby optimizing matcha tea flavors. A total of 2788 differentially expressed genes (DEGs) were identified, of which 1151 and 1637 were respectively upregulated and downregulated in response to shading. The GO and KEGG enrichment analyses indicated that most of the DEGs were associated with metabolic processes (e.g., MAPK signaling, plant-pathogen interactions, and phenylpropanoid biosynthesis). Therefore, shading may modulate tea plant metabolism, signaling, biosynthetic activities, and environment-related changes to gene transcription. The expression of amino acid permeases (APP) encoding genes was downregulated in tea plants. Thus, shading influences theanine biosynthesis and the AAP-mediated distribution of theanine in tea plants.

High-Light-Induced Degradation of Photosystem II Subunits’ Involvement in the Albino Phenotype in Tea Plants

The light-sensitive (LS) albino tea plant grows albinic shoots lacking chlorophylls (Chls) under high-light (HL) conditions, and the albinic shoots re-green under low light (LL) conditions. The albinic shoots contain a high level of amino acids and are preferential materials for processing quality green tea. The young plants of the albino tea cultivars are difficult to be cultivated owing to lacking Chls. The mechanisms of the tea leaf bleaching and re-greening are unknown. We detected the activity and composition of photosystem II (PSII) subunits in LS albino tea cultivar “Huangjinya” (HJY), with a normal green-leaf cultivar “Jinxuan” (JX) as control so as to find the relationship of PSII impairment to the albino phenotype in tea. The PSII of HJY is more vulnerable to HL-stress than JX. HL-induced degradation of PSII subunits CP43, CP47, PsbP, PsbR. and light-harvest chlorophyll–protein complexes led to the exposure and degradation of D1 and D2, in which partial fragments of the degraded subunits were crosslinked to form larger aggregates. Two copies of subunits PsbO, psbN, and Lhcb1 were expressed in response to HL stress. The cDNA sequencing of CP43 shows that there is no difference in sequences of PsbC cDNA and putative amino acids of CP43 between HJY and JX. The de novo synthesis and/or repair of PSII subunits is considered to be involved in the impairment of PSII complexes, and the latter played a predominant role in the albino phenotype in the LS albino tea plant.

Chloroplastic pentatricopeptide repeat proteins (PPR) in albino plantlets of Agave angustifolia Haw. reveal unexpected behavior

BACKGROUND

Pentatricopeptide repeat (PPR) proteins play an essential role in the post-transcriptional regulation of genes in plastid genomes. Although important advances have been made in understanding the functions of these genes, there is little information available on chloroplastic PPR genes in non-model plants and less in plants without chloroplasts. In the present study, a comprehensive and multifactorial bioinformatic strategy was applied to search for putative PPR genes in the foliar and meristematic tissues of green and albino plantlets of the non-model plant Agave angustifolia Haw.

RESULTS

A total of 1581 PPR transcripts were identified, of which 282 were chloroplastic. Leaf tissue in the albino plantlets showed the highest levels of expression of chloroplastic PPRs. The search for hypothetical targets of 12 PPR sequences in the chloroplast genes of A. angustifolia revealed their action on transcripts related to ribosomes and translation, photosystems, ATP synthase, plastid-encoded RNA polymerase and RuBisCO.

CONCLUSIONS

Our results suggest that the expression of PPR genes depends on the state of cell differentiation and plastid development. In the case of the albino leaf tissue, which lacks functional chloroplasts, it is possible that anterograde and retrograde signaling networks are severely compromised, leading to a compensatory anterograde response characterized by an increase in the expression of PPR genes.

Enhancement of Photosynthetic Capacity in Spongy Mesophyll Cells in White Leaves of Actinidia kolomikta

Considering that Actinidia kolomikta bears abundant white leaves on reproductive branches during blossoming, we hypothesized that the white leaves may maintain photosynthetic capacity by adjustments of leaf anatomy and physiological regulation. To test this hypothesis, leaf anatomy, gas exchange, chlorophyll a fluorescence, and the transcriptome were examined in white leaves of A. kolomikta during flowering. The palisade and spongy mesophyll in the white leaves were thicker than those in green ones. Chloroplast development in palisade parenchyma of white leaves was abnormal, whereas spongy parenchyma of white leaves contained functional chloroplasts. The highest photosynthetic rate of white leaves was ~82% of that of green leaves over the course of the day. In addition, the maximum quantum yield of PSII (F _v/F _m) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas F _v/F _m and quantum yield for electron transport were significantly higher in the spongy mesophyll of white leaves. Photosynthetic capacity regulation of white leaf also was attributed to upregulation or downregulation of some key genes involving in photosynthesis. Particularly, upregulation of sucrose phosphate synthase (SPS), glyeraldehyde-3-phosphate dehydrogenase (GAPDH) and RuBisCO activase (RCA) in white leaf suggested that they might be involved in regulation of sugar synthesis and Rubisco activase in maintaining photosynthetic capacity of white leaf. Conclusions: white leaves contained a thicker mesophyll layer and higher photosynthetic activity in spongy parenchyma cells than those of palisade parenchyma cells. This may compensate for the lowered photosynthetic capacity of the palisade mesophyll. Consequently, white leaves maintain a relatively high photosynthetic capacity in the field.

Identifying key genes involved in yellow leaf variation in 'Menghai Huangye' based on biochemical and transcriptomic analysis

Albino tea plants generally have higher theanine, which causes their tea leaves to taste fresher, and they are an important mutant for the breeding of tea plant varieties. Earlier, we reported an albino germplasm, 'Menghai Huangye' (MHHY), from Yunnan Province and found that it has a lower chlorophyll content during the yellowing stage, but the mechanism underlying low chlorophyll and the yellowing phenotype is still unclear. In this study, the pigment contents of MHHY_May (yellowing, low chlorophyll), MHHY_July (regreening, normal chlorophyll), and YK10_May (green leaves, normal chlorophyll) were determined, and the results showed that the lower chlorophyll content might be an important reason for the formation of the yellowing phenotype of MHHY. Through transcriptome sequencing, we obtained 654 candidates for differentially expressed genes (DEGs), among which 4 genes were related to chlorophyll synthesis, 10 were photosynthesis-related, 34 were HSP family genes, and 19 were transcription factor genes. In addition, we analysed the transcription levels of the key candidate genes in MHHY_May and MHHY_July and found that they are consistent with the expression trends in MHHY_May and YK10_May, which further indicates that the candidate differential genes we identified are likely to be key candidate factors involved in the low chlorophyll content and yellowing of MHHY. In summary, our findings will assist in revealing the low chlorophyll content of MHHY and the formation mechanism of yellowing tea plants and will be applied to the selection and breeding of albino tea cultivars in the future.

Review: the effect of light on the key pigment compounds of photosensitive etiolated tea plant

BACKGROUND

Light is the ultimate energy source of plant photosynthesis, which has an important impact on the growth, development, physiology and biochemistry of tea plant. Photosensitive etiolated tea plant belongs to a kind of colored leaf plant, which is a physiological response to light intensity. Compared with conventional green bud and leaf of tea plant, the accumulation of pigment compounds (chlorophyll and carotenoids, etc.) closely related to a series of reactions of photosynthesis in photosensitive etiolated tea plant is reduced, resulting in the difference of leaf color of tea. This specific tea resource has high application value, among which high amino acid is one of its advantages. It can be used to process high-quality green tea with delicious taste and attractive aroma, which has been widely attention. The mechanism of the color presentation of the etiolated mutant tea leaves has been given a high topic and attention, especially, what changes have taken place in the pigment compounds of tea leaves caused by light, which makes the leaves so yellow. At present, there have been a lot of research and reports.

PURPOSE OF THE REVIEW

We describe the metabolism and differential accumulation of key pigment compounds affecting the leaf color of photosensitive etiolated tea that are triggered by light, and discuss the different metabolism and key regulatory sites of these pigments in different light environments in order to understand the "discoloration" matrix and mechanism of etiolated tea resources, answer the scientific question between leaf color and light. It provides an important strategy for artificial intervention of discoloration of colored tea plant.

CONCLUSION

The differential accumulation of pigment compounds in tea plant can be induced phytochrome in response to the change of light signal. The synthesis of chlorophyll in photoetiolated tea plants is hindered by strong light, among which, the sites regulated by coproporphyrinogen III oxidase and chlorophyllide a oxidase is sensitive to light and can be inhibited by strong light, resulting in the aggravation of leaf etiolation. The phenomenon can be disappeared or weakened by shading or reducing light intensity, and the leaf color is greenish, but the increase of chlorophyll-b accumulation is more than that of chlorophyll-a. The synthesis of carotenoids is inhibited strong light, and high the accumulation of carotenoids is reduced by shading. Most of the genes regulating carotenoids are up-regulated by moderate shading and down-regulated by excessive shading. Therefore, the accumulation of these two types of pigments in photosensitive etiolated tea plants is closely related to the light environment, and the leaf color phenotype shape of photosensitive etiolated tea plants can be changed by different light conditions, which provides an important strategy for the production and management of tea plant.

Screening the Key Region of Sunlight Regulating the Flavonoid Profiles of Young Shoots in Tea Plants (Camellia sinensis L.) Based on a Field Experiment

Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes.

Menghai Huangye, a novel albino tea germplasm with high theanine content and a high catechin index

Yunnan Province has a very wide diversity of tea germplasm resources. A variety of special tea germplasms with outstanding traits have been discovered, including tea germplasms with high anthocyanin content and low caffeine content. Albino tea cultivars generally have higher contents of theanine that contribute to the umami taste, and the quality of tea brewed from it is higher. The catechin index (CI), the ratio of dihydroxylated catechins (DIC) to trihydroxylated catechins (TRIC), is a crucial index of suitability for processing tea. In this study, the albino tea plant Menghai Huangye (MHHY) with yellow leaves was identified. Analysis of the biochemical components revealed that MHHY was enriched in theanine and the total catechins (TC) were lower than Yunkang 10 (YK10). In addition, the CI value of MHHY was extremely significantly higher than that of YK10. Metabolic profile of catechins and the related gene expression profile analysis found that the coordinated expression of the key branch genes F3'H and F3'5'Ha for the synthesis of DIC and TRIC in tea plant was closely related to the high CI and low TC of MHHY. Further analysis of the F3'H promoter showed that a 284-bp deletion mutation was present in the F3'H promoter of MHHY, containing the binding sites of the transcriptional repressor MYB4 involved in flavonoid metabolism, which might be an important reason for the up-regulated expression of F3'H in MHHY. Overall, this study provides a theoretical basis for understanding the characteristics of albino tea germplasm resources and efficiently utilizing high-CI tea germplasm resources.

Development of a novel green tea quality roadmap and the complex sensory-associated characteristics exploration using rapid near-infrared spectroscopy technology

Nondestructive instrumental identification of the green tea quality instead of professional human panel tests is highly desired for industrial application recently. The special flavor is a key quality-trait that influence consumer preference. However, flavonoids, as well as sensory-associated compounds, which play a critical role in the quality-traits profile of green tea samples have been poorly investigated. In this study, we were proposing an objective and accurate near infrared spectroscopy (NIRS) profile to support quality control within the entire green tea sensory evaluation chain, the complexity of green tea samples' sensory analysis was performed by two complementary methods: the standard calculation and the novel NIRS roadmap coupled with chemometrics. The green tea samples' physical quality, gustatory index, and nutritional index were measured respectively, which taking into consideration the gustatory evaluation of green tea for five commercially representative overall quality ("very bad", "bad", "regular", "good" and "excellent"). Our findings highlight the underexplored role of NIRS in chemical-to-sensory relationships and its widespread importance and utility in green tea quality improvement. Collectively, the comprehensive characterization of sensory-associated attribution allowed the identification of a wide array of spectrometric features, mostly related to moisture, soluble solids (SS), tea polyphenol (TPP), epigallocatechin gallate (EGCG), epicatechin (EC) and tea polysaccharide (TPS), which can be used as putative biomarkers to rapidly evaluate the green tea flavor variations related to rank differences. Otherwise, the NIRS' data were split into the calibration (n = 80) and prediction (n = 40) set independently, which showed high correlation coefficient with Rp-values of 0.9024, 0.9020 in physical and total cup quality, respectively. In this research, we demonstrated that NIRS was an easily-generated strategy and able to close the loop to feedback into the process for advanced process control. However, the established models should be improved by more green tea samples from different regions.