15 December 2021, Volume 41 Issue 6

    

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Review
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  Research Advance of Tea Plant Genome and Sequencing Technologies

  WANG Pengjie, YANG Jiangfan, ZHANG Xingtan, YE Naixing

  Journal of Tea Science. 2021, 41(6): 743-752.

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  The tea plant has the characteristics of high heterozygosity, large genome and high duplication, which has led to the slow progress of the preliminary research on the tea plant genomes. The rapid development of genome sequencing technologies has strongly promoted the deciphering and improvement of the tea plant genomes. This article reviewed the development of genome sequencing technologies, and classified the assembly and research progress of tea plant genomes in recent years according to the draft level, chromosome level and haplotype level. By discussing the future application and development direction of tea plant genomes, it provided a reference for the functional genomics research and precision molecular breeding in tea plants.
Research Paper
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  The Functional Identification of Two Alternative Splicing Transcripts of CsNES

  ZHOU Hanchen, LEI Pandeng

  Journal of Tea Science. 2021, 41(6): 753-760.

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  CsNES is a key enzyme for the formation of (E)-nerolidol in tea plants. According to the analysis of full-length transcriptome and genome data, it is shown that CsNES has two shorter alternative splicing transcripts besides the full-length transcript. The rapid amplification of cDNA ends (RACE) result indicates that the CsNES undergoes 5' alternative splicing in the second and third exons, respectively, which were named as CsNES-2 and CsNES-3. The recombinant proteins of CsNES-2 and CsNES-3 possess strong activities to catalyze the FPP into (E)-nerolidol and weak activities to hydrolyze FPP into (Z)-nerolidol. The gene expression analysis shows that CsNES-2 and CsNES-3 had higher expression levels in tea flower compared to those in tea leaves. Their expressions in young leaves were higher than those in mature leaves. Furthermore, the expression levels of CsNES-2 and CsNES-3 were induced by the MeJA treatment. This study identified two alternative splicing transcripts of the CsNES gene and gave insights into the regulation of gene alternative splicing in terpenoids metabolism in Camellia sinensis.
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  Cloning and Magnesium Transport Function Analysis of CsMGTs Genes in Tea Plants (Camellia sinensis)

  TANG Lei, XIAO Luodan, HUANG Yifan, XIAO Bin, GONG Chunmei

  Journal of Tea Science. 2021, 41(6): 761-776.

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  Magnesium (Mg²⁺), as the central atom of chlorophyll, is the most abundant divalent cation in plant cells. Magnesium is also an activator of various enzymes, especially theanine synthase, whose activity depends on Mg²⁺ concentration and is often used as a characteristic component of special fertilizer for tea plants. Therefore, it is very important for both the growth and development of tea plants and the formation of tea quality. The MRS2/MGT magnesium transporter family plays an important role in maintaining the absorption and transport of Mg²⁺, intracellular balance and stress tolerance in plants. In order to explore the functions of the MRS2/MGT magnesium transport genes in tea plants, this study cloned four MRS2/MGT magnesium transporter genes (namely CsMGT1, CsMGT2, CsMGT2.1 and CsMGT3, respectively) from tea cultivar ‘Shaancha 1'. Bioinformatics analysis shows that the four proteins all contain two transmembrane domains and a conserved GMN tripeptide motif at the C-terminal. Phylogenetic analysis shows that CsMGT1 is a member of Clade C, while CsMGT2, CsMGT2.1 and CsMGT3 belong to Clade B, and the four encoded proteins are most closely related to the woody Poncirus trifoliata MGT family. Real-time fluorescence quantitative PCR (RT-qPCR) shows that CsMGT1, CsMGT2, CsMGT2.1 and CsMGT3 were constitutively expressed in the roots, stems, leaves and flowers of tea plants, and the roots and leaves all showed different degrees of response to Mg²⁺. Functional complementation tests in a magnesium deletion mutant strain MM281 of Salmonella typhimurium show that both CsMGT1 and CsMGT2 possessed Mg²⁺ transport function, and the Mg²⁺ transport function of CsMGT1 was superior to that of CsMGT2, while CsMGT2.1 and CsMGT3 had almost no Mg²⁺ transport function. The results of this study enriched the biological functions of tea plant CsMGTs family, and laid a foundation for further utilization of magnesium through magnesium transporters in tea plants.
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  Complete Chloroplast Genome of Camellia sinensis cv. Xinyang 10 and Its Phylogenetic Evolution

  YAN Minghui, LIU Ke, WANG Man, LYU Ying, ZHANG Qian

  Journal of Tea Science. 2021, 41(6): 777-788.

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  Camellia sinensis cv. Xinyang 10 is a national excellent cultivar suitable for producing Xinyangmaojian. However, its origin and evolutionary relationship with other tea cultivars are still unknown. This study obtained the complete chloroplast genome of C. sinensis cv. Xinyang 10 by using MGI2000 sequencing platform, and then analyzed the chloroplast genome structure. A chloroplast genome phylogenetic analysis of 46 species was also conducted to infer the position of C. sinensis cv. Xinyang 10. The results show that: (1) the chloroplast genome of Xinyang 10 is 157 041 bp in length, including a pair of inverted repeat regions (IR, 26 078 bp), a large single-copy region (LSC, 86 594 bp) and a small single-copy region (SSC, 18 291 bp). A total of 113 genes are annotated, including 79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes. (2) 74 SSR loci were detected in the chloroplast genome of Xinyang 10, most of the SSRs were composed of A/T. (3) The cluster analysis using Bayesian method shows that Xinyang 10 had the closest genetic relationship with C. sinensis cv. Tieluohan. Both cultivars may share the same female parent as their chloroplast genomes were identical. Xinyang 10 also had a close relationship with two Korean tea (Chamnok and Sangmok), Baijiguan and C. sinensis var. Dehungensis. The results provided a basis for further research on the origin and evolution of tea and molecular breeding.
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  Analysis of Gene Expression Related to Anthocyanin Regulation of ‘P113' Purple Strain of Camellia tachangensis F. C. Zhang in Different Seasons

  LIU Xia, LI Fang, SONG Qinfei, NIU Suzhen, LYU Litang

  Journal of Tea Science. 2021, 41(6): 789-801.

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  In order to clarify the molecular mechanism of anthocyanin accumulation and the expression characteristics of related genes in the synthetic pathway of anthocyanin in Camellia tachangensis F. C. Zhang purple bud line P113 in different seasons, one bud and two leaves of P113 in spring, summer and autumn were analyzed by RNA-Seq and UHPLC-MS/MS. The results show that the 10 anthocyanin contents changed with seasons, and 4 of them were up-regulated with the change of spring, summer and autumn, which were consistent with leaf color phenotype of ‘P113'. The expression patterns of structural genes PAL, C4H, 4CL, CHS, F3H and F3'5'H were basically the same, which were up-regulated in summer, but not significantly changed in autumn. The two differentially expressed 4CL genes were up-regulated in summer. The gene expression patterns of F3H, DFR and ANS were similar, and their expressions were up-regulated in summer and down-regulated in autumn. One of the two F3'H genes was down-regulated in summer, and one was up-regulated with seasonal changes. The 13 genes of FLS were all up-regulated in summer, but they showed different expression patterns in autumn. The modifier gene LAR had two expression patterns in summer and autumn. There was only 1 differentially expressed gene in ANR that was up-regulated with seasonal changes. Among the three UGT79B1 genes, one was down-regulated in summer, up-regulated in autumn, and the rest two genes were up-regulated in summer, but not significantly changed in autumn. Seven differentially expressed CCoAOMT genes were up-regulated in summer. Two of them down regulated in autumn, and the rest five genes were not significant changed. The regulatory genes bHLH and MYB were up-regulated with seasonal changes, and had a positive relationship with anthocyanin biosynthesis. The results show that the expressions of structural genes, modifier genes and regulatory genes of ‘P113' (Camellia tachangensis F. C. Zhang) had certain time characteristics in different seasons, which led to the differences in anthocyanin accumulation.
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  Research on the Regulation Relationship between Endogenous Hormones in Tea Shoots and Leaf Color Formation

  GAO Chenxi, HUANG Yan, LI Jing, SUN Yue, CHEN Zhiheng, LIN Lin, CHEN Zhidan, SUN Weijiang, ZHONG Lei

  Journal of Tea Science. 2021, 41(6): 802-812.

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  Three purple tea cultivar, Zifuxing 1, Zijuan, Hongye 1, and two green leaf cultivar Rougui and Fuding Dabaicha, as well as the albino tea cultivar, Baijiguan, were used as test materials to reveal the relationship between the accumulation of color-presenting substances and endogenous hormones in tea plants. The contents of major color-presenting substances, anthocyanin, chlorophyll, carotenoids and phytohormones (ABA, JA and SA) were determined in different tea cultivars. The results show that purple teas generally contained higher anthocyanin and ABA contents, which showed a highly significantly positive correlation. While ABA had a significantly negative correlation with chlorophyll and carotenoids. The correlation between ABA and anthocyanin changing patterns among different leaf positions of purple tea and the expression patterns of relative genes were also analyzed, which indicates that ABA might play a positive effect on anthocyanin synthesis in tea plants.
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  Analysis of Bud and Leaf Characters and Photosynthetic Characteristics of Three Tea Cultivars in Sichuan

  XIE Wengang, CHEN Wei, TAN Liqiang, YAN Linfeng, TANG Qian

  Journal of Tea Science. 2021, 41(6): 813-822.

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  In order to ascertain the photosynthetic performance and production potential of tea plants, three characteristic cultivars in Sichuan, including ‘Emeiwenchun', ‘Chuancha 2' and ‘Ziyan', were used as test materials, and the green leaf cultivar ‘Fudingdabaicha' and purple cultivar ‘Zijuan' were used as control. The photosynthetic index, chlorophyll fluorescence, photosynthetic pigment content and bud and leaf characteristics of these cultivars in spring and summer were determined. The results show that in spring and summer, the net photosynthetic rate (P_n) and water use efficiency (WUE) of the leaves of ‘Chuancha 2' were higher. Its ΦPSⅡ primary light energy conversion efficiency (F_v/F_m) and potential activity (F_v/F₀) were the highest. The photochemical quenching coefficient (qP), the relative share of the photochemical reaction (P) in the energy distribution of the photosystem ΦPSⅡ, the relative share of the reaction center dissipation (E_X) and the carotenoid content of ‘Chuancha 2' were also higher. ‘Emeiwenchun' had the highest P_n and WUE in spring, but low P_n in summer. Its ΦPSⅡ primary light energy conversion efficiency (F_v/F_m) and potential activity (Fv/F₀) were the lowest. The ΦPSⅡ effective photochemical efficiency (F_v'/F_m' ) and ΦPSⅡ actual photosynthetic capacity (PhiPS2) of ‘Emeiwenchun' were the slowest. The effective photochemical efficiency (F_v'/F_m') of ΦPSⅡ of ‘Ziyan' was the highest in spring and summer, and its Pn and photosynthetic pigment contents were higher. Compared with the data in spring, the summer transpiration rate (T_r) and stomatal limit value (L_s) were increased, while WUE and intercellular carbon dioxide concentration (Ci) were decreased in all cultivars. In terms of yield, the yield of ‘Chuancha 2' was significantly higher than those of other cultivars. The yield of ‘Emeiwenchun' was not significantly different from that of ‘Fudingdabaicha', and that of ‘Ziyan' was significantly lower than that of ‘Fudingdabaicha' (P<0.05). It was found that ‘Chuancha 2' had higher photosynthetic efficiency and WUE, and its yield was the highest. ‘Emeiwenchun' had relatively higher yield, photosynthetic capacity and WUE in spring, but lower in summer. The purple cultivar ‘Ziyan' had higher photosynthetic pigment and photosynthetic capacity, but lower yield.
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  Effects of Theaflavin-3,3'-O-Digallate on Vascular Endothelial Injury and Inflammation in Rats with Diabetes Mellitus

  DENG Zhihui, ZENG Jie, FU Hongjuan, CHANG Hui

  Journal of Tea Science. 2021, 41(6): 823-830.

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  To investigate the protective effect and mechanism of theaflavin-3,3'-O-digallate (TFDG) on vascular endothelial injury and inflammation in rats with diabetes mellitus, diabetic rats were made by high fat feed and streptozotocin injection and then divided into model group (CON), 5 mg·kg^-1 and 10 mg·kg^-1 TFDG intervention group (TFDG5 and TFDG10). The normal rats were taken as control group (NC). After 8 weeks of treatment, the pathological changes of abdominal aorta were observed. Plasma IL-6, IL-1β and TNF-α were detected by ELISA. The protein expression was detected by Western blot. Compared with CON, TFDG administration has no significant effects on body weight and fasting blood glucose. Pathological sections show that the injury of aorta tissue in TFDG group was improved compared with that in CON group. At the same time, the level of plasma inflammatory factors was significantly decreased, the level of plasma NO was significantly increased, and the level of MDA in aorta tissue was decreased in TFDG group. Further studies show that TFDG could down-regulate NLRP3, caspase-1 and IL-1β expressions in the aorta of diabetic rats. TFDG effectively protected vascular endothelial injury and inhibit inflammatory response in diabetic rats, and its mechanism might be through down-regulation of NLRP3 inflammatory pathway.
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  L-Theanine Ameliorated Clinical Symptoms in Letrozole-Induced Polycystic Ovary Syndrome Rats

  HUANG Qiuping, XIE Chenyang, LI Xinyu, JIN Bin, ZENG Zhen, QIAN Bo, DAI Ling, SONG Jiale

  Journal of Tea Science. 2021, 41(6): 831-842.

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  To explore the improvement effect of L-theanine (LTA) on the clinical symptoms of letrozole-induced polycystic ovary syndrome (PCOS) rats, twenty-eight female SD rats were randomly divided into control group, PCOS group, PCOS+low-dose LTA group, and PCOS+high-dose LTA group with 7 rats in each group. In the modeling stage, except for the control group, the other three groups were administered letrozole continuously for 28 days to induce the PCOS model. During the intervention phase, the normal control group and the PCOS group were given continuous gastric administration with normal saline, and the rats in the two LTA groups were given continuous gastric administration with the corresponding dose of LTA intervention for 30 days. The results show that compared with the PCOS group, the serum testosterone (T), luteinizing hormone (LH), insulin (INS), triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), lipopolysaccharide (LPS) levels and homeostasis model assessment-insulin resistance (HOMA-IR) index in the LTA intervention group were significantly reduced (P<0.05), high-density lipoprotein cholesterol (HDL-C) was significantly increased (P<0.05), ratio of luteinizing hormone to follicle stimulating hormone (LH/FSH), fasting plasma glucose (FPG) and body weight were decreased (P>0.05). The serum estradiol (E2) of rats in the low-dose LTA intervention group was significantly increased (P<0.05). Follicle stimulating hormone (FSH) of mice in the high-dose LTA intervention group was significantly increased (P<0.05). At the same time, rat estrous cycle disorder and polycystic lesions of ovarian tissue were improved to a certain extent compared with PCOS group. The results show that LTA intervention can effectively regulate the secretion of sex hormones in PCOS rats, restore the regular changes of the estrus cycle, improve their ovarian polycystic lesions, and significantly improve insulin resistance (IR) and blood lipid metabolism disorders in PCOS rats and inhibit abnormal levels of lipopolysaccharide (LPS) secretion.
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  Study on Bioavailability of Fluorine in Different Extracts of A Dark Tea

  SU Dan, ZHANG Haojie, WEN Xiaoju, ZHANG Wei, YU Zhi, NI Dejiang, CHEN Yuqiong

  Journal of Tea Science. 2021, 41(6): 843-853.

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  In this study, absorption, transportation and bioavailability of fluorine in different extracts of a dark tea were evaluated in the Caco-2 cell line model. The results show that the fluorine contents in different extracts of dark tea were significantly different. The fluorine content of the crude polysaccharide fraction (RTP) was the highest, which was 2.17 times that of the water extract (TE). Fluorine content in dialyzed polysaccharide (DTP) was significantly reduced, which was only 1/22 of the fluorine content in RTP and 1/10 of the fluorine content in TE. The forward and reverse transport of fluorine in cell model had time and dose effects, and increased with the increase of time and concentration. After the first 1 h treatment, the forward and reverse transport of fluorine in NaF was the highest, while that in DTP was the lowest, which were significantly different from other treatments. There was no significant difference between the TE and RTP treatments. The apparent permeability coefficient (P_app) decreased with the prolonging of treatment time. The P_app of fluorine in NaF was more than 1×10^-5 cm·s^-1 within 4 h, indicating its bioavailability was good. The P_app of fluorine in TE and RTP decreased to less than 1×10^-5 cm·s^-1 after 2 h of treatment, indicating its bioavailability was moderate. the P_app of fluorine in DTP was the smallest at all stages, and was less than 1×10^-5 cm·s^-1 after 1 h of treatment, indicating its bioavailability was low. Fluorine in NaF, TE or DTP was mainly transported by passive diffusion within the tested concentration range, while fluorine in RTP had an active transport at a higher concentration. In conclusion, in the intestinal epitheliums model, the fluorine in the dark tea has lower bioavailability than that in NaF, and the binding form of the fluorine in the dark tea might affect its bioavailability.
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  Study on the Tea Quality Changes and Predictions during the Microwave Fixation Process by Machine Vision

  WU Xin, SONG Feihu, PEI Yongsheng, ZHU Guanyu, JIANG Lebing, NING Wenkai, LI Zhenfeng, LIU Benying

  Journal of Tea Science. 2021, 41(6): 854-864.

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  Tea polyphenol, amino acid and moisture contents are important indicators of tea quality. Traditional detection methods have long cycles and complex processes. In this paper, machine vision was used to monitor the color and texture of tea leaves in real time during the microwave fixation process. The moisture content was detected online and the tea polyphenol and amino acid contents were also measured. The results show that the color, texture features and moisture content, tea polyphenol, amino acid contents all showed regular changes during the fixation process and had significant correlations. The principal component analysis was used to analyze the color and texture features and the first 3 principal components were taken to establish extreme learning machine (ELM), genetic neural network (GA-BP), and convolutional neural network (CNN) models to predict the quality. The results show that ELM, GA-BP and CNN models were more suitable for the prediction of moisture, tea polyphenol and amino acid contents, respectively, and their accuracies were all above 0.99. The research results show that it is feasible to predict the moisture, tea polyphenol and amino acid contents during the fixation process by monitoring the color and texture features of tea in real time.
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  Did the “Belt and Road” Initiative Promote the Export of China's tea? ——An Empirical Study Based on the Generalized DID

  WANG Chunxiao, GAO Feng, CHEN Fuqiao, ZENG Liang

  Journal of Tea Science. 2021, 41(6): 865-875.

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  The “Belt and Road” Initiative is a great opportunity for China's tea export. But the existing literatures are short of the evaluation of the policy effect. Based on the panel data of China and 40 major tea importing countries and regions, the difference-in-difference model (Generalized DID) was used to evaluate the promote effect of the “Belt and Road” Initiative to China's tea export. The results show that under the control of other variables, the “Belt and Road” Initiative had a positive effect to promote the growth of the export value of China's tea. Products heterogeneity analysis shows that the “Belt and Road” Initiative significantly promoted the export growth of green tea, but it had no significant effect on black tea. In addition, among the control variables, the improvement of per capital GDP and economic openness could significantly promote the export growth of China's tea. Finally, some suggestions were put forward for China's tea export trade to seize the opportunity.
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  Analysis on the Cause of Fluctuation of Tea Export Trade between China and the United States——Based on the Modified CMS Model

  LIU Shiyu, LI Daohe

  Journal of Tea Science. 2021, 41(6): 876-888.

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  Based on the analysis of the current situation of China's tea export trade to the United States, this paper used a modified constant market share model (CMS) to study the causes of fluctuations of China's tea export trade to US from 2000 to 2019. The results indicate that the increase of tea import demand in the US market was the most important driving force for the growth of China's tea export, while the competitiveness effect and second-order effect played a strong reverse role. The results of RCA indicate that the export competitiveness of all kinds of Chinese tea in the US market tended to decline over recent years. In addition, the export structure of Chinese tea did not meet the demand structure of the US market, and the rise of tea production costs also hindered the growth of China's tea export to the US market.