Albino Tea Cultivar Research Articles

Effects of Photoperiod and Light Quality on Germination and Growth of Camellia sinensis 'HuangKui'.

Light, as a critical environmental factor, plays a pivotal role in photosynthesis, ultimately influencing the timing of bud flush in tea plants. However, the synergistic effects of different photoperiods and light qualities on the timing of bud flush in the albino tea cultivar 'HuangKui' (later germination variety) remain unknown. Thus, the objective of this study was to investigate the effects of different photoperiods (12L/12D, 14L/10D, 16L/8D, and 18L/6D, where L = the number of daylight hours and D = the number of hours of darkness) and ratios of red (R) to blue (B) light (R/B 1:1, R/B 1:2, R/B 1:3, and R/B 2:1) on the germination and growth of the albino tea variety 'HuangKui'. In our study, we examined how different photoperiods and red light and blue light affected tea germination and growth by investigating the timing of bud flush, photosynthesis, chlorophyll content, and growth indicators. First, our study showed that 'HuangKui' germinated 4 days, 2 days, and 1 day earlier under the 16L/8D photoperiod at the one bud and one leaf period compared with plants cultivated under the 12L/12D, 14L/10D, and 18L/6D photoperiods under light simulating the solar spectrum. Also, the growth of 'HuangKui' was maximumly promoted under the 16L/8D photoperiod treatment. Additionally, the earliest germination of 'HuangKui' was observed for the 16L/8D photoperiod under the R/B 2:1 (red/blue) treatment compared with the other treatments. Moreover, the greatest plant height, length of the new shoots, and new leaf areas were detected in the albino tea variety 'HuangKui' under R/B 2:1. Moreover, the contents of auxin (indole acetic acid, IAA) and trans-zeatin (tZ) under R/B 2:1 were significantly higher than those under the R/B 1:1 and control treatments with the 16L/8D photoperiod. Additionally, the auxin-related expression levels of CsIAA13, CsGH3.1, CsAUX1, and CsARF2 under the R/B 2:1 treatment were significantly higher than those in the control. The expression of CsARR-B, a positive regulator of cytokinin-related genes, was significantly higher under the R/B 2:1 treatment than under the control treatment, while the opposite result was found for the expression of the negative regulator CsARR-A. Therefore, the R/B 2:1 treatment with the 16L/8D photoperiod was an appropriate means of timing the bud flush for the albino tea variety 'HuangKui', which may be related to IAA or tZ signal transduction. In conclusion, our research offers a novel lighting strategy that promotes the germination and growth of albino tea cultivars.

Optimization of nutrient management improves productivity, quality and sustainability of albino tea cultivar Baiye-1.

Proper nutrient management is crucially important to the sustainable development of tea production. Compared to normal green-leaf cultivars, albino tea cultivars produce green tea of superior quality characterized by high contents of amino acids as a result of the hydrolysis of chloroplast proteins at albinism. However, the advantage of albino tea cultivars was offset by inferior growth and yield performance because of low contents of chlorophylls and limited photosynthesis capacity. Our understanding about the nutrition characteristics of albino tea cultivars was very limited. A four-year field experiment was conducted to develop proper nutrient management for Baiye-1 to overcome its weakness of low productivity without a tradeoff in tea quality and environmental risks. The nutrient management schemes were formulated by optimizing the rate and ratio of nitrogen (N), phosphorus, potassium and magnesium together with substitution of chemical fertilizers with organic manures. The total amounts of nutrients in the optimized schemes were reduced by 25% compared to the local farmers' practice (FP). Results showed that optimized rates and ratio of nutrients together with partial substitution of chemical fertilizers with rapeseed cake manure more considerably improved albino tea yield, the contents of free amino acids, total polyphenol and catechins relative to FP. Partial substitution of chemical fertilizers with commercial livestock manure decreased tea quality, which was likely caused by a dilution effect of increasing tea yield and decreasing N status of tea plants. Full organic substitution of chemical fertilizers by rapeseed cake manure improved tea yield and quality but had relatively low agronomic efficiency and profit. The effect of optimized nutrient management schemes was associated with the improvement of nutritional status in tea plants. The present work demonstrated that the optimization of nutrient management considerably improved albino tea yield, quality and profit while decreased the application rate of fertilizers and the intensity of greenhouse gas emissions.

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.

Metabolomics and quantitative descriptive analysis reveal the relationship between metabolites and taste attributes of flowers in two types of albino tea cultivars

Albino tea cultivars have a much higher flowering capacity than green leaf cultivars, and the sensory qualities of the flowers of albino tea cultivars are also unique. Whereas, the relationship of metabolic differences with taste quality in flowers of albino tea cultivars (temperature-sensitive cultivars Baiye 1 Hao and light-sensitive cultivars Huangjinya and Yujinxiang) (BY1H, HJY and YJX) are not clear currently. In this study, taste profiles and metabolic differences of flowers of three albino tea cultivars were analyzed by quantitative analysis, widely targeted metabolomics and sensory quantitative descriptive analysis. The taste of flowers of three tea cultivars has a certain bitter, astringency and slightly numbing, but also an umami and sweetness, making the overall flavor harmonious. BY1H has a slightly bitter taste and possesses higher levels of catechins, quercetin glycosides, myricetin glycosides and alkaloids, while YJX and HJY have a sweeter and more umami taste with higher levels of amino acids, nucleotides and their derivatives and organic acids. Notably, quercetin glycosides were found to be the specific compounds that distinguish Baiye 1 Hao from other flowers of tea cultivars. These findings provide a comprehensive understanding of the sensory and metabolic characteristics of flowers in two types of albino tea cultivars.

Genome-Wide Identification and Characterization of Tea SGR Family Members Reveal Their Potential Roles in Chlorophyll Degradation and Stress Tolerance

Photosynthesis plays vital roles in plant growth and development. Stay-green (SGR) proteins are responsible for chlorophyll degradation and photosynthetic metabolism. To identify SGR family members and determine their potential functions in tea plants, we identified and cloned three SGR genes. Phylogenetic analysis revealed that the tea SGR homologs were classified into the SGR subfamily (named CsSGR1 and CsSGR2) and the SGRL subfamily (named CsSGRL). Cis-element analysis indicated that the promoters of CsSGR1, CsSGR2 and CsSGRL contained light-, phytohormone- and stress-related elements. Subcellular localization confirmed that CsSGR1 was localized in the chloroplast, while CsSGR2 and CsSGRL were localized in the chloroplast, membrane and nucleus. The RT-qPCR results showed that the three genes in the matures of albino tea cultivars were expressed higher than in the green tea cultivar. However, only CsSGR2-overexpressing tobacco leaves exhibited a yellowish phenotype and significantly lower Fv/Fm values. CsSGR1 and CsSGR2 exhibited similar expression patterns in different tissues after infection with the pathogen Colletotrichum camelliae, which was opposite to the pattern observed for CsSGRL. In addition, CsSGR1 was significantly induced in response to cold stress, SA, JA and ABA in C. camelliae. These findings identified valuable candidate genes for elucidating the mechanism of leaf albinism, stress response and phytohormone signaling in tea plants.

The light-harvesting chlorophyll a/b-binding proteins of photosystem II family members are responsible for temperature sensitivity and leaf color phenotype in albino tea plant

IntroductionLight-harvesting chlorophyll a/b-binding (LHCB) protein complexes of photosystem II are integral to the formation of thylakoid structure and the photosynthetic process. They play an important role in photoprotection, a crucial process in leaf development under low-temperature stress. Nonetheless, potential key genes directly related to low-temperature response and albino phenotype have not been precisely identified in tea plant. Moreover, there are no studies simultaneously investigating multiple albino tea cultivars with different temperature sensitivity. ObjectivesThe study aimed to clarify the basic characteristics of CsLHCB gene family members, and identify critical CsLHCB genes potentially influential in leaf color phenotypic variation and low-temperature stress response by contrasting green and albino tea cultivars. Concurrently, exploring the differential expression of the CsLHCB gene family across diverse temperature-sensitive albino tea cultivars. MethodsWe identified 20 putative CsLHCB genes according to phylogenetic analysis. Evolutionary relationships, gene duplication, chromosomal localization, and structures were analyzed by TBtools; the physiological and biochemical characteristics were analyzed by protein analysis websites; the differences in coding sequences and protein accumulation in green and albino cultivars, gene expression with maturity were tested by molecular biology technology; and protein interaction was analyzed in the STRING database. ResultsAll genes were categorized into seven groups, mapping onto 7 chromosomes, including three tandem and one segmental duplication. They all own a conserved chlorophyll A-B binding protein domain. The expression of CsLHCB genes was tissue-specific, predominantly in leaves. CsLHCB5 may play a key role in the process of leaf maturation and senescence. In contrast to CsLHCB5, CsLHCB1.1, CsLHCB2, and CsLHCB3.2 were highly conserved in amino acid sequence between green and albino cultivars. In albino tea cultivars, unlike in green cultivars, the expression of CsLHCB1.1, CsLHCB1.2, and CsLHCB2 was down-regulated under low-temperature stress. The accumulation of CsLHCB1 and CsLHCB5 proteins was lower in albino tea cultivars. Greater accumulation of CsLHCB2 protein was detected in RX1 and RX2 compared to other albino cultivars. ConclusionsCsLHCB1.1, CsLHCB1.2, and CsLHCB2 play a role in the response to low-temperature stress. The amino acid sequence site mutation of CsLHCB5 would distinguish the green and albino tea cultivars. The less accumulation of CsLHCB1 and CsLHCB5 had a potential influence on albino leaves. Albino cultivars more sensitive to temperature exhibited lower CsLHCB gene expression. CsLHCB2 may serve as an indicator of temperature sensitivity differences in albino tea cultivars. This study could provide a reference for further studies of the functions of the CsLHCB family and contribute to research on the mechanism of the albino in tea plant.

Metabolomic and transcriptomic analyses reveal the biosynthetic mechanisms of pigments and main taste compounds in an albino tea cultivar.

Significant variations in leaf colours, pigment contents, and main taste compounds in young shoots from albino tea plants (Camellia sinensis) influence tea flavour. However, the seasonal metabolic pattern and molecular regulatory mechanism of these metabolites remain largely elusive. Herein, we conducted morphological, biochemical, metabolomic and transcriptomic analyses between an albino tea cultivar 'Zhonghuang 3' ('ZH3') and a green strain 'Tai cha 15' ('TC15') at four-time points (April 12, May 31, July 14, and August 17) to elucidate dynamic changes in these compounds and predict the relationships among transcription factors (TFs), target genes (TGs), and metabolite abundance. Generally, leaf colours and pigment contents were significantly lighter and lower, respectively, in 'ZH3' than in 'TC15' from spring to summer, but were subsequently similar. Compared to 'TC15', 'ZH3' had a lower and broader phenol/ammonia ratio as well as stable caffeine content and showed more significantly different metabolites and differentially expressed genes. The relationship between pigments, main taste compounds, and their biosynthetic genes, as well as TFs and their TGs, had genetic specificity. These results suggested that the biosynthesis of these compounds was probably both season- and variety-dependent. In total, 12 models of the TF-TG-metabolite regulatory network were proposed to uncover the biosynthetic and regulatory mechanisms of these metabolites in tea plants. A high correlation was observed between some structural genes and TFs with the accumulation of these metabolites. These findings provide novel insights into the regulatory mechanisms underlying accumulation of pigments and main taste compounds in tea plants.

CsRVE1 promotes seasonal greening of albino Camellia sinensis cv. Huangkui by activating chlorophyll biosynthesis.

Seasonal greening is a crucial survival strategy for albino tea cultivars, during which dysfunctional chloroplasts recover and chlorophyll biosynthesis increases in albino leaves. However, the regulatory mechanisms of seasonal greening in albino tea plants remain unclear. Here, we report that CsRVE1, a nuclear-located Myb-like transcription factor, can positively modulate the seasonal greening of albino Camellia sinensis cv. Huangkui leaves by activating the expression of genes involved in light harvesting and chlorophyll biosynthesis. The transcriptional expression of CsRVE1 increased during seasonal greening and was tightly correlated with increases in the expression of genes involved in light harvesting (CsLhcb) and chlorophyll biosynthesis (CsCHLH, CsHEMA1 and CsCAO). In vivo and in vitro molecular analyses showed that CsRVE1 can directly bind to the promoters of CsLhcb, CsCHLH and CsPORA, eventually leading to chlorophyll accumulation in tea leaves. Furthermore, transient suppression of CsRVE1 in tea leaves led to a decrease in target gene expression. In contrast, the overexpression of CsRVE1 in Arabidopsis led to chlorophyll increases and the activation of AtLhcb, AtPORA, AtCHLH, etc. These results identify CsRVE1 as an important promoter of seasonal greening that functions by regulating genes involved in chlorophyll biosynthesis in albino tea plants and shed new light on the regulatory mechanisms of leaf phenotypes in plants.

Chemical composition and anti-cholesterol activity of tea (Camellia sinensis) flowers from albino cultivars.

Albino tea cultivars are mutant tea plants with altered metabolisms. Current studies focus on the leaves while little is known about the flowers. To evaluate tea flowers from different albino cultivars, the chemical composition and anti-cholesterol activity of tea flowers from three albino cultivars (i.e., Baiye No.1, Huangjinya, and Yujinxiang) were compared. According to the results, tea flowers from Yujinxiang had more amino acids but less polyphenols than tea flowers from the other two albino cultivars. A reduced content of procyanidins and a high chakasaponins/floratheasaponins ratio were characteristics of tea flowers from Yujinxiang. In vitro anti-cholesterol activity assays revealed that tea flowers from Yujinxiang exhibited stronger activity in decreasing the micellar cholesterol solubility, but not in cholesterol esterase inhibition and bile salt binding. It was noteworthy that there were no specific differences on the chemical composition and anti-cholesterol activity between tea flowers from albino cultivars and from Jiukeng (a non-albino cultivar). These results increase our knowledges on tea flowers from different albino cultivars and help food manufacturers in the cultivar selection of tea flowers for use.

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

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.

Genome-wide identification of RNA editing sites in chloroplast transcripts and multiple organellar RNA editing factors in tea plant (Camellia sinensis L.): Insights into the albinism mechanism of tea leaves

RNA editing is a post-transcriptional modification process, the chloroplast genes of which are involved in the process of chloroplast development in plant. However, the RNA editing sites of chloroplast genes remains unknown. In this study, we identified 39 RNA editing sites in 18 chloroplast genes from chloroplast genome of C. sinensis. Furthermore, the feature, structures and specificity of RNA editing sites were systematic analyzed. The differential editing efficiency were examined at 11 RNA editing sites among C. sinensis var. sinensis ‘Huabai 1′, ‘Baiye 1′ and ‘Longjing 43′. Meanwhile, we identified 10 C. sinensis MORFs from five subgroups and performed comparative analyses of chromosome locations, duplication model and expression profiles. Expression analysis showed that the expression level of CsMORF9.2 was down-regulated significantly in ‘Huabai 1′ albino tea cultivar. This study provides a foundation for further reveal in the role of chloroplast RNA editing in albinism process of tea leaves.

Glycinebetaine facilitates the photosynthesis of albino tea under low temperature by regulating related gene methylation

• Glycinebetaine (GB) increased net photosynthetic rate of albino tea by 45.3% at low temperature. • GB raised the methylation of photosynthetic-related genes and chlorophyll contents. • Facilitating photosynthesis by GB was correlative to related gene methylation. • GB may play as a methyl donor for gene methylation of albino tea leaves. The frequent occurrence of adverse weather conditions in early spring caused by global climate change has seriously restricted the physiological metabolism and growth of plants in recent years. As a low temperature sensitive albino tea cultivar, white leaf No. 1 (WL-1) has been seriously affected. Regulation of DNA methylation (an epigenetic regulator) due to global climate change by glycinebetaine (GB, a bioactive methyl donor) has been often observed in animals/humans, but little is known about whether it is linked to gene methylation priming responses of plants to low temperature. Herein, the effects of foliar application of GB on photosynthesis, photosynthetic pigment synthesis and related genes methylation of WL-1 functional leaves under low temperature were investigated. Results showed that the transpiration efficiency and chlorophyll contents of WL-1 functional leaves under low temperature condition were significantly improved by the application of GB ( P < 0.05), and the net photosynthetic rate was increased by 45.3%. In addition, the application of GB promoted the methylation of most methyltransferase and demethylase genes, PSⅡ component genes and some chlorophyll synthesis genes in WL-1 functional leaves under low temperature. It was verified that the changes of photosynthetic parameters and chlorophyll content may be correlative to related gene methylation. Together, present study suggests important roles of GB in facilitating photosynthesis of albino tea functional leaves under low temperature by regulating related gene methylation.

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.

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.

Quantitative trait loci mapping for free amino acid content using an albino population and SNP markers provides insight into the genetic improvement of tea plants.

Free amino acids are one of the main chemical components in tea, and they contribute to the pleasant flavor, function, and quality of tea, notably the level of theanine. Here, a high-density genetic map was constructed to characterize quantitative trait loci (QTLs) for free amino acid content. A total of 2688 polymorphic SNP markers were obtained using genotyping-by-sequencing (GBS) based on 198 individuals derived from a pseudotestcross population of "Longjing 43" × "Baijiguan", which are elite and albino tea cultivars, respectively. The 1846.32cM high-density map with an average interval of 0.69cM was successfully divided into 15 linkage groups (LGs) ranging from 93.41cM to 171.28cM. Furthermore, a total of 4 QTLs related to free amino acid content (theanine, glutamate, glutamine, aspartic acid and arginine) identified over two years were mapped to LG03, LG06, LG11 and LG14. The phenotypic variation explained by these QTLs ranged from 11.8% to 23.7%, with an LOD score from 3.56 to 7.7. Furthermore, several important amino acid metabolic pathways were enriched based on the upregulated differentially expressed genes (DEGs) among the offspring. These results will be essential for fine mapping genes involved in amino acid pathways and diversity, thereby providing a promising avenue for the genetic improvement of tea plants.

Chemical Constituents of Green Teas Processed from Albino Tea Cultivars with White and Yellow Shoots

Chemical Constituents of Green Teas Processed from Albino Tea Cultivars with White and Yellow Shoots

Transcriptomic and biochemical analysis reveal differential regulatory mechanisms of photosynthetic pigment and characteristic secondary metabolites between high amino acids green-leaf and albino tea cultivars

It is generally believed that albino tea cultivars contain high amino acid content, and numerous studies have used them as materials to reveal L-theanine metabolism mechanism. However, few studies on the research of high amino acid green-leaf tea cultivars were reported. Here, high amino acid green-leaf tea cultivars, ‘Baojing Huangjincha1’ (BJ1) and ‘Huangjincha2’ (HJC2) have been discovered. In this study, biochemical ingredients and transcriptomes of high amino acids green-leaf tea cultivars (BJ1, HJC2) and albino tea cultivars, ‘Baiye1’ (BY1) and ‘Huangjinya’ (HJY) were analyzed and compared. Biochemical analyses showed that the contents of chlorophyll and carotenoids in albino tea cultivars (BY1, HJY) were much lower than that in green-leaf tea cultivars (BJ1, HJC2), whereas increases were noted in the ratio of carotenoids to chlorophyll. The content of catechins was lower in HJC2, BY1 and HJY than that in BJ1. The content of L-theanine also showed considerable variability among four tea cultivars. Especially, HJC2 with dark-green leaves contained the highest L-theanine and lowest catechins content. At transcription level, the results revealed expression patterns of genes related to chlorophyll biosynthesis were significantly up-regulated in HJC2. Suppressed expressions of CsCHS in HJC2, CsPAL in BY1, and CsF3′5′H in HJY were responsible for the lower catechins content, respectively. Furthermore, we also found that CsGOGAT and CsGS/TS were key genes leading to differences in the accumulation patterns of L-theanine between HJC2 and BY1. These findings provide basis for further research on regulatory mechanisms of pigments and characteristic secondary metabolites in tea plants.

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.

Low temperature effects on carotenoids biosynthesis in the leaves of green and albino tea plant (Camellia sinensis (L.) O. Kuntze)

Tea plant (Camellia sinensis (L.) O. Kuntze) is one of the most important economic crops worldwide, and it has a positive effect on human health. The low temperature in late autumn and early/late spring cold often cause damage to the normal physiological activities of tea plant, thereby reducing the quality and yield of tea. As one of the essential pigment of higher plant, carotenoids play an important role in the physiological activities of higher plant. In addition, as an important precursor of tea aroma volatiles, carotenoids are the important factors involved in the formation of tea quality. In this study, the main carotenoids, lutein and β-carotene, in leaves of common green tea cultivar 'Longjing 43′ and albino tea cultivar 'White leaf No.1′ were detected after low temperature treatment at 4 ℃. The results showed that the contents of lutein and β-carotene in 'Longjing 43′ were higher than that in 'White leaf No.1′, respectively. The chlorophyll content in two tea cultivars decreased and was significant positive correlation with two kinds of carotenoid content at low temperature. Under low temperature, the genes related to the biosynthesis pathway of methylerythritol 4-phosphate (MEP) and carotenoids all showed varying degrees of response with the changes of lutein and β-carotene content. The relative expression levels of CsDXS1, CsPSY1 and CsCHXB were up-regulated and higher than other related genes. Expression analysis of carotenoids biosynthesis genes and its correlation with carotenoids accumulation confirmed the regulatory role of structural genes in tea plant at low temperature. Promoter prediction results showed that the CsDXR, CsHDS1 and CsCHXB contain low-temperature response element LTR. This study provides reference for further study on the dynamic changes of carotenoids during the growth of tea plant.

An RNA-seq Analysis Reveals Differential Transcriptional Responses to Different Light Qualities in Leaf Color of Camellia sinensis cv. Huangjinya

‘Huangjinya’ is a novel light-sensitive albino tea cultivar. Previously we have found that the leaves exhibit varying degrees of yellow coloration after being exposed to different light qualities, including red light (RL), blue light (BL), red + blue light (RB) and white light (WL). To understand the transcriptional response of different light qualities in leaf coloration of ‘Huangjinya’, RNA-seq analysis with three biological replicates was performed to identify differentially expressed genes (DEGs) involved in pigment metabolism pathways. With regard to porphyrin and chlorophyll metabolism, the protochlorophyllide oxidoreductase (POR) was upregulated and chlorophyllase (Chlase) was downregulated under RL compared with WL, which contributed to high chlorophyll content in ‘Huangjinya’. The upregulated POR and magnesium chelatase H subunit (CHLH) were identified under RB. BL significantly promoted carotenoid biosynthesis, accompanied by the related upregulated genes. However, upregulated xanthoxin dehydrogenase (ABA2) reduced carotenoid content under BL. Zeaxanthin epoxidase (ZEP) was upregulated and ABA2 was downregulated under RB, resulting in high accumulation of carotenoid content. BL and RL upregulated expressions of genes involved in flavonoid biosynthesis in ‘Huangjinya’. Differential expressions of genes involved in flavonoid biosynthesis was considered as the results of leaf color change. In addition, the genes related to photosynthesis were downregulated under RL, whereas these were upregulated under BL when compared with WL. In conclusion, the effect of light quality on the leaf coloration of ‘Huangjinya’ was mainly dependent on chlorophyll content by altering corresponding genes expressions. RL may promote the accumulation of chlorophyll in ‘Huangjinya’ leaves by upregulating the expression of genes related to chlorophyll synthesis (e.g., POR) and downregulating expression of genes related to chlorophyll degradation (e.g., Chlase). BL could upregulate the expression of genes related to both biosynthesis (e.g., POR, hemA) and degradation (e.g., Chlase) of chlorophyll, resulting in little change in leaf color of ‘Huangjinya’ under blue light when compared with white light. Upregulated genes involved in chlorophyll biosynthesis (e.g., POR, CHLH) induced greener color of ‘Huangjinya’ treated with RB.