Proteomic analysis of Camellia sinensis (L.) reveals a synergistic network in the response to drought stress and recovery

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

INTRODUCTION

Light-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.

OBJECTIVES

The 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.

METHODS

We 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 tea cultivars, gene expression with maturity were tested by molecular biology technology; and protein interaction was analyzed in the STRING database.

RESULTS

All genes were categorized into seven groups, mapping onto 7 chromosomes, including three tandem and one segmental duplications. 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 tea 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.

CONCLUSIONS

CsLHCB1.1, CsLHCB1.2, and CsLHCB2 played 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 Chl 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.

Strigolactone enhances tea plant adaptation to drought and Phyllosticta theicola petch by regulating caffeine content via CsbHLH80

Strigolactones (SLs) play crucial roles in both plant growth and stress responses. However, their impact on the secondary metabolites of woody plants remains elusive. Here, we found that exogenous strigolactone analogue GR24 positively regulates tea plant flavor secondary metabolites, concurrently inhibiting caffeine biosynthesis and promoting the accumulation of caffeine catabolic pathway products. In this process, SL directly or indirectly inhibits the expression of CsSAMSs by inducing CsbHLH80, thereby reducing caffeine biosynthesis. Furthermore, CsbHLH80 enhances caffeine degradation, leading to increased allantoin. Under normal conditions, heightened allantoin reduces abscisic acid (ABA) accumulation. This inhibition reverses under drought stress. Increased ABA significantly enhances tea plant tolerance to both drought and Phyllosticta theicola Petch. In summary, this study offers novel insights for improving tea plant adaptation and quality in arid regions, particularly emphasizing the selection of stress-tolerant varieties and the refinement of production measures with a focus on high-quality production and environmentally friendly biological control methods.

Impact of Mild Field Drought on the Aroma Profile and Metabolic Pathways of Fresh Tea (Camellia sinensis) Leaves Using HS-GC-IMS and HS-SPME-GC-MS

Aroma plays a pivotal role in defining tea quality and distinctiveness, and tea producers have often observed that specific drought conditions are closely associated with the formation and accumulation of characteristic aroma compounds in tea leaves. However, there is still limited understanding of the differential strategies employed by various tea cultivars in response to drought stress for the accumulation of key volatile aroma compounds in fresh tea leaves, as well as the associated metabolic pathways involved in aroma formation. In this study, two widely cultivated tea cultivars in China, Fuding Dabai (FD) and Wuniuzao (WNZ), were examined to assess the impact of mild field drought stress on the composition and accumulation of key volatile aroma compounds in fresh leaves using headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid phase micro-extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) technologies. Results revealed that drought stress led to a substantial increase in the diversity of volatile compounds (VOCs) in FD, while WNZ exhibited a notable rise in low-threshold VOC concentrations, amplifying sweet, floral, fruity, and earthy aroma profiles in post-drought fresh leaves. Through partial least squares discriminant analysis (PLS-DA) of HS-GC-IMS and HS-SPME-GC-MS data, integrating variable importance projection (VIP) scores and odor activity values (OAVs) above 1, 9, and 13, key odor-active compounds were identified as potential markers distinguishing the drought responses in the two cultivars. These compounds serve as crucial indicators of the aromatic profile shifts induced by drought, providing insights into the differential metabolic strategies of the cultivars. Additionally, KEGG enrichment analysis revealed 12 metabolic pathways, such as terpenoid biosynthesis, fatty acid synthesis, cutin, suberine, and wax biosynthesis, and phenylalanine metabolism, which may play crucial roles in the formation and accumulation of VOCs in tea leaves under drought stress. These findings provide a comprehensive framework for understanding the cultivar-specific mechanisms of aroma formation and accumulation in tea leaves under mild drought conditions.

Proteomic and physiological signatures of altitude adaptation in a Myrsine coriacea population under common garden conditions

Plants exhibit phenotypic plasticity in response to environmental variations, which can lead to stable genetic and physiological adaptations if exposure to specific conditions is prolonged. Myrsine coriacea demonstrates this through its ability to thrive in diverse environments. The objective of the article is to investigate potential differences in protein accumulation and physiological responses of M. coriacea by cultivating plants from seeds collected from four populations at different altitudes in a common garden experiment. Additionally, we aim to evaluate whether these differences exhibit genetic fixation. Through integrated physiological and proteomic analyses, we identified 170 differentially accumulated proteins and observed significant physiological differences among the populations. The high-altitude population (POP1) exhibited a unique proteomic profile with significant down-regulation of proteins involved in carbon fixation and energy metabolism, suggesting a potential reduction in photosynthetic efficiency. Physiological analyses showed lower leaf nitrogen content, net CO2 assimilation rate, specific leaf area, and relative growth rate in stem height for POP1, alongside higher leaf carbon isotopic composition (δ13C) and leaf carbon (C) content. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriacea and underscore the importance of local adaptations. SIGNIFICANCE: We investigate the adaptive responses of M. coriacea, a shrub with a broad phenotypic range, by cultivating plants from seeds collected at four different altitudes in a common garden experiment. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriacea and underscore the importance of local adaptations in the face of climate change. This study contributes to advancing our understanding of the influence of altitude-specific selection pressures on the molecular biology and physiology of plants in natural populations. Our findings provide valuable insights that enhance our ability to predict and comprehend how plants respond to climate change.

Proteomics and phosphoproteomics reveal the different drought-responsive mechanisms of priming with (Z)-3-hexenyl acetate in two tea cultivars

Drought is an important abiotic stress that constrains the quality and quantity of tea plants. The green leaf volatiles Z-3-hexenyl acetate (Z-3-HAC) have been reported to play an essential role in stress responses. However, the underlying mechanisms of drought tolerance in tea plants remain elusive. This study investigated the physiological, proteomic, and phosphoproteomic profiling of two tea plant varieties of Longjingchangye (LJCY) and Zhongcha 108 (ZC108) with contrasting drought tolerance characteristics under drought stress. Physiological data showed that spraying Z-3-HAC exhibited higher activities of superoxide dismutase (SOD) and catalase (CAT) in both LJCY and ZC108 but lower content of malondialdehyde (MDA) in LJCY under drought stress. The proteomic and phosphoproteomic analysis suggested that the drought tolerance mechanism of Z-3-HAC in LJCY and ZC108 was different. Proteomic analyses revealed that Z-3-HAC enhanced the drought tolerance of LJCY by fructose metabolism while enhancing the drought tolerance of ZC108 by promoting glucan biosynthesis and galactose metabolism. Furthermore, the differential abundance phosphoproteins (DAPPs) related to intracellular protein transmembrane transport and protein transmembrane transport were enriched in LJCY, and the regulation of response to osmotic stress and regulation of mRNA processing were enriched in ZC108. In addition, protein-phosphoprotein interactions (PPI) analyses suggested that energy metabolism and starch and sucrose metabolic processes might play critical roles in LJCY and ZC108, respectively. These results will help to understand the mechanisms by which Z-3-HAC enhances the drought resistance of tea plants at the protein level. SIGNIFICANT: Green leaf volatiles (GLVs) are important volatile organic compounds that play essential roles in plant defense against biotic and abiotic stresses. To understand the mechanisms of Z-3-HAC in improving the drought tolerance of tea plants, two contrasting drought tolerance varieties (LJCY and ZC108) were comparatively evaluated by proteomics and phosphoproteomics. This analysis evidenced changes in the abundance of proteins involved in energy metabolism and starch and sucrose metabolic processes in LJCY and ZC108, respectively. These proteins may elucidate new molecular aspects of the drought resistance mechanism of Z-3-HAC, providing a theoretical basis for drought resistance breeding of tea plants.

Functional Analysis of a Methyltransferase Involved in Anthocyanin Biosynthesis from Blueberries (Vaccinium corymbosum)

Anthocyanins are natural water-soluble pigments that widely exist in plants, with various biological activities, including antioxidant, anti-obesity, and anti-diabetic activities. Currently, monomeric anthocyanins are mainly obtained through natural sources, which limits their availability. In the biosynthesis of anthocyanins, anthocyanin methyltransferases are recognized to play important roles in the water solubility and structural stability of anthocyanins. Blueberries are a rich source of anthocyanins with more than 30 chemical structures. However, the enzymes that were responsible for the methylation of anthocyanidin cores in blueberries had not been reported. Here, blueberries (Vaccinium corymbosum) have been selected as the candidate for characterization of the key enzyme. Phylogenic analysis, enzymatic activity assay, homology modeling, molecular simulation, protein expression and purification assay, site-directed mutation, isothermal titration calorimetry assay, and enzyme kinetic assay were used to identify the enzymatic function and molecular mechanism of VcOMT, which was responsible for the methylation of anthocyanidin cores. VcOMT could use delphinidin as a substrate but not cyanidin, petunidin, anthocyanins, flavonols, and flavonol glycosides. Ile191 and Glu198 were both identified as important amino acid residues for the binding interactions of anthocyanidins with VcOMT.

Integrating transcriptomics and metabolomics to analyze quinoa (Chenopodium quinoa Willd.) responses to drought stress and rewatering

The crop production of quinoa (Chenopodium quinoa Willd.), the only plant meeting basic human nutritional requirements, is affected by drought stress. To better understand the drought tolerance mechanism of quinoa, we screened the drought-tolerant quinoa genotype "Dianli 129" and studied the seedling leaves of the drought-tolerant quinoa genotype after drought and rewatering treatments using transcriptomics and targeted metabolomics. Drought-treatment, drought control, rewatering-treated, and rewatered control were named as DR, DC, RW, and RC, respectively. Among four comparison groups, DC vs. DR, RC vs. RW, RW vs. DR, and RC vs. DC, we identified 10,292, 2,307, 12,368, and 3 differentially expressed genes (DEGs), and 215, 192, 132, and 19 differentially expressed metabolites (DEMs), respectively. A total of 38,670 genes and 142 pathways were annotated. The results of transcriptome and metabolome association analysis showed that gene-LOC110713661 and gene-LOC110738152 may be the key genes for drought tolerance in quinoa. Some metabolites accumulated in quinoa leaves in response to drought stress, and the plants recovered after rewatering. DEGs and DEMs participate in starch and sucrose metabolism and flavonoid biosynthesis, which are vital for improving drought tolerance in quinoa. Drought tolerance of quinoa was correlated with gene expression differences, metabolite accumulation and good recovery after rewatering. These findings improve our understanding of drought and rewatering responses in quinoa and have implications for the breeding of new drought-tolerance varieties while providing a theoretical basis for drought-tolerance varieties identification.

Full-length transcriptional analysis reveals the complex relationship of leaves and roots in responses to cold-drought combined stress in common vetch

Plant responses to single or combined abiotic stresses between aboveground and underground parts are complex and require crosstalk signaling pathways. In this study, we explored the transcriptome data of common vetch (Vicia sativa L.) subjected to cold and drought stress between leaves and roots via meta-analysis to identify the hub abiotic stress-responsive genes. A total of 4,836 and 3,103 differentially expressed genes (DEGs) were identified in the leaves and roots, respectively. Transcriptome analysis results showed that the set of stress-responsive DEGs to concurrent stress is distinct from single stress, indicating a specialized and unique response to combined stresses in common vetch. Gene Ontology (GO) enrichment analyses identified that "Photosystem II," "Defence response," and "Sucrose synthase/metabolic activity" were the most significantly enriched categories in leaves, roots, and both tissues, respectively. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis results indicated that "ABC transporters" are the most enriched pathway and that all of the genes were upregulated in roots. Furthermore, 29 co-induced DEGs were identified as hub genes based on the consensus expression profile module of single and co-occurrence stress analysis. In transgenic yeast, the overexpression of three cross-stress tolerance candidate genes increased yeast tolerance to cold-drought combined stress. The elucidation of the combined stress-responsive network in common vetch to better parse the complex regulation of abiotic responses in plants facilitates more adequate legume forage breeding for combined stress tolerance.

Camellia sinensis small GTPase gene (CsRAC1) involves in response to salt stress, drought stress and ABA signaling pathway

RAC/ROP gene (RACs) is a plant-specific small GTPases. RACs play an irreplaceable role in the tissue dynamics of cytoskeleton, vesicle transport and hormone signal transmission in plants. In the present study, a novel gene from RACs family, CsRAC1, was identified from tea [Camellia sinensis (L.) O. Kuntze]. CsRAC1 contained a 591-bp open reading frame and encoded a putative protein of 197 amino acids. Subcellular localization analysis in leaves of transgenic tobacco and root tips of Arabidopsis thaliana showed that CsRAC1 targeted the nucleus and cell membrane. The expression of CsRAC1 induced by abiotic stresses such as cold, heat, drought, salt and abscisic acid has also been verified by RT-qPCR. Further verification of biological function of CsRAC1 showed that overexpression of CsRAC1 increased the sensitivity of A. thaliana to salt stress, improved the tolerance of mature A. thaliana to drought stress, and enhanced the inhibition of ABA on seed germination of A. thaliana. In addition, the antioxidant system regulated by CsRAC1 mainly worked in mature A. thaliana. The results indicate that CsRAC1 is involved in the response of C. sinensis to salt, drought stress and ABA signaling pathway.

Research progress on the response of tea catechins to drought stress

Drought stress (DS) is the most important abiotic stress affecting yield and quality of tea worldwide. DS causes oxidative stress to cells due to the accumulation of reactive oxygen species (ROS). As non-enzymatic antioxidants, tea catechins can scavenge excess ROS in response to DS. Further, catechin accumulation contributes to the formation of oxidative polymerization products (e.g. theaflavins and thearubigins) that improve the quality of black tea. However, there are no systematic reports on the response of tea catechins to DS. First, we reviewed the available literature on the response of tea plants to DS. Second, we summarized the current knowledge of ROS production in tea leaves under DS and typical antioxidant response mechanisms. Third, we conducted a detailed review of the changes in catechin levels in tea under different drought conditions. We found that the total amounts of catechin and o-quinone increased under DS conditions. We propose that the possible mechanisms underlying tea catechin accumulation under DS conditions include (i) autotrophic formation of o-quinone, (ii) polymerization of proanthocyanidins that directly scavenge excess ROS, and (iii) formation of metal ion complexes and by influencing the antioxidant systems that indirectly eliminate excess ROS. Finally, we discuss ways of potentially improving black tea quality using drought before picking in the summer/fall dry season. In summary, we mainly discuss the antioxidant mechanisms of tea catechins under DS and the possibility of using drought to improve black tea quality. Our review provides a theoretical basis for the production of high-quality black tea under DS conditions. © 2021 Society of Chemical Industry.

Genome-Wide Identification and Expression Patterns of the C2H2-Zinc Finger Gene Family Related to Stress Responses and Catechins Accumulation in Camellia sinensis [L.] O. Kuntze

The C2H2-zinc finger protein (C2H2-ZFP) is essential for the regulation of plant development and widely responsive to diverse stresses including drought, cold and salt stress, further affecting the late flavonoid accumulation in higher plants. Tea is known as a popular beverage worldwide and its quality is greatly dependent on the physiological status and growing environment of the tea plant. To date, the understanding of C2H2-ZFP gene family in Camellia sinensis [L.] O. Kuntze is not yet available. In the present study, 134 CsC2H2-ZFP genes were identified and randomly distributed on 15 chromosomes. The CsC2H2-ZFP gene family was classified into four clades and gene structures and motif compositions of CsC2H2-ZFPs were similar within the same clade. Segmental duplication and negative selection were the main forces driving the expansion of the CsC2H2-ZFP gene family. Expression patterns suggested that CsC2H2-ZFPs were responsive to different stresses including drought, salt, cold and methyl jasmonate (MeJA) treatment. Specially, several C2H2-ZFPs showed a significant correlation with the catechins content and responded to the MeJA treatment, which might contribute to the tea quality and specialized astringent taste. This study will lay the foundations for further research of C2H2-type zinc finger proteins on the stress responses and quality-related metabolites accumulation in C. sinensis.

Genome-wide identification, characterization, and expression analysis of tea plant autophagy-related genes (CsARGs) demonstrates that they play diverse roles during development and under abiotic stress

Background

Autophagy, meaning ‘self-eating’, is required for the degradation and recycling of cytoplasmic constituents under stressful and non-stressful conditions, which helps to maintain cellular homeostasis and delay aging and longevity in eukaryotes. To date, the functions of autophagy have been heavily studied in yeast, mammals and model plants, but few studies have focused on economically important crops, especially tea plants (Camellia sinensis). The roles played by autophagy in coping with various environmental stimuli have not been fully elucidated to date. Therefore, investigating the functions of autophagy-related genes in tea plants may help to elucidate the mechanism governing autophagy in response to stresses in woody plants.

Results

In this study, we identified 35 C. sinensis autophagy-related genes (CsARGs). Each CsARG is highly conserved with its homologues from other plant species, except for CsATG14. Tissue-specific expression analysis demonstrated that the abundances of CsARGs varied across different tissues, but CsATG8c/i showed a degree of tissue specificity. Under hormone and abiotic stress conditions, most CsARGs were upregulated at different time points during the treatment. In addition, the expression levels of 10 CsARGs were higher in the cold-resistant cultivar ‘Longjing43’ than in the cold-susceptible cultivar ‘Damianbai’ during the CA period; however, the expression of CsATG101 showed the opposite tendency.

Conclusions

We performed a comprehensive bioinformatic and physiological analysis of CsARGs in tea plants, and these results may help to establish a foundation for further research investigating the molecular mechanisms governing autophagy in tea plant growth, development and response to stress. Meanwhile, some CsARGs could serve as putative molecular markers for the breeding of cold-resistant tea plants in future research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07419-2.

Survival strategies based on the hydraulic vulnerability segmentation hypothesis, for the tea plant [Camellia sinensis(L.) O. Kuntze] in long-term drought stress condition

Tea plants are important economic perennial crops that can be negatively impacted by drought stress (DS). However, their survival strategies in long-term DS conditions and the accumulation and influence of metabolites and mineral elements (MEs) in their organs, when facing hydraulic vulnerability segmentation, require further investigation. The MEs and metabolites in the leaf, stem, and root after long-term DS (20 d) were examined here, using inductively coupled plasma optical emission spectrometry (ICP-OES) and liquid chromatograph-mass spectrometry (LC-MS). The accumulation patterns of 116 differentially accumulated metabolites (DAMs) and nine MEs were considerably affected in all organs. The concentration of all MEs varied significantly in at least one organ, while the K and Ca levels were markedly altered in all three. Most DAM levels increased in the stem but decreased in the root and leaf, implying that vulnerability segmentation may occur with long-term DS. The typical nitrogen- and carbon-compound levels similarly increased in the stem and decreased in the leaf and root, as the plant might respond to long-term DS by stabilizing respiration, promoting nitrogen recycling, and free radical scavenging. Correlation analysis showed several possible DAM-ME interactions and an association between Mn and flavonoids. Thus, survival strategies under long-term DS included sacrificing distal/vulnerable organs and accumulating function-specialized metabolites and MEs to mitigate drought-induced oxidative damage. This is the first study that reports substance fluctuations after long-term DS in different organs of plants, and highlights the need to use whole plants to fully comprehend stress response strategies.

Drought stress triggers proteomic changes involving lignin, flavonoids and fatty acids in tea plants

Drought stress triggers a series of physiological and biochemical changes in tea plants. It is well known that flavonoids, lignin and long-chain fatty acids play important roles in drought resistance. However, changes in proteins related to these three metabolic pathways in tea plants under drought stress have not been reported. We analysed the proteomic profiles of tea plants by tandem mass tag and liquid chromatography-tandem mass spectrometry. A total of 4789 proteins were identified, of which 11 and 100 showed up- and downregulation, respectively. The proteins related to the biosynthesis of lignin, flavonoids and long-chain fatty acids, including phenylalanine ammonia lyase, cinnamoyl-CoA reductase, peroxidase, chalcone synthase, flavanone 3-hydroxylase, flavonol synthase, acetyl-CoA carboxylase 1,3-ketoacyl-CoA synthase 6 and 3-ketoacyl-CoA reductase 1, were downregulated. However, the contents of soluble proteins, malondialdehyde, total phenols, lignin and flavonoids in the tea plants increased. These results showed that tea plants might improve drought resistance by inhibiting the accumulation of synthases related to lignin, flavonoids and long-chain fatty acids. The proteomic spectrum of tea plants provides a scientific basis for studying the pathways related to lignin, flavonoid and long-chain fatty acid metabolism in response to drought stress.

Exogenous abscisic acid induces the lipid and flavonoid metabolism of tea plants under drought stress

Abscisic acid (ABA) is an important phytohormone responsible for activating drought resistance, but the regulation mechanism of exogenous ABA on tea plants under drought stress was rarely reported. Here, we analyzed the effects of exogenous ABA on genes and metabolites of tea leaves under drought stress using transcriptomic and metabolomic analysis. The results showed that the exogenous ABA significantly induced the metabolic pathways of tea leaves under drought stress, including energy metabolism, amino acid metabolism, lipid metabolism and flavonoids biosynthesis. In which, the exogenous ABA could clearly affect the expression of genes involved in lipid metabolism and flavonoid biosynthesis. Meanwhile, it also increased the contents of flavone, anthocyanins, flavonol, isoflavone of tea leaves under drought stress, including, kaempferitrin, sakuranetin, kaempferol, and decreased the contents of glycerophospholipids, glycerolipids and fatty acids of tea leaves under drought stress. The results suggested that the exogenous ABA could alleviate the damages of tea leaves under drought stress through inducing the expression of the genes and altering the contents of metabolites in response to drought stress. This study will be helpful to understand the mechanism of resilience to abiotic stress in tea plant and provide novel insights into enhancing drought tolerance in the future.

TeaCoN: a database of gene co-expression network for tea plant (Camellia sinensis)

Background

Tea plant (Camellia sinensis) is one of the world’s most important beverage crops due to its numerous secondary metabolites conferring tea quality and health effects. However, only a small fraction of tea genes (especially for those metabolite-related genes) have been functionally characterized to date. A cohesive bioinformatics platform is thus urgently needed to aid in the functional determination of the remaining genes.

Description

TeaCoN, a database of gene co-expression network for tea plant, was established to provide genome-wide associations in gene co-expression to survey gene modules (i.e., co-expressed gene sets) for a function of interest. TeaCoN featured a comprehensive collection of 261 high-quality RNA-Seq experiments that covered a wide range of tea tissues as well as various treatments for tea plant. In the current version of TeaCoN, 31,968 (94% coverage of the genome) tea gene models were documented. Users can retrieve detailed co-expression information for gene(s) of interest in four aspects: 1) co-expressed genes with the corresponding Pearson correlation coefficients (PCC-values) and statistical P-values, 2) gene information (gene ID, description, symbol, alias, chromosomal location, GO and KEGG annotation), 3) expression profile heatmap of co-expressed genes across seven main tea tissues (e.g., leaf, bud, stem, root), and 4) network visualization of co-expressed genes. We also implemented a gene co-expression analysis, BLAST search function, GO and KEGG enrichment analysis, and genome browser to facilitate use of the database.

Conclusion

The TeaCoN project can serve as a beneficial platform for candidate gene screening and functional exploration of important agronomical traits in tea plant. TeaCoN is freely available at http://teacon.wchoda.com.

Fulvic acid ameliorates drought stress-induced damage in tea plants by regulating the ascorbate metabolism and flavonoids biosynthesis

Background

Fulvic acid (FA) is a kind of plant growth regulator, which can promote plant growth, play an important role in fighting against drought, improve plant stress resistance, increase production and improve quality. However, the function of FA in tea plants during drought stress remain largely unknown.

Results

Here, we examined the effects of 0.1 g/L FA on genes and metabolites in tea plants at different periods of drought stress using transcriptomics and metabolomics profiles. Totally, 30,702 genes and 892 metabolites were identified. Compared with controlled groups, 604 and 3331 differentially expressed metabolite genes (DEGs) were found in FA-treated tea plants at 4 days and 8 days under drought stress, respectively; 54 and 125 differentially expressed metabolites (DEMs) were also found at two time points, respectively. Bioinformatics analysis showed that DEGs and DEMs participated in diverse biological processes such as ascorbate metabolism (GME, AO, ALDH and L-ascorbate), glutathione metabolism (GST, G6PDH, glutathione reduced form and CYS-GYL), and flavonoids biosynthesis (C4H, CHS, F3’5’H, F3H, kaempferol, quercetin and myricetin). Moreover, the results of co-expression analysis showed that the interactions of identified DEGs and DEMs diversely involved in ascorbate metabolism, glutathione metabolism, and flavonoids biosynthesis, indicating that FA may be involved in the regulation of these processes during drought stress.

Conclusion

The results indicated that FA enhanced the drought tolerance of tea plants by (i) enhancement of the ascorbate metabolism, (ii) improvement of the glutathione metabolism, as well as (iii) promotion of the flavonoids biosynthesis that significantly improved the antioxidant defense of tea plants during drought stress. This study not only confirmed the main strategies of FA to protect tea plants from drought stress, but also deepened the understanding of the complex molecular mechanism of FA to deal with tea plants to better avoid drought damage.

Cloning and characterization of two chlorophyll A/B binding protein genes and analysis of their gene family in Camellia sinensis

In this study, two chlorophyll A/B binding protein (CAB) genes (CsCP1 and CsCP2) in tea plant were cloned. The proteins encoded by these genes belong to the external or internal antenna proteins of PS II, respectively. They may be the targets of physiological regulation for tea leaf cell PS II because they all contain multiple functional domains and modifiable sites. The CAB gene family in the tea genome consists of 25 homologous genes. We measured the expression patterns of ten genes in the CsCP1 and CsCP2 subfamily under six different stresses. CsCP1 expression was inhibited in response to 6 kinds of stress; CsCP2 expression was slightly upregulated only after cold stress and ABA treatment. However, the expression levels of CSA016997 and CSA030476 were upregulated significantly in the six stresses. The results suggested that the 10 CAB genes may have different functions in tea leaves. Moreover, changes in the expression of the 10 genes under stress appear to be related to ABA- and MeJA-dependent signalling pathways, and their responses to MeJA treatment is faster than those to ABA. In addition, we introduced our experiences for cloning the genes in the context of complex genomes.

Regulation of color transition in purple tea (Camellia sinensis)

Comparative proteomics and metabolomics study of juvenile green, light purple and dark purple leaf to identify key proteins and metabolites that putatively govern color transition in Camellia sinensis. Color transition from juvenile green to dark purple leaf in Camellia sinensis is a complex process and thought to be regulated by an intricate balance of genes, proteins and metabolites expression. A molecular-level understanding of proteins and metabolites expression is needed to define metabolic process underpinning color transition in C. sinensis. Here, purple leaf growth of C. sinensis cultivar was divided into three developmental stages viz. juvenile green (JG), light purple (LP) and dark purple (DP) leaf. Scanning electron microscope (SEM) analysis revealed a clear morphological variation such as cell size, shape and texture as tea leaf undergoing color transition. Proteomic and metabolomic analyses displayed the temporal changes in proteins and metabolites that occur in color transition process. In total, 211 differentially expressed proteins (DEPs) were identified presumably involved in secondary metabolic processes particularly, flavonoids/anthocyanin biosynthesis, phytohormone regulation, carbon and nitrogen assimilation and photosynthesis, among others. Subcellular localization of three candidate proteins was further evaluated by their transient expression in planta. Interactome study revealed that proteins involved in primary metabolism, precursor metabolite, photosynthesis, phytohormones, transcription factor and anthocyanin biosynthesis were found to be interact directly or indirectly and thus, regulate color transition from JG to DP leaf. The present study not only corroborated earlier findings but also identified novel proteins and metabolites that putatively govern color transition in C. sinensis. These findings provide a platform for future studies that may be utilized for metabolic engineering/molecular breeding in an effort to develop more desirable traits.

Transcriptomic and metabolomic profiling of Camellia sinensis L. cv. 'Suchazao' exposed to temperature stresses reveals modification in protein synthesis and photosynthetic and anthocyanin biosynthetic pathways

To determine the mechanisms in tea plants responding to temperature stresses (heat and cold), we examined the global transcriptomic and metabolomic profiles of the tea plant cultivar 'Suchazao' under moderately low temperature stress (ML), severely low temperature stress (SL), moderately high temperature stress (MH) and severely high temperature stress (SH) using RNA-seq and high performance liquid chromatography tandem mass spectrometry/mass spectrometry (HPLC-MS/MS), respectively. The identified differentially expressed genes indicated that the synthesis of stress-resistance protein might be redirected to cope with the temperature stresses. We found that heat shock protein genes Hsp90 and Hsp70 played more critical roles in tea plants in adapting to thermal stress than cold, while late embryogenesis abundant protein genes (LEA) played a greater role under cold than heat stress, more types of zinc finger genes were induced under cold stress as well. In addition, energy metabolisms were inhibited by SH, SL and ML. Furthermore, the mechanisms of anthocyanin synthesis were different under the cold and heat stresses. Indeed, the CsUGT75C1 gene, encoding UDP-glucose:anthocyanin 5-O-glucosyl transferase, was up-regulated in the SL-treated leaves but down-regulated in SH. Metabolomics analysis also showed that anthocyanin monomer levels increased under SL. These results indicate that the tea plants share certain foundational mechanisms to adjust to both cold and heat stresses. They also developed some specific mechanisms for surviving the cold or heat stresses. Our study provides effective information about the different mechanisms tea plants employ in surviving cold and heat stresses, as well as the different mechanisms of anthocyanin synthesis, which could speed up the genetic breeding of heat- and cold-tolerant tea varieties.

Genome-wide identification, characterization, and expression analysis of nucleotide-binding leucine-rich repeats gene family under environmental stresses in tea (Camellia sinensis)

Plants often use nucleotide-binding leucine-rich repeats (NLRs) to recognize specific virulence proteins and activate the hypersensitive response thereby defending against invaders. However, data on NLRs and the resistance mechanism of NLR protein mediation in tea plant are extremely limited. In this study, 400 and 303 CsNLRs were identified from the genomes of C. sinensis var. sinensis (CSS) and C. sinensis var. assamica (CSA), respectively. Phylogenetic analysis revealed that the numbers in CNL groups are predominant in both CSS and CSA. RNA-Seq revealed that the expression of CsNLRs is induced by Colletotrichum fructicola, cold, drought, salt stress and exogenous methyl jasmonate. The 21 CsCNLs that are highly expressed in tea plant under biotic and abiotic stresses as well as during bud dormancy and in different tissues are identified. Gene structure analysis revealed several cis-regulatory elements associated with phytohormones and light responsiveness in the promoter regions of these 21 CsCNLs.

Global Ubiquitome Profiling Revealed the Roles of Ubiquitinated Proteins in Metabolic Pathways of Tea Leaves in Responding to Drought Stress

Drought stress often affects the expression of genes and proteins in tea plants. However, the global profiling of ubiquitinated (Kub) proteins in tea plants remains unearthed. Here, we performed the ubiquitome in tea leaves under drought stress using antibody-based affinity enrichment coupled with LC-MS/MS analysis. In total, 1,409 lysine Kub sites in 781 proteins were identified, of which 14 sites in 12 proteins were up-regulated and 123 sites in 91 proteins down-regulated under drought stress. The identified Kub proteins were mainly located in the cytosol (31%), chloroplast (27%) and nuclear (19%). Moreover, 5 conserved motifs in EK^ub, EXXXK^ub, K^ubD, K^ubE and K^ubA were extracted. Several Kub sites in ubiquitin-mediated proteolysis-related proteins, including RGLG2, UBC36, UEV1D, RPN10 and PSMC2, might affect protein degradation and DNA repair. Plenty of Kub proteins related to catechins biosynthesis, including PAL, CHS, CHI and F3H, were positively correlated with each other due to their co-expression and co-localization. Furthermore, some Kub proteins involved in carbohydrate and amino acid metabolism, including FBPase, FBA and GAD1, might promote sucrose, fructose and GABA accumulation in tea leaves under drought stress. Our study preliminarily revealed the global profiling of Kub proteins in metabolic pathways and provided an important resource for further study on the functions of Kub proteins in tea plants.