Roots Of Tea Plants Research Articles

Real-Time In Situ Tracking of the Penetration and Uptake Behavior of Nano-pesticides in Tea Plants Using Surface-Enhanced Raman Spectroscopy.

In situ monitoring of the uptake and transportation process of nano-pesticides during crop growth remains challenging thus far. In this report, the different three sizes of surface-enhanced Raman spectroscopy probes of nano-pesticides loaded with ferbam and acetamiprid are representative non-systemic or systemic pesticides, respectively. The probes were verified to have strong signals of the Raman spectrum enhancement effect. They were further applied on the leaves and roots of tea plants. Within 5 h, the nano-pesticides of 50 nm and 100 nm except 150 nm probes could rapidly penetrate young tea leaves to a depth of about 150-290 μm. Whereas none of the probes were observed to penetrate mature leaves and roots of tea plants. The result showed that the penetration rate depended on the size of the nano-pesticides and the structure or maturity of the plant tissue rather than the loaded pesticides. The penetration rate of small-sized nano-pesticides in young tea leaves is the fastest.

The combined analysis of transcriptome and phytohormone provides new insights into signaling mechanism for lateral root formation of tea plant (Camellia sinensis)

The growth and development of lateral roots (LRs) determine the nutrient absorption and environmental adaptability of tea plant, playing a crucial role in the economic efficiency of tea plantations. However, the molecular mechanisms underlying the formation of LRs in tea plant remain unreported. In this study, we established a LRs induction system in tea plants by exogenously adding N-1-naphthylphthalamic acid (NPA) and naphthaleneacetic acid (NAA). The molecular mechanisms of LRs formation were analyzed through transcriptomics and endogenous hormone measurements. Results showed that NAA treatment could counteract the inhibitory effect of NPA on LRs formation and promote the generation of LRs in tea plant. The addition of exogenous NAA reduced the levels of auxin and zeatin in the root tips while increasing the content of abscisic acid (ABA). Transcriptomic analysis at four time points (2, 6, 12, and 24 h) after NAA vs. MOCK treatment revealed 78 different expression genes (DEGs) associated with plant hormone signaling pathways. Among these, the auxin signaling pathway was the most significant in responding to the LRs formation in tea plant. Weighted Gene Co-Expression Network Analysis (WGCNA) identified the Mitogen-Activated Protein Kinases (MAPK) signaling pathway as responsive to NAA treatment, participating in the formation of LRs in tea plant. This study provides potential signaling pathways for the investigation of LRs formation in tea plant and identifies candidate genes for further research into tea plant root system architecture (RSA).

Root-specific theanine metabolism and regulation at the single-cell level in tea plants (Camellia sinensis)

Root-synthesized secondary metabolites are critical quality-conferring compounds of foods, plant-derived medicines, and beverages. However, information at a single-cell level on root-specific secondary metabolism remains largely unexplored. L-Theanine, an important quality component of tea, is primarily synthesized in roots, from which it is then transported to new shoots of tea plant. In this study, we present a single-cell RNA sequencing (scRNA-seq)-derived map for the tea plant root, which enabled cell-type-specific analysis of glutamate and ethylamine (two precursors of theanine biosynthesis) metabolism, and theanine biosynthesis, storage, and transport. Our findings support a model in which the theanine biosynthesis pathway occurs via multicellular compartmentation and does not require high co-expression levels of transcription factors and their target genes within the same cell cluster. This study provides novel insights into theanine metabolism and regulation, at the single-cell level, and offers an example for studying root-specific secondary metabolism in other plant systems.

Metals geochemistry and ecological risk assessment in lateritic soils and their transfer to tea plants

ABSTRACT Tea plant cultivation has been demonstrated to change the physicochemical properties of soils and metal bioavailability. The present study reported the geochemistry of four selected metals (Fe, Mn, Cr, and Ni) in lateritic soil cores regarding various depths cultivated with tea plants of different ages (3, 6, and 10 years old). The ecological risk and bioaccumulation of these metals in tea plants were also evaluated. The results indicate the acidic property of tea plant cultivation soils (pH < 4.5) and highlight further soil acidification due to long-term cultivation. The soils were strongly affected by farming methods and showed high levels (average from all soil cores) of total organic carbon contents (4.0% w/w), total nitrogen (2806 mg kg−1), and total phosphorus (1730 mg kg−1). We suggest that the selected metals originated naturally, supported by a high percentage in residual fractions from the results of soil sequential extraction (over 95% for Mn, Fe, and Ni and ∼ 90% for Cr). These metals exhibited no ecological risk to the adjacent environment. Mn showed the highest bioavailability, possibly due to the acidic soils and nitrogen fertiliser applications, increasing the release of Mn from soils. Mn also exhibited the highest bioconcentration factor (BCF) among four metals and 2.4 ÷ 6.5-folds higher BCFs in tea leaves than in roots. Despite the dominant content of Fe in soils (average of 20% w/w), Fe indicated lower amounts in tea leaves than Mn (average of 513 mg kg−1 vs 1354 mg kg−1). This could be attributed to the formation of Fe-rich root coatings on the tea plant root surface as a barrier to prevent Fe from translocating to other higher tea plant parts. Ni and Cr, as potentially toxic metals, were found at the lowest contents in tea leaves with low BCFs, indicating consumer safety in terms of exposure by these metals.

Bacteria from tea plant roots boost maize seed growth

Bacteria from tea plant roots boost maize seed growth

Genome-Wide Identification of Selenium-Responsive MicroRNAs in Tea Plant (Camellia sinensis L. O. Kuntze)

Anadequate selenium (Se) intake can enhance human immunity and prevent diseases development. About one billion people in the world have varying degrees of Se deficiency in the world. Organic Se from tea infusion is the most easily absorbed and utilized Se form by the human body. Therefore the production of tea plants rich in Se is an effective way to increase Se dietary intake, but there are few studies on the involvement and functions of miRNAs in the responses of tea plants after Se treatment. MicroRNAs (miRNAs) are endogenous (non-coding) single-stranded RNAs that play crucial roles in regulating plant nutrient element acquisition and accumulation. Physiological analysis discovered that the total Se content in tea plant roots markedly increased under 0.05 mmol·L−1 selenite treatment, with no toxicity symptoms in the leaves and roots. To screen the miRNAs responsive to Se treatment in tea plants, miRNA libraries were constructed from the tea cultivar “Echa 1”. Using high-throughput sequencing, 455 known miRNAs and 203 novel miRNAs were identified in this study. In total, 13 miRNAs were selected that were differentially expressed in tea plants’ roots under 0.05 mmol·L−1 selenite treatments. Gene Ontology enrichment analysis revealed that the target genes of the differentially expressed miRNAs mainly belonged to the metabolic process, membrane, and catalytic activity ontologies. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis suggested that beta-alanine, taurine, hypotaurine, and sulfur metabolism were the most enriched pathways among the differentially expressed miRNAs, implying their involvement in Se accumulation and tolerance in tea plants. Further characterization of the data revealed that the number of novel miRNAs was comparable to that of known miRNAs, indicating that novel miRNAs significantly contributed to the regulation of Se accumulation in tea plant roots. Thisstudy lays the foundation for further research on the regulatory mechanisms underlying Se accumulation and tolerance in tea plants, providing targets to molecular breeding strategies for improving tea nutritional properties.

Influence of Tea Plant Roots for Soil Slope Strengthening: Case Studies and Numerical Investigation

Influence of Tea Plant Roots for Soil Slope Strengthening: Case Studies and Numerical Investigation

Uptake and translocation of organic pollutants in Camellia sinensis (L.): a review.

Camellia sinensis (L.) is a perennial evergreen woody plant with the potential for environmental pollution due to its unique growth environment and extended growth cycle. Pollution sources and pathways for tea plants encompass various factors, including atmospheric deposition, agricultural inputs of chemical fertilizers and pesticide, uptake from soil, and sewage irrigation. During the cultivation phase, Camellia sinensis (L.) can absorb organic pollutants through its roots and leaves. This review provides an overview of the uptake and translocation mechanisms involving the absorption of polycyclic aromatic hydrocarbons (PAHs), pesticides, anthraquinone (AQ), perchlorate, and other organic pollutants by tea plant roots. Additionally, we summarize how fresh tea leaves can be impacted by spraying pesticide and atmospheric sedimentation. In conclusion, this review highlights current research progress in understanding the pollution risks associated with Camellia sinensis (L.) and its products, emphasizing the need for further investigation and providing insights into potential future directions for research in this field.

Identification and expression analysis of the KNOX genes during organogenesis and stress responseness in Camellia sinensis (L.) O. Kuntze.

Tea plant (Camellia sinensis L.), whose leaves are the major reproductive organs, has been cultivated and consumed widely for its economic and health benefits. The Knotted1-like Homeobox (KNOX) proteins play significant roles in leaf morphology formation and development. However, the functions of KNOX proteins in tea plants are still unknown. Here, 11 CsKNOX genes from the tea plants were cloned and divided into Class I, II, and KNATM clades based on their protein sequences. These 11 CsKNOX genes were mapped on 8 out of 15 tea plant chromosomes, all localized in the nucleus. Specific spatiotemporal expression patterns of CsKNOX genes were found in various tissues and different development periods of buds, flowers, and roots of tea plants. Meanwhile, transcript levels of CsKNOX in tea leaves were strongly correlated with the accumulation of flavan-3-ols and proanthocyanidins. It was found that most of the CsKNOX genes could respond to drought, salt, cold, and exogenous MeJA and GA3 by analysis of transcriptomics data and promoter elements. The protein interaction analysis showed that CsKNOX could cooperate with CsAS1 and other critical functional proteins. In conclusion, this research provided the basic information for the functions of the CsKNOX family during organogenesis and stress response in tea plants, which was necessary for further functional characterization verification.

Multi-Omics Analysis Reveals Mechanisms of Strong Phosphorus Adaptation in Tea Plant Roots.

Low phosphorus (P) is a major limiting factor for plant growth in acid soils, which are preferred by tea plants. This study aims to investigate the unique mechanisms of tea plant roots adaptation to low-P conditions. Tea plant roots were harvested for multi-omics analysis after being treated with 0 µmol·L-1 P (0P) and 250 µmol·L-1 P (250P) for 30 days. Under 250P conditions, root elongation was significantly inhibited, and the density of lateral roots was dramatically increased. This suggests that 250P may inhibit the elongation of tea plant roots. Moreover, the P concentration in roots was about 4.58 times higher than that under 0P, indicating that 250P may cause P toxicity in tea plant roots. Contrary to common plants, the expression of CsPT1/2 in tea plant roots was significantly increased by four times at 250P, which indicated that tea plant roots suffering from P toxicity might be due to the excessive expression of phosphate uptake-responsible genes under 250P conditions. Additionally, 94.80% of P-containing metabolites accumulated due to 250P stimulation, most of which were energy-associated metabolites, including lipids, nucleotides, and sugars. Especially the ratio of AMP/ATP and the expression of energy sensor CsSnRKs were inhibited by P application. Therefore, under 250P conditions, P over-accumulation due to the excessive expression of CsPT1/2 may inhibit energy metabolism and thus the growth of tea plant roots.

Oxidative stress inhibition and whitening effects of tea plant root's crude saponin

The aim of this research was to investigate the inhibitory effects of oxidative stress, tyrosinase, L-DOPA auto-oxidation, and melanogenesis for whitening effect using tea plant root’s crude saponin. The inhibitory effects of oxidative stress, tyrosinase, L-DOPA auto-oxidation, and melanogenesis increased depending on the concentration of tea plant root's crude saponin. when the concentration of tea plant root’s crude saponin was increased from 50 µg/mL. to 500 µg/mL with SNP 0.3 mM, the survival rate of HepG2 cell was increased from 57.58% to 65.78%, which was about 1.36 fold increase compared negative control without saponin. The maximum inhibitory activity of tyrosinase in Clone-M3 cell was obtained, 61.34% when the tea plant root’s saponin concentrations was 300 µg/mL. The maximum activity of L-DOPA auto-oxidation inhibition was 36.24% at 300 µg/mL. It was confirmed that this plays a major role in the reaction of converting L-tyrosine, which is known to slow down the initial rate determination step, into DOPA in melanin production. The melanin inhibitory activity in Clone-M3 cell with α-MSH were increased from 3.71% to 27.84%, when the crude saponin concentrations were increased from 25µg/mL, to 300µg/mL. Tea plant root’s crude saponin means that it is effective in inhibiting melanin production by inhibiting the activity of tyrosinase proteins in Clone-M3 cells.

Magnesium promotes tea plant growth via enhanced glutamine synthetase-mediated nitrogen assimilation.

Acidic tea (Camellia sinensis) plantation soil usually suffers from magnesium (Mg) deficiency, and as such, application of fertilizer containing Mg can substantially increase tea quality by enhancing the accumulation of nitrogen (N)-containing chemicals such as amino acids in young tea shoots. However, the molecular mechanisms underlying the promoting effects of Mg on N assimilation in tea plants remain unclear. Here, both hydroponic and field experiments were conducted to analyze N, Mg, metabolite contents, and gene expression patterns in tea plants. We found that N and amino acids accumulated in tea plant roots under Mg deficiency, while metabolism of N was enhanced by Mg supplementation, especially under a low N fertilizer regime. 15N tracing experiments demonstrated that assimilation of N was induced in tea roots following Mg application. Furthermore, weighted gene correlation network analysis (WGCNA) analysis of RNA-seq data suggested that genes encoding glutamine synthetase isozymes (CsGSs), key enzymes regulating N assimilation, were markedly regulated by Mg treatment. Overexpression of CsGS1.1 in Arabidopsis (Arabidopsis thaliana) resulted in a more tolerant phenotype under Mg deficiency and increased N assimilation. These results validate our suggestion that Mg transcriptionally regulates CsGS1.1 during the enhanced assimilation of N in tea plant. Moreover, results of a field experiment demonstrated that high Mg and low N had positive effects on tea quality. This study deepens our understanding of the molecular mechanisms underlying the interactive effects of Mg and N in tea plants while also providing both genetic and agronomic tools for future improvement of tea production.

Insights into the functional role of tea microbes on tea growth, quality and resistance against pests and diseases

Tea is an economical and most widely used beverage across the globe owing to its unique fragrance and flavor. Plant microbe interaction has emerged as an important topic which got the attention of scientists to improve plant performance. Tea microbes remained a prominent research topic for scientists over the years as tea microbes helps in nutrient cycling and stress management which in turn improve the tea growth, yield and quality. The roots of tea plants are colonized by various microbes including arbuscular mycorrhizal fungi (AMF), bacterial communities, and endophytes increase root growth, development and nutrient uptake which in turn improve tea growth, yield and quality. These microbes also increase the concentration of nutrients, amino acids, soluble proteins, flavonoids, catechuic acid, glucose, fructose, sucrose contents caffeine, and polyphenols concentration in tea plants. Besides this, these microbes also protect the tea plants from harmful pest and diseases which in turn leads to an appreciable improvement in plant growth and development. The most important goal of any farming system is to establish a system with production of maximum food while minimizing impacts on the environment. The present review article highlights the role of various microbes in improving the growth, yield and quality of tea plants. In addition, we also discussed the research gaps to improve our understanding about the role of tea microbes in improving tea growth, yield, pest and diseases resistance. We believe that this review will provide a better insight into the existing knowledge of tea microbes in improving tea growth and yield.

L-theanine exuded from Camellia sinensis roots regulates element cycling in soil by shaping the rhizosphere microbiome assembly

Root exudate metabolites are a key medium for the interaction between plants and soil microbiota. L-theanine is a unique non-protein amino acid critical for the flavor and potential health benefits of tea products; however, its biological function in tea plants is not well understood. As L-theanine is mainly synthesized in the roots of tea plants, we hypothesized that L-theanine could affect the function of the rhizosphere microbiota by modulating microbial assembly. In the present study, L-theanine was detected in the exudates of tea plant roots using liquid chromatography-mass spectrometry. Additionally, 16S rRNA gene sequencing revealed that L-theanine significantly altered the structure of the rhizosphere microbiota and selectively shaped rhizosphere microbial assembly. Moreover, metagenomic data showed that L-theanine affected the abundance of genes encoding element cycling in soil. Interestingly, the denitrification and complete nitrification pathways were significantly inhibited by L-theanine by decreasing the narH, napA, and napB genes abundance. These findings provide new insights into the biological function of L-theanine, as well as the implications of interactions between tea plant root exudates and the rhizosphere microbiome.

Tea plant roots respond to aluminum-induced mineral nutrient imbalances by transcriptional regulation of multiple cation and anion transporters

BackgroundTea is one of the most popular non-alcoholic beverages in the world for its flavors and numerous health benefits. The tea tree (Camellia sinensis L.) is a well-known aluminum (Al) hyperaccumulator. However, it is not fully understood how tea plants have adapted to tolerate high concentrations of Al, which causes an imbalance of mineral nutrition in the roots.ResultsHere, we combined ionomic and transcriptomic profiling alongside biochemical characterization, to probe the changes of metal nutrients and Al responsive genes in tea roots grown under increasing concentrations of Al. It was found that a low level of Al (~ 0.4 mM) maintains proper nutrient balance, whereas a higher Al concentration (2.5 mM) compromised tea plants by altering micro- and macro-nutrient accumulation into roots, including a decrease in calcium (Ca), manganese (Mn), and magnesium (Mg) and an increase in iron (Fe), which corresponded with oxidative stress, cellular damage, and retarded root growth. Transcriptome analysis revealed more than 1000 transporter genes that were significantly changed in expression upon Al exposure compared to control (no Al) treatments. These included transporters related to Ca and Fe uptake and translocation, while genes required for N, P, and S nutrition in roots did not significantly alter. Transporters related to organic acid secretion, together with other putative Al-tolerance genes also significantly changed in response to Al. Two of these transporters, CsALMT1 and CsALS8, were functionally tested by yeast heterologous expression and confirmed to provide Al tolerance.ConclusionThis study shows that tea plant roots respond to high Al-induced mineral nutrient imbalances by transcriptional regulation of both cation and anion transporters, and therefore provides new insights into Al tolerance mechanism of tea plants. The altered transporter gene expression profiles partly explain the imbalanced metal ion accumulation that occurred in the Al-stressed roots, while increases to organic acid and Al tolerance gene expression partly explains the ability of tea plants to be able to grow in high Al containing soils. The improved transcriptomic understanding of Al exposure gained here has highlighted potential gene targets for breeding or genetic engineering approaches to develop safer tea products.

Characteristics and Physiological Effects of Hydroponically Cultured Roots of the Tea Plant (Camellia sinensis)

Green tea has been reported to result in improvements in a range of health parameters. However, most research has only documented the effects of green tea brewed from leaves or leaf extracts. In addition to the leaves, the roots of tea plants also possess unique properties because of their requirements for growth, which may enable them to have useful physiological effects. We used a hydroponic system to grow the plants and explored the physiological effects of the roots, which biosynthesize one of the rarest functional amino acids, theanine (γ-ethylamide-L-glutamic acid). The level of theanine was much higher in the roots than in the leaves, and the roots also differed in other aspects of their chemical composition. We evaluated the effects of tea-root extract on the cognitive function and emotions of aged rats. Our results show that, in the object recognition test, aged rats drinking tea-root extract tended to show improved cognitive function and were more relaxed than the control group, which drank tap water. Furthermore, using a mouse model of human aging, we found that the average life span of mice that consumed the root extract was significantly increased. We suggest that tea roots contain unique components that may improve impaired physiological functions, and we therefore propose tea-root extract as a novel nutraceutical.

Arbuscular Mycorrhizal Fungus Alters Root System Architecture in Camellia sinensis L. as Revealed by RNA-Seq Analysis.

Arbuscular mycorrhizal fungus (AMF), forming symbiosis with most terrestrial plants, strongly modulates root system architecture (RSA), which is the main characteristic of root in soil, to improve plant growth and development. So far, the studies of AMF on tea plant seedlings are few and the relevant molecular mechanism is not deciphered. In this study, the 6-month-old cutting seedlings of tea plant cultivar “Wancha No.4” were inoculated with an AMF isolate, Rhizophagus intraradices BGC JX04B and harvested after 6 months of growth. The indexes of RSA and sugar contents in root were determined. The transcriptome data in root tips of mycorrhizal and non-mycorrhizal cutting seedlings were obtained by RNA-sequence (Seq) analysis. The results showed that AMF significantly decreased plant growth, but increased the sucrose content in root and the higher classes of lateral root (LR) formation (third and fourth LR). We identified 2047 differentially expressed genes (DEGs) based on the transcriptome data, and DEGs involved in metabolisms of phosphorus (42 DEGs), sugar (39), lipid (67), and plant hormones (39) were excavated out. Variation partitioning analysis showed all these four categories modulated the RSA. In phosphorus (P) metabolism, the phosphate transport and release (DEGs related to purple acid phosphatase) were promoted by AMF inoculation, while DEGs of sugar transport protein in sugar metabolism were downregulated. Lipid metabolism might not be responsible for root branching but for AMF propagation. With respect to phytohormones, DEGs of auxin (13), ethylene (14), and abscisic acid (5) were extensively affected by AMF inoculation, especially for auxin and ethylene. The further partial least squares structural equation modeling analysis indicated that pathways of P metabolism and auxin, as well as the direct way of AMF inoculation, were of the most important in AMF promoting root branching, while ethylene performed a negative role. Overall, our data revealed the alterations of genome-wide gene expression in tea plant roots after inoculation with AMF and provided a molecular basis for the regulatory mechanism of RSA (mainly root branching) changes induced by AMF.

The GC-TOF/MS-based Metabolomic analysis reveals altered metabolic profiles in nitrogen-deficient leaves and roots of tea plants (Camellia sinensis)

BackgroundNitrogen (N) fertilizer is commonly considered as one of the most important limiting factors in the agricultural production. As a result, a large amount of N fertilizer is used to improve the yield in modern tea production. Unfortunately, the large amount of N fertilizer input has led to increased plant nitrogen-tolerance and decreased amplitude of yield improvement, which results in significant N loss, energy waste and environment pollution. However, the effects of N-deficiency on the metabolic profiles of tea leaves and roots are not well understood.ResultsIn this study, seedlings of Camellia sinensis (L.) O. Kuntze Chunlv 2 were treated with 3 mM NH4NO3 (Control) or without NH4NO3 (N-deficiency) for 4 months by sandy culture. The results suggested that N-deficiency induced tea leaf chlorosis, impaired biomass accumulation, decreased the leaf chlorophyll content and N absorption when they were compared to the Control samples. The untargeted metabolomics based on GC-TOF/MS approach revealed a discrimination of the metabolic profiles between N-deficient tea leaves and roots. The identification and classification of the altered metabolites indicated that N deficiency upregulated the relative abundances of most phenylpropanoids and organic acids, while downregulated the relative abundances of most amino acids in tea leaves. Differentially, N-deficiency induced the accumulation of most carbohydrates, organic acids and amino acids in tea roots. The potential biomarkers screened in N-deficient leaves compared to Control implied that N deficiency might reduce the tea quality. Unlike the N-deficient leaves, the potential biomarkers in N-deficient roots indicated an improved stress response might occur in tea roots.ConclusionsThe results demonstrated N deficiency had different effects on the primary and secondary metabolism in tea leaves and roots. The findings of this study will facilitate a comprehensive understanding of the N-deficient tea plants and provide a valuable reference for the optimized N nutrient management and the sustainable development in the tea plantations.

Transcriptome analysis identifies CsNRT genes involved in nitrogen uptake in tea plants, with a major role of CsNRT2.4

Tea trees have a high demand for nitrogen (N) fertilizer to improve the yield and quality of tea. In this research, transcriptome analysis revealed the effect of N starvation and resupply upon N uptake in tea plants. We identified 4098 differentially expressed genes (DEGs) that were significantly enriched in amino acid and N metabolism and were extensively mapped to the tea genome. The CsNRT gene family plays vital roles in the nitrogen uptake of tea plants. The full CDS sequences of CsNRT1.1, CsNRT1.2, CsNRT1.5, CsNRT1.7, CsNRT2.4, CsNRT2.5, CsNRT3.1 and CsNRT3.2 were cloned. One-year-old cutting seedlings of Zhongcha302 (ZC302) were selected for hydroponic culture and were used for gene expression analysis. The seedlings were resupplied with 0.2 and 2 mM N after N starvation. The results of the gene expression under different N treatments and in various tissues indicated that the expression of CsNRT2.4 was highly expressed in tea roots and was greatly induced by N. Overexpressed CsNRT2.4 in transgenic Arabidopsis thaliana increased the root lengths and fresh weights and improved the NO3− uptake rate in the Arabidopsis roots at a low NO3− level. Thus, we inferred that CsNRT2.4 was a key gene for N uptake in tea plant roots. This study provides new insights into the molecular mechanisms of tea plant responses to N resupply and reveals hub genes for improving nitrogen usage efficiency (NUE) in tea plants.

Nitrogen-Regulated Theanine and Flavonoid Biosynthesis in Tea Plant Roots: Protein-Level Regulation Revealed by Multiomics Analyses.

Theanine and flavonoids (especially proanthocyanidins) are the most important and abundant secondary metabolites synthesized in the roots of tea plants. Nitrogen promotes theanine and represses flavonoid biosynthesis in tea plant roots, but the underlying mechanism is still elusive. Here, we analyzed theanine and flavonoid metabolism in tea plant roots under nitrogen deficiency and explored the regulatory mechanism using proteome and ubiquitylome profiling together with transcriptome data. Differentially expressed proteins responsive to nitrogen deficiency were identified and found to be enriched in flavonoid, nitrogen, and amino acid metabolism pathways. The proteins responding to nitrogen deficiency at the transcriptional level, translational level, and both transcriptional and translational levels were classified. Nitrogen-deficiency-responsive and ubiquitinated proteins were further identified. Our results showed that most genes encoding enzymes in the theanine synthesis pathway, such as CsAlaDC, CsGDH, and CsGOGATs, were repressed by nitrogen deficiency at transcriptional and/or protein level(s). While a large number of enzymes in flavonoid metabolism were upregulated at the transcriptional and/or translational level(s). Importantly, the ubiquitylomic analysis identified important proteins, especially the hub enzymes in theanine and flavonoid biosynthesis, such as CsAlaDC, CsTSI, CsGS, CsPAL, and CsCHS, modified by ubiquitination. This study provided novel insights into the regulation of theanine and flavonoid biosynthesis and will contribute to future studies on the post-translational regulation of secondary metabolism in tea plants.