Proanthocyanidin-Aluminum Complexes Improve Aluminum Resistance and Detoxification of Camellia sinensis

Antioxidant Extracts from Greek and Spanish Olive Leaves: Antimicrobial, Anticancer and Antiangiogenic Effects

Olea europaea L. is the most valuable species of the Olea type, and its products offer a wide range of therapeutical uses. The olive tree has been extensively studied for its nourishing qualities, and the "Mediterranean diet", which includes virgin olive oil as a key dietary component, is strongly associated with a reduced risk of cardiovascular disease and various malignancies. Olive leaves, a by-product in the olive harvesting process, are valued as a resource for developing novel phytomedicines. For this purpose, two ethanolic extracts obtained from Olivae folium from Spain (OFS) and Greece (OFG) were investigated. Our findings contribute to a wider characterization of olive leaves. Both extracts displayed important amounts of phenolic compounds and pentacyclic triterpenes, OFG having higher concentrations of both polyphenols, such as oleuropein and lutein, as well as triterpenes, such as oleanolic acid and maslinic acid. The antioxidant capacity is similar for the two extracts, albeit slightly higher for OFG, possibly due to metal polyphenol complexes with antioxidant activity. The extracts elicited an antimicrobial effect at higher doses, especially against Gram-positive bacteria, such as Streptococcus pyogenes. The extract with lower inorganic content and higher content of polyphenols and triterpenic acids induced a strong anti-radical capacity, a selective cytotoxic effect, as well as antimigratory potential on A375 melanoma cells and antiangiogenic potential on the CAM. No irritability and a good tolerability were noted after evaluating the extracts on the in vivo Hen's Egg Test-Chorioallantoic Membrane (HET-CAM). Therefore, the present data are suggestive for the possible use of the two types of olive leaf products as high-antioxidant extracts, potentially impacting the healthcare system through their use as antimicrobial agents and as anticancer and anti-invasion treatments for melanoma.

Genome-wide identification, expression profiling, and protein interaction analysis of the CCoAOMT gene family in the tea plant (Camellia sinensis)

BACKGROUND

The caffeoyl-CoA-O methyltransferase (CCoAOMT) family plays a crucial role in the oxidative methylation of phenolic substances and is involved in various plant processes, including growth, development, and stress response. However, there is a limited understanding of the interactions among CCoAOMT protein members in tea plants.

RESULTS

In this study, we identified 10 members of the CsCCoAOMT family in the genome of Camellia sinensis (cultivar 'HuangDan'), characterized by conserved gene structures and motifs. These CsCCoAOMT members were located on six different chromosomes (1, 2, 3, 4, 6, and 14). Based on phylogenetic analysis, CsCCoAOMT can be divided into two groups: I and II. Notably, the CsCCoAOMT members of group Ia are likely to be candidate genes involved in lignin biosynthesis. Moreover, through the yeast two-hybrid (Y2H) assay, we established protein interaction networks for the CsCCoAOMT family, revealing 9 pairs of members with interaction relationships.

CONCLUSIONS

We identified the CCoAOMT gene family in Camellia sinensis and conducted a comprehensive analysis of their classifications, phylogenetic and synteny relationships, gene structures, protein interactions, tissue-specific expression patterns, and responses to various stresses. Our findings shed light on the evolution and composition of CsCCoAOMT. Notably, the observed interaction among CCoAOMT proteins suggests the potential formation of the O-methyltransferase (OMT) complex during the methylation modification process, expanding our understanding of the functional roles of this gene family in diverse biological processes.

Malate production, sugar metabolism, and redox homeostasis in the leaf growth zone of Rye (Secale cereale) increase stress tolerance to aluminum stress: A biochemical and genome-wide transcriptional study

Global soil acidification is increasing, enlarging aluminum (Al) availability in soils, leading to reductions in plant growth. This study investigates the effect of Al stress on the leaf growth zones of Rye (Secale cereale, cv Beira). Kinematic analysis showed that the effect of Al on leaf growth rates was mainly due to a reduced cell production rate in the meristem. Transcriptomic analysis identified 2272 significantly (log2fold > |0.5| FDR < 0.05) differentially expressed genes (DEGs) for Al stress. There was a downregulation in several DEGs associated with photosynthetic processes and an upregulation in genes for heat/light response, and H2O2 production in all leaf zones. DEGs associated with heavy metals and malate transport were increased, particularly, in the meristem. To determine the putative function of these processes in Al tolerance, we performed biochemical analyses comparing the tolerant Beira with an Al sensitive variant RioDeva. Beira showed improved sugar metabolism and redox homeostasis, specifically in the meristem compared to RioDeva. Similarly, a significant increase in malate and citrate production, which are known to aid in Al detoxification in plants, was found in Beira. This suggests that Al tolerance in Rye is linked to its ability for Al exclusion from the leaf meristem.

A Review on Rhizosphere Microbiota of Tea Plant (Camellia sinensis L): Recent Insights and Future Perspectives

Rhizosphere microbial colonization of the tea plant provides many beneficial functions for the host, But the factors that influence the composition of these rhizosphere microbes and their functions are still unknown. In order to explore the interaction between tea plants and rhizosphere microorganisms, we summarized the current studies. First, the review integrated the known rhizosphere microbial communities of tea tree, including bacteria, fungi, and arbuscular mycorrhizal fungi. Then, various factors affecting tea rhizosphere microorganisms were studied, including: endogenous factors, environmental factors, and agronomic practices. Finally, the functions of rhizosphere microorganisms were analyzed, including (a) promoting the growth and quality of tea trees, (b) alleviating biotic and abiotic stresses, and (c) improving soil fertility. Finally, we highlight the gaps in knowledge of tea rhizosphere microorganisms and the future direction of development. In summary, understanding rhizosphere microbial interactions with tea plants is key to promoting the growth, development, and sustainable productivity of tea plants.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

Flavonoid metabolites in tea plant (Camellia sinensis) stress response: Insights from bibliometric analysis

In the context of global climate change, tea plants are at risk from elevating environmental stress factors. Coping with this problem relies upon the understanding of tea plant stress response and its underlying mechanisms. Over the past two decades, research in this field has prospered with the contributions of scientists worldwide. Aiming in providing a comprehensive perspective of the research field related to tea plant stress response, we present a bibliometric analysis of the this area. Our results demonstrate the most studied stresses, global contribution, authorship and collaboration, and trending research topics. We highlight the importance of flavonoid metabolites in tea plant stress response, particularly their role in maintaining redox homeostasis, yield, and adjusting tea quality under stress conditions. Further research on the flavonoid response under various stress conditions can promote the development of cultivation measures, thereby improving stress resistance and tea quality.

Effect of Soil Acidification on the Production of Se-Rich Tea

Selenium (Se)-enriched tea is a well-regarded natural beverage that is often consumed for its Se supplementation benefits. However, the production of this tea, particularly in Se-abundant tea plantations, is challenging due to soil acidification. Therefore, this study aimed to investigate the effects of changes in Se under acidified soil conditions. Eight tea plantation soil monitoring sites in Southern Jiangsu were first selected. Simulated acid rain experiments and experiments with different acidification methods were designed and soil pH, as well as various Al-ion and Se-ion concentrations were systematically determined. The data were analyzed using R statistical software, and a correlation analysis was carried out. The results indicated that as the pH value dropped, exchangeable selenium (Exc-Se) and residual selenium (Res-Se) were transformed into acid-soluble selenium (Fmo-Se) and manganese oxide selenium (Om-Se). As the pH increased, exchange state aluminum (Alex) and water-soluble aluminum (Alw) decreased, Fmo-Se and Om-Se declined, and Exc-Se and Res-Se increased, a phenomenon attributed to the weakened substitution of Se ions by Al ions. In the simulated acid rain experiment, P1 compared to the control (CK), the pH value of the YJW tea plantation decreased by 0.13, Exc-Se decreased by 4 ug mg-1, Res-Se decreased by 54.65 ug kg-1, Fmo-Se increased by 2.78 ug mg-1, and Om-Se increased by 5.94 ug mg-1 while Alex increased by 28.53 mg kg-1. The decrease in pH led to an increase in the content of Alex and Alw, which further resulted in the conversion of Exc-Se to Fmo-Se and Om-Se. In various acidification experiments, compared with CK, the pH value of T6 decreased by 0.23, Exc-Se content decreased by 8.35 ug kg-1, Res-Se content decreased by 40.62 ug kg-1, and Fmo-Se content increased by 15.52 ug kg-1 while Alex increased by 33.67 mg kg-1, Alw increased by 1.7 mg kg-1, and Alh decreased by 573.89 mg kg-1. Acidification can trigger the conversion of Exc-Se to Fmo-Se and Om-Se, while the content of available Se may decrease due to the complexation interplay between Alex and Exc-Se. This study provides a theoretical basis for solving the problem of Se-enriched in tea caused by soil acidification.

Functional diversity of subgroup 5 R2R3-MYBs promoting proanthocyanidin biosynthesis and their key residues and motifs in tea plant

The tea plant (Camellia sinensis) is rich in polyphenolic compounds. Particularly, flavan-3-ols and proanthocyanidins (PAs) are essential for the flavor and disease-resistance property of tea leaves. The fifth subgroup of R2R3-MYB transcription factors comprises the primary activators of PA biosynthesis. This study showed that subgroup 5 R2R3-MYBs in tea plants contained at least nine genes belonging to the TT2, MYB5, and MYBPA types. Tannin-rich plants showed an expansion in the number of subgroup 5 R2R3-MYB genes compared with other dicotyledonous and monocot plants. The MYBPA-type genes of tea plant were slightly expanded. qRT-PCR analysis and GUS staining analysis of promoter activity under a series of treatments revealed the differential responses of CsMYB5s to biotic and abiotic stresses. In particular, CsMYB5a, CsMYB5b, and CsMYB5e responded to high-intensity light, high temperature, MeJA, and mechanical wounding, whereas CsMYB5f and CsMYB5g were only induced by wounding. Three genetic transformation systems (C. sinensis, Nicotiana tabacum, and Arabidopsis thaliana) were used to verify the biological function of CsMYB5s. The results show that CsMYB5a, CsMYB5b, and CsMYB5e could promote the gene expression of CsLAR and CsANR. However, CsMYB5f and CsMYB5g could only upregulate the gene expression of CsLAR but not CsANR. A series of site-directed mutation and domain-swapping experiments were used to verify functional domains and key amino acids of CsMYB5s responsible for the regulation of PA biosynthesis. This study aimed to provide insight into the induced expression and functional diversity model of PA biosynthesis regulation in tea plants.

Al-induced CsUGT84J2 enhances flavonol and auxin accumulation to promote root growth in tea plants

Although Al is not necessary or even toxic to most plants, it is beneficial for the growth of tea plants. However, the mechanism through which Al promotes root growth in tea plants remains unclear. In the present study, we found that flavonol glycoside levels in tea roots increased following Al treatment, and the Al-induced UDP glycosyltransferase CsUGT84J2 was involved in this mechanism. Enzyme activity assays revealed that rCsUGT84J2 exhibited catalytic activity on multiple types of substrates, including phenolic acids, flavonols, and auxins in vitro. Furthermore, metabolic analysis with UPLC-QqQ-MS/MS revealed significantly increased flavonol and auxin glycoside accumulation in CsUGT84J2-overexpressing Arabidopsis thaliana. In addition, the expression of genes involved in the flavonol pathway as well as in the auxin metabolism, transport, and signaling pathways was remarkably enhanced. Additionally, lateral root growth and exogenous Al stress tolerance were significantly improved in transgenic A. thaliana. Moreover, gene expression and metabolic accumulation related to phenolic acids, flavonols, and auxin were upregulated in CsUGT84J2-overexpressing tea plants but downregulated in CsUGT84J2-silenced tea plants. In conclusion, Al treatment induced CsUGT84J2 expression, mediated flavonol and auxin glycosylation, and regulated endogenous auxin homeostasis in tea roots, thereby promoting the growth of tea plants. Our findings lay the foundation for studying the precise mechanisms through which Al promotes the growth of tea plants.

Metabolomic Study of Flavonoids in Camellia drupifera under Aluminum Stress by UPLC-MS/MS

Aluminum (Al) affects the yield of forest trees in acidic soils. The oil tea plant (Camellia drupifera Lour.) has high Al tolerance, with abundant phenolic compounds in its leaves, especially flavonoid compounds. The role of these flavonoids in the Al resistance of oil tea plants is unclear. In this metabolomic study of C. drupifera under Al stress, ultra-pressure liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) was utilized to identify metabolites, while principal component analysis, cluster analysis, and orthogonal partial least squares discriminant analysis were applied to analyze the data on the flavonoid metabolites. The leaf morphology of C. drupifera revealed significant damage by excess aluminum ions under each treatment compared with the control group. Under Al stress at 2 mmol/L (GZ2) and 4 mmol/L (GZ4), the total flavonoid content in C. drupifera leaves reached 24.37 and 35.64 mg/g, respectively, which are significantly higher than the levels measured in the control group (CK) (p < 0.01). In addition, we identified 25 upregulated and 5 downregulated metabolites in the GZ2 vs. CK comparison and 31 upregulated and 7 downregulated flavonoid metabolites in GZ4 vs. CK. The results demonstrate that different levels of Al stress had a significant influence on the metabolite profile of C. drupifera. It was found that the abundance of the 24 differential flavonoid metabolites was gradually elevated with increasing concentrations of Al stress, including catechin, epicatechin, naringenin-7-glucoside, astilbin, taxifolin, miquelianin, quercitrin, and quercimeritrin. Moreover, the most significant increase in antioxidant activity (about 30%) was observed in C. drupifera precultured in leaf extracts containing 7.5 and 15 μg/mL of active flavonoids. The qRT-PCR results showed that the expression levels of key genes involved in the synthesis of flavonoids were consistent with the accumulation trends of flavonoids under different concentrations of Al. Therefore, our results demonstrate the key role of flavonoid compounds in the oil tea plant C. drupifera in response to Al stress, which suggests that flavonoid metabolites in C. drupifera, as well as other aluminum-tolerant plants, may help with detoxifying aluminum.

Aluminum in plant: Benefits, toxicity and tolerance mechanisms

Aluminum (Al) is the third most ubiquitous metal in the earth's crust. A decrease in soil pH below 5 increases its solubility and availability. However, its impact on plants depends largely on concentration, exposure time, plant species, developmental age, and growing conditions. Although Al can be beneficial to plants by stimulating growth and mitigating biotic and abiotic stresses, it remains unknown how Al mediates these effects since its biological significance in cellular systems is still unidentified. Al is considered a major limiting factor restricting plant growth and productivity in acidic soils. It instigates a series of phytotoxic symptoms in several Al-sensitive crops with inhibition of root growth and restriction of water and nutrient uptake as the obvious symptoms. This review explores advances in Al benefits, toxicity and tolerance mechanisms employed by plants on acidic soils. These insights will provide directions and future prospects for potential crop improvement.

Flavonol-Aluminum Complex Formation: Enhancing Aluminum Accumulation in Tea Plants

Polyphenol-rich tea plants are aluminum (Al) accumulators. Whether an association exists between polyphenols and Al accumulation in tea plants remains unclear. This study revealed that the accumulation of the total Al and bound Al contents were both higher in tea samples with high flavonol content than in low, and Al accumulation in tea plants was significantly and positively correlated with their flavonol content. Furthermore, the capability of flavonols combined with Al was higher than that of epigallocatechin gallate (EGCG) and root proanthocyanidins (PAs) under identical conditions. Flavonol-Al complexes signals (94 ppm) were detected in the tender roots and old leaves of tea plants through solid-state ²⁷Al nuclear magnetic resonance (NMR) imaging, and the strength of the signals in the high flavonol content tea samples was considerably stronger than that in the low flavonol content tea samples. This study provides a new perspective for studying Al accumulation in different tea varieties.

Metallophenolomics: A Novel Integrated Approach to Study Complexation of Plant Phenolics with Metal/Metalloid Ions

Plant adaptive strategies have been shaped during evolutionary development in the constant interaction with a plethora of environmental factors, including the presence of metals/metalloids in the environment. Among adaptive reactions against either the excess of trace elements or toxic doses of non-essential elements, their complexation with molecular endogenous ligands, including phenolics, has received increasing attention. Currently, the complexation of phenolics with metal(loid)s is a topic of intensive studies in different scientific fields. In spite of the numerous studies on their chelating capacity, the systemic analysis of phenolics as plant ligands has not been performed yet. Such a systematizing can be performed based on the modern approach of metallomics as an integral biometal science, which in turn has been differentiated into subgroups according to the nature of the bioligands. In this regard, the present review summarizes phenolics–metal(loid)s’ interactions using the metallomic approach. Experimental results on the chelating activity of representative compounds from different phenolic subgroups in vitro and in vivo are systematized. General properties of phenolic ligands and specific properties of anthocyanins are revealed. The novel concept of metallophenolomics is proposed, as a ligand-oriented subgroup of metallomics, which is an integrated approach to study phenolics–metal(loid)s’ complexations. The research subjects of metallophenolomics are outlined according to the methodology of metallomic studies, including mission-oriented biometal sciences (environmental sciences, food sciences and nutrition, medicine, cosmetology, coloration technologies, chemical sciences, material sciences, solar cell sciences). Metallophenolomics opens new prospects to unite multidisciplinary investigations of phenolic–metal(loid) interactions.

Ligand-Tuned Multi-Color Luminescence of Single Aluminum (III) Ion Atomic Centers and Their Selective Sensitivity to Different Metal Ions

Achieving multi-color luminescence with a single atomic center in transition metal complexes is a challenge. In this work, luminescent materials with tunable emission properties were realized by complexation between aluminum (III) ions with the ligands 3-hydroxyflavone (3-HF) and 5,7-dichloro-8-hydroxyquinoline (DCHQ). Aluminum (III) complexes with a single ligand emitted blue from 3-HF and green from DCHQ. High quantum yields (QYs) of 29.42% and 37.00% were also obtained, respectively. DFT calculations revealed details of the photophysical properties of the complexes. Correspondingly, cyan light emission was obtained if these two complexes were mixed together, from which the emission wavelength was located at 470 nm and the QY was 20.52%, under 290 nm excitation. More importantly, the cyan light emitted by the mixtures had selective sensitivity to different metal ions, resulting in either quenching the fluorescence (in the case of Fe3+) or enhancing the fluorescence (in the case of In3+). The fluorescence enhancement effect of In3+ on metal complexes has not been previously reported, neither for transition metal nor lanthanide ions. The linear quenching behavior of Fe3+ functions in the 50–700 μM concentration range, and the linear enhancement behavior of In3+ is demonstrated in the 300–800 mM concentration range.

Molecular mechanisms for pH-mediated amelioration of aluminum-toxicity revealed by conjoint analysis of transcriptome and metabolome in Citrus sinensis roots

Little is known about the effects of pH-aluminum (Al) interactions on gene expression and/or metabolite profiles in plants. Eleven-week-old seedlings of Citrus sinensis were fertilized with nutrient solution at an Al level of 0 or 1 mM and a pH of 3.0 or 4.0 for 18 weeks. Increased pH mitigated Al-toxicity-induced accumulation of callose, an Al-sensitive marker. In this study, we identified more differentially expressed genes and differentially abundant metabolites in pH 4.0 + 1 mM Al-treated roots (P4AR) vs pH 4.0 + 0 mM Al-treated roots (P4R) than in pH 3.0 + 1 mM Al-treated roots (P3AR) vs pH 3.0 + 0 mM Al-treated roots (P3R), suggesting that increased pH enhanced root metabolic adaptations to Al-toxicity. Further analysis indicated that increased pH-mediated mitigation of root Al-toxicity might be related to several factors, including: enhanced capacity to maintain the homeostasis of phosphate and energy and the balance between generation and scavenging of reactive oxygen species and aldehydes; and elevated accumulation of secondary metabolites such as polyphenol, proanthocyanidins and phenolamides and adaptations of cell wall and plasma membrane to Al-toxicity.

Aluminum-tolerant, growth-promoting endophytic bacteria as contributors in promoting tea plant growth and alleviating aluminum stress

Unlike that of other crops, the growth of tea plants can be promoted by aluminum, but its regulation mechanism remains unclear. Some endophytes can also promote growth of plant hosts. In this paper, tea roots treated with aluminum were used to study the growth-promoting traits and aluminum tolerance of endophytes. Meta-16S rDNA analysis revealed that Burkholderia was enriched in tea roots after aluminum treatment, and it was the dominant strain for hydroponic tea roots and field tea roots. Actinomycetes constituted the dominant strains in hydroponic tea seedlings treated with aluminum. Sixteen endophytic bacteria, including 12 strains of Firmicutes, 2 strains of Proteobacteria and 2 strains of Actinomycetes, were isolated and identified from hydroponic tea roots treated with different aluminum concentrations. Growth-promoting activity analysis showed that the isolated endophytic bacteria all had more than one plant growth-promoting trait. Among them, B4 (Bacillus nealsonii), B8 (Brevibacterium frigoritolerans) and A2 (Nocardia nova) bacteria each had three growth-promoting traits. Aluminum tolerance ability analysis indicated that endophyte A1 (Leifsonia shinshuensis) had the strongest aluminum tolerance ability, up to 200 mg l-1 aluminum. Plant-bacteria interactions showed that endophytes A1, A2 and B4 and their synthetic community all had a growth-promoting effect on the growth of wheat lateral roots. Moreover, endophytes A1 and B4 alleviated aluminum stress in wheat. Endophyte A1 also promoted the growth of tea cuttings, especially lateral roots, with/without aluminum. Taken together, aluminum enhanced the distribution of aluminum-tolerant and growth-promoting bacteria, thereby promoting the growth of tea roots. This study provides a new aspect for research on the mechanism by which aluminum promotes tea plant growth.

CsHCT-Mediated Lignin Synthesis Pathway Involved in the Response of Tea Plants to Biotic and Abiotic Stresses

Many studies have shown that phenolic compounds such as lignin and flavonoids enhance plant resistance. Tea plants are rich in flavonoid compounds. Whether these compounds are related to tea plant resistance is unclear. In this study, an interesting conclusion was drawn on the basis of experimental results: in response to abiotic stress (except for sucrose treatment), gene expression was increased in the phenylpropanoid and lignin pathways and was reduced in the flavonoid pathway in tea plants. CsHCTs, the genes located at the branch point of the lignin and flavonoid pathways, are most suitable for regulating the ratio of carbon flow in the lignin pathway and flavonoid synthesis. Enzymatic and genetic modification experiments proved that CsHCTs encode hydroxycinnamoyl-coenzyme A:shikimate/quinate hydroxycinnamoyl transferase in vitro and in vivo. Furthermore, the genetic modification results showed that the contents of phenolic acids and lignin were increased in tobacco and Arabidopsis plants overexpressing CsHCTs, whereas the content of flavonol glycosides was decreased. Both types of transgenic plants showed resistance to many abiotic stresses and bacterial infections. We speculate that CsHCTs participate in regulation of the metabolic flow of carbon from the flavonoid pathway to the chlorogenic acid, caffeoylshikimic acid, and lignin pathways to increase resistance to biotic and abiotic stresses.

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.

Hormone Orchestrates a Hierarchical Transcriptional Cascade That Regulates Al-Induced De Novo Root Regeneration in Tea Nodal Cutting

The aluminum in acid soils is very rhizotoxic to most plant species, but it is essential for root growth and development in Camellia sinensis. However, the molecular basis of Al-mediated signaling pathways in root regeneration of tea plants is largely unclear. In this study, we profiled the physiological phenotype, transcriptome, and phytohormones in the process using stems treated with Al (0.3 mM) and control (0.02 mM). The anatomical analysis showed that the 0.3 mM Al-treated stem began to develop adventitious root (AR) primordia within 7 days, ARs occurred after 21 days, while the control showed a significant delay. We further found that the expression patterns of many genes involved in the biosynthesis of ZT, ACC, and JA were stimulated by Al on day 3; also, the expression profiles of auxin transporter-related genes were markedly increased under Al during the whole rooting process. Moreover, the expression of these genes was strongly correlated with the accumulation of ZT, ACC, JA, and IAA. CsERFs, CsMYBs, and CsWRKYs transcription factor genes with possible crucial roles in regulating AR regeneration were also uncovered. Our findings suggest that multiple phytohormones and genes related to their biosynthesis form a hierarchical transcriptional cascade during Al-induced de novo root regeneration in tea nodal cuttings.

Metal and Metalloid Toxicity in Plants: An Overview on Molecular Aspects

Worldwide, the effects of metal and metalloid toxicity are increasing, mainly due to anthropogenic causes. Soil contamination ranks among the most important factors, since it affects crop yield, and the metals/metalloids can enter the food chain and undergo biomagnification, having concomitant effects on human health and alterations to the environment. Plants have developed complex mechanisms to overcome these biotic and abiotic stresses during evolution. Metals and metalloids exert several effects on plants generated by elements such as Zn, Cu, Al, Pb, Cd, and As, among others. The main strategies involve hyperaccumulation, tolerance, exclusion, and chelation with organic molecules. Recent studies in the omics era have increased knowledge on the plant genome and transcriptome plasticity to defend against these stimuli. The aim of the present review is to summarize relevant findings on the mechanisms by which plants take up, accumulate, transport, tolerate, and respond to this metal/metalloid stress. We also address some of the potential applications of biotechnology to improve plant tolerance or increase accumulation.

Recent Advances in Understanding Mechanisms of Plant Tolerance and Response to Aluminum Toxicity

Aluminum (Al) toxicity is a major environmental stress that inhibits plant growth and development. There has been impressive progress in recent years that has greatly increased our understanding of the nature of Al toxicity and its mechanisms of tolerance. This review describes the transcription factors (TFs) and plant hormones involved in the adaptation to Al stress. In particular, it discusses strategies to confer plant resistance to Al stress, such as transgenic breeding, as well as small molecules and plant growth-promoting rhizobacteria (PGPRs) to alleviate Al toxicity. This paper provides a theoretical basis for the enhancement of plant production in acidic soils.

Metabolics and ionomics responses of tea leaves (Camellia sinensis (L.) O. Kuntze) to fluoride stress

Tea plant (Camellia sinensis (L.) O. Kuntze) is known to accumulate high concentrations of fluoride (F) in its leaves; however, the underlying mechanism of F accumulation remains unclear. The main objective of this study was to investigate the homeostatic self-defense mechanisms of tea leaves to F supplementation (0, 5, 20, and 50 mgL^-1) by metabolomics and ionomics. We identified a total of 96 up-regulated and 40 down-regulated metabolites in tea leaves treated with F. Of these different compounds, minor polypeptides, carbohydrates and amino acids played valuable roles in the F-tolerating mechanism of tea plant. After F treatments, the concentrations of sodium (Na), ferrum (Fe), manganese (Mn), and molybdenum (Mo) were significantly increased in tea leaves, whereas the aluminum (Al) was decreased. These findings suggest that the ionic balance and metabolites are attributable to the development of F tolerance, providing new insight into tea plant adaptation to F stress.

Roles of specialized metabolites in biological function and environmental adaptability of tea plant (Camellia sinensis) as a metabolite studying model

Background

Aim of review

Key scientific concepts of review