CsFEX, a Fluoride Export Protein Gene from Camellia sinensis, Alleviates Fluoride Toxicity in Transgenic Escherichia coli and Arabidopsis thaliana

Root-specific expression of CsNPF2.3 is involved in modulating fluoride accumulation in tea plant (Camellia sinensis)

Fluoride (F) is a nonessential but potentially harmful element for plants, especially when present in excess. The tea plant is known for its ability to hyperaccumulate F from the soil and eventually accumulates in the leaves; however, how the tea plant transports F to the leaves remains unclear. Here, we found that Se can significantly decrease the transport efficiency of F from root to leaf. Therefore, RNA-Sequencing was performed on tea roots cotreated with selenite and fluoride, and then we isolated a plasma membrane-localized F transporter CsNPF2.3 from tea plant roots and examined its role in transport of F in tea plants. The results showed that CsNPF2.3 exhibited F transport activity when heterologously expressed in yeast. Expression pattern analysis revealed that CsNPF2.3 is expressed in epidermal cells, cortex cells, and xylem parenchyma cells in roots. Overexpression of CsNPF2.3 in tea roots significantly increased F content in the root, stem, and leaf, and enhanced the transport efficiency of F from root to leaf. Furthermore, in nine tea cultivars, CsNPF2.3 expression in the root was significantly positively correlated with F content in the leaf and root, and the transport efficiency of F from root to leaf. Altogether, these findings suggest that CsNPF2.3 was involved in uptake and transport of F in tea plants.

Fluorine accumulation characteristics of 85 tea tree (Camellia sinensis) varieties and its potential risk assessment

Tea tree is a fluorine (F)-enriched plant, leading to much concern about the safety of drinking tea from tea tree (Camellia sinensis (L.) Kuntze). Tea tree is a perennial leaf-harvested crop, and tea production in China is generally categorized as spring tea, summer tea and autumn tea in its annual growth rounds. However, the seasonally dynamic changes of F content and accumulation in the leaves and its drinking safety are poorly understood. In this study, 85 tea varieties cultivated under the same conditions were investigated to analyze the seasonal variation of F content and it's relationships with F accumulation, aluminum (Al), calcium (Ca) and manganese (Mn) and hazard quotient (HQ) in young leaves (one bud and two leaves, YL) and mature leaves (canopy leaves, ML). The average F contents and accumulations were 350 mg kg-1 and 203 g ha-1 in YL, and they were 2451 mg kg-1 and 2578 g ha-1 in ML, respectively, with F mainly accumulated in ML. As the growing season progresses, the F content showed a gradual increase in YL, while a decrease in ML, inferring that F may be redistributed from mature leaves to young leaves. Additionally, the F content was quite different among tea varieties which are suitable for processing oolong tea, green tea, and black tea, with higher F accumulation in oolong tea varieties than in green and black tea varieties. Moreover, F content and accumulation could be obviously affected by the geographical origin of the tea tree varieties, with significantly higher F content in the varieties from F rich fluorite belts than other regions. Furthermore, F content and accumulation showed a significant positive correlation with the content of Al and Mn (p < 0.05). Based on a daily tea consumption of 8.7 g, the HQ was investigated to show that the proportion of tea leaves with HQ<1 made from spring, summer and autumn tender leaves of 85 varieties was 100 %, 90.6 % and 50.6 %, respectively, indicating that the tea with the best drinking safety comes from spring, followed by summer, and then autumn. This result suggests that it could be necessary to avoid planting tea trees in fluorite mining areas, choose low F tea tree varieties, and control the tenderness of fresh leaves in order to ensure the safety of tea drinking.

The fluoride exporter (CsFEX) regulates fluoride uptake/accumulation in Camellia sinensis under different pH

Fluoride (F) can be absorbed from the environment and hyperaccumulate in leaves of Camellia sinensis without exhibiting any toxic symptoms. Fluoride exporter in C. sinensis (CsFEX) could transport F to extracellular environment to alleviate F accumulation and F toxicity, but its functional mechanism remains unclear. Here, combining with pH condition of C. sinensis growth, the characteristics of CsFEX and mechanism of F detoxification were further explored. The results showed that F accumulation was influenced by various pH, and pH 4.5 and 6.5 had a greater impact on the F accumulation of C. sinensis. Through Non-invasive Micro-test Technology (NMT) detection, it was found that F uptake/accumulation of C. sinensis and Arabidopsis thaliana might be affected by pH through changing the transmembrane electrochemical proton gradient of roots. Furthermore, diverse expression patterns of CsFEX were induced by F treatment under different pH, which was basically up-regulated in response to high F accumulation, indicating that CsFEX was likely to participate in the process of F accumulation in C. sinensis and this process might be regulated by pH. Additionally, CsFEX functioned in the mitigation of F sensitivity and accumulation strengthened by lower pH in Escherichia coli and A. thaliana. Moreover, the changes of H+ flux and potential gradient caused by F were relieved as well in transgenic lines, also suggesting that CsFEX might play an important role in the process of F accumulation. Above all, F uptake/accumulation were alleviated in E. coli and A. thaliana by CsFEX through exporting F-, especially at lower pH, implying that CsFEX might regulate F accumulation in C. sinensis.

Defluorination of monofluorinated alkane by Rhodococcus sp. NJF-7 isolated from soil

Microbial degradation of fluorinated compounds raised significant attention because of their widespread distribution and potential environmental impacts. Here, we report a bacterial isolate, Rhodococcus sp. NJF-7 capable of defluorinating monofluorinated medium-chain length alkanes. This isolate consumed 2.29 ± 0.13 mmol L- 1 of 1-fluorodecane (FD) during a 52 h incubation period, resulting in a significant release of inorganic fluoride amounting to 2.16 ± 0.03 mmol L- 1. The defluorination process was strongly affected by the initial FD concentration and pH conditions, with lower pH increasing fluoride toxicity to bacterial cells and inhibiting enzymatic defluorination activity. Stoichiometric conversion of FD to fluoride was observed at neutral pH with resting cells, while defluorination was significantly lower at reduced pH (6.5). The discovery of the metabolites decanoic acid and methyl decanoate suggests that the initial attack by monooxygenases may be responsible for the biological defluorination of FD. The findings here provide new insights into microbial defluorination processes, specifically aiding in understanding the environmental fate of organic semi-fluorinated alkane chemicals.

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.

Fluoride transport in Arabidopsis thaliana plants is impaired in Fluoride EXporter (FEX) mutants

Fluoride is an environmental toxin prevalent in water, soil, and air. A fluoride transporter called Fluoride EXporter (FEX) has been discovered across all domains of life, including bacteria, single cell eukaryotes, and all plants, that is required for fluoride tolerance. How FEX functions to protect multicellular plants is unknown. In order to distinguish between different models, the dynamic movement of fluoride in wildtype (WT) and fex mutant plants was monitored using [18F]fluoride with positron emission tomography. Significant differences were observed in the washout behavior following initial fluoride uptake between plants with and without a functioning FEX. [18F]Fluoride traveled quickly up the floral stem and into terminal tissues in WT plants. In contrast, the fluoride did not move out of the lower regions of the stem in mutant plants resulting in clearance rates near zero. The roots were not the primary locus of FEX action, nor did FEX direct fluoride to a specific tissue. Fluoride efflux by WT plants was saturated at high fluoride concentrations resulting in a pattern like the fex mutant. The kinetics of fluoride movement suggested that FEX mediates a fluoride transport mechanism throughout the plant where each individual cell benefits from FEX expression.

The role of plant growth promoting rhizobacteria in strengthening plant resistance to fluoride toxicity: a review

A wide variety of bacteria are present in soil but in rhizospheric area, the majority of microbes helps plant in defending diseases and facilitate nutrient uptake. These microorganisms are supported by plants and they are known as plant growth-promoting rhizobacteria (PGPR). The PGPRs have the potential to replace chemical fertilizers in a way that is more advantageous for the environment. Fluoride (F) is one of the highly escalating, naturally present contaminants that can be hazardous for PGPRs because of its antibacterial capacity. The interactions of F with different bacterial species in groundwater systems are still not well understood. However, the interaction of PGPR with plants in the rhizosphere region reduces the detrimental effects of pollutants and increases plants' ability to endure abiotic stress. Many studies reveal that PGPRs have developed F defense mechanisms, which include efflux pumps, Intracellular sequestration, enzyme modifications, enhanced DNA repair mechanism, detoxification enzymes, ion transporter/antiporters, F riboswitches, and genetic mutations. These resistance characteristics are frequently discovered by isolating PGPRs from high F-contaminated areas or by exposing cells to fluoride in laboratory conditions. Numerous studies have identified F-resistant microorganisms that possess additional F transporters and duplicates of the well-known targets of F. Plants are prone to F accumulation despite the soil's low F content, which may negatively affect their growth and development. PGPRs can be used as efficient F bioremediators for the soil environment. Environmental biotechnology focuses on creating genetically modified rhizobacteria that can degrade F contaminants over time. The present review focuses on a thorough systemic analysis of contemporary biotechnological techniques, such as gene editing and manipulation methods, for improving plant-microbe interactions for F remediation and suggests the importance of PGPRs in improving soil health and reducing the detrimental effects of F toxicity. The most recent developments in the realm of microbial assistance in the treatment of F-contaminated environments are also highlighted.

Hierarchical camellia-like metal–organic frameworks via a bimetal competitive coordination combined with alkaline-assisted strategy for boosting selective fluoride removal from brick tea

Developing an efficient and easy scale-up adsorbent with excellent fluoride adsorption and selectivity from brick tea is urgently desired. However, the separation of fluoride from tea is particularly challenging due to it contains abundant active compounds. Herein, we report ultrahigh fluoride adsorption from brick tea by a hierarchical camellia-like bimetallic metal-organic frameworks (MOFs). The hierarchical camellia-like Ca₂Al₁Fu is fabricated via a Ca/Al competitive coordination combined with alkaline-assisted strategy to tailor the morphology and porous structure. Subsequently, we systematically explore how the kinetic, thermodynamic, pH, and coexisting ions parameters employed during fluoride adsorption influence the resulting uptake behavior of Ca₂Al₁Fu. Further, sensory evaluation of the tea after adsorption is explored to determine the optimal dose that makes Ca₂Al₁Fu as a practical adsorbent for application. Importantly, the fluoride adsorption capacity of optical CaAlFu with mixed CaAl metals molar ratio of 2:1 is 3.15 and 2.11 times higher than that of pristine CaFu and AlFu, respectively. Theoretical results reveal that the boosting selective fluoride removal can be ascribed to the specific interactions between fluoride and CaAl coordinatively unsaturated bimetallic centers. These results present an effective design strategy for the construction of bimetallic MOFs with hierarchically porous structures for broad prospect in adsorption-based applications.

CsMYB Transcription Factors Participate in Jasmonic Acid Signal Transduction in Response to Cold Stress in Tea Plant (Camellia sinensis)

Low-temperature stress is an increasing problem for the cultivation of tea (Camellia sinensis), with adverse effects on plant growth and development and subsequent negative impacts on the tea industry. Methyl jasmonate (MeJA), as a plant inducer, can improve the cold-stress tolerance in tea plants. R2R3-MYB transcription factors (TFs) are considered potentially important regulators in the resistance to cold stress in plants. However, the molecular mechanisms, by which MYB TFs via the jasmonic acid pathway respond to cold stress in the tea plant, remain unknown. In this study, physiological and biochemical assays showed that exogenous MeJA application could effectively promote ROS scavenging in the tea plant under cold stress, maintaining the stability of the cell membrane. Sixteen R2R3-MYB TFs genes were identified from the tea plant genome database. Quantitative RT-PCR analysis showed that three CsMYB genes were strongly induced under a combination of MeJA and cold-stress treatment. Subcellular localization assays suggest CsMYB45, CsMYB46, and CsMYB105 localized in the nucleus. Exogenous MeJA treatment enhanced the overexpression of CsMYB45, CsMYB46, and CsMYB105 in E. coli and improved the growth and survival rates of recombinant cells compared to an empty vector under cold stress. Yeast two-hybrid and bimolecular fluorescence complementation experiments confirmed that CsMYB46 and CsMYB105 interacted with CsJAZ3, CsJAZ10, and CsJAZ11 in the nucleus. Taken together, these results highlight that CsMYB45, CsMYB46, and CsMYB105 are not only key components in the cold-stress signal response pathway but also may serve as points of confluence for cold stress and JA signaling pathways. Furthermore, our findings provide new insight into how MYB TFs influence cold tolerance via the jasmonic acid pathway in tea and provide candidate genes for future functional studies and breeding.

Camellia sinensis Chloroplast Fluoride Efflux Gene CsABCB9 Is Involved in the Fluoride Tolerance Mechanism

Soil is a main source of fluoride for plants. The tea plants (Camellia sinensis) accumulate excessive amounts of fluoride in their leaves compared to other plants, but their fluoride tolerance mechanism is poorly understood. A chloroplast fluoride efflux gene (CsABCB9) was newly discovered by using transcriptome analysis, cloned from Camellia sinensis, and its function was demonstrated in the fluoride detoxication mechanism in Escherichia coli/Xenopus laevis oocytes and Arabidopsis thaliana. CsABCB9 is expressed in tea leaves upon F− treatment. The growth of tea, E. coli, and Arabidopsis were inhibited by F− treatment. However, growth of CsABCB9-overexpression in E. coli was shown to increase with lower fluoride content under F− treatment compared to the control. Furthermore, chlorophyll, xanthophyll and soluble sugar contents of CsABCB9-overexpression in Arabidopsis were improved under F− treatment compared to the wild type. CsABCB9 functions in fluoride transport, and the mechanism by which CsABCB9 improves fluoride resistance in tea is mainly chloroplast protection through fluoride efflux.

The performance of water-soluble fluoride transformation in soil-tea-tea infusion chain system and the potential health risk assessment

BACKGROUND

Water-soluble fluoride (WS-F) can be absorbed directly by tea plants from soil and comprises a major source of dietary F in tea consumers. To reveal the WS-F accumulation in tea leaves and assess WS-F health risks, 70 sets of samples including tea leaves at three maturity stages and corresponding topsoil were collected from Xinyang, China. The WS-F contents in tea samples and pH values in soil samples were determined.

RESULTS

The contents of WS-F in tea leaves exhibited a positive correlation with leaf maturity. The contents of WS-F in tea leaves showed a positive correlation with WS-F contents in the soil as the soil pH value exceeds 5. All the bud with two leaves samples, 84.29% of the third to sixth leaves samples, and 78.57% mature leaves samples in 5-min infusion tend to be no health threat. The leaching characteristics of WS-F from tea leaves were influenced by the leaf maturity and soaking time.

CONCLUSION

Taking measures to control pH and WS-F concentration of plantations soil, as well as drinking tea infusion made from young leaves or reducing soaking time could decrease the WS-F health risk. © 2021 Society of Chemical Industry.

Nothing lasts forever: understanding microbial biodegradation of polyfluorinated compounds and perfluorinated alkyl substances

Poly- and perfluorinated chemicals, including perfluorinated alkyl substances (PFAS), are pervasive in today's society, with a negative impact on human and ecosystem health continually emerging. These chemicals are now subject to strict government regulations, leading to costly environmental remediation efforts. Commercial polyfluorinated compounds have been called 'forever chemicals' due to their strong resistance to biological and chemical degradation. Environmental cleanup by bioremediation is not considered practical currently. Implementation of bioremediation will require uncovering and understanding the rare microbial successes in degrading these compounds. This review discusses the underlying reasons why microbial degradation of heavily fluorinated compounds is rare. Fluorinated and chlorinated compounds are very different with respect to chemistry and microbial physiology. Moreover, the end product of biodegradation, fluoride, is much more toxic than chloride. It is imperative to understand these limitations, and elucidate physiological mechanisms of defluorination, in order to better discover, study, and engineer bacteria that can efficiently degrade polyfluorinated compounds.

Exploring the Effects of Magnesium Deficiency on the Quality Constituents of Hydroponic-Cultivated Tea (Camellia sinensis L.) Leaves

Magnesium (Mg) plays important roles in photosynthesis, sucrose partitioning, and biomass allocation in plants. However, the specific mechanisms of tea plant response to Mg deficiency remain unclear. In this study, we investigated the effects of Mg deficiency on the quality constituents of tea leaves. Our results showed that the short-term (7 days) Mg deficiency partially elevated the concentrations of polyphenols, free amino acids, and caffeine but decreased the contents of chlorophyll and Mg. However, long-term (30 days) Mg-deficient tea displayed decreased contents of these constituents. Particularly, Mg deficiency increased the index of catechins' bitter taste and the ratio of total polyphenols to total free amino acids. Moreover, the transcription of key genes involved in the biosynthesis of flavonoid, caffeine, and theanine was differentially affected by Mg deficiency. Additionally, short-term Mg deficiency induced global transcriptome change in tea leaves, in which a total of 2522 differentially expressed genes were identified involved in secondary metabolism, amino acid metabolism, and chlorophyll metabolism. These results may help to elucidate why short-term Mg deficiency partially improves the quality constituents of tea, while long-term Mg-deficient tea may taste more bitter, more astringent, and less umami.

Functional and molecular characterization of fluoride exporter (FEX) from rice and its constitutive overexpression in Nicotiana benthamiana to promote fluoride tolerance

KEY MESSAGE

Early induction of OsFEX was insufficient for fluoride adaptation in IR-64. Overexpression of OsFEX in yeast and Nicotiana benthamiana enhanced fluoride tolerance. The present study delineates the regulation of fluoride exporter (FEX) in the fluoride-sensitive rice cultivar, IR-64 and its efficacy in generating high fluoride tolerance in transgenic Nicotiana benthamiana. Gene and protein expression profiling revealed that OsFEX exhibited early induction during fluoride stress in the vegetative and reproductive tissues of IR-64, although the expression was suppressed upon prolonged stress treatment. Analysis of OsFEX promoter in transgenic N. benthamiana, using β-glucuronidase reporter assay confirmed its early inducible nature, since the reporter expression and activity peaked at 12 h of NaF stress, after which it was lowered. OsFEX expression was up regulated in the presence of gibberellic acid (GA) and melatonin, while it was suppressed by abscisic acid (ABA). Complementation of ΔFEX1ΔFEX2 yeast mutants with OsFEX enabled high fluoride tolerance, thus validating the functional efficiency of the transgene. Bioassay of transgenic N. benthamiana lines, expressing OsFEX either under its own promoter or under CaMV35S promoter, established that constitutive overexpression, rather than early induction of OsFEX was essential and crucial for generating fluoride tolerance in the transgenics. Overall, the suppression of OsFEX in the later growth phases of stressed IR-64 due to enhanced ABA conservation and lowered synthesis of GA, as supported by the application of the respective phytohormone biosynthetic inhibitors, such as sodium tungstate and paclobutrazol, accounted for the fluoride-hyperaccumulative nature of the rice cultivar.

The fluoride transporter FLUORIDE EXPORTER (FEX) is the major mechanism of tolerance to fluoride toxicity in plants

Fluoride is everywhere in the environment, yet it is toxic to living things. How biological organisms detoxify fluoride has been unknown until recently. Fluoride-specific ion transporters in both prokaryotes (Fluoride channel; Fluc) and fungi (Fluoride Exporter; FEX) efficiently export fluoride to the extracellular environment. FEX homologues have been identified throughout the plant kingdom. Understanding the function of FEX in a multicellular organism will reveal valuable knowledge about reducing toxic effects caused by fluoride. Here we demonstrate the conserved role of plant FEX (FLUORIDE EXPORTER) in conferring fluoride tolerance. Plant FEX facilitates the efflux of toxic fluoride ions from yeast cells and is required for fluoride tolerance in plants. A CRISPR/Cas9-generated mutation in Arabidopsis thaliana FEX renders the plant vulnerable to low concentrations (100 µM) of fluoride at every stage of development. Pollen is particularly affected, failing to develop even at extremely low levels of fluoride in the growth medium. The action of the FEX membrane transport protein is the major fluoride defense mechanism in plants.

Genome-wide analysis of fluoride exporter genes in plants

Fluoride exporter genes (FEX) are known for the expulsion of cytoplasmic fluoride, thus preventing fluoride toxicity in plants. In this study, 31 FEX genes were identified across 19 plant species. Camphor Resistance (CrcB) domain was found to be present in all the identified FEX genes in plants. FEX genes were sequentially very conserved among the plants and are located mostly in chloroplast and mitochondria. The tertiary structure (3D) of AtFEX1 suggests that FEX genes of plants possess pore I and pore II, necessary for fluoride export. The TTFSGWNQ and GCLSTVSTF motifs were found to be well conserved in pore I and pore II. Phenylalanine (Phe/F) was also present in both the motifs, necessary for fluoride ions recognition and export. Cis-acting analysis in promoter sequences of plant FEX revealed several elements associated with various functions such as phytohormone signaling, integrating biotic and abiotic stress responses in plants. Prolong fluoride exposure causes necrosis in young leaves in Vigna radiata. Expression of VrFEX1 and VrFEX2 were highly induced under exogenous fluoride, thus suggesting a possible role in fluoride detoxification.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02677-z.

Fluoride absorption, transportation and tolerance mechanism in Camellia sinensis, and its bioavailability and health risk assessment: a systematic review

Tea is the one of the most popular non-alcoholic caffeinated beverages in the world. Tea is produced from the tea plant (Camellia sinensis (L.) O. Kuntze), which is known to accumulate fluoride. This article systematically analyzes the literature concerning fluoride absorption, transportation and fluoride tolerance mechanisms in tea plants. Fluoride bioavailability and exposure levels in tea infusions are also reviewed. The circulation of fluoride within the tea plantation ecosystems is in a positive equilibrium, with greater amounts of fluoride introduced to tea orchards than removed. Water extractable fluoride and magnesium chloride (MgCl₂ ) extractable fluoride in plantation soil are the main sources of absorption by tea plant root via active trans-membrane transport and anion channels. Most fluoride is readily transported through the xylem as F^- /F-Al complexes to leaf cell walls and vacuole. The findings indicate that tea plants employ cell wall accumulation, vacuole compartmentalization, and F-Al complexes to co-detoxify fluoride and aluminum, a possible tolerance mechanism through which tea tolerates higher levels of fluoride than most plants. Furthermore, dietary and endogenous factors influence fluoride bioavailability and should be considered when exposure levels of fluoride in commercially available dried tea leaves are interpreted. The relevant current challenges and future perspectives are also discussed. © 2020 Society of Chemical Industry.

Membrane Exporters of Fluoride Ion

Microorganisms contend with numerous and unusual chemical threats and have evolved a catalog of resistance mechanisms in response. One particularly ancient, pernicious threat is posed by fluoride ion (F^-), a common xenobiotic in natural environments that causes broad-spectrum harm to metabolic pathways. This review focuses on advances in the last ten years toward understanding the microbial response to cytoplasmic accumulation of F^-, with a special emphasis on the structure and mechanisms of the proteins that microbes use to export fluoride: the CLC^F family of F^-/H⁺ antiporters and the Fluc/FEX family of F^- channels.

Two New Members of CsFEXs Couple Proton Gradients to Export Fluoride and Participate in Reducing Fluoride Accumulation in Low-Fluoride Tea Cultivars

The accumulation of fluoride in tea leaves from various cultivars exhibits significant differences. However, the molecular basis and mechanism remain largely unknown. Here, we reported that two genes of CsFEX (fluoride export genes in Camellia sinensis), CsFEX1 and CsFEX2, transport fluoride out of cells, alleviate the cellular fluoride toxin, and rescue the yeast mutant (FEX1ΔFEX2Δ) and Arabidopsis mutant (fex), as their efflux activities are coupled with proton gradients. Further analysis found that CsFEX1 and CsFEX2 localize to the plasma membrane both in yeast and Arabidopsis cells. CsFEX2 is more effective to reduce fluoride toxicity in yeast and Arabidopsis compared with CsFEX1 even at low pH. CsFEX2 induced by fluoride treatment is around tenfold higher in a low-fluoride cultivar (Yunkang 10) than that in a high-fluoride cultivar (Pingyang Tezaocha), suggesting that CsFEX2 possibly plays a critical role in reducing fluoride accumulation in tea leaves.