Glutaredoxin GRXS16 mediates brassinosteroid-induced apoplastic H2O2 production to promote pesticide metabolism in tomato

Organ-level distribution tandem mass spectrometry analysis of three structural types of brassinosteroids in rapeseed

Background

Brassinosteroids (BRs) are a class of naturally occurring steroidal phytohormones mediating a wide range of pivotal developmental and physiological functions throughout the plant's life cycle. Therefore, it is of great significance to determine the content and the distribution of BRs in plants.Regretfully, although a large number of quantitative methods for BRs by liquid chromatography-tandem mass spectrometry (LC-MS/MS) have been reported, the in planta distribution of BRs is still unclear because of their lower contents in plant tissues and the lack of effective ionizable groups in their chemical structures.

Methods

We stablished a novel analytical method of BRs based on C18 cartridge solid-phase extraction (SPE) purification, 4-(dimethylamino)-phenylboronic acid (DMAPBA) derivatization, and online valve-switching system coupled with ultra-high performance liquid chromatography-electro spray ionization-triple quadrupole mass spectrometry (UHPLC-ESI-MS/MS). This method has been used to quantify three structural types of BRs (epibrassinolide, epicastasterone, and 6-deoxo-24-epicastaster one) in different organs of Brassica napus L. (rapeseed).

Results

We obtained the contents of three structural types of BRs in various organ tissues of rapeseed. The contents of three BRs in rapeseed flowers were the highest, followed by tender pods. The levels of three BRs all decreased during the maturation of the organs. We outlined the spatial distribution maps of three BRs in rapeseed based on these results, so as to understand the spatial distribution of BRs at the visual level.

Conclusions

Our results provided useful information for the precise in situ localization of BRs in plants and the metabolomic research of BRs in future work. The in planta spatial distribution of BRs at the visual level has been studied for the first time.

Recent Advances in Studying the Regulation of Fruit Ripening in Tomato Using Genetic Engineering Approaches

Tomato (Solanum lycopersicum L.) is one of the most commercially essential vegetable crops cultivated worldwide. In addition to the nutritional value, tomato is an excellent model for studying climacteric fruits' ripening processes. Despite this, the available natural pool of genes that allows expanding phenotypic diversity is limited, and the difficulties of crossing using classical selection methods when stacking traits increase proportionally with each additional feature. Modern methods of the genetic engineering of tomatoes have extensive potential applications, such as enhancing the expression of existing gene(s), integrating artificial and heterologous gene(s), pointing changes in target gene sequences while keeping allelic combinations characteristic of successful commercial varieties, and many others. However, it is necessary to understand the fundamental principles of the gene molecular regulation involved in tomato fruit ripening for its successful use in creating new varieties. Although the candidate genes mediate ripening have been identified, a complete picture of their relationship has yet to be formed. This review summarizes the latest (2017-2023) achievements related to studying the ripening processes of tomato fruits. This work attempts to systematize the results of various research articles and display the interaction pattern of genes regulating the process of tomato fruit ripening.

Interactive effect of 24-epibrassinolide and plant growth promoting rhizobacteria inoculation restores photosynthetic attributes in Brassica juncea L. under chlorpyrifos toxicity

Chlorpyrifos (CP) is a commonly used organophosphorous pesticide that is frequently utilised in the agricultural industry because of its great efficiency and inexpensive cost. The focus of the present study was to assess the impact of CP toxicity on Brassica juncea L. and to unravel the ameliorative potential of phytohormone, 24-epibrassinolide (EBL) mediated plant-microbe (Pseudomonas aeruginosa (B1), Burkholderia gladioli (B2)) interaction in B. juncea L. The maximum significant increment in the total chlorophyll, carotenoids, xanthophyll, anthocyanin and flavonoid content with EBL and B2 treatment in CP stressed B. juncea seedlings on spectrophotometric analysis were observed. Autofluorescence imaging of photosynthetic pigments i.e. chlorophyll, carotenoids, and total phenols with confocal microscopy showed maximum fluorescence with EBL and B2. Furthermore, when compared to CP stressed seedlings, scanning electron microscopy (SEM) study of the abaxial surface of leaves revealed a recovery in stomatal opening. The supplementation of EBL and PGPR (plant growth promoting rhizobacteria) improved the level of psb A (D1 subunit PSII) and psb B (CP 47 subunit of PSII) genes expression. The expression analysis of chalcone synthase (CHS), Phenylalanine ammonialyase (PAL), Phyotene synthase (PSY) with RT-PCR system showed up-regulation in the expression when supplemented with EBL and PGPR. As a result, the current study suggests that EBL and PGPR together, can reduce CP-induced toxicity in B. juncea seedlings and recovering the seedling biomass.

Reactive oxygen species signaling is involved in melatonin-induced reduction of chlorothalonil residue in tomato leaves

Pesticide overuse has led to serious global concerns regarding food safety and environmental pollution. Although the reduction of pesticide residue is critical, our knowledge about induced pesticide metabolism in plants remains fragmentary. Melatonin (N-acetyl-5-methoxytryptamine) is an effective stress-relieving agent in both animals and plants, but little is known about the melatonin signaling mechanism and its effect on pesticide metabolism in plants. Here, we found that exogenous melatonin treatment significantly reduced chlorothalonil residue by 41 % but suppression of endogenous melatonin accumulation increased chlorothalonil residue in tomato leaves. Moreover, melatonin increased photosynthesis, Fv/Fm, Calvin cycle enzyme activity, antioxidant enzyme activity, glutathione pool, and RESPIRATORY BURST HOMOLOG1 (RBOH1) expression in tomato leaves. However, the upregulation of RBOH1, CYP724B2, GST1, GST2, GSH and ABC, the increased glutathione concentrations and the activity of detoxification enzymes due to melatonin treatment were all significantly attenuated by the treatment with an NADPH oxidase inhibitor and a ROS scavenger, indicating a clear relationship between the reduction of pesticide residue and induction in detoxifying enzymes and genes upon melatonin treatment in an apoplastic H₂O₂-dependent manner. These results reveal that melatonin-induced reduction in chlorothalonil residue is mediated by H₂O₂ signaling in tomato leaves.

Quantitative determination and removal of pesticide residues in fresh vegetables and fruit products by LC-MS/MS and GC-MS/MS

Pesticides are the potent agrochemicals used to successfully manage, repel, or stop pests and weeds in agricultural production. This study analyzed 222 pesticide active substances in 90 samples of seven different vegetables and fruits acquired from producers through liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry/mass spectrometry (GC-MS/MS) technology. The validation parameters of each pesticide's active substances were determined. The LOD, LOQ values, and recovery studies of the 222 active substances were 3.00, 10.00 ng/g, and between 76.07 and 108.08%, respectively. The correlation coefficients and measurement uncertainty were determined to be between 0.990-0.999 and 8.91-31.46%, respectively. There were active substances of chlorpyrifos, acetamiprid, azoxystrobin, difenoconazole, malathion, dieldrin, boscalid, triticonazole, tebuconazole, triadimenol, trifloxystrobin, pirimicarb, and dodine among the vegetable and fruit samples used in the study. There were no active substances in 55 (61%) samples. Among the 35 samples (39%), 31 samples (34%) contained only one active substance, whereas four (5%) contained two active substances. However, the amount of active substances in six (7%) samples was above the maximum residue levels (MRL) limits. Various processes used in the study revealed that peeling was the most effective pesticide residue removal strategy. The washing procedure also proved that it reduced some pesticide residues but failed to eliminate all pesticides. The peeling process successfully reduced a significant amount of the active substances from the products, however, residues remained. Washing the fruits with hot water was also effective in removing residues. As a result, analyses of the peeled sections yielded higher pesticide residue concentrations than those of the entire product.

Phytochemical and physiological reactions of feverfew (Tanacetum parthenium (L.) Schultz Bip) to TiO2 nanoparticles

Nanomaterials can be used as elicitors for improving the biosynthesis of secondary metabolites in medicinal plants. The present study was conducted to assay the titanium dioxide-nanoparticles (TiO₂-NPs) effects on feverfew (Tanacetum parthenium) as an anti-cancer plant. The study showed that TiO₂-NPs application increased the amounts of the main compounds and oxygenated monoterpene in essential oils, thereby causing an improvement in the quantity and quality of the essential oils compared to control. The highest effect was related to 1500 ppm TiO₂-NPs concentration. Regarding parthenolide, TiO₂-NPs had no positive effect on parthenolide content and the highest content was observed in control. Increasing the concentrations over 1500 ppm resulted in a decrease in chlorophyll content, capitule diameter, flower yield, and harvest index compared to other concentrations and control. Additionally, the results indicated that TiO₂-NPs foliar spray reduced flower number, biological yield, fresh weight, and dry weights compared with untreated plants. The increase in quality and content of essential oil and lack of increase in parthenolide content, and reproductive and vegetative characteristics showed that TiO₂-NPs mainly affected the content and composition of essential oil. Totally, the application of TiO2-NPs in terms of positive effect on the yield and metabolites (without damaging biological effects) can be recommended and followed up to the concentration of 1000 ppm. Overall, the results indicated that improving the synthesis of valuable medicinal metabolites using TiO₂-NPs has promising results depending on the type of species, concentration used and target metabolites.

New Formulation to Accelerate the Degradation of Pesticide Residues: Composite Nanoparticles of Imidacloprid and 24-Epibrassinolide

Pest control effectiveness and residues of pesticides are contradictory concerns in agriculture and environmental conservation. On the premise of not affecting the insecticidal effect, the pesticide residues in the later stage should be degraded as fast as possible. In the present study, composite nanoparticles in a double-layer structure, consisting of imidacloprid (IMI) in the outer layer and plant hormone 24-epibrassinolide (24-EBL) in the inner layer, were prepared by the W/O/W solvent evaporation method using Eudragit RL/RS and polyhydroxyalkanoate as wall materials. The release of IMI in the outer layer was faster and reached the maximum within 24 h, while the release of 24-EBL in the inner layer was slower and reached the maximum within 96 h. The contact angle of the composite nanoparticles was half that of the 5% IMI emulsifiable concentrate (EC), and the deposition of composite nanoparticles on rice was twice that of 5% IMI EC, which increased the pesticide utilization efficiency. Compared with the common pesticide, 5% IMI EC, the insecticidal effect of the composite nanoparticles was stronger than that of planthoppers, with a much lower final residue amount on rice after 21 days. The composite nanoparticles prepared in this study to achieve sustained release of pesticides and, meanwhile, accelerate the degradation of pesticide residues have a strong application potential in agriculture for controlling pests and promoting crop growth.

γ-Aminobutyric acid (GABA) improves pesticide detoxification in plants

It is important to ensure food safety to study the technology and mechanism of pesticide residues degradation in crops. Though γ-aminobutyric acid (GABA) has been widely reported to involve in plant stress resistance, whether exogenous application or endogenous regulation of GABA by gene-editing technology can promote the pesticide detoxification is not clear in plants. Using tomato and chlorothalonil (CHT) as research models, we discovered that exogenous application of GABA or endogenous elevation of GABA by knockout of pyruvate-dependent GABA transaminase promoted both CHT metabolism and plant stress tolerance to CHT. This is closely related to the active adaptation of GABA to CHT stress by regulating the plant GABA shunt pathway and polyamine pathway. The transcriptome data revealed 17 target genes that may be closely related to the involvement of GABA in CHT metabolism, including 4 peroxidases, 5 glycosyltransferases, 4 glutathione S-transferases, and 4 ABC transporters. In addition, the glutathione detoxification pathway and antioxidative enzyme also actively participated in the GABA-induced CHT detoxification process, which played an important role in relieving CHT stress. As a result, GABA significantly increased the photosynthetic capacity of tomato leaves under CHT stress. While studying photosynthesis, we unexpectedly found that GABA promotes stomatal closure in terms of decreased stomatal conductance and stomatal diameter. This result implies that GABA can reduce CHT absorption by regulating stomatal movement in leaves. Together, we provided a novel viewpoint that foliar application of GABA or metabolic engineering of GABA is an effective approach to reduce the risk of pesticide contamination in crop production.

Glutathione Promotes Degradation and Metabolism of Residual Fungicides by Inducing UDP-Glycosyltransferase Genes in Tomato

Reduced glutathione (GSH) is a key antioxidant, which plays a crucial role in the detoxification of xenobiotics in plants. In the present study, glutathione could reduce chlorothalonil (CHT) residues in tomatoes by inducing the expression of the UDP-glycosyltransferase (UGT) gene. In plants, UGT is an important glycosylation catalyst, which can respond to stresses in time by activating plant hormones and defense compounds. Given the importance of plant growth and development, the genome-wipe analyses of Arabidopsis and soybean samples have been carried out, though not on the tomato, which is a vital vegetable crop. In this study, we identified 143 UGT genes in the tomato that were unevenly distributed on 12 chromosomes and divided into 16 subgroups and found that a variety of plant hormones and stress response cis-elements were discovered in the promoter region of the SlUGT genes, indicating that the UGT genes were involved in several aspects of the tomato stress response. Transcriptome analysis and results of qRT-PCR showed that most SlUGT genes could be induced by CHT, and the expression of these genes was regulated by glutathione. In addition, we found that SlUGT genes could participate in plant detoxification through interaction with transcription factors. These findings further clarify the potential function of the UGT gene family in the detoxification of exogenous substances in tomatoes and provide valuable information for the future study of functional genomics of tomatoes.

Metabolomics Mechanism and Lignin Response to Laxogenin C, a Natural Regulator of Plants Growth

Laxogenin C (LGC) is a natural spirostanol deriving from plant hormone which has shown growing regulation similar to those of brassinosteroids. In the present study, LGC showed a promoting effect on tomato seed germination and seedling growth in a dose-dependent manner. We applied LC-MS/MS to investigate metabolome variations in the tomato treated with LGC, which revealed 10 differential metabolites (DMs) related to KEGG metabolites, associated with low and high doses of LGC. Enrichment and pathway mapping based on the KEGG database indicated that LGC regulated expressions of 2-hydroxycinnamic acid and l-phenylalanine to interfere with phenylalanine metabolism and phenylpropanoids biosynthesis. The two pathways are closely related to plant growth and lignin formation. In our further phenotypic verification, LGC was confirmed to affect seedling lignification and related phenylpropanoids, trans-ferulic acid and l-phenylalanine levels. These findings provided a metabolomic aspect on the plant hormone derivates and revealed the affected metabolites. Elucidating their regulation mechanisms can contribute to the development of sustainable agriculture. Further studies on agrichemical development would provide eco-friendly and efficient regulators for plant growth control and quality improvement.

Regulation of chlorothalonil degradation by molecular hydrogen

Pesticides can accumulate throughout the food chain to potentially endanger human health. Although molecular hydrogen (H₂) is widely used in industry and medicine, its application in agriculture is just beginning. This study showed that H₂ enhances the degradation of the fungicide chlorothalonil (CHT) in plants, but does not reduce its antifungal efficacy. Pharmacological evidence confirmed the contribution of H₂-stimulated brassinosteroids (BRs) in the above responses. The genetic increased endogenous H₂ with overexpression of hydrogenase 1 gene (CrHYD1) from Chlamydomonas reinhardtii in Arabidopsis not only increased BRs levels, but also eventually intensified the degradation of CHT. Expression of genes encoding some enzymes responsible for detoxification in tomato and Arabidopsis were also stimulated. Contrasting responses were observed after the pharmacological removal of endogenous BR. We further proved that H₂ control of CHT degradation was relatively universal, with at least since its degradation in Chinese cabbage, cucumber, radish, alfalfa, rice, and rapeseed were differentially enhanced by H₂. Collectively, above results clearly indicated that both exogenously and endogenously applied with H₂ could stimulate degradation of CHT partially via BR-dependent detoxification. These results may open a new window for environmental-friendly hydrogen-based agriculture.

Exogenous 24-epibrassinolide activates detoxification enzymes to promote degradation of boscalid in cherry tomatoes

BACKGROUND

Boscalid is often used to extend the storage time of postharvest cherry tomato. Pesticide residue has become an issue of food safety. This study sought to investigate the spatial distribution of boscalid residue in cherry tomato fruits and to determine the effect of 24-epibrassinolide (EBR) in promoting boscalid degradation.

RESULTS

Boscalid could quickly penetrate into cherry tomatoes, but mainly remained in the peel. The migration of boscalid from the peel into the core was a time-consuming and complex process during storage. After 72 h, boscalid residues in the pulp and the core began to accumulate gradually. The exogenous application of EBR activated peroxidase, glutathione reductase and glutathione S-transferase, and effectively promoted the degradation of boscalid by a maximum decrease of 44.8% in peel, 54.0% in pulp and 71.2% in core.

CONCLUSION

As one of the common pesticides, boscalid had a strong ability to enter the cherry tomato and thus become a potential risk for public consumption. Therefore, rational use of pesticides is recommended. The results of this study indicate that the possible risk of boscalid residue could be alleviated by EBR pretreatment through activating detoxification enzymes. © 2020 Society of Chemical Industry.

CC-type glutaredoxin, OsGrx_C7 plays a crucial role in enhancing protection against salt stress in rice

Soil salinity is one of the critical issue worldwide that adversely affect soil fertility. Salt stress significantly limits crop yield and grain quality; therefore, there is an urgent need to develop a strategy to improve salt stress tolerance. In present study, we reported that rice glutaredoxin (OsGrx_C7) plays a positive response in salt induced stress. Gene expression analysis, silencing, and overexpression of OsGrx_C7 gene were used to discover the role of OsGrx_C7 in response to salt stress. Gene expression analysis suggested that OsGrx_C7 expression was induced under salt stress and ubiquitously expressed in rice including root and shoot. The silencing of osgrx_c7 gene leads to increased sensitivity to salt stress, indicating its importance in salt stress tolerance. A gain-of-function approach showed that OsGrx_C7 may act as an important determinant in salt stress, compared with WT, and revealed higher biomass accumulation, improved root and plant growth under salt stress. Under salt stress condition, OsGrx_C7 overexpressing rice plants showed lower level of lipid peroxidation and Na⁺/K⁺ ratio, while proline accumulation, soluble sugar content and GSH/GSSG ratio was higher compared to WT. Furthermore, expression analysis suggested that OsGrx_C7 acted as positive regulator of salt tolerance by reinforcing the expression of transporters (OsHKT2;1, OsHKT1;5 and OsSOS1) engaged in Na⁺ homeostasis in overexpressing plants. Overall our study revealed that OsGrx_C7 emerged as a key mediator in response to salt stress in rice and could be used for engineering tolerance against salt stress in rice and other crops.

Glutaredoxin like protein (RtGRL1) regulates H2O2 and Na+ accumulation by maintaining the glutathione pool during abiotic stress

Reaumuria trigyna, an endangered recretohalophyte, is a small archaic wild shrub endemic to arid and semiarid plateau regions of Inner Mongolia, China. Based on salt-related transcriptomic data, we isolated a GRX family gene, glutaredoxin like protein (RtGRL1), from R. trigyna that is associated with the removal of active oxygen and regulation of redox status. RtGRL1 encodes a plasma membrane and chloroplast-localized protein induced by salt, cold, drought stress, ABA, and H₂O₂. In Arabidopsis thaliana, ectopically expressed RtGRL1 positively regulated biomass accumulation, chlorophyll content, germination rate, and primary root length under salt and drought stress. Overexpression of RtGRL1 induced expression of genes related to antioxidant enzymes and proline biosynthesis, thus increasing glutathione biosynthesis, glutathione-dependent detoxification of reactive oxygen species (ROS), and proline content under stress. Changes in RtGRL1 expression consistently affected glutathione/oxidizedglutathione and ascorbate/dehydroascorbate ratios and H₂O₂ concentrations. Furthermore, RtGRL1 promoted several GSH biosynthesis gene transcripts, decreased leaf Na⁺ content, and maintained lower Na⁺/K⁺ ratios in transgenic A. thaliana compared to wild type plants. These results suggest a critical link between RtGRL1 and ROS modulation, and contribute to a better understanding of the mechanisms governing plant responses to drought and salt stress.

S-Adenosyl-l-Methionine Promotes Metabolism of Fungicides in Cabernet Sauvignon (Vitis vinifera L.) Berries

Fungicides are commonly used to prevent and treat grape (Vitis vinifera L.) diseases; however, they are potentially toxic to humans. Herein, we show that the application of S-adenosyl-l-methionine (SAM) accelerated the metabolism of various fungicides in Cabernet Sauvignon berries. The substances and enzymes involved in the metabolism of fungicides were analyzed to elucidate the effects of SAM. Results showed that SAM improved the production rate of superoxide anion, the hydrogen peroxide content, and the activities of superoxide dismutase, catalase, and peroxidase in azoxystrobin-treated berries. Additionally, SAM had a positive effect on the content of reduced glutathione and on the activities of glutathione S-transferase, glutathione reductase, and glutathione peroxidase. Importantly, the stimulatory effect of SAM on fungicide metabolism was also observed for metalaxyl and thiophanate-methyl. These results suggest that SAM can be used to improve food safety.

Trichoderma asperellum reduces phoxim residue in roots by promoting plant detoxification potential in Solanum lycopersicum L

Phoxim, a broad-spectrum organophosphate pesticide, is widely used in agriculture to control insect pests in vegetable crops as well as in farm mammals. However, the indiscriminate use of phoxim has increased its release into the environment, leading to the contamination of plant-based foods such as vegetables. In this study, we investigated the effect of Trichoderma asperellum (TM, an opportunistic fungus) on phoxim residue in tomato roots and explored the mechanisms of phoxim metabolism through analysis of detoxification enzymes and gene expression. Degradation kinetics of phoxim showed that TM inoculation rapidly and significantly reduced phoxim residues in tomato roots. Phoxim concentrations at 5d, 10d and 15d post treatment were 75.12, 65.71 and 77.45% lower in TM + phoxim than only phoxim treatment, respectively. The TM inoculation significantly increased the glutathione (GSH) content, the activity of glutathione S-transferase (GST) and the transcript levels of GSH, GST1, GST2 and GST3 in phoxim-treated roots. In addition, the activity of peroxidase and polyphenol peroxidase involved in the xenobiotic conversion also increased in TM + phoxim treatment. The expression of detoxification genes, such as CYP724B2, GR, ABC2 and GPX increased by 3.82, 3.08, 7.89 and 2.46 fold, respectively in TM + phoxim compared with only phoxim. Similarly, the content of ascorbate (AsA) and the ratio of AsA to dehydroascorbate increased by 45.16% and 57.34%, respectively in TM + phoxim-treated roots. Our results suggest that TM stimulates plant detoxification potential in all three phases (conversion, conjugation and sequestration) of xenobiotc metabolism, leading to a reduced phoxim residue in tomato roots.

Dopamine alleviates bisphenol A-induced phytotoxicity by enhancing antioxidant and detoxification potential in cucumber

Bisphenol A (BPA) is an emerging organic pollutant, widely distributed in environment. Plants can uptake and metabolize BPA, but BPA accumulation induces phytotoxicity. In this study, we administered dopamine, a kind of catecholamines with strong antioxidative potential, to unveil its role in cucumber tolerance to BPA stress. The results showed that exposure to BPA (20 mg L^-1) for 21 days significantly reduced growth and biomass accumulation in cucumber seedlings as revealed by decreased lengths and dry weights of shoots and roots. While BPA exposure decreased the chlorophyll content, cell viability and root activity, it remarkably increased reactive oxygen species (ROS) accumulation, electrolyte leakage and malondialdehyde (MDA) content, suggesting that BPA induced oxidative stress in cucumber. However, exogenous dopamine application significantly improved the photosynthetic pigment content, root cell viability, growth and biomass accumulation, and decreased the ROS and MDA levels by increasing the activity of antioxidant enzymes under BPA stress. Further analysis revealed that dopamine application significantly increased the glutathione content and the transcripts and activity of glutathione S-transferase under co-administration of dopamine and BPA compared with only BPA treatment. Moreover, dopamine decreased the BPA content in both leaves and roots, suggesting that dopamine promoted BPA metabolism by enhancing the glutathione-dependent detoxification. Our results show that dopamine has a positive role against BPA phytotoxicity and it may reduce the risks-associated with the dietary intake of BPA through consumption of vegetables.

Glutaredoxin S25 and its interacting TGACG motif-binding factor TGA2 mediate brassinosteroid-induced chlorothalonil metabolism in tomato plants

The presence of pesticide residues in fresh fruits and vegetables poses a serious threat to human health. Brassinosteroids (BRs) can reduce pesticide residues in plants, but the underlying mechanisms still remain unclear. Here, we identified a tomato glutaredoxin gene GRXS25 which was induced by 24-epibrassinolide (EBR) and chlorothalonil (CHT) in a way dependent on apoplastic reactive oxygen species (ROS). Silencing of GRXS25 in tomato abolished EBR-induced glutathione S-transferases (GSTs) gene expression and activity, leading to an increased CHT residue. Yeast two-hybrid and bimolecular fluorescence complementation assays showed protein-protein interaction between GRXS25 and a transcription factor TGA2. Electrophoretic mobility shift and chromatin immunoprecipitation assays indicated that TGA2 factor bound to the TGACG-motif in the GST3 promoter. While silencing of TGA2 strongly compromised, overexpression of TGA2 enhanced expression of GST genes and CHT residue metabolism. Our results suggest that BR-induced apoplastic ROS trigger metabolism of pesticide residue in tomato plants through activating TGA2 factor via GRXS25-dependent posttranslational redox modification. Activation of plant detoxification through physiological approaches has potential implication in improving the food safety of agricultural products.

Expression and functional analysis of the propamocarb-related gene CsMAPEG in cucumber

BACKGROUND

Propamocarb (PM) is one of the main pesticides used for controlling cucumber downy mildew. However, due to its volatility and internal absorption, PM can easily form pesticide residues on cucumber fruits that seriously endanger human health and pollute the environment. The breeding of new cucumber varieties with a low abundance of PM residues via genetic methods constitutes an effective strategy for reducing pesticide residues and improving cucumber safety and quality. To help elucidate the molecular mechanism resulting in a low PM residue abundance in cucumber, we used the cucumber cultivar 'D0351' (which has the lowest PM residue content) as the test material and identified genes related to low PM residue abundance through high-throughput tag-sequencing (Tag-Seq).

RESULTS

CsMAPEG was constitutively expressed and showed both varietal and organizational differences. This gene was strongly expressed in 'D0351'. The expression levels of CsMAPEG in different cucumber tissues under PM stress were as follows: fruit>leaf>stem>root. CsMAPEG can respond to salicylic acid (SA), gibberellin (GA) and Corynespora cassiicola Wei (Cor) stress and thus plays an important regulatory role in plant responses to abiotic and biological stresses. The PM residue abundance in the fruits of CsMAPEG-overexpressing plants was lower than those found in antisense CsMAPEG plants and wild-type plants at all tested time points. The results revealed that CsMAPEG played a positive role in reducing the PM residue abundance. A CsMAPEG sense construct increased the contents of SOD, POD and GST in cucumber fruits, enhanced the degradation and metabolism of PM in cucumber, and thus effectively reduced the pesticide residue abundance in cucumber fruits.

CONCLUSIONS

The expression patterns of CsMAPEG in cucumber cultivars with high and low pesticide residue abundances and a transgenic verification analysis showed that CsMAPEG can actively respond to PM stress and effectively reduce the PM residue abundance in cucumber fruits. The results of this study will help researchers further elucidate the mechanism responsible for a low PM residue abundance in cucumber and lay a foundation for the breeding of new agricultural cucumber varieties with low pesticide residue abundances.