Differential Roles of Tau Class Glutathione S-Transferases in Oxidative Stress

A novel OsGST gene encoding 9glutathione reductase negatively regulates cadmium accumulation in rice

Cadmium (Cd) accumulates in rice and then moves up the food chain, causing serious health problems for humans. Glutathione S-transferase (GST) binds exogenous hazardous compounds to glutathione (GSH), which performs a variety of roles in plant responses to Cd stress. Here, Cd stimulated the transcripts of a novel OsGST gene, and the OsGST protein, which was localized in the nucleus and cytoplasm, was also induced by Cd. In OsGST deletion mutant lines generated by CRISPR/Cas9, more Cd was accumulated, and Cd hypersensitive phenotypes were observed, while transgenic lines overexpressing OsGST exhibited enhanced Cd tolerance and less Cd accumulation. Further analysis indicated that the osgst mutants exhibited considerably greater reactive oxygen species (ROS) and higher GSH level, and the antioxidant activity associated genes' expression were down-regulated, imply that OsGST controlled rice Cd accumulation and resistance through preserving the equilibrium of the GSH and redox in rice.

Embryo growth alteration and oxidative stress responses in germinating Cucurbita pepo seeds exposed to cadmium and copper toxicity

This study investigated the influence of cadmium (Cd) and copper (Cu) heavy metals on germination, metabolism, and growth of zucchini seedlings (Cucurbita pepo L.). Zucchini seeds were subjected to two concentrations (100 and 200 μM) of CdCl2 and CuCl2. Germination parameters, biochemical and phytochemical attributes of embryonic axes were assessed. Results revealed that germination rate remained unaffected by heavy metals (Cd, Cu). However, seed vigor index (SVI) notably decreased under Cd and Cu exposure. Embryonic axis length and dry weight exhibited significant reductions, with variations depending on the type of metal used. Malondialdehyde and H2O2 content, as well as catalase activity, did not show a significant increase at the tested Cd and Cu concentrations. Superoxide dismutase activity decreased in embryonic axis tissues. Glutathione S-transferase activity significantly rose with 200 μM CdCl2, while glutathione content declined with increasing Cd and Cu concentrations. Total phenol content and antioxidant activity increased at 200 μM CuCl2. In conclusion, Cd and Cu heavy metals impede zucchini seed germination efficiency and trigger metabolic shifts in embryonic tissue cells. Response to metal stress is metal-specific and concentration-dependent. These findings contribute to understanding the intricate interactions between heavy metals and plant physiology, aiding strategies for mitigating their detrimental effects on plants.

Integrated Transcriptome and Proteome Analysis Reveals the Regulatory Mechanism of Root Growth by Protein Disulfide Isomerase in Arabidopsis

Protein disulfide isomerase (PDI, EC 5.3.4.1) is a thiol-disulfide oxidoreductase that plays a crucial role in catalyzing the oxidation and rearrangement of disulfides in substrate proteins. In plants, PDI is primarily involved in regulating seed germination and development, facilitating the oxidative folding of storage proteins in the endosperm, and also contributing to the formation of pollen. However, the role of PDI in root growth has not been previously studied. This research investigated the impact of PDI gene deficiency in plants by using 16F16 [2-(2-Chloroacetyl)-2,3,4,9-tetrahydro-1-methyl-1H-pyrido[3,4-b]indole-1-carboxylic acid methyl ester], a small-molecule inhibitor of PDI, to remove functional redundancy. The results showed that the growth of Arabidopsis roots was significantly inhibited when treated with 16F16. To further investigate the effects of 16F16 treatment, we conducted expression profiling of treated roots using RNA sequencing and a Tandem Mass Tag (TMT)-based quantitative proteomics approach at both the transcriptomic and proteomic levels. Our analysis revealed 994 differentially expressed genes (DEGs) at the transcript level, which were predominantly enriched in pathways associated with "phenylpropane biosynthesis", "plant hormone signal transduction", "plant-pathogen interaction" and "starch and sucrose metabolism" pathways. Additionally, we identified 120 differentially expressed proteins (DEPs) at the protein level. These proteins were mainly enriched in pathways such as "phenylpropanoid biosynthesis", "photosynthesis", "biosynthesis of various plant secondary metabolites", and "biosynthesis of secondary metabolites" pathways. The comprehensive transcriptome and proteome analyses revealed a regulatory network for root shortening in Arabidopsis seedlings under 16F16 treatment, mainly involving phenylpropane biosynthesis and plant hormone signal transduction pathways. This study enhances our understanding of the significant role of PDIs in Arabidopsis root growth and provides insights into the regulatory mechanisms of root shortening following 16F16 treatment.

Growth, Physiological, and Biochemical Variations in Tomatoes after Infection with Different Density Levels of Meloidogyne enterolobii

Meloidogyne enterolobii is an extremely important plant parasitic nematode. Tomato (Solanum lycopersicum) is an essential worldwide vegetable, and M. enterolobii poses a major threat to its production. The present research investigated the effects of different levels of inoculum density of M. enterolobii (100, 500, 1000, 1500, and 2000 second-stage juveniles (J2s)/plant) on tomato growth, physiological, and biochemical changes at 7, 14, 21, and 28 days post-inoculation (dpi). The negative impact of M. enterolobii on plants gradually increased when the inoculum level increased. Therefore, M. enterolobii population densities (500-2000 J2s/plant) significantly (p < 0.05) reduced plant growth, photosynthetic pigmentation, gas exchange, and chlorophyll fluorescence compared to control plants, while the low population density (100 J2s/plant) showed very little influence. Furthermore, plants with the highest M. enterolobii inoculum (2000 J2s/plant) exhibited a greater number of egg masses and galls. The inoculum densities of M. enterolobii exhibited a notable correlation with the significant elevation of both malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, which are recognized as very detrimental stresses in plants. Similarly, a rise in the activity of several defensive antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), indicates the defensive mechanism used to combat the oxidative destruction produced by M. enterolobii. The specific activity of glutathione (GSH) and ascorbate (ASA) increased as potent antioxidant defense molecules in response to induced oxidative damage. In addition, our findings also demonstrated that the highest population density (2000 J2s/plant) increased the secondary metabolites responsible for scavenging oxidative stress in the plants. However, further research is required to explore the underlying reasons for this phenomenon and to develop efficient chemical or biocontrol strategies for managing M. enterolobii.

Quercetin attenuates environmental Avermectin-induced ROS accumulation and alleviates gill damage in carp through activation of the Nrf2 pathway

Avermectin (AVM) is one of the most often used insecticides which is toxic to aquatic organisms, and cause oxidative-induced damages to the fish respiratory organ, the "gills". To better understand the mechanism by which an antioxidant reduces AVM-induced gill damage, we investigated the effects of Quercetin (Que) on AVM induction of oxidative stress to inhibit damages to the gills using common carp as a model organism. The Que is a fruit and vegetable rich flavonoid with antioxidant activity. In this study, four groups were created: the Control group, the Que group (400 mg/kg), the AVM group (2.404 μg/L), and the Que plus AVM group. The analytical methods were pathological structure examination, qPCR, Reactive Oxygen Species (ROS) and Western blot. The results showed that Que alleviated AVM-induced oxidative stress, inflammatory damage and apoptosis in the carp gills by activating the Nrf2 pathway. The mechanism was that Que alleviated the accumulation of ROS, reduced the balance between oxidation and antioxidant disrupted by AVM exposure, lowered the content of lipid peroxidation produced malondialdehyde (MDA), and increased the content of antioxidant enzymes including glutathione (GSH) and catalase (CAT). Nrf2 pathway was activated. Meanwhile, Que inhibited gill apoptosis in carp by decreasing the levels of Bax, Cytochrome C, Caspase9, Cleaved-Caspase3 and reduced Bcl2. This has important implications for future studies on Que and AVM. New suggestions are provided to reduce the threat of aquatic environmental pollution.

Combination of transcriptomic, proteomic, and degradomic profiling reveals common and distinct patterns of pathogen-induced cell death in maize

Regulated cell death (RCD) is crucial for plant development, as well as in decision-making in plant-microbe interactions. Previous studies revealed components of the molecular network controlling RCD, including different proteases. However, the identity, the proteolytic network as well as molecular components involved in the initiation and execution of distinct plant RCD processes, still remain largely elusive. In this study, we analyzed the transcriptome, proteome, and N-terminome of Zea mays leaves treated with the Xanthomonas effector avrRxo1, the mycotoxin Fumonisin B1 (FB1), or the phytohormone salicylic acid (SA) to dissect plant cellular processes related to cell death and plant immunity. We found highly distinct and time-dependent biological processes being activated on transcriptional and proteome levels in response to avrRxo1, FB1, and SA. Correlation analysis of the transcriptome and proteome identified general, as well as trigger-specific markers for cell death in Zea mays. We found that proteases, particularly papain-like cysteine proteases, are specifically regulated during RCD. Collectively, this study characterizes distinct RCD responses in Z. mays and provides a framework for the mechanistic exploration of components involved in the initiation and execution of cell death.

Glutathione Transferases Are Involved in the Genotype-Specific Salt-Stress Response of Tomato Plants

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (EGSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between EGSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

Genetic control of tolerance to drought stress in soybean

BACKGROUND

Drought stress limits the production of soybean [Glycine max (L.) Merr.], which is the most grown high-value legume crop worldwide. Breeding for drought tolerance is a difficult endeavor and understanding the genetic basis of drought tolerance in soybean is therefore crucial for harnessing the genomic regions involved in the tolerance mechanisms. A genome-wide association study (GWAS) analysis was applied in a soybean germplasm collection (the EUCLEG collection) of 359 accessions relevant for breeding in Europe, to identify genomic regions and candidate genes involved in the response to short duration and long duration drought stress (SDS and LDS respectively) in soybean.

RESULTS

The phenotypic response to drought was stronger in the long duration drought (LDS) than in the short duration drought (SDS) experiment. Over the four traits considered (canopy wilting, leaf senescence, maximum absolute growth rate and maximum plant height) the variation was in the range of 8.4-25.2% in the SDS, and 14.7-29.7% in the LDS experiments. The GWAS analysis identified a total of 17 and 22 significant marker-trait associations for four traits in the SDS and LDS experiments, respectively. In the genomic regions delimited by these markers we identified a total of 12 and 16 genes with putative functions that are of particular relevance for drought stress responses including stomatal movement, root formation, photosynthesis, ABA signaling, cellular protection and cellular repair mechanisms. Some of these genomic regions co-localized with previously known QTLs for drought tolerance traits including water use efficiency, chlorophyll content and photosynthesis.

CONCLUSION

Our results indicate that the mechanism of slow wilting in the SDS might be associated with the characteristics of the root system, whereas in the LDS, slow wilting could be due to low stomatal conductance and transpiration rates enabling a high WUE. Drought-induced leaf senescence was found to be associated to ABA and ROS responses. The QTLs related to WUE contributed to growth rate and canopy height maintenance under drought stress. Co-localization of several previously known QTLs for multiple agronomic traits with the SNPs identified in this study, highlights the importance of the identified genomic regions for the improvement of agronomic performance in addition to drought tolerance in the EUCLEG collection.

Gene family evolution and natural selection signatures in Datura spp. (Solanaceae)

Elucidating the diversification process of congeneric species makes it necessary to identify the factors promoting species variation and diversification. Comparative gene family analysis allows us to elucidate the evolutionary history of species by identifying common genetic/genomic mechanisms underlying species responses to biotic and abiotic environments at the genomic level. In this study, we analyzed the high-quality transcriptomes of four Datura species, D. inoxia, D. pruinosa, D. stramonium, and D. wrightii. We performed a thorough comparative gene family analysis to infer the role of selection in molecular variation, changes in protein physicochemical properties, and gain/loss of genes during their diversification processes. The results revealed common and species-specific signals of positive selection, physicochemical divergence and/or expansion of metabolic genes (e.g., transferases and oxidoreductases) associated with terpene and tropane metabolism and some resistance genes (R genes). The gene family analysis presented here is a valuable tool for understanding the genome evolution of economically and ecologically significant taxa such as the Solanaceae family.

Biochemical and Structural Insights on the Poplar Tau Glutathione Transferase GSTU19 and 20 Paralogs Binding Flavonoids

Glutathione transferases (GSTs) constitute a widespread superfamily of enzymes notably involved in xenobiotic detoxification and/or in specialized metabolism. Populus trichocarpa genome (V4.1 assembly, Phytozome 13) consists of 74 genes coding for full-length GSTs and ten likely pseudogenes. These GSTs are divided into 11 classes, in which the tau class (GSTU) is the most abundant with 54 isoforms. PtGSTU19 and 20, two paralogs sharing more than 91% sequence identity (95% of sequence similarity), would have diverged from a common ancestor of P. trichocarpa and P. yatungensis species. These enzymes display the distinctive glutathione (GSH)-conjugation and peroxidase activities against model substrates. The resolution of the crystal structures of these proteins revealed significant structural differences despite their high sequence identity. PtGSTU20 has a well-defined deep pocket in the active site whereas the bottom of this pocket is disordered in PtGSTU19. In a screen of potential ligands, we were able to identify an interaction with flavonoids. Some of them, previously identified in poplar (chrysin, galangin, and pinocembrin), inhibited GSH-conjugation activity of both enzymes with a more pronounced effect on PtGSTU20. The crystal structures of PtGSTU20 complexed with these molecules provide evidence for their potential involvement in flavonoid transport in P. trichocarpa.

Redox and Hormonal Changes in the Transcriptome of Grape (Vitis vinifera) Berries during Natural Noble Rot Development

Noble rot is a favorable form of the interaction between grape (Vitis spp.) berries and the phytopathogenic fungus Botrytis cinerea. The transcriptome pattern of grapevine cells subject to natural noble rot development in the historic Hungarian Tokaj wine region has not been previously published. Furmint, a traditional white Tokaj variety suited to develop great quality noble rot was used in the experiments. Exploring a subset of the Furmint transcriptome redox and hormonal changes distinguishing between noble rot and bunch rot was revealed. Noble rot is defined by an early spike in abscisic acid (ABA) accumulation and a pronounced remodeling of ABA-related gene expression. Transcription of glutathione S-transferase isoforms is uniquely upregulated, whereas gene expression of some sectors of the antioxidative apparatus (e.g., catalases, carotenoid biosynthesis) is downregulated. These mRNA responses are lacking in berries exposed to bunch rot. Our results help to explain molecular details behind the fine and dynamic balance between noble rot and bunch rot development.

Non-synonymous substitution of evolutionarily conserved residue in Tau class glutathione transferases alters structural and catalytic features

Plant-specific tau glutathione transferases (GSTs) are basically involved in catalysing γ-glutathione (GSH)-dependent conjugation reactions with pesticides and herbicides, which play an important role in the detoxification of pollutants. Given the lack of systematic biochemical and structural information on tau GSTs, the study of their mediated defence mechanisms against toxic compounds has been greatly hindered. Here, we reveal the importance of the Ile residue closely interacting with GSH for the structural stability and catalytic function of GST. Evolutionary conservation analysis indicated that the crucial G-site Ile55 in the SbGSTU6 was converted to Thr53 of SbGSTU7. The comparative biochemical data on SbGSTU6, SbGSTU7 and their mutants showed that the substitution of Ile by Thr caused significant decrease in the affinity and catalytic efficiency of the GSTs. The unfavourable structural flexibility and pKa distribution of the active cavity residues were also demonstrated. Crystallography studies and molecular dynamics simulations showed that the conversion resulted in the hydrogen bond recombination with GSH and conformational rearrangement of GST active cavity, in which the Ile residue was more conducive to the formation of enzyme substrate complexes. The extensive biochemical and structural data not only reveal the critical role of the conserved G-site Ile residue in catalysing GSH-conjugate reactions but also provide valuable resources for the development of GST engineering in analytical and agricultural biotechnology.

Crosstalk between the redox signalling and the detoxification: GSTs under redox control?

Reactive oxygen species (ROS), antioxidants and their reduction-oxidation (redox) states all contribute to the redox homeostasis, but glutathione is considered to be the master regulator of it. We aimed to understand the relationship between the redox potential and the diverse glutathione transferase (GST) enzyme family by comparing the stress responses of two tomato cultivars (Solanum lycopersicum 'Moneymaker' and 'Ailsa Craig'). Four-week-old plants were treated by two concentrations of mannitol, NaCl and salicylic acid. The lower H₂O₂ and malondialdehyde contents indicated higher stress tolerance of 'Moneymaker'. The redox status of roots was characterized by measuring the reduced and oxidized form of ascorbate and glutathione spectrophotometrically after 24 h. The redox potential of 'Ailsa Craig' was more oxidized compared to 'Moneymaker' even under control conditions and became more positive due to treatments. High-throughput quantitative real-time PCR revealed that besides overall higher expression levels, SlGSTs were activated more efficiently in 'Moneymaker' due to stresses, resulting in generally higher GST and glutathione peroxidase activities compared to 'Ailsa Craig'. The expression level of SlGSTs correlated differently, however Pearson's correlation analysis showed usually strong positive correlation between SlGST transcription and glutathione redox potential. The possible redox regulation of SlGST expressions was discussed.

Quercetin antagonizes imidacloprid-induced mitochondrial apoptosis through PTEN/PI3K/AKT in grass carp hepatocytes

Imidacloprid (IMI) is widely used in agriculture, and is toxic to non-target aquatic species. Quercetin (Que) is a flavonoid abundant in fruits and vegetables that exhibits anti-oxidant activity. In the present study, we treated grass carp hepatocytes (L8824) with 0.1 μM Que and/or 1 mM IMI for 24 h to explore the effect of Que on IMI-induced mitochondrial apoptosis. We found that IMI exposure enhanced reactive oxygen species (ROS) generation, inhibiting the activities of SOD, CAT and T-AOC, exacerbating the accumulation of MDA, aggravating the expression of mitochondrial apoptosis pathway (Cyt-C, BAX, Caspase9 and Caspase3) related genes and decreased the expression of anti-apoptosis gene B-cell lymphoma-2 (Bcl-2). In addition, Que and IMI co-treatment significantly restored the activity of anti-oxidant enzymes, downregulated ROS level and apoptosis rate, thereby alleviating the depletion of mitochondrial membrane potential (ΔΨm) and the expression of cytochrome c (Cyt-C), Bcl-2-associated X (BAX), and cysteinyl aspartate specific proteinases (Caspase9 and 3), increasing the Bcl-2 level. Furthermore, we elucidated that Que could inhibit the expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), thus activating phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway to attenuate IMI-induced apoptosis. Molecular docking provides assertive evidence for the interaction between Que ligand and PTEN receptor. Consequently, these results indicate that Que effectively antagonizes IMI-induced mitochondrial apoptosis in grass carp hepatocytes via regulating the PTEN/PI3K/AKT pathway.

Salt stress improves thermotolerance and high-temperature bioethanol production of multi-stress-tolerant Pichia kudriavzevii by stimulating intracellular metabolism and inhibiting oxidative damage

BACKGROUND

High-temperature bioethanol production benefits from yeast thermotolerance. Salt stress could induce obvious cross-protection against heat stress of Pichia kudriavzevii, contributing to the improvement of its thermotolerance and bioethanol fermentation. However, the underlying mechanisms of the cross-protection remain poorly understood.

RESULTS

Salt stress showed obvious cross-protection for thermotolerance and high-temperature ethanol production of P. kudriavzevii observed by biomass, cell morphology and bioethanol production capacity. The biomass and ethanol production of P. kudriavzevii at 45 °C were, respectively, improved by 2.6 and 3.9 times by 300 mmol/L NaCl. Metabolic network map showed that salt stress obviously improved the key enzymes and intermediates in carbohydrate metabolism, contributing to the synthesis of bioethanol, ATP, amino acids, nucleotides, and unsaturated fatty acids, as well as subsequent intracellular metabolisms. The increasing trehalose, glycerol, HSPs, and ergosterol helped maintain the normal function of cell components. Heat stress induced serious oxidative stress that the ROS-positive cell rate and dead cell rate, respectively, rose from 0.5% and 2.4% to 28.2% and 69.2%, with the incubation temperature increasing from 30 to 45 °C. The heat-induced ROS outburst, oxidative damage, and cell death were obviously inhibited by salt stress, especially the dead cell rate which fell to only 20.3% at 300 mmol/L NaCl. The inhibiting oxidative damage mainly resulted from the abundant synthesis of GSH and GST, which, respectively, increased by 4.8 and 76.1 times after addition of 300 mmol/L NaCl. The improved bioethanol production was not only due to the improved thermotolerance, but resulted from the up-regulated alcohol dehydrogenases and down-regulated aldehyde dehydrogenases by salt stress.

CONCLUSION

The results provide a first insight into the mechanisms of the improved thermotolerance and high-temperature bioethanol production of P. kudriavzevii by salt stress, and provide important information to construct genetic engineering yeasts for high-temperature bioethanol production.

Glutathione S-Transferases in Cancer

In humans, the glutathione S-transferases (GST) protein family is composed of seven members that present remarkable structural similarity and some degree of overlapping functionalities. GST proteins are crucial antioxidant enzymes that regulate stress-induced signaling pathways. Interestingly, overactive GST proteins are a frequent feature of many human cancers. Recent evidence has revealed that the biology of most GST proteins is complex and multifaceted and that these proteins actively participate in tumorigenic processes such as cell survival, cell proliferation, and drug resistance. Structural and pharmacological studies have identified various GST inhibitors, and these molecules have progressed to clinical trials for the treatment of cancer and other diseases. In this review, we discuss recent findings in GST protein biology and their roles in cancer development, their contribution in chemoresistance, and the development of GST inhibitors for cancer treatment.

Compensation of Mutation in Arabidopsis glutathione transferase (AtGSTU) Genes under Control or Salt Stress Conditions

Glutathione transferases (GSTs) play a crucial role in detoxification processes due to the fact of their glutathione (GSH) conjugating activity, and through glutathione peroxidase or dehydroascorbate reductase (DHAR) activities, they influence the redox state of GSH and ascorbate (AsA). The plant-specific tau (GSTU) group is the largest class of Arabidopsis GSTs, and their members are involved in responses to different abiotic stresses. We investigated the effect of salt stress on two-week-old Arabidopsis thaliana wild-type (Col-0), Atgstu19 and Atgstu24 mutant plants after applying 150 mM NaCl for two days. The Atgstu19 seedlings had lower GST activity and vitality both under control conditions and after salt stress than the wild-type, but the level of total ROS was similar to the Col-0 plants. The GST activity of the knockout Atgstu24 mutant was even higher under control conditions compared to the Col-0 plants, while the ROS level and its vitality did not differ significantly from the wild-type. Analysis of the AtGSTU expression pattern revealed that the mutation in a single AtGSTU gene was accompanied by the up- and downregulation of several other AtGSTUs. Moreover, elevated AsA and GSH levels, an altered GSH redox potential and increased DHAR and glutathione reductase activities could help to compensate for the mutation of AtGSTU genes. The observed changes in the mutants suggest that the investigated isoenzymes influence the redox homeostasis under control conditions and after NaCl treatment in Arabidopsis seedlings. These data indicate for the first time the more general role of a temporary shift of redox status as part of GST mechanisms and regulation.

Comparative Transcriptomic Response of Two Pinus Species to Infection with the Pine Wood Nematode Bursaphelenchus xylophilus

Pine wilt disease (PWD) caused by pine wood nematode (PWN), Bursaphelenchus xylophilus, is a serious threat to global forest populations of conifers, in particular Pinus spp. Recently, the presence of PWN was reported in dead Yunnan pine (Pinus yunnanensis) trees under natural conditions. To further understand the potential impact caused by PWN in Yunnan pine populations, a transcriptional profiling analysis was performed over different time points (0 hours (h), 6 h, 24 h, 48 h, and 7 days) after PWN inoculation. A total of 9961 differentially expressed genes were identified after inoculation, which suggested a dynamic response against the pathogen, with a more intense pattern at 48 h after inoculation. The results also highlighted a set of biological mechanisms triggered after inoculation that provide valuable information regarding the response of Yunnan pine to PWN infection. When compared with maritime pine (Pinus pinaster), the Yunnan pine response was less complex and involved a smaller number of differentially expressed genes, which may be associated with the increased degree of resistance to PWN displayed by Yunnan pine. These results revealed different strategies to cope with PWN infection by these two pine species, which display contrasting degrees of susceptibility, especially in the timely perception of the infection and response magnitude.

Comparative analyses of glutathione system of vacuoles and leucoplasts isolated from the storage parenchyma cells of dormant red beetroots (Beta vulgaris L.)

The role of glutathione in the plant vacuole is still being debated. In the present paper, the redox state of glutathione and the activity of glutathione S-transferase (GST, E 2.5.1.18) in the vacuole compared to those in leucoplast have been studied. Organelles were isolated from dormant red beet (Beta vulgaris L.) taproots. Two generally used approaches have been applied to quantitatively assess the content of glutathione. Initially, levels of glutathione were measured in isolated organelles after labeling with monochlorobimane (MCB) and imaging with the use of confocal laser scanning microscopy. However, there are factors limiting the specificity of this method, because of which the resulting concentrations of vacuolar GSH have been underestimated. Another approach used was HPLC, which allows to simultaneously quantify the reduced glutathione (GSH) and glutathione disulfide (GSSG). The concentration of the total glutathione (GSHt) and GSSG in vacuoles determined with the aid of HPLC-UV was higher in comparison to that in the leucoplasts. The reduction potential (E_h) for the glutathione couple in the vacuoles was more positive (-163 mV), than that in plastids (-282 mV). The relatively rapid increase in fluorescence in the isolated vacuoles and plastids during MCB-labeling has indicated to the contribution of GSTs, since the conjugation of GSH to bimane is catalysed by these enzymes. The GST activity in the vacuoles has been assessed to be quite high compared to that of leucoplasts. The number of isoforms of GSTs also differed markedly in vacuoles and plastids. Collectively, our findings suggest the idea that the glutathione accumulated by central vacuole seems to contribute to the redox processes and to the detoxification, which can take place in this compartment.

CRISPR/Cas9-Mediated SlNPR1 mutagenesis reduces tomato plant drought tolerance

BACKGROUND

NPR1, nonexpressor of pathogenesis-related gene 1, is a master regulator involved in plant defense response to pathogens, and its regulatory mechanism in the defense pathway has been relatively clear. However, information about the function of NPR1 in plant response to abiotic stress is still limited. Tomato is the fourth most economically crop worldwide and also one of the best-characterized model plants employed in genetic studies. Because of the lack of a stable tomato NPR1 (SlNPR1) mutant, little is known about the function of SlNPR1 in tomato response to biotic and abiotic stresses.

RESULTS

Here we isolated SlNPR1 from tomato 'Ailsa Craig' and generated slnpr1 mutants using the CRISPR/Cas9 system. Analysis of the cis-acting elements indicated that SlNPR1 might be involved in tomato plant response to drought stress. Expression pattern analysis showed that SlNPR1 was expressed in all plant tissues, and it was strongly induced by drought stress. Thus, we investigated the function of SlNPR1 in tomato-plant drought tolerance. Results showed that slnpr1 mutants exhibited reduced drought tolerance with increased stomatal aperture, higher electrolytic leakage, malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels, and lower activity levels of antioxidant enzymes, compared to wild type (WT) plants. The reduced drought tolerance of slnpr1 mutants was further reflected by the down-regulated expression of drought related key genes, including SlGST, SlDHN, and SlDREB.

CONCLUSIONS

Collectively, the data suggest that SlNPR1 is involved in regulating tomato plant drought response. These results aid in further understanding the molecular basis underlying SlNPR1 mediation of tomato drought sensitivity.

De Novo Transcriptome Sequencing of the Deep-Sea-Derived Fungus Dichotomomyces cejpii and Analysis of Gliotoxin Biosynthesis Genes

Gliotoxin, produced by fungi, is an epipolythiodioxopiperazine (ETP) toxin with bioactivities such as anti-liver fibrosis, antitumor, antifungus, antivirus, antioxidation, and immunoregulation. Recently, cytotoxic gliotoxins were isolated from a deep-sea-derived fungus, Dichotomomyces cejpii. However, the biosynthetic pathway for gliotoxins in D. cejpii remains unclear. In this study, the transcriptome of D. cejpii was sequenced using an Illumina Hiseq 2000. A total of 19,125 unigenes for D. cejpii were obtained from 9.73 GB of clean reads. Ten genes related to gliotoxin biosynthesis were annotated. The expression levels of gliotoxin-related genes were detected through quantitative real-time polymerase chain reaction (qRT-PCR). The GliG gene, encoding a glutathione S-transferase (DC-GST); GliI, encoding an aminotransferase (DC-AI); and GliO, encoding an aldehyde reductase (DC-AR), were cloned and expressed, purified, and characterized. The results suggested the important roles of DC-GST, DC-AT, and DC-AR in the biosynthesis of gliotoxins. Our study on the genes related to gliotoxin biosynthesis establishes a molecular foundation for the wider application of gliotoxins from D. cejpii in the biomedical industry in the future.

Genome-Wide Identification, Characterization, and Expression Profiling of Glutathione S-Transferase (GST) Family in Pumpkin Reveals Likely Role in Cold-Stress Tolerance

Plant growth and development can be adversely affected by cold stress, limiting productivity. The glutathione S-transferase (GST) family comprises important detoxifying enzymes, which play major roles in biotic and abiotic stress responses by reducing the oxidative damage caused by reactive oxygen species. Pumpkins (Cucurbitamaxima) are widely grown, economically important, and nutritious; however, their yield can be severely affected by cold stress. The identification of putative candidate genes responsible for cold-stress tolerance, including the GST family genes, is therefore vital. For the first time, we identified 32 C. maxima GST (CmaGST) genes using a combination of bioinformatics approaches and characterized them by expression profiling. These CmaGST genes represent seven of the 14 known classes of plant GSTs, with 18 CmaGSTs categorized into the tau class. The CmaGSTs were distributed across 13 of pumpkin's 20 chromosomes, with the highest numbers found on chromosomes 4 and 6. The large number of CmaGST genes resulted from gene duplication; 11 and 5 pairs of CmaGST genes were segmental- and tandem-duplicated, respectively. In addition, all CmaGST genes showed organ-specific expression. The expression of the putative GST genes in pumpkin was examined under cold stress in two lines with contrasting cold tolerance: cold-tolerant CP-1 (C. maxima) and cold-susceptible EP-1 (Cucurbita moschata). Seven genes (CmaGSTU3, CmaGSTU7, CmaGSTU8, CmaGSTU9, CmaGSTU11, CmaGSTU12, and CmaGSTU14) were highly expressed in the cold-tolerant line and are putative candidates for use in breeding cold-tolerant crop varieties. These results increase our understanding of the cold-stress-related functions of the GST family, as well as potentially enhancing pumpkin breeding programs.

Genome-wide association mapping of resistance to a Brazilian isolate of Sclerotinia sclerotiorum in soybean genotypes mostly from Brazil

BACKGROUND

Sclerotinia Stem Rot (SSR), caused by the fungal pathogen Sclerotinia sclerotiorum, is ubiquitous in cooler climates where soybean crops are grown. Breeding for resistance to SSR remains challenging in crops like soybean, where no single gene provides strong resistance, but instead, multiple genes work together to provide partial resistance. In this study, a genome-wide association study (GWAS) was performed to dissect the complex genetic architecture of soybean quantitative resistance to SSR and to provide effective molecular markers that could be used in breeding programs. A collection of 420 soybean genotypes were selected based on either reports of resistance, or from one of three different breeding programs in Brazil, two commercial, one public. Plant genotype sensitivity to SSR was evaluated by the cut stem inoculation method, and lesion lengths were measured at 4 days post inoculation.

RESULTS

Genotyping-by-sequencing was conducted to genotype the 420 soybean lines. The TASSEL 5 GBSv2 pipeline was used to call SNPs under optimized parameters, and with the extra step of trimming adapter sequences. After filtering missing data, heterozygosity, and minor allele frequency, a total of 11,811 SNPs and 275 soybean genotypes were obtained for association analyses. Using a threshold of FDR-adjusted p-values <0.1, the Compressed Mixed Linear Model (CMLM) with Genome Association and Prediction Integrated Tool (GAPIT), and the Fixed and Random Model Circulating Probability Unification (FarmCPU) methods, both approaches identified SNPs with significant association to disease response on chromosomes 1, 11, and 18. The CMLM also found significance on chromosome 19, whereas FarmCPU also identified significance on chromosomes 4, 9, and 16.

CONCLUSIONS

These similar and yet different results show that the computational methods used can impact SNP associations in soybean, a plant with a high degree of linkage disequilibrium, and in SSR resistance, a trait that has a complex genetic basis. A total of 125 genes were located within linkage disequilibrium of the three loci shared between the two models. Their annotations and gene expressions in previous studies of soybean infected with S. sclerotiorum were examined to narrow down the candidates.

Genome-wide identification and expression analysis of glutathione S-transferase gene family in tomato: Gaining an insight to their physiological and stress-specific roles

Glutathione S-transferase (GST) refers to one of the major detoxifying enzymes that plays an important role in different abiotic and biotic stress modulation pathways of plant. The present study aimed to a comprehensive genome-wide functional characterization of GST genes and proteins in tomato (Solanum lycopersicum L.). The whole genome sequence analysis revealed the presence of 90 GST genes in tomato, the largest GST gene family reported till date. Eight segmental duplicated gene pairs might contribute significantly to the expansion of SlGST gene family. Based on phylogenetic analysis of tomato, rice, and Arabidopsis GST proteins, GST family members could be further divided into ten classes. Members of each orthologous class showed high conservancy among themselves. Tau and lambda are the major classes of tomato; while tau and phi are the major classes for rice and Arabidopsis. Chromosomal localization revealed highly uneven distribution of SlGST genes in 13 different chromosomes, where chromosome 9 possessed the highest number of genes. Based on publicly available microarray data, expression analysis of 30 available SlGST genes exhibited a differential pattern in all the analyzed tissues and developmental stages. Moreover, most of the members showed highly induced expression in response to multiple biotic and abiotic stress inducers that could be harmonized with the increase in total GST enzyme activity under several stress conditions. Activity of tomato GST could be enhanced further by using some positive modulators (safeners) that have been predicted through molecular docking of SlGSTU5 and ligands. Moreover, tomato GST proteins are predicted to interact with a lot of other glutathione synthesizing and utilizing enzymes such as glutathione peroxidase, glutathione reductase, glutathione synthetase and γ-glutamyltransferase. This comprehensive genome-wide analysis and expression profiling would provide a rational platform and possibility to explore the versatile role of GST genes in crop engineering.

Disulfide bond formation protects Arabidopsis thaliana glutathione transferase tau 23 from oxidative damage

BACKGROUND

Glutathione transferases play an important role as detoxifying enzymes. In A. thaliana, elevated levels of reactive oxygen species (ROS), provoked during biotic and abiotic stress, influence the activity of GSTU23. The aim of this study is to determine the impact of oxidative stress on the function and structure of GSTU23.

METHODS

The impact of oxidation on the function of GSTU23 was studied using a glutathione transferase biochemical assay and mass spectrometry. With kinetics, circular dichroism and thermodynamics, we compared reduced with oxidized GSTU23. X-ray crystal structures of GSTU23 visualize the impact of oxidation on methionines and cysteines.

RESULTS

In the presence of 100μM H₂O₂, oxidation of the methionine side-chain to a sulfoxide is the prominent post-translational modification, which can be reduced by C. diphtheriae MsrA and MsrB. However, increasing the level to 200μM H₂O₂ results in a reversible intramolecular disulfide between Cys65-Cys110, which is substrate for glutaredoxin. Under these oxidizing conditions, GSTU23 undergoes a structural change and forms a more favourable enzyme-substrate complex to overcome k_cat decrease.

CONCLUSIONS AND SIGNIFICANCE

At lower H₂O₂ levels (100μM), GSTU23 forms methionine sulfoxides. Specifically, oxidation of Met14, located near the catalytic Ser13, could interfere with both GSH binding and catalytic activation. At higher H₂O₂ levels (200μM), the Cys65-Cys110 disulfide bond protects other cysteines and also methionines from overoxidation. This study shows the impact of oxidative stress on GSTU23 regulated by methionine sulfoxide reductases and glutaredoxin, and the mechanisms involved in maintaining its catalytic functionality under oxidizing conditions.

Comprehensive genome-wide analysis of Glutathione S-transferase gene family in potato (Solanum tuberosum L.) and their expression profiling in various anatomical tissues and perturbation conditions

Glutathione S-transferases (GSTs) are ubiquitous enzymes which play versatile functions including cellular detoxification and stress tolerance. In this study, a comprehensive genome-wide identification of GST gene family was carried out in potato (Solanum tuberosum L.). The result demonstrated the presence of at least 90 GST genes in potato which is greater than any other reported species. According to the phylogenetic analyses of Arabidopsis, rice and potato GST members, GSTs could be subdivided into ten different classes and each class is found to be highly conserved. The largest class of potato GST family is tau with 66 members, followed by phi and lambda. The chromosomal localization analysis revealed the highly uneven distribution of StGST genes across the potato genome. Transcript profiling of 55 StGST genes showed the tissue-specific expression for most of the members. Moreover, expression of StGST genes were mainly repressed in response to abiotic stresses, while largely induced in response to biotic and hormonal elicitations. Further analysis of StGST gene's promoter identified the presence of various stress responsive cis-regulatory elements. Moreover, one of the highly stress responsive StGST members, StGSTU46, showed strong affinity towards flurazole with lowest binding energy of -7.6kcal/mol that could be used as antidote to protect crop against herbicides. These findings will facilitate the further functional and evolutionary characterization of GST genes in potato.

Insights into ligand binding to a glutathione S-transferase from mango: Structure, thermodynamics and kinetics

We studied a mango glutathione S-transferase (GST) (Mangifera indica) bound to glutathione (GSH) and S-hexyl glutathione (GSX). This GST Tau class (MiGSTU) had a molecular mass of 25.5 kDa. MiGSTU Michaelis-Menten kinetic constants were determined for their substrates obtaining a Km, Vmax and kcat for CDNB of 0.792 mM, 80.58 mM min-1 and 68.49 s-1 respectively and 0.693 mM, 105.32 mM min-1 and 89.57 s-1, for reduced GSH respectively. MiGSTU had a micromolar affinity towards GSH (5.2 μM) or GSX (7.8 μM). The crystal structure of the MiGSTU in apo or bound to GSH or GSX generated a model that explains the thermodynamic signatures of binding and showed the importance of enthalpic-entropic compensation in ligand binding to Tau-class GST enzymes.

Genome-wide identification and expression analysis of glutathione S-transferase gene family in tomato: Gaining an insight to their physiological and stress-specific roles

Glutathione S-transferase (GST) refers to one of the major detoxifying enzymes that plays an important role in different abiotic and biotic stress modulation pathways of plant. The present study aimed to a comprehensive genome-wide functional characterization of GST genes and proteins in tomato (Solanum lycopersicum L.). The whole genome sequence analysis revealed the presence of 90 GST genes in tomato, the largest GST gene family reported till date. Eight segmental duplicated gene pairs might contribute significantly to the expansion of SlGST gene family. Based on phylogenetic analysis of tomato, rice, and Arabidopsis GST proteins, GST family members could be further divided into ten classes. Members of each orthologous class showed high conservancy among themselves. Tau and lambda are the major classes of tomato; while tau and phi are the major classes for rice and Arabidopsis. Chromosomal localization revealed highly uneven distribution of SlGST genes in 13 different chromosomes, where chromosome 9 possessed the highest number of genes. Based on publicly available microarray data, expression analysis of 30 available SlGST genes exhibited a differential pattern in all the analyzed tissues and developmental stages. Moreover, most of the members showed highly induced expression in response to multiple biotic and abiotic stress inducers that could be harmonized with the increase in total GST enzyme activity under several stress conditions. Activity of tomato GST could be enhanced further by using some positive modulators (safeners) that have been predicted through molecular docking of SlGSTU5 and ligands. Moreover, tomato GST proteins are predicted to interact with a lot of other glutathione synthesizing and utilizing enzymes such as glutathione peroxidase, glutathione reductase, glutathione synthetase and γ-glutamyltransferase. This comprehensive genome-wide analysis and expression profiling would provide a rational platform and possibility to explore the versatile role of GST genes in crop engineering.

Structural evidence for Arabidopsis glutathione transferase AtGSTF2 functioning as a transporter of small organic ligands

Glutathione transferases (GSTs) are involved in many processes in plant biochemistry, with their best characterised role being the detoxification of xenobiotics through their conjugation with glutathione. GSTs have also been implicated in noncatalytic roles, including the binding and transport of small heterocyclic ligands such as indole hormones, phytoalexins and flavonoids. Although evidence for ligand binding and transport has been obtained using gene deletions and ligand binding studies on purified GSTs, there has been no structural evidence for the binding of relevant ligands in noncatalytic sites. Here we provide evidence of noncatalytic ligand‐binding sites in the phi class GST from the model plant Arabidopsis thaliana, AtGSTF2, revealed by X‐ray crystallography. Complexes of the AtGSTF2 dimer were obtained with indole‐3‐aldehyde, camalexin, the flavonoid quercetrin and its non‐rhamnosylated analogue quercetin, at resolutions of 2.00, 2.77, 2.25 and 2.38 Å respectively. Two symmetry‐equivalent‐binding sites (L1) were identified at the periphery of the dimer, and one more (L2) at the dimer interface. In the complexes, indole‐3‐aldehyde and quercetrin were found at both L1 and L2 sites, but camalexin was found only at the L1 sites and quercetin only at the L2 site. Ligand binding at each site appeared to be largely determined through hydrophobic interactions. The crystallographic studies support previous conclusions made on ligand binding in noncatalytic sites by AtGSTF2 based on isothermal calorimetry experiments (Dixon et al. (2011) Biochem J 438, 63–70) and suggest a mode of ligand binding in GSTs commensurate with a possible role in ligand transport.

Genome-wide Association Study Identifies New Loci for Resistance to Sclerotinia Stem Rot in Brassica napus

Sclerotinia stem rot (SSR) caused by the necrotrophic fungus Sclerotinia sclerotiorum is a major disease in rapeseed (Brassica napus) worldwide. Breeding for SSR resistance in B. napus, as in other crops, relies only on germplasms with quantitative resistance genes. A better understanding of the genetic basis for SSR resistance in B. napus thus holds promise for the genetic improvement of disease resistance. In the present study, a genome-wide association study (GWAS) for SSR resistance in B. napus were performed using an association panel of 448 accessions genotyped with the Brassica 60K Infinium® single-nucleotide polymorphism (SNP) array. A total of 26 SNPs corresponding to three loci, DSRC4, DSRC6, and DSRC8 were associated with SSR resistance. Haplotype analysis showed that the three favorable alleles for SSR resistance exhibited cumulative effects. After aligning SSR resistance quantitative trait loci (QTL) identified in the present and previous studies to the B. napus reference genome, one locus (DSRC6) was found to be located within the confidence interval of a QTL identified in previous QTL mapping studies and another two loci (DSRC4 and DSRC8) were considered novel loci for SSR resistance. A total of 39 candidate genes were predicted for the three loci based on the GWAS combining with the differentially expressed genes identified in previous transcriptomics analyses.

Antioxidant defense gene analysis in Brassica oleracea and Trifolium repens exposed to Cd and/or Pb

This study focused on the expression analysis of antioxidant defense genes in Brassica oleracea and in Trifolium repens. Plants were exposed for 3, 10, and 56 days in microcosms to a field-collected suburban soil spiked by low concentrations of cadmium and/or lead. In both species, metal accumulations and expression levels of genes encoding proteins involved and/or related to antioxidant defense systems (glutathione transferases, peroxidases, catalases, metallothioneins) were quantified in leaves in order to better understand the detoxification processes involved following exposure to metals. It appeared that strongest gene expression variations in T. repens were observed when plants are exposed to Cd (metallothionein and ascorbate peroxidase upregulations) whereas strongest variations in B. oleracea were observed in case of Cd/Pb co-exposures (metallothionein, glutathione transferase, and peroxidase upregulations). Results also suggest that there is a benefit to use complementary species in order to better apprehend the biological effects in ecotoxicology.

ROS-Mediated Inhibition of S-nitrosoglutathione Reductase Contributes to the Activation of Anti-oxidative Mechanisms

Nitric oxide (NO) has emerged as a signaling molecule in plants being involved in diverse physiological processes like germination, root growth, stomata closing and response to biotic and abiotic stress. S-nitrosoglutathione (GSNO) as a biological NO donor has a very important function in NO signaling since it can transfer its NO moiety to other proteins (trans-nitrosylation). Such trans-nitrosylation reactions are equilibrium reactions and depend on GSNO level. The breakdown of GSNO and thus the level of S-nitrosylated proteins are regulated by GSNO-reductase (GSNOR). In this way, this enzyme controls S-nitrosothiol levels and regulates NO signaling. Here we report that Arabidopsis thaliana GSNOR activity is reversibly inhibited by H₂O₂in vitro and by paraquat-induced oxidative stress in vivo. Light scattering analyses of reduced and oxidized recombinant GSNOR demonstrated that GSNOR proteins form dimers under both reducing and oxidizing conditions. Moreover, mass spectrometric analyses revealed that H₂O₂-treatment increased the amount of oxidative modifications on Zn²⁺-coordinating Cys47 and Cys177. Inhibition of GSNOR results in enhanced levels of S-nitrosothiols followed by accumulation of glutathione. Moreover, transcript levels of redox-regulated genes and activities of glutathione-dependent enzymes are increased in gsnor-ko plants, which may contribute to the enhanced resistance against oxidative stress. In sum, our results demonstrate that reactive oxygen species (ROS)-dependent inhibition of GSNOR is playing an important role in activation of anti-oxidative mechanisms to damping oxidative damage and imply a direct crosstalk between ROS- and NO-signaling.

Plant glutathione peroxidases: emerging role of the antioxidant enzymes in plant development and stress responses

The plant glutathione peroxidase (GPX) family consists of multiple isoenzymes with distinct subcellular locations which exhibit different tissue-specific expression patterns and environmental stress responses. Contrary to most of their counterparts in animal cells, plant GPXs contain cysteine instead of selenocysteine in their active site and while some of them have both glutathione peroxidase and thioredoxin peroxidase functions, the thioredoxin regenerating system is much more efficient in vitro than the glutathione system. At present, the function of these enzymes in plants is not completely understood. The occurrence of thiol-dependent activities of plant GPX isoenzymes suggests that - besides detoxification of H2O2 and organic hydroperoxides - they may be involved in regulation of the cellular redox homeostasis by maintaining the thiol/disulfide or NADPH/NADP(+) balance. GPXs may represent a link existing between the glutathione- and the thioredoxin-based system. The various thiol buffers, including Trx, can affect a number of redox reactions in the cells most probably via modulation of thiol status. It is still required to identify the in vivo reductant for particular GPX isoenzymes and partners that GPXs interact with specifically. Recent evidence suggests that plant GPXs does not only protect cells from stress induced oxidative damage but they can be implicated in plant growth and development. Following a more general introduction, this study summarizes present knowledge on plant GPXs, highlighting the results on gene expression analysis, regulation and signaling of Arabidopsis thaliana GPXs and also suggests some perspectives for future research.

Genome-wide identification and analysis of drought-responsive genes and microRNAs in tobacco

Drought stress response is a complex trait regulated at transcriptional and post-transcriptional levels in tobacco. Since the 1990s, many studies have shown that miRNAs act in many ways to regulate target expression in plant growth, development and stress response. The recent draft genome sequence of Nicotiana benthamiana has provided a framework for Digital Gene Expression (DGE) and small RNA sequencing to understand patterns of transcription in the context of plant response to environmental stress. We sequenced and analyzed three Digital Gene Expression (DGE) libraries from roots of normal and drought-stressed tobacco plants, and four small RNA populations from roots, stems and leaves of control or drought-treated tobacco plants, respectively. We identified 276 candidate drought responsive genes (DRGs) with sequence similarities to 64 known DRGs from other model plant crops, 82 were transcription factors (TFs) including WRKY, NAC, ERF and bZIP families. Of these tobacco DRGs, 54 differentially expressed DRGs included 21 TFs, which belonged to 4 TF families such as NAC (6), MYB (4), ERF (10), and bZIP (1). Additionally, we confirmed expression of 39 known miRNA families (122 members) and five conserved miRNA families, which showed differential regulation under drought stress. Targets of miRNAs were further surveyed based on a recently published study, of which ten targets were DRGs. An integrated gene regulatory network is proposed for the molecular mechanisms of tobacco root response to drought stress using differentially expressed DRGs, the changed expression profiles of miRNAs and their target transcripts. This network analysis serves as a reference for future studies on tobacco response stresses such as drought, cold and heavy metals.

Oxidative stress and DNA damage induced by imidacloprid in zebrafish (Danio rerio)

Imidacloprid is a neonicotinoid insecticide that can have negative effects on nontarget animals. The present study was conducted to assess the toxicity of various imidacloprid doses (0.3, 1.25, and 5 mg/mL) on zebrafish sampled after 7, 14, 21, and 28 days of exposure. The levels of catalase (CAT), superoxide dismutase (SOD), reactive oxygen species (ROS), glutathione-S-transferase (GST), and malondialdehyde (MDA) and the extent of DNA damage were measured to evaluate the toxicity of imidacloprid on zebrafish. SOD and GST activities were noticeably increased during early exposure but were inhibited toward the end of the exposure period. In addition, the CAT levels decreased to the control level following their elevation during early exposure. High concentrations of imidacloprid (1.25 and 5 mg/L) induced excessive ROS production and markedly increased MDA content on the 21st day of exposure. DNA damage was dose- and time-dependent. In conclusion, the present study showed that imidacloprid can induce oxidative stress and DNA damage in zebrafish.

Engineering monoterpene production in yeast using a synthetic dominant negative geranyl diphosphate synthase

Monoterpenes have an established use in the food and cosmetic industries and have recently also found application as advanced biofuels. Although metabolic engineering efforts have so far achieved significant yields of larger terpenes, monoterpene productivity is lagging behind. Here, we set out to establish a monoterpene-specific production platform in Saccharomyces cerevisiae and identified the sequential reaction mechanism of the yeast farnesyl diphosphate synthase Erg20p to be an important factor limiting monoterpene yield. To overcome this hurdle, we engineered Erg20p into a geranyl diphosphate synthase and achieved a significant increase in monoterpene titers. To further improve production, we converted the engineered geranyl diphosphate synthase into a dominant negative form, so as to decrease the ability of the endogenous Erg20p to function as a farnesyl diphosphate synthase, without entirely abolishing sterol biosynthesis. Fusion of the synthetic dominant negative Erg20p variant with the terpene synthase, combined with yeast strain engineering, further improved monoterpene yields and achieved an overall 340-fold increase in sabinene yield over the starting strain. The design described here can be readily incorporated to any dedicated yeast strain, while the developed plasmid vectors and heterozygous ERG20 deletion yeast strain can also be used as a plug-and-play system for enzyme characterization and monoterpene pathway elucidation.

Glutathione transferase supergene family in tomato: Salt stress-regulated expression of representative genes from distinct GST classes in plants primed with salicylic acid

A family tree of the multifunctional proteins, glutathione transferases (GSTs, EC 2.5.1.18) was created in Solanum lycopersicum based on homology to known Arabidopsis GSTs. The involvement of selected SlGSTs was studied in salt stress response of tomato primed with salicylic acid (SA) or in un-primed plants by real-time qPCR. Selected tau GSTs (SlGSTU23, SlGSTU26) were up-regulated in the leaves, while GSTs from lambda, theta, dehydroascorbate reductase and zeta classes (SlGSTL3, SlGSTT2, SlDHAR5, SlGSTZ2) in the root tissues under salt stress. Priming with SA exhibited a concentration dependency; SA mitigated the salt stress injury and caused characteristic changes in the expression pattern of SlGSTs only at 10(-4) M concentration. SlGSTF4 displayed a significant up-regulation in the leaves, while the abundance of SlGSTL3, SlGSTT2 and SlGSTZ2 transcripts were enhanced in the roots of plants primed with high SA concentration. Unexpectedly, under high salinity the SlDHAR2 expression decreased in primed roots as compared to the salt-stressed plants, however, the up-regulation of SlDHAR5 isoenzyme contributed to the maintenance of DHAR activity in roots primed with high SA. The members of lambda, theta and zeta class GSTs have a specific role in salt stress acclimation of tomato, while SlGSTU26 and SlGSTF4, the enzymes with high glutathione conjugating activity, characterize a successful priming in both roots and leaves. In contrast to low concentration, high SA concentration induced those GSTs in primed roots, which were up-regulated under salt stress. Our data indicate that induction of GSTs provide a flexible tool in maintaining redox homeostasis during unfavourable conditions.

Two pear glutathione S-transferases genes are regulated during fruit development and involved in response to salicylic acid, auxin, and glucose signaling

Two genes encoding putative glutathione S-transferase proteins were isolated from pear (Pyrus pyrifolia) and designated PpGST1 and PpGST2. The deduced PpGST1 and PpGST2 proteins contain conserved Glutathione S-transferase N-terminal domain (GST_N) and Glutathione S-transferase, C-terminal domain (GST_C). Using PCR amplification technique, the genomic clones corresponding to PpGST1 and PpGST2 were isolated and shown to contain two introns and a singal intron respectively with typical GT/AG boundaries defining the splice junctions. Phylogenetic analysis clearly demonstrated that PpGST1 belonged to Phi class of GST superfamilies and had high homology with apple MdGST, while PpGST2 was classified into the Tau class of GST superfamilies. The expression of PpGST1 and PpGST2 genes was developmentally regulated in fruit. Further study demonstrated that PpGST1 and PpGST2 expression was remarkably induced by glucose, salicylic acid (SA) and indole-3-aceticacid (IAA) treatments in pear fruit, and in diseased fruit. These data suggested that PpGST1 and PpGST2 might be involved in response to sugar, SA, and IAA signaling during fruit development of pear.

Importance of bacillithiol in the oxidative stress response of Staphylococcus aureus

In Staphylococcus aureus, the low-molecular-weight thiol called bacillithiol (BSH), together with cognate S-transferases, is believed to be the counterpart to the glutathione system of other organisms. To explore the physiological role of BSH in S. aureus, we constructed mutants with the deletion of bshA (sa1291), which encodes the glycosyltransferase that catalyzes the first step of BSH biosynthesis, and fosB (sa2124), which encodes a BSH-S-transferase that confers fosfomycin resistance, in several S. aureus strains, including clinical isolates. Mutation of fosB or bshA caused a 16- to 60-fold reduction in fosfomycin resistance in these S. aureus strains. High-pressure liquid chromatography analysis, which quantified thiol extracts, revealed some variability in the amounts of BSH present across S. aureus strains. Deletion of fosB led to a decrease in BSH levels. The fosB and bshA mutants of strain COL and a USA300 isolate, upon further characterization, were found to be sensitive to H2O2 and exhibited decreased NADPH levels compared with those in the isogenic parents. Microarray analyses of COL and the isogenic bshA mutant revealed increased expression of genes involved in staphyloxanthin synthesis in the bshA mutant relative to that in COL under thiol stress conditions. However, the bshA mutant of COL demonstrated decreased survival compared to that of the parent in human whole-blood survival assays; likewise, the naturally BSH-deficient strain SH1000 survived less well than its BSH-producing isogenic counterpart. Thus, the survival of S. aureus under oxidative stress is facilitated by BSH, possibly via a FosB-mediated mechanism, independently of its capability to produce staphyloxanthin.

Cryptogein-induced transcriptional reprogramming in tobacco is light dependent

The fungal elicitor cryptogein triggers a light-dependent hypersensitive response in tobacco (Nicotiana tabacum). To assess the effect of light on this nonhost resistance in more detail, we studied various aspects of the response under dark and light conditions using the tobacco-cryptogein experimental system. Here, we show that light drastically alters the plant's transcriptional response to cryptogein, notably by dampening the induction of genes involved in multiple processes, such as ethylene biosynthesis, secondary metabolism, and glutathione turnover. Furthermore, chlorophyll fluorescence measurements demonstrated that quantum yield and functioning of the light-harvesting antennae decreased simultaneously, indicating that photoinhibition underlies the observed decreased photosynthesis and that photooxidative damage might be involved in the establishment of the altered response. Analysis of the isomer distribution of hydroxy fatty acids illustrated that, in the light, lipid peroxidation was predominantly due to the production of singlet oxygen. Differences in (reduced) glutathione concentrations and the rapid development of symptoms in the light when cryptogein was coinfiltrated with glutathione biosynthesis inhibitors suggest that glutathione might become a limiting factor during the cryptogein-induced hypersensitive response in the dark and that this response might be modified by an increased antioxidant availability in the light.

The glutathione transferase of Nicotiana benthamiana NbGSTU4 plays a role in regulating the early replication of Bamboo mosaic virus

Bamboo mosaic virus (BaMV) is a single-stranded positive-sense RNA virus. One of the plant glutathione S-transferase (GST) genes, NbGSTU4, responds as an upregulated gene in Nicotiana benthamiana post BaMV infection. In order to identify the role of NbGSTU4 in BaMV infection, the expression of NbGSTU4 was knocked down using a virus-induced gene silencing technique or was transiently expressed in N. benthamiana in BaMV inoculation. The results show a significant decrease in BaMV RNA accumulation when the expression level of NbGSTU4 is reduced; whereas the viral RNA accumulation increases when NbGSTU4 is transiently expressed. Furthermore, this study identified that the involvement of NbGSTU4 in viral RNA accumulation occurs by its participation in the viral early replication step. The findings show that the NbGSTU4 protein expressed from Escherichia coli can interact with the 3' untranslated region (UTR) of the BaMV RNA in vitro in the presence of glutathione (GSH). The addition of GSH in the in vitro replication assay shows an enhancement of minus-strand but not plus-strand RNA synthesis. The results suggest that the plant GST protein plays a role in binding viral RNA and delivering GSH to the replication complex to create a reduced condition for BaMV minus-strand RNA synthesis.

System-wide hypersensitive response-associated transcriptome and metabolome reprogramming in tomato

The hypersensitive response (HR) is considered to be the hallmark of the resistance response of plants to pathogens. To study HR-associated transcriptome and metabolome reprogramming in tomato (Solanum lycopersicum), we used plants that express both a resistance gene to Cladosporium fulvum and the matching avirulence gene of this pathogen. In these plants, massive reprogramming occurred, and we found that the HR and associated processes are highly energy demanding. Ubiquitin-dependent protein degradation, hydrolysis of sugars, and lipid catabolism are used as alternative sources of amino acids, energy, and carbon skeletons, respectively. We observed strong accumulation of secondary metabolites, such as hydroxycinnamic acid amides. Coregulated expression of WRKY transcription factors and genes known to be involved in the HR, in addition to a strong enrichment of the W-box WRKY-binding motif in the promoter sequences of the coregulated genes, point to WRKYs as the most prominent orchestrators of the HR. Our study has revealed several novel HR-related genes, and reverse genetics tools will allow us to understand the role of each individual component in the HR.

Transcriptomic profiling of the salt-stress response in the wild recretohalophyte Reaumuria trigyna

Background

Reaumuria trigyna is an endangered small shrub endemic to desert regions in Inner Mongolia. This dicotyledonous recretohalophyte has unique morphological characteristics that allow it to tolerate the stress imposed by semi-desert saline soil. However, it is impossible to explore the mechanisms underlying this tolerance without detailed genomic information. Fortunately, newly developed high-throughput sequencing technologies are powerful tools for de novo sequencing to gain such information for this species.

Results

Two sequencing libraries prepared from control (C21) and NaCl-treated samples (T43) were sequenced using short reads sequencing technology (Illumina) to investigate changes in the R. trigyna transcriptome in response to salt stress. Among 65340 unigenes, 35495 (52.27%) were annotated with gene descriptions, conserved domains, gene ontology terms, and metabolic pathways with a cut-off E-value of 10^-5. These included 44 Gene Ontology (GO) terms, 119 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and 25 Clusters of Orthologous Groups families. By comparing the transcriptomes from control and NaCl-treated plants, 5032 genes showed significantly differences in transcript abundance under salt stress (false discovery rate ≤ 0.001 and |log₂Ratio| ≥ 1). These genes were significantly enriched in 29 KEGG pathways and 26 GO terms. The transcription profiles indicated that genes related to ion transport and the reactive oxygen species scavenging system were relevant to the morphological and physiological characteristics of this species. The expression patterns of 30 randomly selected genes resulted from quantitative real-time PCR were basically consistent with their transcript abundance changes identified by RNA-seq.

Conclusions

The present study identified potential genes involved in salt tolerance of R. trigyna. The globally sequenced genes covered a considerable proportion of the R. trigyna transcriptome. These data represent a genetic resource for the discovery of genes related to salt tolerance in this species, and may be a useful source of reference sequences for closely related taxa. These results can also further our understanding of salt tolerance in other halophytes surviving under sodic stress.

Gsta4 Null Mouse Embryonic Fibroblasts Exhibit Enhanced Sensitivity to Oxidants: Role of 4-Hydroxynonenal in Oxidant Toxicity

The alpha class glutathione s-transferase (GST) isozyme GSTA4-4 (EC2.5.1.18) exhibits high catalytic efficiency to-wards 4-hydroxynon-2-enal (4-HNE), a major end product of oxidative stress induced lipid peroxidation. Exposure of cells and tissues to heat, radiation, and chemicals has been shown to induce oxidative stress resulting in elevated concentrations of 4-HNE that can be detrimental to cell survival. Alternatively, at physiological levels 4-HNE acts as a signaling molecule conveying the occurrence of oxidative events initiating the activation of adaptive pathways. To examine the impact of oxidative/electrophilic stress in a model with impaired 4-HNE metabolizing capability, we disrupted the Gsta4 gene that encodes GSTA4-4 in mice. The effect of electrophile and oxidants on embryonic fibroblasts (MEF) isolated from wild type (WT) and Gsta4 null mice were examined. Results indicate that in the absence of GSTA4-4, oxidant-induced toxicity is potentiated and correlates with elevated accumulation of 4-HNE adducts and DNA damage. Treatment of Gsta4 null MEF with 1,1,4-tris(acetyloxy)-2(E)-nonene [4-HNE(Ac)₃], a pro-drug form of 4-HNE, resulted in the activation and phosphorylation of the c-jun-N-terminal kinase (JNK), extracellular-signal-regulated kinases (ERK 1/2) and p38 mitogen activated protein kinases (p38 MAPK) accompanied by enhanced cleavage of caspase-3. Interestingly, when recombinant mammalian or invertebrate GSTs were delivered to Gsta4 null MEF, activation of stress-related kinases in 4-HNE(Ac)₃ treated Gsta4 null MEF were inversely correlated with the catalytic efficiency of delivered GSTs towards 4-HNE. Our data suggest that GSTA4-4 plays a major role in protecting cells from the toxic effects of oxidant chemicals by attenuating the accumulation of 4-HNE.

Purification and partial characterization of glutathione S-transferases from three field populations of Panonychus citri (Acari: Tetranychidae)

Glutathione S-transferases (GSTs) play central roles in phase II detoxification of both xenobiotics (drugs, insecticides, and herbicides) and endogenous compounds in almost all living organisms. In this study, we successfully purified the GSTs from the citrus red mite, Panonychus citri, by affinity chromatography on Glutathione Sepharose 4B and compared the biochemical characterizations of the purified GSTs from three field populations [beibei (BB), wanzhou (WZ), and zhongxian (ZX)]. SDS-PAGE revealed that the molecular weight of GSTs from three populations consisted of two subunits of 27.3 and 26.1 kDa. The specific activity of the purified GSTs from the WZ and ZX populations was increased 1.5- and 3.8-fold, respectively, compared with the BB population. Accordingly, the pyridaben susceptibility of WZ and ZX populations was less compared with BB population. Kinetic analyses showed that the WZ and ZX populations had higher substrate specificity compared with the BB population based on the values of k (cat) and k (cat) /K (m) to both reduced glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB). The in vitro inhibition studies of GSTs indicated that the I (50) values of pyridaben from WZ and ZX populations of P. citri expressed 1.6- and 4.4-fold decreases, respectively, compared to the I (50) value of pyridaben from the BB population. In conclusion, all evidence suggested that the purified GSTs may partially contribute to the susceptibility of acaricide pyridaben in field populations of P. citri.