Tandemly duplicated Safener-induced glutathione S-transferase genes from Triticum tauschii contribute to genome- and organ-specific expression in hexaploid wheat

Transcriptome and metabolome analysis of stress tolerance to aluminium in Vitis quinquangularis

Transcriptional and metabolic regulation of aluminium tolerance of Chinese wild Vitis quinquangularis after Al treatment for 12 h: genes and pathways related to stress resistance are activated to cope with Al stress. The phytotoxicity of aluminium (Al) has become a major issue in inhibiting plant growth in acidic soils. Chinese wild Vitis species have excellent stress resistance. In this study, to explore the mechanism underlying Al tolerance in Chinese wild Vitis quinquangularis, we conducted a transcriptome analysis to understand the changes in gene expression and pathways in V. quinquangularis leaves after Al treatment for 12 h (Al_12 h). Compared with the control (CK) treatment, 2266 upregulated differentially expressed genes (DEGs) and 2943 downregulated DEGs were identified after Al treatment. We analysed the top 60 upregulated DEGs and found that these genes were related mostly to cell wall organization or biogenesis, transition metal ion binding, etc. Another analysis of all the upregulated DEGs showed that genes related to the ABC transport pathway, salicylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA) hormone signalling pathway were expressed. Transcriptome and metabolome analysis revealed that genes and metabolites (phenylalanine, cinnamate and quercetin) related to the phenylalanine metabolic pathway were expressed. In summary, the results provide a new contribution to a better understanding of the metabolic changes that occur in grapes after Al stress as well as to research on improving the resistance of grape cultivars.

Naphthalic anhydride decreases persistence of alachlor and atrazine and elevates tolerance of maize

The present study aimed at alleviating the impacts of alachlor (Ala) or atrazine (Atr) on maize growth by seed-dressing with naphthalic anhydride (NA, 0.4% w/w by seed weight). The dressed and undressed seeds were germinated for 10 days and treated with Ala or Atr at 3.2 or 1.8 kg ha^-1, respectively, then the herbicide residues were determined in shoots one day after treatment. Atr residues were higher than Ala and remained in the same level for the 2^nd day then retracted consistently up to 12 days. Meanwhile, GSH and GST were significantly induced while growth parameters were reduced; the effect of Atr was higher than Ala. Nonetheless, ABA, phenolics and anthocyanins as well as PAL, TAL and CI were increased but IAA was decreased coincidently with enhanced IAA-O and peroxidase. The immediate detection of the herbicide residues could conclude that growth reduction as elucidated from the decreased IAA concomitant with elevating ABA, phenolics and anthocyanin contents and enzyme activities are consequences of the herbicide persistence. The drop of IAA was preceded by the stimulation of IAA-O and peroxidase while the increased phenolics and anthocyanins followed PAL, TAL and CI stimulation confirming the regulatory roles of these enzymes. The application of NA greatly lowered the herbicide residues concurrently with ameliorations in growth parameters, GSH, GST, and maintained the balancing of secondary metabolites and plant growth regulators. Lowering Ala and Atr residues by NA in synchronization with enhanced GSH and GST could conclude that NA encouraged the detoxification of the herbicide. Moreover, the balances of IAA, ABA, phenolics and anthocyanins were mostly maintained in normal levels concomitantly with growth ameliorations suggesting that phytohormones and secondary metabolites are involved in the elevation of maize tolerance to Ala and Atr.

Genome-wide identification of the glutathione transferase superfamily in the model organism Brachypodium distachyon

The detoxification of harmful metabolites can determine the effectiveness of plant stress responses. Scavenging some of these toxic stress by-products through the reduced form of glutathione is catalysed by members of the glutathione transferase (GST) enzyme superfamily. The involvement of these enzymes was studied in the model organism Brachypodium distachyon (L.)P.Beauv. Bd21 and in its derivative Bd21-3, a more drought tolerant line. Osmotic stress treatment resulted in a decrease in the water potential of both Brachypodium genotypes, the difference between the control and treated plant's ψw decreased by the last sampling day in Bd21-3, suggesting some degree of adaptation to the applied osmotic stress. Increased GST activity revealed a severe defence reaction against the harmful imbalance of the redox environment. Screening for the gene sequences led to the identification of 91 full-length or partial GST sequences. Although purple false brome has a relatively small genome, the number of identified GST genes was almost as high as the number predicted in wheat. The estimation of GST expression showed stress-induced differences: higher expression levels or the fast induction of BdGSTF8, BdGSTU35 and BdGSTU42 gene products presumably indicate a strong detoxification under osmotic stress.

Transcriptome Profiling and Genome-Wide Association Studies Reveal GSTs and Other Defense Genes Involved in Multiple Signaling Pathways Induced by Herbicide Safener in Grain Sorghum

Herbicide safeners protect cereal crops from herbicide injury by inducing genes and proteins involved in detoxification reactions, such as glutathione S-transferases (GSTs) and cytochrome P450s (P450s). Only a few studies have characterized gene or protein expression profiles for investigating plant responses to safener treatment in cereal crops, and most transcriptome analyses in response to safener treatments have been conducted in dicot model species that are not protected by safener from herbicide injury. In this study, three different approaches were utilized in grain sorghum (Sorghum bicolor (L.) Moench) to investigate mechanisms involved in safener-regulated signaling pathways. An initial transcriptome analysis was performed to examine global gene expression in etiolated shoot tissues of hybrid grain sorghum following treatment with the sorghum safener, fluxofenim. Most upregulated transcripts encoded detoxification enzymes, including P450s, GSTs, and UDP-dependent glucosyltransferases (UGTs). Interestingly, several of these upregulated transcripts are similar to genes involved with the biosynthesis and recycling/catabolism of dhurrin, an important chemical defense compound, in these seedling tissues. Secondly, 761 diverse sorghum inbred lines were evaluated in a genome-wide association study (GWAS) to determine key molecular-genetic factors governing safener-mediated signaling mechanisms and/or herbicide detoxification. GWAS revealed a significant single nucleotide polymorphism (SNP) associated with safener-induced response on chromosome 9, located within a phi-class SbGST gene and about 15-kb from a different phi-class SbGST. Lastly, the expression of these two candidate SbGSTs was quantified in etiolated shoot tissues of sorghum inbred BTx623 in response to fluxofenim treatment. SbGSTF1 and SbGSTF2 transcripts increased within 12-hr after fluxofenim treatment but the level of safener-induced expression differed between the two genes. In addition to identifying specific GSTs potentially involved in the safener-mediated detoxification pathway, this research elucidates a new direction for studying both constitutive and inducible mechanisms for chemical defense in cereal crop seedlings.

Plant Glutathione Transferases and Light

The activity and expression of glutathione transferases (GSTs) depend on several less-known endogenous and well-described exogenous factors, such as the developmental stage, presence, and intensity of different stressors, as well as on the absence or presence and quality of light, which to date have received less attention. In this review, we focus on discussing the role of circadian rhythm, light quality, and intensity in the regulation of plant GSTs. Recent studies demonstrate that diurnal regulation can be recognized in GST activity and gene expression in several plant species. In addition, the content of one of their co-substrates, reduced glutathione (GSH), also shows diurnal changes. Darkness, low light or shade mostly reduces GST activity, while high or excess light significantly elevates both the activity and expression of GSTs and GSH levels. Besides the light-regulated induction and dark inactivation of GSTs, these enzymes can also participate in the signal transduction of visible and UV light. For example, red light may alleviate the harmful effects of pathogens and abiotic stressors by increasing GST activity and expression, as well as GSH content in leaves of different plant species. Based on this knowledge, further research on plants (crops and weeds) or organs and temporal regulation of GST activity and gene expression is necessary for understanding the complex regulation of plant GSTs under various light conditions in order to increase the yield and stress tolerance of plants in the changing environment.

Rhizoremediation prospects of Polyaromatic hydrocarbon degrading rhizobacteria, that facilitate glutathione and glutathione-S-transferase mediated stress response, and enhance growth of rice plants in pyrene contaminated soil

Rhizoremediation is a strategy where pollutant degrading bacteria are augmented through plant roots using plant-microbe interaction. Therefore, for effective rhizoremediation of pyrene contaminated soil, bacterial strains were experimented for amelioration of stress response in host plant along with biodegradation ability. A total of 28 bacteria, having ability to degrade polycyclic aromatic hydrocarbons were isolated from contaminated sites and checked for their plant growth promoting attributes, such as indole acetic acid (IAA) production, phosphate solubilization, atmospheric nitrogen fixation and siderophore release. Among these isolates, Klebsiella pneumoniae AWD5 was found to degrade 60% of pyrene. While other isolates, i.e. Alcaligenes faecalis BDB4, Pseudomonas fragi DBC, Pseudomonas aeruginosa PDB1, Acinetobactor sp. PDB4 degraded 48.5%, 50.29%, 31.3% and 36% of pyrene, respectively, after 6 days of incubation. K. pneumoniae AWD5 produced 94.2 μg/ml IAA and 3.1 mM/mg/h unit of ACC deaminase, which was best among eighteen indole acetic acid producers and five of the 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing isolates. P. aeruginosa PDB1 resulted in highest phosphate solubilization activity of 875.26 ng/ml of soluble phosphate among seven phosphate solubilizers. The isolates AWD5 and PDB1 both have shown a good amount of siderophore release (56.3% and 84.3% unit). There was 19.1% increase in shoot length of rice seedlings treated with PDB1 in presence of pyrene. Similarly, 26.5% increase in the root length of AWD5 treated rice was recorded in pyrene contaminated soil. Bacterial inoculation also induced and improved the stress response in host plant, in presence of pyrene, as suggested by the superoxide dismutase, glutathione and glutathione-S-transferase activities in rice.

Quantitative Proteomics Analysis of Lettuce (Lactuca sativa L.) Reveals Molecular Basis-Associated Auxin and Photosynthesis with Bolting Induced by High Temperature

Bolting is a key process in the growth and development of lettuce (Lactuca sativa L.). A high temperature can induce early bolting, which decreases both the quality and production of lettuce. However, knowledge of underlying lettuce bolting is still lacking. To better understand the molecular basis of bolting, a comparative proteomics analysis was conducted on lettuce stems, during the bolting period induced by a high temperature (33 °C) and a control temperature (20 °C) using iTRAQ-based proteomics, phenotypic measures, and biological verifications using qRT-PCR and Western blot. The high temperature induced lettuce bolting, while the control temperature did not. Of the 5454 identified proteins, 619 proteins presented differential abundance induced by high-temperature relative to the control group, of which 345 had an increased abundance and 274 had a decreased abundance. Proteins with an abundance level change were mainly enriched in pathways associated with photosynthesis and tryptophan metabolism involved in auxin (IAA) biosynthesis. Moreover, among the proteins with differential abundance, proteins associated with photosynthesis and tryptophan metabolism were increased. These findings indicate that a high temperature enhances the function of photosynthesis and IAA biosynthesis to promote the process of bolting, which is in line with the physiology and transcription level of IAA metabolism. Our data provide a first comprehensive dataset for gaining novel understanding of the molecular basis underlying lettuce bolting induced by high temperature. It is potentially important for further functional analysis and genetic manipulation for molecular breeding to breed new cultivars of lettuce to restrain early bolting, which is vital for improving vegetable quality.

Transgenic Arabidopsis Plants Expressing Grape Glutathione S-Transferase Gene (VvGSTF13) Show Enhanced Tolerance to Abiotic Stress

Although glutathione S-transferase (GST, EC 2.5.1.18) is thought to play important roles in abiotic stress, limited information is available regarding the function of its gene in grapes. In this study, a GST gene from grape, VvGSTF13, was cloned and functionally characterized. Transgenic Arabidopsis plants containing this gene were normal in terms of growth and maturity compared with control plants but had enhanced resistance to salt, drought, and methyl viologen stress. The increased tolerance of the transgenic plants correlated with changes in activities of antioxidative enzymes. Our results indicate that the gene from grape plays a positive role in improving tolerance to salinity, drought, and methyl viologen stresses in Arabidopsis.

Testing a chemical series inspired by plant stress oxylipin signalling agents for herbicide safening activity

BACKGROUND

Herbicide safening in cereals is linked to a rapid xenobiotic response (XR), involving the induction of glutathione transferases (GSTs). The XR is also invoked by oxidized fatty acids (oxylipins) released during plant stress, suggesting a link between these signalling agents and safening. To examine this relationship, a series of compounds modelled on the oxylipins 12-oxophytodienoic acid and phytoprostane 1, varying in lipophilicity and electrophilicity, were synthesized. Compounds were then tested for their ability to invoke the XR in Arabidopsis and protect rice seedlings exposed to the herbicide pretilachlor, as compared with the safener fenclorim.

RESULTS

Of the 21 compounds tested, three invoked the rapid GST induction associated with fenclorim. All compounds possessed two electrophilic carbon centres and a lipophilic group characteristic of both oxylipins and fenclorim. Minor effects observed in protecting rice seedlings from herbicide damage positively correlated with the XR, but did not provide functional safening.

CONCLUSION

The design of safeners based on the characteristics of oxylipins proved successful in deriving compounds that invoke a rapid XR in Arabidopsis but not in providing classical safening in a cereal. The results further support a link between safener and oxylipin signalling, but also highlight species-dependent differences in the responses to these compounds. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Glutathione S-Transferases: Role in Combating Abiotic Stresses Including Arsenic Detoxification in Plants

Arsenic (As), naturally occurring metalloid and a potential hazardous material, is found in low concentrations in the environment and emerges from natural sources and anthropogenic activities. The presence of As in ground water, which is used for irrigation, is a matter of great concern since it affects crop productivity and contaminates food chain. In plants, As alters various metabolic pathways in cells including the interaction of substrates/enzymes with the sulfhydryl groups of proteins and the replacement of phosphate in ATP for energy. In addition, As stimulates the generation of free radicals and reactive oxygen species (ROS), resulting in oxidative stress. Glutathione S-transferases (GSTs) quench reactive molecules with the addition of glutathione (GSH) and protect the cell from oxidative damage. GSTs are a multigene family of isozymes, known to catalyze the conjugation of GSH to miscellany of electrophilic and hydrophobic substrates. GSTs have been reported to be associated with plant developmental processes and are responsive to multitude of stressors. In past, several studies suggested involvement of plant GST gene family in As response due to the requirement of sulfur and GSH in the detoxification of this toxic metalloid. This review provides updated information about the role of GSTs in abiotic and biotic stresses with an emphasis on As uptake, metabolism, and detoxification in plants. Further, the genetic manipulations that helped in enhancing the understanding of the function of GSTs in abiotic stress response and heavy metal detoxification has been reviewed.

Biochemical characterization of metabolism-based atrazine resistance in Amaranthus tuberculatus and identification of an expressed GST associated with resistance

Rapid detoxification of atrazine in naturally tolerant crops such as maize (Zea mays) and grain sorghum (Sorghum bicolor) results from glutathione S-transferase (GST) activity. In previous research, two atrazine-resistant waterhemp (Amaranthus tuberculatus) populations from Illinois, U.S.A. (designated ACR and MCR), displayed rapid formation of atrazine-glutathione (GSH) conjugates, implicating elevated rates of metabolism as the resistance mechanism. Our main objective was to utilize protein purification combined with qualitative proteomics to investigate the hypothesis that enhanced atrazine detoxification, catalysed by distinct GSTs, confers resistance in ACR and MCR. Additionally, candidate AtuGST expression was analysed in an F₂ population segregating for atrazine resistance. ACR and MCR showed higher specific activities towards atrazine in partially purified ammonium sulphate and GSH affinity-purified fractions compared to an atrazine-sensitive population (WCS). One-dimensional electrophoresis of these fractions displayed an approximate 26-kDa band, typical of GST subunits. Several phi- and tau-class GSTs were identified by LC-MS/MS from each population, based on peptide similarity with GSTs from Arabidopsis. Elevated constitutive expression of one phi-class GST, named AtuGSTF2, correlated strongly with atrazine resistance in ACR and MCR and segregating F₂ population. These results indicate that AtuGSTF2 may be linked to a metabolic mechanism that confers atrazine resistance in ACR and MCR.

Signal transduction during wheat grain development

This review examines the signaling pathways from the developmental and environmental point of view and the interactions among external conditions, hormonal regulations, and sugarsensing in wheat. Grain development is the key phase of reproductive growth that is closely associated with vegetative organ senescence, initiation of grain filling, pre-stored assimilates remobilization, and maturation. Senescence is characterized by loss of chlorophyll and the degradation of proteins, nucleic acids, lipids as well as nutrient exports to the sink. The initiation and progression of vegetative organ senescence are under the control of an array of environmental signals (such as biotic and abiotic stresses, darkness, and nutrient availability) and endogenous factors (including aging, multiple hormones, and sugar availability). This review will discuss the major breakthroughs in signal transduction for the wheat (Triticum aestivum) grain development achieved in the past several years, with focuses on the regulation of senescence, reserves remobilization and biosynthesis of main components of the grain. Different mechanisms of diverse signals in controlling different phrases of wheat grain development, and cross talks between different signaling pathways will also be discussed. For perspectives, key signaling networks for grain development remain to be elucidated, including cross talks and the interactions between various environmental factors and internal signals.

Over-expression of a rice tau class glutathione s-transferase gene improves tolerance to salinity and oxidative stresses in Arabidopsis

Glutathione S-transferases (GSTs) are multifunctional proteins encoded by large gene family in plants, which play important role in cellular detoxification of several endobiotic and xenobiotic compounds. Previously, we suggested the diverse roles of rice GST gene family members in plant development and various stress responses based on their differential expression. In this study, we report the functional characterization of a rice tau class GST gene, OsGSTU4. OsGSTU4 fusion protein was found to be localized in nucleus and cytoplasm. The over-expression of OsGSTU4 in E. coli resulted in better growth and higher GST activity under various stress conditions. Further, we raised over-expression transgenic Arabidopsis plants to reveal its in planta function. These transgenic lines showed reduced sensitivity towards plant hormones, auxin and abscisic acid. Various analyses revealed improved tolerance in transgenic Arabidopsis plants towards salinity and oxidative stresses, which may be attributed to the lower accumulation of reactive oxygen species and enhanced GST activity. In addition, microarray analysis revealed up-regulation of several genes involved in stress responses and cellular detoxification processes in the transgenic plants as compared to wild-type. These results suggest that OsGSTU4 can be used as a good candidate for the generation of stress-tolerant crop plants.

GSTF1 Gene Expression Analysis in Cultivated Wheat Plants under Salinity and ABA Treatments

Most plants encounter stress such as drought and salinity that adversely affect growth, development and crop productivity. The expression of the gene glutathione-s-transferases (GST) extends throughout various protective mechanisms in plants and allows them to adapt to unfavorable environmental conditions. GSTF1 (the first phi GSTFs class) gene expression patterns in the wheat cultivars Mahuti and Alamut were studied under salt and ABA treatments using a qRT-PCR technique. Results showed that gene expression patterns were significantly different in these two cultivars. Data showed that in Mahuti, there was an increase of transcript accumulation under salt and ABA treatments at 3h, 10h and 72h respectively. In Alamut, however, the pattern of transcript accumulation was different; the maximum was at 3h. In contrast, there were no significant differences observed between the cultivars for GSTF1 gene expression profiles at three levels of NaCl concentration (50, 100, and 200 mM) or in ABA (Abscisic Acid) treatment. It is likely that difference of gene expression patterns between the cultivars (Mahuti as a salt tolerant cultivar and Alamut as a salt sensitive cultivar) is due to distinct signaling pathways which activate GSTF1 expression. Lack of a significant difference between the GSTF1 gene expression profile under salt and ABA treatments suggests that the GSTF1 gene is not induced by stress stimuli. Of course it is possible that other levels of NaCl and ABA treatments cause a change in the GSTF1 gene.

Isohydric and anisohydric strategies of wheat genotypes under osmotic stress: biosynthesis and function of ABA in stress responses

Changes in water potential (ψw), stomatal conductance, abscisic acid (ABA) accumulation, expression of the major genes involved in ABA biosynthesis, activities of abscisic aldehyde oxidase (AO, EC 1.2.3.1) and antioxidant enzymes were studied in two wheat cultivars with contrasting acclimation strategies subjected to medium strength osmotic stress (-0.976MPa) induced by polyethylene glycol (PEG 6000). Because the biosynthetic pathway of ABA involves multiple gene products, the aim of this study was to unravel how these genes are regulated in isohydric and anisohydric wheat genotypes. In the root tissues of the isohydric cultivar, Triticum aestivum cv. Kobomugi, osmotic stress increased the transcript levels of 9-cis-epoxycarotenoid dioxygenase (NCED) gene, controlling the rate limiting step of ABA biosynthesis. Moreover, this cultivar exhibited a higher basal activity and a higher induction of aldehyde oxidase isoenzymes (AAO2-AAO3), responsible for converting ABAldehyde to ABA. It was found that the fast activation of the ABA biosynthesis in the roots generated an enhanced ABA pool in the shoot, which brought about a faster closure of the stomata upon increasing osmotic stress and, as a result, the plants could maintain ψw in the tissues close to the control level. In contrast, the anisohydric genotype, cv. GK Öthalom, exhibited a moderate induction of ABA biosynthesis in the roots, leading to the maintenance but no increase in the concentration of ABA on the basis of tissue water content in the leaves. Due to the slower response of their stomata to water deficit, the tissues of cv. GK Öthalom have to acclimate to much more negative water potentials during increasing osmotic stress. A decreased activity of superoxide dismutase (SOD) was found in the leaves and roots of both cultivars exposed to osmotic stress, but in the roots elevated activities of catalase (CAT), peroxidase (POX), glutathione reductase (GR) and glutathione transferase (GST) were detected in the isohydric cultivar, suggesting that this genotype was more successful in the elimination of reactive oxygen species caused by the stress conditions.

Proteomic analysis of the low mutation rate of diploid male gametes induced by colchicine in Ginkgo biloba L

Colchicine treatment of G. biloba microsporocytes results in a low mutation rate in the diploid (2n) male gamete. The mutation rate is significantly lower as compared to other tree species and impedes the breeding of new economic varieties. Proteomic analysis was done to identify the proteins that influence the process of 2n gamete formation in G. biloba. The microsporangia of G. biloba were treated with colchicine solution for 48 h and the proteins were analyzed using 2-D gel electrophoresis and compared to protein profiles of untreated microsporangia. A total of 66 proteins showed difference in expression levels. Twenty-seven of these proteins were identified by mass spectrometry. Among the 27 proteins, 14 were found to be up-regulated and the rest 13 were down-regulated. The identified proteins belonged to five different functional classes: ATP generation, transport and carbohydrate metabolism; protein metabolism; ROS scavenging and detoxifying enzymes; cell wall remodeling and metabolism; transcription, cell cycle and signal transduction. The identification of these differentially expressed proteins and their function could help in analysing the mechanism of lower mutation rate of diploid male gamete when the microsporangium of G. biloba was induced by colchicine.

Analysis of expression profiles of selected genes associated with the regenerative property and the receptivity to gene transfer during somatic embryogenesis in Triticum aestivum L

The physiological, biochemical and molecular mechanisms regulating the initiation of a regenerative pathway remain partially unknown. Efforts to identify the biological features that confer transformation ability, or the tendency of some cells to induce transgene silencing, would help to improve plant genetic engineering. The objective of our study was to monitor the evolution of plant cell competencies in relation to both in vitro tissue culture regeneration and the genetic transformation properties. We used a simple wheat regeneration procedure as an experimental model for studying the regenerative capacity of plant cells and their receptivity to direct gene transfer over the successive steps of the regenerative pathway. Target gene profiling studies and biochemical assays were conducted to follow some of the mechanisms triggered during the somatic-to-embryogenic transition (i.e. dedifferentiation, cell division activation, redifferentiation) and affecting the accessibility of plant cells to receive and stably express the exogenous DNA introduced by bombardment. Our results seem to indicate that the control of cell-cycle (S-phase) and host defense strategies can be crucial determinants of genetic transformation efficiency. The results from studies conducted at macro-, micro- and molecular scales are then integrated into a holistic approach that addresses the question of tissue culture and transgenesis competencies more broadly. Through this multilevel analysis we try to establish functional links between both regenerative capacity and transformation receptiveness, and thereby to provide a more global and integrated vision of both processes, at the core of defense/adaptive mechanisms and survival, between undifferentiated cell proliferation and organization.

Molecular cloning and expression of five glutathione S-transferase (GST) genes from Banana (Musa acuminata L. AAA group, cv. Cavendish)

Three tau class MaGSTs responded to abiotic stress, MaGSTF1 and MaGSTL1 responded to signaling molecules, they may play an important role in the growth of banana plantlet. Glutathione S-transferases (GST) are multifunctional detoxification enzymes that participate in a variety of cellular processes, including stress responses. In this study, we report the molecular characteristics of five GST genes (MaGSTU1, MaGSTU2, MaGSTU3, MaGSTF1 and MaGSTL1) cloned from banana (Musa acuminate L. AAA group, cv. Cavendish) using a RACE-PCR-based strategy. The predicted molecular masses of these GSTs range from 23.4 to 27.7 kDa and their pIs are acidic. At the amino acid level, they share high sequence similarity with GSTs in the banana DH-Pahang (AA group) genome. Phylogenetic analysis showed that the deduced amino acid sequences of MaGSTs also have high similarity to GSTs of other plant species. Expression analysis by semi-quantitative RT-PCR revealed that these genes are differentially expressed in various tissues. In addition, their expression is regulated by various stress conditions, including exposure to signaling molecules, cold, salinity, drought and Fusarium oxysporum f specialis(f. Sp) cubense Tropical Race 4 (Foc TR4) infection. The expression of the tau class MaGSTs (MaGSTU1, MaGSTU2 and MaGSTU3) mainly responded to cold, salinity and drought while MaGSTF1 and MaGSTL1 expressions were upregulated by signaling molecules. Our findings suggest that MaGSTs play a key role in both development and abiotic stress responses.

Protective responses induced by herbicide safeners in wheat

Safeners are agrochemicals which enhance tolerance to herbicides in cereals including wheat (Triticum aestivum L.) by elevating the expression of xenobiotic detoxifying enzymes, such as glutathione transferases (GSTs). When wheat plants were spray-treated with three safener chemistries, namely cloquintocet mexyl, mefenpyr diethyl and fenchlorazole ethyl, an apparently identical subset of GSTs derived from the tau, phi and lambda classes accumulated in the foliage. Treatment with the closely related mefenpyr diethyl and fenchlorazole ethyl enhanced seedling shoot growth, but this effect was not determined with the chemically unrelated cloquintocet mexyl. Focussing on cloquintocet mexyl, treatments were found to only give a transient induction of GSTs, with the period of elevation being dose dependent. Examining the role of safener metabolism in controlling these responses, it was determined that cloquintocet mexyl was rapidly hydrolysed to the respective carboxylic acid. Studies with cloquintocet showed that the acid was equally effective at inducing GSTs as the ester and appeared to be the active safener. Studies on the tissue induction of GSTs showed that whilst phi and tau class enzymes were induced in all tissues, the induction of the lambda enzymes was restricted to the meristems. To test the potential protective effects of cloquintocet mexyl in wheat on chemicals other than herbicides, seeds were pre-soaked in safeners prior to sowing on soil containing oil and a range of heavy metals. Whilst untreated seeds were unable to germinate on the contaminated soil, safener treatments resulted in seedlings briefly growing before succumbing to the pollutants. Our results show that safeners exert a range of protective and growth promoting activities in wheat that extend beyond enhancing tolerance to herbicides.

The impact of photoperiod insensitive Ppd-1a mutations on the photoperiod pathway across the three genomes of hexaploid wheat (Triticum aestivum)

Flowering time is a trait that has been extensively altered during wheat domestication, enabling it to be highly productive in diverse environments and providing a rich source of variation for studying adaptation mechanisms. Hexaploid wheat is ancestrally a long-day plant, but many environments require varieties with photoperiod insensitivity (PI) that can flower in short days. PI results from mutations in the Ppd-1 gene on the A, B or D genomes, with individual mutations conferring different degrees of earliness. The basis of this is poorly understood. Using a common genetic background, the effects of A, B and D genome PI mutations on genes of the circadian clock and photoperiod pathway were studied using genome-specific expression assays. Ppd-1 PI mutations did not affect the clock or immediate clock outputs, but affected TaCO1 and TaFT1, with a reduction in TaCO1 expression as TaFT1 expression increased. Therefore, although Ppd-1 is related to PRR genes of the Arabidopsis circadian clock, Ppd-1 affects flowering by an alternative route, most likely by upregulating TaFT1 with a feedback effect that reduces TaCO1 expression. Individual genes in the circadian clock and photoperiod pathway were predominantly expressed from one genome, and there was no genome specificity in Ppd-1 action. Lines combining PI mutations on two or three genomes had enhanced earliness with higher levels, but not earlier induction, of TaFT1, showing that there is a direct quantitative relationship between Ppd-1 mutations, TaFT1 expression and flowering.

Isolation and characterization of a rice glutathione S-transferase gene promoter regulated by herbicides and hormones

OsGSTL2, encoding glutathione S-transferase, is a lambda class gene on chromosome 3 of rice (Oryza sativa L.). RNA blot analysis and semi-quantitative RT-PCR assays demonstrated that the transcription of OsGSTL2 in rice roots treated with chlorsulfuron increased significantly. To further understand OsGSTL2 promoter activity, a DNA fragment (GST2171) of 2,171 bp upstream of the OsGSTL2 coding region was isolated. In silico sequence analysis revealed that this fragment contains stress-regulated regulatory elements, hormone-responsive elements and three transposable elements. To define the core promoter sequence, a series of 5' truncation derivatives of GST2171 were fused to uidA gene. The chimeric genes were introduced into rice plants via Agrobacterium-mediated transformation. The expression of the GST2171::GUS transgene varied considerably. GUS staining indicated that the uidA gene is expressed in young seedlings, older leaves, flowering glumes and seeds, but not in older roots. Quantitative fluorescence assays revealed that the expression of the uidA gene is strong in young seedlings and decreases gradually over a period of 25 days. To our surprise, among the 5' truncation derivatives, the shortest promoter GST525 showed the highest GUS expression, and the second shortest promoter GST962 showed the lowest GUS expression. The uidA gene expression in the roots of transgenic rice seedlings is upregulated by chlorsulfuron, glyphosate, salicylic acid (SA) and naphthalene acetic acid (NAA). The possible roles of the repetitive elements on the OsGSTL2 promoter were discussed in terms of transcription repression and promoter induction by herbicides and hormones.

Glutathione transferase activity and expression patterns during grain filling in flag leaves of wheat genotypes differing in drought tolerance: Response to water deficit

Total glutathione S-transferase (GST, EC 2.5.1.18) and glutathione peroxidase (GPOX) activity were measured spectrophotometrically in Triticum aestivum cv. MV Emese and cv. Plainsman (drought tolerant) and cv. GK Elet and Cappelle Desprez (drought-sensitive) flag leaves under control and drought stress conditions during the grain-filling period, in order to reveal possible roles of different GST classes in the senescence of flag leaves. Six wheat GSTs, members of 3 GST classes, were selected and their regulation by drought and senescence was investigated. High GPOX activity (EC 1.11.1.9) was observed in well-watered controls of the drought-tolerant Plainsman cultivar. At the same time, TaGSTU1B and TaGSTF6 sequences, investigated by real-time PCR, showed high-expression levels that increased with time, indicating that the gene products of these genes may play important roles in monocarpic senescence of wheat. Expression of these genes was also induced by drought stress in all of the four investigated cultivars, but extremely high transcript amounts were detected in cv. Plainsman. Our data indicate genotypic variations of wheat GSTs. Expression levels and early induction of two senescence-associated GSTs under drought during grain filling in flag leaves correlated with high yield stability.

Biochemical and physiological characterization of a tau class glutathione transferase from rice (Oryza sativa)

The classical phase II detoxification glutathione transferases (GSTs) are key metabolic enzymes that catalyze the conjugation of glutathione to various electrophilic compounds. A tau class GST gene (OsGSTU17) was cloned from rice, which encodes a protein of 223 amino acid residues with a calculated molecular mass of 25.18 kDa. The recombinant OsGSTU17 formed a homodimer protein and showed GSH-conjugating activity with various xenobiotics. Kinetic analysis with respect to NBD-Cl as substrate revealed a K(m) of 0.324 mM and V(max) of 0.219 micromol/min per mg of protein. The enzyme had a maximum activity at pH 7.5, and a high thermal stability with 81% of its initial activity at 55 degrees C for 15 min. Site-directed mutagenesis revealed that Ser15 in the N-terminal domain is a critical catalytic residue, responsible for stabilisation of the thiolate anion of enzyme-bound glutathione. OsGSTU17 mRNA was expressed in different tissues of rice, both above and below ground. The relative transcript levels of OsGSTU17 mRNA varied significantly among the tissues in response to CDNB, hydrogen peroxide and atrazine treatments, indicating the gene has diverse regulation mechanisms in response to abiotic stresses.

Gene duplication, transfer, and evolution in the chloroplast genome

In addition to the nuclear genome, organisms have organelle genomes. Most of the DNA present in eukaryotic organisms is located in the cell nucleus. Chloroplasts have independent genomes which are inherited from the mother. Duplicated genes are common in the genomes of all organisms. It is believed that gene duplication is the most important step for the origin of genetic variation, leading to the creation of new genes and new gene functions. Despite the fact that extensive gene duplications are rare among the chloroplast genome, gene duplication in the chloroplast genome is an essential source of new genetic functions and a mechanism of neo-evolution. The events of gene transfer between the chloroplast genome and nuclear genome via duplication and subsequent recombination are important processes in evolution. The duplicated gene or genome in the nucleus has been the subject of several recent reviews. In this review, we will briefly summarize gene duplication and evolution in the chloroplast genome. Also, we will provide an overview of gene transfer events between chloroplast and nuclear genomes.

Nonadditive expression of homoeologous genes is established upon polyploidization in hexaploid wheat

Effects of polyploidy in allohexaploid wheat (Triticum aestivum L.) have primarily been ascribed to increases in coding sequence variation and potential to acquire new gene functions through mutation of redundant loci. However, regulatory variation that arises through new promoter and transcription factor combinations or epigenetic events may also contribute to the effects of polyploidization. In this study, gene expression was characterized in a synthetic T. aestivum line and the T. turgidum and Aegilops tauschii parents to establish a timeline for such regulatory changes and estimate the frequency of nonadditive expression of homoeologous transcripts in newly formed T. aestivum. Large-scale analysis of nonadditive gene expression was assayed by microarray expression experiments, where synthetic T. aestivum gene expression was compared to additive model values (mid-parent) calculated from parental T. turgidum and Ae. tauschii expression levels. Approximately 16% of genes were estimated to display nonadditive expression in synthetic T. aestivum. A certain fraction of the genes (2.9%) showed overdominance or underdominance. cDNA-single strand conformation polymorphism analysis was applied to measure expression of homoeologous transcripts and further verify microarray data. The results demonstrate that allopolyploidization, per se, results in rapid initiation of differential expression of homoeologous loci and nonadditive gene expression in T. aestivum.

Safeners coordinately induce the expression of multiple proteins and MRP transcripts involved in herbicide metabolism and detoxification inTriticum tauschii seedling tissues

Chemicals called safeners protect cereal crops from herbicide toxicity. Proteomic methods (2-D PAGE and LC-MS/MS) were utilized to identify safener- and/or herbicide-regulated proteins in three tissues (root, leaf, and coleoptile) of Triticum tauschii seedlings to better understand a safener's mechanism of action. Growth experiments showed that the safener cloquintocet-mexyl protected seedlings from injury by the herbicide dimethenamid. In total, 29 safener-induced and 10 herbicide-regulated proteins were identified by LC-MS/MS. These proteins were classified into two major categories based on their expression patterns, and were further classified into several functional groups. Surprisingly, mutually exclusive sets of proteins were identified following herbicide or safener treatment, suggesting that different signaling pathways may be recruited. Safener-responsive proteins, mostly involved in xenobiotic detoxification, also included several new proteins that had not been previously identified as safener-responsive, whereas herbicide-regulated proteins belonged to several classes involved in general stress responses. Quantitative RT-PCR revealed that multidrug resistance-associated protein (MRP) transcripts were highly induced by safeners and two MRP genes were differentially expressed. Our results indicate that safeners protect T. tauschii seedlings from herbicide toxicity by coordinately inducing proteins involved in an entire herbicide detoxification pathway mainly in the coleoptile and root, thereby protecting new leaves from herbicide injury.

Catalytic activity, duplication and evolution of the CYP98 cytochrome P450 family in wheat

A burst of evolutionary duplication upon land colonization seems to have led to the large superfamily of cytochromes P450 in higher plants. Within this superfamily some clans and families are heavily duplicated. Others, such as genes involved in the phenylpropanoid pathway have led to fewer duplication events. Eight coding sequences belonging to the CYP98 family reported to catalyze the 3-hydroxylation step in this pathway were isolated from Triticum aestivum (wheat) and expressed in yeast. Comparison of the catalytic properties of the recombinant enzymes with those of CYP98s from other plant taxa was coupled to phylogenetic analyses. Our results indicate that the unusually high frequency of gene duplication in the wheat CYP98 family is a direct or indirect result from ploidization. While ancient duplication led to evolution of enzymes with different substrate preferences, most of recent duplicates underwent silencing via degenerative mutations. Three of the eight tested CYP98s from wheat have phenol meta-hydroxylase activity, with p-coumaroylshikimate being the primary substrate for all of these, as it is the case for CYP98s from sweet basil and Arabidopsis thaliana. However, CYP98s from divergent taxa have acquired different additional subsidiary activities. Some of them might be significant in the metabolism of various free or conjugated phenolics in different plant species. One of the most significant is meta-hydroxylation of p-coumaroyltyramine, predominantly by the wheat enzymes, for the synthesis of suberin phenolic monomers. Homology modeling, confirmed by directed mutagenesis, provides information on the protein regions and structural features important for some observed changes in substrate selectivity. They indicate that the metabolism of quinate ester and tyramine amide of p-coumaric acid rely on the same recognition site in the protein.

Transcriptional analysis between two wheat near-isogenic lines contrasting in aluminum tolerance under aluminum stress

To understand the mechanisms of aluminum (Al) tolerance in wheat (Triticum aestivum L.), suppression subtractive hybridization (SSH) libraries were constructed from Al-stressed roots of two near-isogenic lines (NILs). A total of 1,065 putative genes from the SSH libraries was printed in a cDNA array. Relative expression levels of those genes were compared between two NILs at seven time points of Al stress from 15 min to 7 days. Fifty-seven genes were differentially expressed for at least one time point of Al treatment. Among them, 28 genes including genes for aluminum-activated malate transporter-1, ent-kaurenoic acid oxidase-1, beta-glucosidase, lectin, histidine kinase, and phospoenolpyruvate carboxylase showed more abundant transcripts in Chisholm-T and therefore may facilitate Al tolerance. In addition, a set of genes related to senescence and starvation of nitrogen, iron, and sulfur, such as copper chaperone homolog, nitrogen regulatory gene-2, yellow stripe-1, and methylthioribose kinase, was highly expressed in Chisholm-S under Al stress. The results suggest that Al tolerance may be co-regulated by multiple genes with diverse functions, and those genes abundantly expressed in Chisholm-T may play important roles in enhancing Al tolerance. The down-regulated genes in Chisholm-S may repress root growth and restrict uptake of essential nutrient elements, and lead to root senescence.

Organ-specific expression of glutathione S-transferases and the efficacy of herbicide safeners in Arabidopsis

The functions of plant glutathione S-transferases (GSTs) under normal growth conditions are poorly understood, but their activity as detoxification enzymes has been harnessed in agriculture for selective weed control. Herbicide safeners protect monocot crops from herbicide injury but have little effect on weedy monocot or dicot species. Protection by safeners is associated with expression of herbicide-metabolizing enzymes including GSTs, but the basis for selective action of safeners between monocots and dicots is not known. To address this question we have studied the response of Arabidopsis (Arabidopsis thaliana) to various safeners. Benoxacor, fenclorim, and fluxofenim did not protect Arabidopsis from herbicide injury but did induce RNA expression of the glutathione-conjugate transporters encoded by AtMRP1, AtMRP2, AtMRP3, and AtMRP4. These safeners also induced the organ-specific expression of AtGSTU19 and AtGSTF2, two previously characterized Arabidopsis GSTs from different classes of this enzyme family. RNA hybridization, immunoblot, and reporter gene analyses indicated expression of AtGSTU19 induced by safeners predominated in roots. To test the hypothesis that increased expression of AtGSTU19 would be sufficient to provide tolerance to chloroacetamide herbicides, a chimeric gene was produced containing the open reading frame for this GST driven by a constitutive promoter. Plants containing this transgene had a modest increase in AtGSTU19 protein, predominantly in roots, but this had no effect on tolerance to chloroacetamide herbicides. The localized induction of GSTs by safeners in roots of Arabidopsis may explain why these compounds are unable to provide herbicide tolerance to dicot plant species.

How can we use genomics to improve cereals with rice as a reference genome?

Rice serves as a model crop for cereal genomics. The availability of complete genome sequences, together with various genomic resources available for both rice and Arabidopsis, have revolutionized our understanding of the genetic make-up of crop plants. Both macrocolinearity revealed by comparative mapping and microcolinearity revealed by sequence comparisons among the grasses indicate that sequencing and functional analysis of the rice genome will have a significant impact on other cereals in terms of both genomic studies and crop improvement. The availability of mutants, introgression libraries, and advanced transformation techniques make functional genomics in rice and other cereals more manageable than ever before. A wide array of genetic markers, including anchor markers for comparative mapping, SSRs and SNPs are widely used in genetic mapping, germplasm evaluation and marker assisted selection. An integrated database that combines genome information for rice and other cereals is key to the effective utilization of all genomics resources for cereal improvement. To maximize the potential of genomics for plant breeding, experiments must be further miniaturized and costs must be reduced. Many techniques, including targeted gene disruption or allele substitution, insertional mutagenesis, RNA interference and homologous recombination, need to be refined before they can be widely used in functional genomic analysis and plant breeding.

Expression of glutathione-S-transferase and its role in plant growth and development in vivo and shoot morphogenesis in vitro

The enzymes glutathione-S-transferases (GSTs, E.C.2.5.1.18) have been associated with detoxification of xenobiotics, limiting oxidative damage and other stress responses in plants. In this study, we report the isolation of a mustard gene, BjGSTF2, homologous to the phi class GSTs and changes in plant growth in vivo and shoot regeneration in vitro were related to GST expression. GST transcripts accumulated differentially in mustard organs, where transcript was most abundant in root. Tissues incubated at high temperature or in the presence of exogenous H2O2, HgCl2, 1-aminocyclopropane-1-carboxylate, salicylic acid and paraquat upregulated GST expression, whereas spermidine was inhibitory. To investigate the in vivo function of GST, transgenic Arabidopsis thalianaplants expressing sense (GST-S6), antisense (GST-A4) and double-stranded BjGSTF2 (GST-DS1) RNAs were generated. GST-S6 was shown to flower two days earlier and was relatively more tolerant to HgCl2 and paraquat, whereas GST-DS1 with least stress tolerance flowered one week later compared to WT and GST-A4. In shoot regeneration response, tissues originated from GST-S6 were highly regenerative, whereas no shoot regeneration was observed in GST-DS1 tissues after 30 days of culture. Results of this study provide the evidence showing that GST plays a role in plant growth and development in vivo and shoot regeneration in vitro.

Osgstu3andosgtu4, encoding tau class glutathioneS-transferases, are heavy metal- and hypoxic stress-induced and differentially salt stress-responsive in rice roots1

Glutathione S-transferases (GSTs) have poorly understood roles in plant responses to environmental stresses. A polyethylene glycol (PEG)-induced tau class GST was identified in rice roots by protein microsequencing. PEG and the heavy metals Cd (20 microM), Zn (30 microM), Co and Ni rapidly and markedly induced osgstu4 and osgstu3 in rice seedling roots. Osgstu4 and osgstu3 were also induced in roots by hypoxic stress but not by cold nor heat shock. Salt stress and abscisic acid (ABA) rapidly induced osgstu3 in rice roots, whereas osgstu4 exhibited a late salt stress and no ABA response. Salicylic acid, jasmonic acid and the auxin alpha-naphthalene acetic acid triggered osgstu4 and osgstu3 expression. Osgstu4 and osgstu3 were rapidly and markedly induced by the antioxidant dithiothreitol and the strong oxidant hydrogen peroxide, which suggested that redox perturbations and reactive oxygen species are involved in their stress response regulations.

Tissue-specific expression and localization of safener-induced glutathione S-transferase proteins in Triticum tauschii

Glutathione S-transferase (GST; EC 2.5.1.18) gene expression was examined in the coleoptile and new leaf tissue of etiolated shoots of the diploid wheat species Triticum tauschii (Coss.) Schmal., which is considered to be a progenitor and the D-genome donor to cultivated, hexaploid bread wheat Triticum aestivum L. GST expression (mRNA, protein, and enzyme activity with a herbicide substrate) in these shoot tissues was examined in response to herbicide safener treatment. Two different antibody probes, raised against the same safener-inducible GST protein (TtGSTU1) but differing in their specificity, were utilized to determine tissue distribution and subcellular localization of GST proteins in etiolated shoots. GST transcripts, immunoreactive GST proteins, and herbicide-metabolizing activity were all highest in the coleoptile of etiolated, safener-treated T. tauschii shoots. Anti-GST immunolabeling was strongest in the outer epidermal and adjoining sub-epidermal cells in both coleoptiles and new leaves following safener treatment. Our data indicate that safeners protect grass crops from herbicide injury by dramatically inducing the expression of GST proteins in the outer cell layers of the coleoptile, which prevents the herbicide from reaching the sensitive new leaves of etiolated shoots as they emerge from the soil.

Comparison of genes among cereals

Comparison of partially sequenced cereal genomes suggests a mosaic structure consisting of recombinationally active gene-rich islands that are separated by blocks of high-copy DNA. Annotation of the whole rice genome suggests that most, but not all, cereal genes are present within the rice genome and that the high number of reported genes in this genome is probably due to duplications. Within the cereals, macrocolinearity is conserved but, at the level of individual genes, microcolinearity is frequently disrupted. Preliminary evidence from limited comparative analysis of sequenced orthologous genomic segments suggests that local gene amplification and translocation within a plant genome may be linked in some cases.