Characterization of an ethylene-responsive glutathione S-transferase gene cluster in carnation

Insights into the functional characterization of DIR proteins through genome-wide in silico and evolutionary studies: a systematic review

Dirigent proteins (DIRs) are a new class of proteins that were identified during the 8-8' lignan biosynthetic pathway and involves the formation of ( +) or ( -)-pinoresinol through stereoselective coupling from E-coniferyl alcohol. These proteins are known to play a vital role in the development and stress response in plants. Various studies have reported the functional and structural characterization of dirigent gene family in different plants using in silico approaches. Here, we have summarized the importance of dirigent proteins in plants and their role in plant stress tolerance by analyzing the genome-wide analysis including gene structure, mapping of chromosomes, phylogenetic evolution, conserved motifs, gene structure, and gene duplications in important plants. Overall, this review would help to compare and clarify the molecular and evolutionary characteristics of dirigent gene family in different plants.

Expression dynamics indicate the role of Jasmonic acid biosynthesis pathway in regulating macronutrient (N, P and K+) deficiency tolerance in rice (Oryza sativa L.)

Expression pattern indicates that JA biosynthesis pathway via regulating JA levels might control root system architecture to improve nutrient use efficiency (NUE) and N, P, K⁺ deficiency tolerance in rice. Deficiencies of macronutrients (N, P and K⁺) and consequent excessive use of fertilizers have dramatically reduced soil fertility. It calls for development of nutrient use efficient plants. Plants combat nutrient deficiencies by altering their root system architecture (RSA) to enhance the acquisition of nutrients from the soil. Amongst various phytohormones, Jasmonic acid (JA) is known to regulate plant root growth and modulate RSA. Therefore, to understand the role of JA in macronutrient deficiency in rice, expression pattern of JA biosynthesis genes was analyzed under N, P and K⁺ deficiencies. Several members belonging to different families of JA biosynthesis genes (PLA1, LOX, AOS, AOC, OPR, ACX and JAR1) showed differential expression exclusively in one nutrient deficiency or in multiple nutrient deficiencies. Expression analysis during developmental stages showed that several genes expressed significantly in vegetative tissues, particularly in root. In addition, JA biosynthesis genes were found to have significant expression under the treatment of different phytohormones, including Auxin, cytokinin, gibberellic acid (GA), abscisic acid (ABA), JA and abiotic stresses, such as drought, salinity and cold. Analysis of promoters of these genes revealed various cis-regulatory elements associated with hormone response, plant development and abiotic stresses. These findings suggest that JA biosynthesis pathway by regulating the level of JA might control the RSA thus, it may help rice plant in combating macronutrient deficiency.

Genome-wide identification, structure analysis and expression profiling of phospholipases D under hormone and abiotic stress treatment in chickpea (Cicer arietinum)

Phospholipases D (PLDs) are phospholipid hydrolyzing enzymes and crucial components of lipid signaling in plants. PLDs are implicated in stress responses in different plants however, characterization of PLDs in chickpea is missing. Here, we identify 13 PLD genes in the chickpea genome. PLD family could be divided into α, β, δ, ε and ζ isoforms based on sequence and structure. Protein remodeling described that chickpea PLDs are composed of defined arrangements of α-helix, β-sheets and short loops. Phylogenetic analysis suggested evolutionary conservation of chickpea PLD family with dicots. In-planta subcellular localization showed the plasma membrane localization of chickpea PLDs. All PLD promoters had hormone and stress related cis-regulatory elements, which suggested overlapping function of PLDs in hormone and abiotic stress signaling. The qRT-PCR expression analysis revealed that most PLD genes are differentially expressed in multiple abiotic stresses (drought, salt and cold stress). Moreover, several PLD genes had overlapping expression in abiotic stress and ABA and JA treatment. These observations indicate the involvement of PLD gene family in cross-talk of phytohormone and abiotic stress signaling in chickpea. Thus, present study opens new avenues of utilizing PLD related information for understanding hormone-regulated abiotic stress signaling in legume crops.

Maleic hydrazide elicits global transcriptomic changes in chemically topped tobacco to influence shoot bud development

MAIN CONCLUSION

Transcriptomic analysis revealed maleic hydrazide suppresses apical and axillary bud development by altering the expression of genes related to meristem development, cell division, DNA replication, DNA damage and recombination, and phytohormone signaling. Topping (removal of apical buds) is a common agricultural practice for some crop plants including cotton, cannabis, and tobacco. Maleic hydrazide (MH) is a systemic suckercide, a chemical that inhibits shoot bud growth, used to control the growth of apical (ApB) and axillary buds (AxB) following topping. However, the influence of MH on gene expression and the underlying molecular mechanism of controlling meristem development are not well studied. Our RNA sequencing analysis showed that MH significantly influences the transcriptomic landscape in ApB and AxB of chemically topped tobacco. Gene ontology (GO) enrichment analysis revealed that upregulated genes in ApB were enriched for phosphorelay signal transduction, and the regulation of transition timing from vegetative to reproductive phase, whereas downregulated genes were largely associated with meristem maintenance, cytokinin metabolism, cell wall synthesis, photosynthesis, and DNA metabolism. In MH-treated AxB, GO terms related to defense response and oxylipin metabolism were overrepresented in upregulated genes. GO terms associated with cell cycle, DNA metabolism, and cytokinin metabolism were enriched in downregulated genes. Expression of KNOX and MADS transcription factor (TF) family genes, known to be involved in meristem development, were affected in ApB and AxB by MH treatment. The promoters of MH-responsive genes are enriched for several known cis-acting elements, suggesting the involvement of a subset of TF families. Our findings suggest that MH affects shoot bud development in chemically topped tobacco by altering the expression of genes related to meristem development, DNA repair and recombination, cell division, and phytohormone signaling.

Glutathione S-transferase M1 and T1 genes deletion polymorphisms and risk of developing essential hypertension: a case-control study in Burkina Faso population (West Africa)

BACKGROUND

Glutathione S-transferases play a key role in the detoxification of persistent oxidative stress products which are one of several risks factors that may be associated with many types of disease processes such as cancer, diabetes, and hypertension. In the present study, we characterize the null genotypes of GSTM1 and GSTT1 in order to investigate the association between them and the risk of developing essential hypertension.

METHODS

We conducted a case-control study in Burkina Faso, including 245 subjects with essential hypertension as case and 269 control subjects with normal blood pressure. Presence of the GSTT1 and GSTM1 was determined using conventional multiplex polymerase chain reaction followed by gel electrophoresis analysis. Biochemical parameters were measured using chemistry analyzer CYANExpert 130.

RESULTS

Chi-squared test shows that GSTT1-null (OR = 1.82; p = 0.001) and GSTM1-active/GSTT1-null genotypes (OR = 2.33; p <  0.001) were significantly higher in cases than controls; the differences were not significant for GSTM1-null, GSTM1-null/GSTT1-active and GSTM1-null/GSTT1-null (p > 0.05). Multinomial logistic regression revealed that age ≥ 50 years, central obesity, family history of hypertension, obesity, alcohol intake and GSTT1 deletion were in decreasing order independent risk factors for essential hypertension. Analysis by gender, BMI and alcohol showed that association of GSTT1-null with risk of essential hypertension seems to be significant when BMI < 30 Kg/m², in non-smokers and in alcohol users (all OR ≥ 1.77; p ≤ 0.008). Concerning GSTT1, GSTM1 and cardiovascular risk markers levels in hypertensive group, we found that subjects with GSTT1-null genotype had higher waist circumference and higher HDL cholesterol level than those with GSTT1-active (all p <  0.005), subjects with GSTM1-null genotype had lower triglyceride than those with GSTM1-active (p = 0.02) and subjects with the double deletion GSTM1-null/GSTT1-null had higher body mass index, higher waist circumference and higher HDL cholesterol than those with GSTM1-active/GSTT1-active genotype (all p = 0.01).

CONCLUSION

Our results confirm that GSTT1-null genotype is significantly associated with risk of developing essential hypertension in Burkinabe, especially when BMI < 30 Kg/m², in non-smokers and in alcohol users, and it showed that the double deletion GSTM1-null/GSTT1-null genotypes may influence body lipids repartition.

Roles of Two Glutathione-Dependent 3,6-Dichlorogentisate Dehalogenases in Rhizorhabdus dicambivorans Ndbn-20 in the Catabolism of the Herbicide Dicamba

The herbicide dicamba is initially demethylated to 3,6-dichlorosalicylate (3,6-DCSA) in Rhizorhabdus dicambivorans Ndbn-20 and is subsequently 5-hydroxylated to 3,6-dichlorogentisate (3,6-DCGA). In the present study, two glutathione-dependent 3,6-DCGA dehalogenases, DsmH1 and DsmH2, were identified in strain Ndbn-20. DsmH2 shared a low identity (only 31%) with the tetrachlorohydroquinone (TCHQ) dehalogenase PcpC from Sphingobium chlorophenolicum ATCC 39723, while DsmH1 shared a high identity (79%) with PcpC. In the phylogenetic tree of related glutathione S-transferases (GSTs), DsmH1 and DsmH2, together with PcpC and the 2,5-dichlorohydroquinone dehalogenase LinD, formed a separate clade. DsmH1 and DsmH2 were synthesized in Escherichia coli BL21 and purified as His-tagged enzymes. Both enzymes required glutathione (GSH) as a cofactor and could 6-dechlorinate 3,6-DCGA to 3-chlorogentisate in vitro DsmH2 had a significantly higher catalytic efficiency toward 3,6-DCGA than DsmH1. Transcription and disruption analysis revealed that DsmH2 but not DsmH1 was responsible for the 6-dechlorination of 3,6-DCGA in strain Ndbn-20 in vivo Furthermore, we propose a novel eta class of GSTs to accommodate the four bacterial dehalogenases PcpC, LinD, DsmH1, and DsmH2.IMPORTANCE Dicamba is an important herbicide, and its use and leakage into the environment have dramatically increased since the large-scale planting of genetically modified (GM) dicamba-resistant crops in 2015. However, the complete catabolic pathway of dicamba has remained unknown, which limits ecotoxicological studies of this herbicide. Our previous study revealed that 3,6-DCGA was an intermediate of dicamba degradation in strain Ndbn-20. In this study, we identified two glutathione-dependent 3,6-DCGA dehalogenases, DsmH1 and DsmH2, and demonstrated that DsmH2 is physiologically responsible for the 6-dechlorination of 3,6-DCGA in strain Ndbn-20. GSTs play an important role in the detoxification and degradation of a variety of endogenous and exogenous toxic compounds. On the basis of their sequence identities, phylogenetic status, and functions, the four bacterial GSH-dependent dehalogenases (PcpC, LinD, DsmH1, and DsmH2) were reclassified as a new eta class of GSTs. This study helps us to elucidate the microbial catabolism of dicamba and enhances our understanding of the diversity and functions of GSTs.

Genome-wide analysis of dirigent gene family in pepper (Capsicum annuum L.) and characterization of CaDIR7 in biotic and abiotic stresses

The dirigent (DIR and DIR-like) proteins involved in lignification, play a pivotal role against biotic and abiotic stresses in plants. However, no information is available about DIR gene family in pepper (Capsicum annuum L.). In this study, 24 putative dirigent genes (CaDIRs) were identified, their gene structure, genome location, gene duplication and phylogenetic relationship were elucidated. Tissue-specific expression analysis displayed the highest transcription levels in flower, stem and leaf. Some CaDIRs were up-regulated by virulent (CaDIR2, 3, 6, 7, 11, 14, 16, 22 and 23) and avirulent (CaDIR3, 5, 7, 16, 20, 22, 23 and 24) Phytophthora capsici strains, as well as by Methyl jasmonate, salicylic acid, NaCl and mannitol stresses. Acid-soluble lignin content increased (103.21%) after P. capsici inoculation (48-hour). Silencing of CaDIR7 weakened plant defense by reducing (~50%) root activity and made plants more susceptible (35.7%) to P. capsici and NaCl (300 mM). Leaf discs of the CaDIR7:silenced plants exposed to NaCl and mannitol (300 mM each), exhibited a significant decrease (56.25% and 48% respectively) in the chlorophyll content. These results suggested that CaDIR7 is involved in pepper defense response against pathogen and abiotic stresses and the study will provide basic insights for future research regarding CaDIRs.

Expression patterns and promoter characteristics of the Vitis quinquangularis VqSTS36 gene involved in abiotic and biotic stress response

Resveratrol is a stilbene compound that is synthesized by plants in response to biotic stress and has been linked to health benefits associated with the consumption of certain foods and food products, such as grapes and wine. The final step in the biosynthesis of resveratrol is catalyzed by the enzyme stilbene synthase (STS). Here, we assessed the expression of two STS genes (VqSTS36 and VpSTS36) from the wild grape species Vitis quinquangularis (accession 'Shang-24'; powdery mildew (PM) resistant) and Vitis pseudoreticulata (accession 'Hunan-1'; PM susceptible) following infection by Uncinula necator (Schw.) Burr, the causal agent of PM disease. Some correlation was observed between the relative levels of STS36 transcript and disease resistance. We also cloned the 5' upstream sequence of both VpSTS36 and VqSTS36 and generated a series of 5' VqSTS36 promoter deletions fused to the GUS reporter gene in order to analyze expression in response to wounding, the application of exogenous stress-associated hormones, and biotic stress in tobacco leaves. The promoter was shown to be induced by the hormone salicylic acid (SA), inoculation with the fungal pathogen Erysiphe cichoracearum, and by wounding. These results suggest that VqSTS36 is regulated by biotic stresses and that it plays an important role in mediating disease resistance in grape.

A Phylogenetically Informed Comparison of GH1 Hydrolases between Arabidopsis and Rice Response to Stressors

Glycoside hydrolases Family 1 (GH1) comprises enzymes that can hydrolyze β-O-glycosidic bond from a carbohydrate moiety. The plant GH1 hydrolases participate in a number of developmental processes and stress responses, including cell wall modification, plant hormone activation or deactivation and herbivore resistance. A large number of members has been observed in this family, suggesting their potential redundant functions in various biological processes. In this study, we have used 304 sequences of plant GH1 hydrolases to study the evolution of this gene family in plant lineage. Gene duplication was found to be a common phenomenon in this gene family. Although many members of GH1 hydrolases showed a high degree of similarity in Arabidopsis and rice, they showed substantial tissue specificity and differential responses to various stress treatments. This differential regulation implies each enzyme may play a distinct role in plants. Furthermore, some of salt-responsive Arabidopsis GH1 hydrolases were selected to test their genetic involvement in salt responses. The knockout mutants of AtBGLU1 and AtBGLU19 were observed to be less-sensitive during NaCl treatment in comparison to the wild type seedlings, indicating their participation in salt stress response. In summary, Arabidopsis and rice GH1 glycoside hydrolases showed distinct features in their evolutionary path, transcriptional regulation and genetic functions.

Molecular characterization of zeta class glutathione S-transferases from Pinus brutia Ten

Glutathione transferases (GSTs; EC 2.5.1.18) play important roles in stress tolerance and metabolic detoxification in plants.In higher plants, studies on GSTs have focussed largely on agricultural plants. There is restricted information about molecular characterization of GSTs in gymnosperms. To date, only tau class GST enzymes have been characterized from some pinus species. For the first time, the present study reports cloning and molecular characterization of two zeta class GST genes, namely PbGSTZ1 and PbGSTZ2 from Pinus brutia Ten., which is an economically important pine native to the eastern Mediterranean region and have to cope with several environmental stress conditions. The PbGSTZ1 gene was isolated from cDNA, whereas PbGSTZ2 was isolated from genomic DNA. Sequence analysis of PbGSTZ1 and PbGSTZ2 revealed the presence of an open reading frame of 226 amino acids with typical consensus sequences of the zeta class plant GSTs. Protein and secondary structure prediction analysis of two zeta class PbGSTZs have shared common features of other plant zeta class GSTs. Genomic clone, PbGSTZ2 gene, is unexpectedly intronless. Extensive sequence analysis of PbGSTZ2, with cDNA clone, PbGSTZ1, revealed 87% identity at nucleotide and 81% identity at amino acid levels with 41 amino acids differences suggesting that genomic PbGSTZ2 gene might be an allelic or a paralogue version of PbGSTZ1.

Two wheat glutathione peroxidase genes whose products are located in chloroplasts improve salt and H2O2 tolerances in Arabidopsis

Oxidative stress caused by accumulation of reactive oxygen species (ROS) is capable of damaging effects on numerous cellular components. Glutathione peroxidases (GPXs, EC 1.11.1.9) are key enzymes of the antioxidant network in plants. In this study, W69 and W106, two putative GPX genes, were obtained by de novo transcriptome sequencing of salt-treated wheat (Triticum aestivum) seedlings. The purified His-tag fusion proteins of W69 and W106 reduced H2O2 and t-butyl hydroperoxide (t-BHP) using glutathione (GSH) or thioredoxin (Trx) as an electron donor in vitro, showing their peroxidase activity toward H2O2 and toxic organic hydroperoxide. GFP fluorescence assays revealed that W69 and W106 are localized in chloroplasts. Quantitative real-time PCR (Q-RT-PCR) analysis showed that two GPXs were differentially responsive to salt, drought, H2O2, or ABA. Isolation of the W69 and W106 promoters revealed some cis-acting elements responding to abiotic stresses. Overexpression of W69 and W106 conferred strong tolerance to salt, H2O2, and ABA treatment in Arabidopsis. Moreover, the expression levels of key regulator genes (SOS1, RbohD and ABI1/ABI2) involved in salt, H2O2 and ABA signaling were altered in the transgenic plants. These findings suggest that W69 and W106 not only act as scavengers of H2O2 in controlling abiotic stress responses, but also play important roles in salt and ABA signaling.

Identification and characterization of transcription factors regulating Arabidopsis HAK5

Potassium (K) is an essential macronutrient for plant growth and reproduction. HAK5, an Arabidopsis high-affinity K transporter gene, plays an important role in K uptake. Its expression is up-regulated in response to K deprivation and is rapidly down-regulated when sufficient K levels have been re-established. To identify transcription factors regulating HAK5, an Arabidopsis TF FOX (Transcription Factor Full-length cDNA Over-eXpressor) library containing approximately 800 transcription factors was used to transform lines previously transformed with a luciferase reporter gene whose expression was driven by the HAK5 promoter. When grown under sufficient K levels, 87 lines with high luciferase activity were identified, and endogenous HAK5 expression was confirmed in 27 lines. Four lines overexpressing DDF2 (Dwarf and Delayed Flowering 2), JLO (Jagged Lateral Organs), TFII_A (Transcription initiation Factor II_A gamma chain) and bHLH121 (basic Helix-Loop-Helix 121) were chosen for further characterization by luciferase activity, endogenous HAK5 level and root growth in K-deficient conditions. Further analysis showed that the expression of these transcription factors increased in response to low K and salt stress. In comparison with controls, root growth under low K conditions was better in each of these four TF FOX lines. Activation of HAK5 expression by these four transcription factors required at least 310 bp of upstream sequence of the HAK5 promoter. These results indicate that at least these four transcription factors can bind to the HAK5 promoter in response to K limitation and activate HAK5 expression, thus allowing plants to adapt to nutrient stress.

Expression pattern, genomic structure, and promoter analysis of the gene encoding stilbene synthase from Chinese wild Vitis pseudoreticulata

The gene encoding stilbene synthase (STS) plays a central role in many biochemical and physiological actions, and its metabolite resveratrol possesses broad-spectrum resistance to pathogens, as well as diverse pharmacological properties, notably an anticancer effect. Here, we report the expression analysis of the gene encoding STS and its promoter function from a powdery mildew (PM)-resistant Chinese wild Vitis pseudoreticulata, and compare it with two PM-susceptible cultivated grapevines, Vitis vinifera cvs. Carignane and Thompson Seedless. We show an unusual expression pattern of STS in V. pseudoreticulata, which differs markedly from that of the cultivated species. Sequence comparisons reveal that the genomic DNA sequences encoding STS in the three grapevines are highly conserved, but a novel residue mutation within the key motif of STS is solely present in V. pseudoreticulata. Moreover, the STS promoter in V. pseudoreticulata displays a significantly different structure from that found in the two V. vinifera. The three promoter-driven GUS differential expression patterns in transformed tobacco plants induced with Alternaria alternata, methyl jasmonate, and wounding indicated that the structurally different STS promoter of V. pseudoreticulata is responsible for its specific regulatory function. We also demonstrate that the expression of STS genes from their native promoters are functional in transformed tobacco and retain pathogen inducibility. Importantly, the genomic DNA-2 of V. pseudoreticulata under its native promoter shows good induction and the maximum level of resveratrol content. These findings further our understanding of the regulation of STS expression in a resistant grapevine and provide a new pathogen-inducible promoter system for the genetic improvement of plant disease resistance.

Regulation and function of the pepper pectin methylesterase inhibitor (CaPMEI1) gene promoter in defense and ethylene and methyl jasmonate signaling in plants

Analysis of the promoters of defense-related genes is valuable for determining stress signaling and transcriptional activation during pathogen infection. Here, we have isolated and functionally characterized the promoter region of the pepper (Capsicum annuum) pectin methylesterase inhibitor 1 (CaPMEI1) gene in transiently transformed tobacco plants and stably transformed Arabidopsis plants. Among four 5' deletion constructs analyzed, the -958-bp CaPMEI1 promoter induced a high level of GUS reporter activity in tobacco leaf tissue, driven by pathogen infection as well as by ethylene and methyl jasmonate (MeJA) treatment. The 204-bp region from -958 bp to -754 bp of the CaPMEI1 promoter is responsible for the stress-responsive expression. In addition, the pepper transcription factor CARAV1 activated the CaPMEI1 promoter in tobacco leaves, whereas the transcription factor CAbZIP1 did not. In the transgenic Arabidopsis plants, the -958 bp CaPMEI1 promoter was functionally regulated by developmental cues, bacterial and oomycete pathogen infections, and treatment with ethylene and MeJA. Histochemical GUS staining analyses of Arabidopsis tissues revealed that the CaPMEI1 promoter was mainly activated in leaf veins in response to various biotic and abiotic stimuli. Together, these results suggest that CaPMEI1 promoter activation may be a critical molecular event for host defense response and ethylene- and MeJA-mediated CaPMEI1 gene expression.

Purification and biochemical properties of glutathione S-transferase from Lactuca sativa

A glutathione S-transferase (GST) from Lactuca sativa was purified to electrophoretic homogeneity approximately 403-fold with a 9.6% activity yield by DEAE-Sephacel and glutathione (GSH)-Sepharose column chromatography. The molecular weight of the enzyme was determined to be approximately 23,000 by SDS-polyacrylamide gel electrophoresis and 48,000 by gel chromatography, indicating a homodimeric structure. The activity of the enzyme was significantly inhibited by ShexylGSH and S-(2,4-dinitrophenyl) glutathione. The enzyme displayed activity towards 1-chloro-2,4-dinitrobenzene, a general GST substrate and high activities towards ethacrynic acid. It also exhibited glutathione peroxidase activity toward cumene hydroperoxide.

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.

Genomic structure and differential expression of two tandem-arranged GSTZ genes in rice

Glutathione S-transferases (GSTs) are scavenging enzymes that detoxify cellular xenobiotics and toxins by catalyzing the conjugation of these substrates with a tripeptide glutathione. GSTs are classified depending on gene organization and sequence similarity. The sequence analysis of genomic DNA for zeta class GST (GSTZ) locus in rice indicated that two homologous GSTZ genes lay in a tandem orientation with a short (0.4 kb) intergenic spacer. The upstream OsGSTZ1 and downstream OsGSTZ2 spanned 3.5 and 3.2 kb with nine coding exons, respectively. The transcript of OsGSTZ1 had a long 3' untranslated region (3' UTR) that was mostly encoded by a 10th noncoding exon, whereas OsGSTZ2 mRNA contained a long 5' UTR. Northern blot analysis showed that OsGSTZ1/2 messages were strongly expressed in leaf blades, while transcripts from roots were low level. Because OsGSTZ1/2 messages in leaf tissues were strongly induced only by water treatment, it was difficult to assay for the induction of OsGSTZ1/2 transcripts by various stress treatments. Thus, using rice culture cells, we analyzed the respective responses of OsGSTZ1 and OsGSTZ2 genes against various treatments by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The results showed that OsGSTZ1 was expressed at a level ca. 1000-fold higher than OsGSTZ2 in suspension cells without stress treatment. OsGSTZ1 was expressed constitutively under various stress conditions. In contrast, the expression of OsGSTZ2 gene was strongly enhanced to 30-fold by treatment with jasmonic acid. These observations suggested that the expression of OsGSTZ1 and OsGSTZ2 genes are differentially regulated in the culture cell of rice.

OsEIN2 is a Positive Component in Ethylene Signaling in Rice

EIN2 is a central signal transducer in the ethylene-signaling pathway, and a unique membrane-anchored protein. By screening a cDNA library, we have isolated a cDNA clone (OsEIN2) that encodes the rice EIN2 homolog. The full-length ORF clone was obtained by reverse transcriptase-polymerase chain reaction. OsEIN2 shares significant amino acid sequence similarity with Arabidopsis EIN2 (57% similarity and 42% identity). Both the numbers and positions of introns and exons in the OsEIN2 and AtEIN2 coding regions are also conserved. To address whether this structural similarity is indicative of functional conservation of the corresponding proteins, we also generated transgenic lines expressing the antisense construct of OsEIN2. Those plants were stunted and shoot elongation was severely inhibited. Their phenotypes were similar to that found with wild-type rice seedlings that were treated with AgNO3, an ethylene signal inhibitor. In the OsEIN2 antisense plants, the expression levels of two ethylene-responsive genes, SC129 and SC255, were decreased compared with the wild types. These results suggest that OsEIN2 is a positive component of the ethylene-signaling pathway in rice, just as AtEIN2 is in Arabidopsis: Our antisense transgenic plants produced approximately 3.5 times more ethylene than the wild-type plants. Expression analysis of rice ACS and ACO genes showed that the transcript levels of OsACS1 and OsACO1 were elevated in the transgenic plants.

Abiotic stress alters transcript profiles and activity of glutathione S-transferase, glutathione peroxidase, and glutathione reductase in Euphorbia esula

Glutathione S-transferase (GST), glutathione peroxidase (GPX), and glutathione reductase (GR) are enzymes that utilize glutathione to play an important role in plant defense mechanisms. In leafy spurge (Euphorbia esula L.), transcript and activity profiles for these enzymes are differentially influenced in tissue exposed to xenobiotic (diclofop-methyl) and environmental stress (cold and drought). Five different EeGST cDNA (including phi, tau, theta, and zeta class GSTs), one EeGPX cDNA, and one EeGR cDNA showed differential expression patterns in leafy spurge plants exposed to diclofop-methyl-, cold- and drought-stress. Tissue treated with diclofop-methyl also had increased GST, GPX and GR activities that were preceded or paralleled by increased gene expression. Transcript profiles resulting from drought-stressed plants were similar to transcript profiles from diclofop-methyl-treated plants but not cold-stressed plants. GPX activity in leafy spurge protein extracts was not bound to either S-hexylglutathione- or glutathione-agarose columns but instead co-migrated with fractions of GST activity that also were not bound by affinity chromatography. Fractions of GST proteins that were bound to S-hexylglutathione revealed that increased GST activity in diclofop-methyl-treated tissue could be identified as phi- and tau-type GSTs.

Characterization of two putative ethylene receptor genes expressed during peach fruit development and abscission

Two peach genes homologous to the Arabidopsis ethylene receptor genes ETR1 and ERS1, named Pp-ETR1 and Pp-ERS1 respectively, have been isolated and characterized. Pp-ETR1 and Pp-ERS1 are conserved in terms of exon numbers and intron positions, although the first and fifth introns of Pp-ETR1 have an unusual length. In addition, two putative polyadenylation sites, that may cause an incomplete splicing at the 3' terminus, are present in the fifth intron. A motif of 28 nt, which shows high homology with ethylene responsive elements found in promoters of genes up-regulated by ethylene, is present in the promoter region of Pp-ERS1. Expression analysis, carried out by quantitative RT-PCR, was performed during fruit development and ripening, and leaf and fruitlet abscission. The level of Pp-ETR1 transcripts remained unchanged in all the tissues and developmental stages examined, whereas Pp-ERS1 mRNA abundance increased in ripening mesocarp, in leaf and fruitlet activated abscission zones, and following propylene application. 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, did not affect Pp-ETR1 transcription, while it down-regulated Pp-ERS1. A rise in ethylene evolution, accompanied by an increase of Pp-ERS1 transcript accumulation occurred within 24 h from the end of 1-MCP treatment. These results indicate that Pp-ERS1 might play a role in abscission and ripening.

Purification of a phi-type glutathione S-transferase from pumpkin flowers, and molecular cloning of its cDNA

A major species of glutathione S-transferase (GST), Pugf, was highly purified from pumpkin flowers. Two-dimensional electrophoresis of the purified enzyme gave two adjacent protein spots. The specific activity of the purified enzyme was 2.4 micromol min(-1) mg(-1) protein for 1-chloro-2,4-dinitrobenzene. This value is one to two orders of magnitude lower than that of pumpkin tau-type GSTs. The expression pattern of Pugf in healthy pumpkin plants and responses to various stresses were examined by western blotting. Pugf was found in high concentrations in petioles, stems, and roots as well as flowers, and was more abundant in expanding young organs than in fully expanded mature organs. Dehydration caused a slight increase in its concentration, but high and low temperatures, salty stress, and 2,4-dichlorophenoxyacetic acid seemed to have no effects. A cDNA encoding Pugf was cloned and sequenced. Sequence comparison with other plant GSTs suggested that it should be classified as a phi-type GST.

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

Glutathione S-transferase (GST) gene expression was examined in several Triticum species, differing in genome constitution and ploidy level, to determine genome contribution to GST expression in cultivated, hexaploid bread wheat (Triticum aestivum). Two tandemly duplicated tau class GST genes (TtGSTU1 and TtGSTU2) were isolated from a single bacterial artificial chromosome clone in a library constructed from the diploid wheat and D genome progenitor to cultivated wheat, Triticum tauschii. The genes are very similar in genomic structure and their encoded proteins are 95% identical. Gene-specific reverse transcriptase-polymerase chain reaction analysis revealed differential transcript accumulation of TtGSTU1 and TtGSTU2 in roots and shoots. Expression of both genes was induced by herbicide safeners, 2,4-dichlorophenoxyacetic acid and abscisic acid, in the shoots of T. tauschii; however, expression of TtGSTU1 was always higher than TtGSTU2. In untreated seedlings, TtGSTU1 was expressed in both shoots and roots, whereas TtGSTU2 expression was only detected in roots. RNA gel-blot analysis of ditelosomic, aneuploid lines that are deficient for 6AS, 6BS, or 6DS chromosome arms of cultivated, hexaploid bread wheat showed differential genome contribution to safener-induced GST expression in shoots compared with roots. The GST genes from the D genome of hexaploid wheat contribute most to safener-induced expression in the shoots, whereas GSTs from the B and D genomes contribute to safener-induced expression in the roots.

Structure, function and evolution of glutathione transferases: implications for classification of non-mammalian members of an ancient enzyme superfamily

The glutathione transferases (GSTs; also known as glutathione S-transferases) are major phase II detoxification enzymes found mainly in the cytosol. In addition to their role in catalysing the conjugation of electrophilic substrates to glutathione (GSH), these enzymes also carry out a range of other functions. They have peroxidase and isomerase activities, they can inhibit the Jun N-terminal kinase (thus protecting cells against H(2)O(2)-induced cell death), and they are able to bind non-catalytically a wide range of endogenous and exogenous ligands. Cytosolic GSTs of mammals have been particularly well characterized, and were originally classified into Alpha, Mu, Pi and Theta classes on the basis of a combination of criteria such as substrate/inhibitor specificity, primary and tertiary structure similarities and immunological identity. Non-mammalian GSTs have been much less well characterized, but have provided a disproportionately large number of three-dimensional structures, thus extending our structure-function knowledge of the superfamily as a whole. Moreover, several novel classes identified in non-mammalian species have been subsequently identified in mammals, sometimes carrying out functions not previously associated with GSTs. These studies have revealed that the GSTs comprise a widespread and highly versatile superfamily which show similarities to non-GST stress-related proteins. Independent classification systems have arisen for groups of organisms such as plants and insects. This review surveys the classification of GSTs in non-mammalian sources, such as bacteria, fungi, plants, insects and helminths, and attempts to relate them to the more mainstream classification system for mammalian enzymes. The implications of this classification with regard to the evolution of GSTs are discussed.

Characterization and expression of two members of the peach 1-aminocyclopropane-1-carboxylate oxidase gene family

The characterization and expression of PP-ACO1 and PP-ACO2, two members of the peach 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO) gene family, are reported. PP-ACO1 is organized in 4 exons interrupted by 3 introns, whereas PP-ACO2 has only 2 of the 3 introns present in PP-ACO1. Comparison of the deduced amino acid sequences of PP-ACO1 and PP-ACO2 reveals a 77.7% identity. PP-ACO1 and PP-ACO2 show highest degree of similarity with petunia (PH-ACO3; 84.1%) and apple (85.4%) ACO genes, respectively. PP-ACO1 is expressed in flowers, fruitlet abscission zones, mesocarp and in young fully expanded leaves. PP-ACO1 transcript accumulation strongly increases during fruitlet abscission, in ripe mesocarp and senescing leaves, and is enhanced by propylene. PP-ACO2 mRNA accumulation is detected in fruits only during early development and is unaffected by propylene treatment. Both ACO genes are expressed in epicotyl and roots of growing seedlings, although a stronger accumulation of PP-ACO2 mRNA is observed.

A genomics approach to the comprehensive analysis of the glutathione S-transferase gene family in soybean and maize

By BLAST searching a large expressed sequence tag database for glutathione S-transferase (GST) sequences we have identified 25 soybean (Glycine max) and 42 maize (Zea mays) clones and obtained accurate full-length GST sequences. These clones probably represent the majority of members of the GST multigene family in these species. Plant GSTs are divided according to sequence similarity into three categories: types I, II, and III. Among these GSTs only the active site serine, as well as another serine and arginine in or near the "G-site" are conserved throughout. Type III GSTs have four conserved sequence patches mapping to distinct structural features. Expression analysis reveals the distribution of GSTs in different tissues and treatments: Maize GSTI is overall the most highly expressed in maize, whereas the previously unknown GmGST 8 is most abundant in soybean. Using DNA microarray analysis we observed increased expression among the type III GSTs after inducer treatment of maize shoots, with different genes responding to different treatments. Protein activity for a subset of GSTs varied widely with seven substrates, and any GST exhibiting greater than marginal activity with chloro-2,4 dinitrobenzene activity also exhibited significant activity with all other substrates, suggesting broad individual enzyme substrate specificity.

Cytochrome P450 enzymes in aquatic invertebrates: recent advances and future directions

A variety of enzymes and other proteins are produced by organisms in response to xenobiotic exposures. Cytochrome P450s (CYP) are one of the major phase I-type classes of detoxification enzymes found in terrestrial and aquatic organisms ranging from bacteria to vertebrates. These enzymes metabolize a wide variety of substrates including endogenous molecules (e.g. fatty acids, eicosenoids, steroids) and xenobiotics (e.g. hydrocarbons, pesticides, drugs). Aquatic invertebrates, especially those in marine habitats, occupy every aspect of the environment, from above the surface (intertidal) to below the sediments. In turn, they have extremely diverse physiologies and are exposed to a vast array of potential toxicants. Aspects of aquatic invertebrate cytochrome P450 enzymes have been studied for the last 25 years. In a few phyla, P450 activities have been measured and are responsive to xenobiotic exposures. Until the last several years, little progress had occurred in the identification of P450 gene diversity in aquatic invertebrates. Molecular biology tools have greatly aided this search, and are likely to identify as much diversity for this protein superfamily as is present in higher marine and terrestrial organisms. Recent work has expanded our knowledge of the CYP superfamily, and new developments will rapidly advance the usefulness of these genes into such fields as biomarker research. Advances of the last decade are reviewed and insights are presented from related insect studies.

Isolation of a zeta class wheat glutathione S-transferase gene

A new Zeta class glutathione S-transferases (GST) gene, pGST, has been cloned from wheat for the first time by the differential display PCR (DD-PCR) method. The genomic sequence of pGST, TA-GSTZ1, contains nine exons that encode a polypeptide of 213 amino acids and eight introns. The deduced amino acid sequence of TA-GSTZ1 as well as the exon:intron placement are more similar to the GSTs of the Zeta class than to the two wheat GSTs reported earlier. The pGST cDNA gene product expressed in Escherichia coli and purified by affinity chromatography showed typical Zeta class GST and glutathione peroxidase activities. Sequence polymorphism in the 3' untranslated region (UTR) of TA-GSTZ1 gene in wheat has been discovered. In this study, an 89 bp sequence is present in the 3' UTR of TA-GSTZ1gene in 16 wheat cultivars but absent in the other five. Although the biological importance of this polymorphism is unknown, it can be useful as a genetic marker in wheat breeding.

RESPONSIVE-TO-ANTAGONIST1, a Menkes/Wilson disease-related copper transporter, is required for ethylene signaling in Arabidopsis

Ethylene is an important regulator of plant growth. We identified an Arabidopsis mutant, responsive-to-antagonist1 (ran1), that shows ethylene phenotypes in response to treatment with trans-cyclooctene, a potent receptor antagonist. Genetic epistasis studies revealed an early requirement for RAN1 in the ethylene pathway. RAN1 was cloned and found to encode a protein with similarity to copper-transporting P-type ATPases, including the human Menkes/Wilson proteins and yeast Ccc2p. Expression of RAN1 complemented the defects of a ccc2delta mutant, demonstrating its function as a copper transporter. Transgenic CaMV 35S::RAN1 plants showed constitutive expression of ethylene responses, due to cosuppression of RAN1. These results provide an in planta demonstration that ethylene signaling requires copper and reveal that RAN1 acts by delivering copper to create functional hormone receptors.

Zeta, a novel class of glutathione transferases in a range of species from plants to humans

Sequence alignment and phylogenetic analysis has identified a new subgroup of glutathione S-transferase (GST)-like proteins from a range of species extending from plants to humans. This group has been termed the Zeta class. An atomic model of the N-terminal domain suggests that the members of the Zeta class have a similar structure to that of other GSTs, binding glutathione in a similar orientation in the G site. Recombinant human GSTZ1-1 has been expressed in Escherichia coli and characterized. The protein is a dimer composed of 24.2 kDa subunits and has minimal glutathione-conjugating activity with ethacrynic acid and 7-chloro-4-nitrobenz-2-oxa-1, 3-diazole. Although low in comparison with other GSTs, GSTZ1-1 has glutathione peroxidase activity with t-butyl and cumene hydroperoxides. The members of the Zeta class have been conserved over a long evolutionary period, suggesting that they might have a role in the metabolism of a compound that is common in many living cells.

Molecular characterization of Fdx1, a putidaredoxin-type [2Fe-2S] ferredoxin able to transfer electrons to the dioxin dioxygenase of Sphingomonas sp. RW1

Bacterium Sphingomonas sp. strain RW1 is, under aerobic conditions, able to degrade dibenzofuran and dibenzo-p-dioxin. The first step of the pathway is performed by a ring-dihydroxylating enzyme. Bunz and Cook have reported the purification and characterization of this dioxin dioxygenase and a ferredoxin able to transfer electrons to the dioxygenase [Bunz, P. V. & Cook, A. M. (1993) J. Bacteriol. 175, 6467-6475]. The gene encoding this [2Fe-2S] ferredoxin was identified by screening a genomic library constructed in pLAFR3 with a probe generated by a nested-PCR amplification. Primers for the amplification were designed based on the N-terminus sequence of the purified ferredoxin and on sequence comparisons with related proteins. Several cosmids were obtained and the ferredoxin gene, fdx1, was subcloned from one of them. The nucleotide sequence of a 4.6-kb DNA fragment encompassing the ferredoxin gene was determined. While in the case of all known multi-component dioxygenases, genes encoding the alpha and beta subunits are found to be contiguous with the gene of the specific electron carrier, the fdx1 gene in Sphingomonas sp. RW1 does not appear to be directly linked with the dioxin dioxygenase genes. Rather, it is clustered with genes apparently encoding two atypical decarboxylases/isomerases and a glutathione S-transferase. The ferredoxin gene was hyperexpressed and the recombinant ferredoxin was purified. Spectroscopic characterization of Fdx1 demonstrated the presence of a putidaredoxin-type [2Fe-2S] cluster in this protein. Its redox potential was determined to be -245 (+/- 5) mV versus the normal hydrogen electrode at 25 degrees C, pH 8.0. Therefore, the protein is closely related to [2Fe-2S] ferredoxins known to be electron donors to monooxygenases involved in hydroxylation of aromatic compounds. Thus, this report provides clear evidence that a putidaredoxin-type [2Fe-2S] ferredoxin, namely Fdx1, is able to transfer electrons to the dioxin dioxygenase of Sphingomonas sp. RW1.

Analysis of a Rhizobium leguminosarum gene encoding a protein homologous to glutathione S-transferases

A novel Rhizobium leguminosarum gene, gstA, the sequence of which indicated that it was a member of the gene family of glutathione S-transferases (GSTs), was identified. The homology was greatest to the GST enzymes of higher plants. The Rhizobium gstA gene was normally expressed at a very low level. The product of gstA was over-expressed and purified from Escherichia coli. It was shown to bind to the affinity matrix glutathione-Sepharose, but no enzymic GST activity with 1-chloro-2,4-dinitrobenzene as substrate was detected. gstA encoded a polypeptide of 203 amino acid residues with a calculated molecular mass of 21990 Da. Transcribed divergently from gstA is another gene, gstR, which was similar in sequence to the LysR family of bacterial transcriptional regulators. A mutation in gstR had no effect on the transcription of itself or gstA under the growth conditions used here. Mutations in gstA and gstR caused no obvious phenotypic defect and the biological functions of these genes remain to be determined.

Structure and expression of a cluster of glutathione S-transferase genes from a marine fish, the plaice (Pleuronectes platessa)

Glutathione S-transferases are involved in the detoxification of reactive electrophilic compounds, including intracellular metabolites, drugs, pollutants and pesticides. A cluster of three glutathione S-transferase genes, designated GSTA, GSTA1 and GSTA2, was isolated from the marine flatfish, plaice (Pleuronectes platessa). GSTA and GSTA1 code for protein products with 76% amino acid identity. GSTA2 appears to contain a single nucleotide deletion which would render any product non-functional. All of these genes consist of six exons of similar sizes and greater than 70% nucleotide identity, and are interrupted by five introns of differing sizes. GSTA and GSTA1 mRNAs were present in a range of tissues, while GSTA2 mRNA was no detected. Expression of GSTA mRNA was increased in plaice intestine and spleen by pretreatment with beta-naphthoflavone, and expression of both GSTA and GSTA1 mRNAs was increased in plaice liver and gill by pretreatment with the peroxisome proliferating agent perfluoro-octanoic acid.

Exploration of the relationship between tetrachlorohydroquinone dehalogenase and the glutathione S-transferase superfamily

Tetrachlorohydroquinone dehalogenase is found in Sphingomonas chlorophenolica, a soil bacterium that degrades pentachlorophenol, a widely used wood preservative. This enzyme converts tetrachlorohydroquinone (TCHQ) to trichlorohydroquinone (TriCHQ) and TriCHQ to dichlorohydroquinone (DCHQ) (Xun et al. (1992) J. Bacteriol. 174, 8003-8007). The reducing equivalents for each step are provided by two molecules of glutathione (Xun et al. (1992) Biochem. Biophys. Res. Commun. 182, 361-366). In addition to the expected TriCHQ and DCHQ products, the enzyme also produces substantial amounts of 2,3,5-trichloro-6-S-glutathionylhydroquinone (GS-TriCHQ) and an unidentified isomer of dichloro-S-glutathionylhydroquinone (GS-DCHQ). Treatment of the purified enzyme with dithiothreitol dramatically decreases the formation of GS-TriCHQ and GS-DCHQ. Furthermore, enzyme in freshly-prepared crude extracts forms only very small amounts of GS-TriCHQ and GS-DCHQ. We conclude that GS-TriCHQ and GS-DCHQ are produced by enzyme that has undergone some type of oxidative damage and are therefore not physiologically relevant products. The fact that the oxidative damage can be repaired by DTT suggests that a cysteine or methionine residue may be involved. We have created the C13S and C156S mutants of the enzyme. The C13S mutant converts TCHQ to GS-TriCHQ and GS-DCHQ, rather than to DCHQ. Thus, Cys13 is required for the reductive dehalogenation of TCHQ. A mechanism for the reaction which involves Cys13 is proposed.

Cloning of a DNA-binding protein that interacts with the ethylene-responsive enhancer element of the carnation GST1 gene

Ethylene transcriptionally activates a glutathione S-transferase gene (GST1) at the onset of the senescence program in carnation (Dianthus caryophyllus L.) flower petals. A 126 bp region of the GST1 promoter sequence has been identified as an ethylene-responsive enhancer element (ERE). In this paper, we demonstrate the ability of nuclear proteins from senescing petals to recognize a 22 bp sequence within the ERE (ERE oligonucleotide). Mutation of the ERE oligonucleotide sequence significantly alters the strength of this nuclear protein-DNA association. The wild-type ERE oligonucleotide sequence was used to isolate a cDNA clone encoding a sequence-specific DNA binding protein. Nucleotide sequencing and deduced amino acid sequence analysis of this cDNA predicted a 32 kDa protein which we have designated carnation ethylene-responsive element-binding protein-1 (CEBP-1). The mRNA expression pattern of CEBP-1 suggests that it is not transcriptionally regulated by ethylene. The amino acid sequence homology of CEBP-1 with other plant nucleic acid binding proteins indicates a conserved nucleic acid binding domain. Within this domain are two highly conserved RNA-binding motifs, RNP-1 and RNP-2. An acidic region and a putative nuclear localization signal are also identified.

THE FUNCTIONS AND REGULATION OF GLUTATHIONE S-TRANSFERASES IN PLANTS

Glutathione S-transferases (GSTs) play roles in both normal cellular metabolism as well as in the detoxification of a wide variety of xenobiotic compounds, and they have been intensively studied with regard to herbicide detoxification in plants. A newly discovered plant GST subclass has been implicated in numerous stress responses, including those arising from pathogen attack, oxidative stress, and heavy-metal toxicity. In addition, plant GSTs play a role in the cellular response to auxins and during the normal metabolism of plant secondary products like anthocyanins and cinnamic acid. This review presents the current knowledge about the functions of GSTs in regard to both herbicides and endogenous substrates. The catalytic mechanism of GST activity as well as the fate of glutathione S-conjugates are reviewed. Finally, a summary of what is known about the gene structure and regulation of plant GSTs is presented.

Isolation and characterization of an auxin-inducible glutathione S-transferase gene of Arabidopsis thaliana

Genes homologous to the auxin-inducible Nt103 glutathione S-transferase (GST) gene of tobacco, were isolated from a genomic library of Arabidopsis thaliana. We isolated a lambda clone containing an auxin-inducible gene, At103-1a, and part of a constitutively expressed gene, At103-1b. The coding regions of the Arabidopsis genes were highly homologous to each other and to the coding region of the tobacco gene but distinct from the GST genes that have been isolated from arabidopsis thusfar. Overexpression of a cDNA clone in Escherichia coli revealed that the AT103-1A protein had GST activity.

Promoter analysis of the auxin-regulated tobacco glutathione S-transferase genes Nt103-1 and Nt103-35

We have analysed the promoter regions of two closely related auxin-regulated glutathione S-transferase genes. All active deletion constructs tested showed expression of the reporter gene beta-glucuronidase (gusA) in root tips of young seedlings and newly developing lateral roots. Auxin treatment greatly enhanced the level of expression. The Nt103-1 promoter region -370/-276 was found to be necessary, at least as a quantitative element to confer auxin-responsiveness to a reporter gene, and sequences responsible for the auxin-responsiveness must be located downstream of -370. The region -651/-370 contains sequence information necessary for uninduced expression. The Nt103-35 promoter manifested its auxin-responsiveness within the -504/-310 region. Electrophoretic mobility shift analysis, using nuclear extracts from tobacco leaves and suspension cells, identified a factor binding to a sequence (ap103, TGAGTCT) at position -560 of the Nt103-1 promoter, which shows homology to the mammalian AP-1 site. A second factor was found to bind a sequence (as103, ATAGCTAAGTGCTTACG) with homology to the CaMV 35S promoter as-1 element. The as103 element is present in both promoters and positioned around -360, so within the region determined to be indispensable for the response to auxin. A third factor was found binding to the -276/-190 region of both promoters. Combined, these data point to the relevance of a 90 bp region for auxin-induced activity of both tobacco genes. The ASF-1 like factor binding to the as103 element within this region might be involved in mediating the auxin response.

Auxin action and auxin-binding proteins

The plant growth regulator auxin mediates an enormous range of developmental and growth responses, some of which are manifest rapidly and others manifest only after considerable lag periods. The protein that perceives auxin, the auxin receptor, has been sought by many laboratories and the search has identified a good number of candidates. However, a receptor must not only bind auxin, but also transduce the auxin stimulus into the responses we recognize. Finding evidence for this second condition has always proved very demanding. A key requisite is a convenient assay for auxin activity and preferably one involving a rapid response because this is likely to be linked directly to the perception event. For one auxin-binding protein (ABP1) there is growing evidence that it is a functional auxin receptor. The assays used in this work have been rapid auxin-induced changes in protoplast electrophysiology. There are many other responses induced rapidly by auxin for which a link to ABP1 has yet to be established. We have reviewed the whole range of rapid auxin-mediated responses and by doing so we hope to have provided a comprehensive picture of the many events to which a receptor (or receptors) must connect. Against this framework we match the known properties of all putative receptors, including ABP1. Not only have we tried to identify auxin-binding proteins unlikely to be receptors, but we also highlight the remaining gaps in our understanding of the more likely receptor candidates. Contents Summary 167 I. Introduction 168 II. Gene activation 168 III. Mutants 179 IV. Auxin-induced elongation growth 179 V. Other auxin-binding proteins 191 VI. Auxins and signal transduction 192 VII. Overview 194 Acknowledgements 195 References 195.

H2O2 from the oxidative burst orchestrates the plant hypersensitive disease resistance response

Microbial elicitors or attempted infection with an avirulent pathogen strain causes the rapid production of reactive oxygen intermediates. We report here that H2O2 from this oxidative burst not only drives the cross-linking of cell wall structural proteins, but also functions as a local trigger of programmed death in challenged cells and as a diffusible signal for the induction in adjacent cells of genes encoding cellular protectants such as glutathione S-transferase and glutathione peroxidase. Thus, H2O2 from the oxidative burst plays a key role in the orchestration of a localized hypersensitive response during the expression of plant disease resistance.

An ethylene-responsive enhancer element is involved in the senescence-related expression of the carnation glutathione-S-transferase (GST1) gene

The increased production of ethylene during carnation petal senescence regulates the transcription of the GST1 gene encoding a subunit of glutathione-S-transferase. We have investigated the molecular basis for this ethylene-responsive transcription by examining the cis elements and trans-acting factors involved in the expression of the GST1 gene. Transient expression assays following delivery of GST1 5' flanking DNA fused to a beta-glucuronidase receptor gene were used to functionally define sequences responsible for ethylene-responsive expression. Deletion analysis of the 5' flanking sequences of GST1 identified a single positive regulatory element of 197 bp between -667 and -470 necessary for ethylene-responsive expression. The sequences within this ethylene-responsive region were further localized to 126 bp between -596 and -470. The ethylene-responsive element (ERE) within this region conferred ethylene-regulated expression upon a minimal cauliflower mosaic virus-35S TATA-box promoter in an orientation-independent manner. Gel electrophoresis mobility-shift assays and DNase I footprinting were used to identify proteins that bind to sequences within the ERE. Nuclear proteins from carnation petals were shown to specifically interact with the 126-bp ERE and the presence and binding of these proteins were independent of ethylene or petal senescence. DNase I footprinting defined DNA sequences between -510 and -488 within the ERE specifically protected by bound protein. An 8-bp sequence (ATTTCAAA) within the protected region shares significant homology with promoter sequences required for ethylene responsiveness from the tomato fruit-ripening E4 gene.

Characterization of two cDNAs (ERD11 and ERD13) for dehydration-inducible genes that encode putative glutathione S-transferases in Arabidopsis thaliana L

Two cDNA clones, designated ERD11 and ERD13, isolated from a cDNA library from Arabidopsis thaliana L. plants dehydrated for 1 h were sequenced and characterized. These clones encoded polypeptides that were homologous to glutathione S-transferases of tobacco and maize. Genomic Southern hybridization suggested that there are a few additional genes showing high similarity to the ERD11 gene in the Arabidopsis genome. The expression of the genes for ERD11 and ERD13 was induced by dehydration, but was not affected by the application of four plant growth regulators, 2,4-dichlorophenoxyacetic acid 6-benzylaminopurine, abscisic acid, or gibberellic acid.

Organization and structure of the 1-aminocyclopropane-1-carboxylate oxidase gene family from Petunia hybrida

In this paper we present the structural analysis of the 1-aminocyclopropane-1-carboxylate (ACC) oxidase gene family from Petunia hybrida. Southern blot analysis and restriction endonuclease mapping showed that two cloned regions of the petunia genome contained sequences highly homologous to a previously isolated ACC oxidase cDNA clone. Nucleotide sequencing of these two regions of the genome showed that each contained two tandemly arranged genes designated ACO1, ACO2, ACO3 and ACO4. Comparison of the nucleotide sequences of the cloned genomic regions with the cDNA clone pPHEFE indicated that ACO1 encoded the transcript in 4 exons interrupted by 3 introns. The other three members of the petunia ACC oxidase gene family shared identical intron numbers and positions with ACO1 and their exons were greater than 80% homologous. Nucleotide substitutions and deletions in the ACO2 gene indicate that it likely represents a pseudogene. Overall homology between ACO1 and ACO2 indicates that this gene cluster arose by a more recent duplication event than the gene duplication giving rise to the ACO3 and ACO4 cluster. The 5-flanking sequences share little overall homology between members of this gene family. However, sequences which likely make up the core promoter of these genes including the TATA box are highly homologous. RNA-based PCR amplification of ACC oxidase cDNAs from ethylene-treated corollas and wounded leaves revealed transcripts for ACO1, ACO3 and ACO4 indicating that a least three of these genes are transcriptionally active. The proteins encoded by ACO1, ACO3 and ACO4 share more than 90% identity with one another and more than 70% identity with ACC oxidases from other species. The ACC oxidase proteins share significant sequence homology with other enzymes that require Fe(II) and ascorbate for catalytic activity.

A flower senescence-related mRNA from carnation encodes a novel protein related to enzymes involved in phosphonate biosynthesis

We have isolated a cDNA clone (pSR132) representing a mRNA which accumulates in senescing carnation flower petals in response to ethylene. In vitro translation of RNA selected by hybridization with pSR132 indicated the mRNA encoded a polypeptide of approximately 36 kDa. This was confirmed by DNA sequence analysis, which predicted a peptide composed of 318 amino acids with a calculated molecular weight of 34.1 kDa. Comparison of the predicted peptide sequence of pSR132 with other proteins compiled in the NBRF data base revealed significant homology with carboxyphosphonoenolpyruvate mutase and phosphoenolpyruvate mutase from Streptomyces hygroscopicus and Tetrahymena pyriformis, respectively. These enzymes are involved in the formation of C-P bonds in the biosynthesis of phosphonates. C-P bonds are found in a wide range of organisms, but their presence or formation in higher plants has not been investigated.