Arabidopsis AtGSTF2 is regulated by ethylene and auxin, and encodes a glutathione S-transferase that interacts with flavonoids

Genome-Wide Analysis of SAUR Gene Family Identifies a Candidate Associated with Fruit Size in Loquat (Eriobotrya japonica Lindl.)

Fruit size is an important fruit quality trait that influences the production and commodity values of loquats (Eriobotrya japonica Lindl.). The Small Auxin Upregulated RNA (SAUR) gene family has proven to play a vital role in the fruit development of many plant species. However, it has not been comprehensively studied in a genome-wide manner in loquats, and its role in regulating fruit size remains unknown. In this study, we identified 95 EjSAUR genes in the loquat genome. Tandem duplication and segmental duplication contributed to the expansion of this gene family in loquats. Phylogenetic analysis grouped the SAURs from Arabidopsis, rice, and loquat into nine clusters. By analyzing the transcriptome profiles in different tissues and at different fruit developmental stages and comparing two sister lines with contrasting fruit sizes, as well as by functional predictions, a candidate gene (EjSAUR22) highly expressed in expanding fruits was selected for further functional investigation. A combination of Indoleacetic acid (IAA) treatment and virus-induced gene silencing revealed that EjSAUR22 was not only responsive to auxin, but also played a role in regulating cell size and fruit expansion. The findings from our study provide a solid foundation for understanding the molecular mechanisms controlling fruit size in loquats, and also provide potential targets for manipulation of fruit size to accelerate loquat breeding.

The Glutathione S-Transferase PtGSTF1 Improves Biomass Production and Salt Tolerance through Regulating Xylem Cell Proliferation, Ion Homeostasis and Reactive Oxygen Species Scavenging in Poplar

Glutathione S-transferases (GSTs) play an essential role in plant cell detoxification and secondary metabolism. However, their accurate functions in the growth and response to abiotic stress in woody plants are still largely unknown. In this work, a Phi class Glutathione S-transferase encoding gene PtGSTF1 was isolated from poplar (P. trichocarpa), and its biological functions in the regulation of biomass production and salt tolerance were investigated in transgenic poplar. PtGSTF1 was ubiquitously expressed in various tissues and organs, with a predominant expression in leaves and inducible expression by salt stress. Transgenic poplar overexpressing PtGSTF1 showed improved shoot growth, wood formation and improved salt tolerance, consistent with the increased xylem cell number and size under normal condition, and the optimized Na⁺ and K⁺ homeostasis and strengthened reactive oxygen species scavenging during salt stress. Further transcriptome analyses demonstrated that the expressions of genes related to hydrolase, cell wall modification, ion homeostasis and ROS scavenging were up- or down-regulated in transgenic plants. Our findings imply that PtGSTF1 improves both biomass production and salt tolerance through regulating hydrolase activity, cell wall modification, ion homeostasis and ROS scavenging in transgenic poplar, and that it can be considered as a useful gene candidate for the genetic breeding of new tree varieties with improved growth under salt stress conditions.

RsGSTF12 Contributes to Anthocyanin Sequestration in Radish (Raphanus sativus L.)

Anthocyanins are water-soluble plant pigments mainly stored in the plant vacuoles. Glutathione S-transferases (GSTs) are a multifunctional enzyme family, which can regulate substance metabolism and biological and abiotic stresses in plants. However, few reports were focused on the involvement of GSTs in anthocyanin sequestration in red skin radish. Here, we identified a glutathione S-transferase gene RsGSTF12 that played roles in anthocyanin sequestration in radish. The bioinformatics analysis revealed that RsGSTF12 belonged to the phi (F) class of glutathione S-transferases and showed a high homology with AtGSTF12, followed by AtGSTF11. The subcellular localization assay showed that RsGSTF12 was located in the endoplasmic reticulum and tonoplast. Temporal and spatial gene expression-specific analyses uncovered a strong correlation of RsGSTF12 with anthocyanin accumulation in radish sprouts. The anthocyanin solubility assay found RsGSTF12 was capable of improving cyanidin water solubility in vitro. Transiently expressing RsGSTF12 in radish cotyledons was able to increase their anthocyanin sequestrations. Furthermore, the functional complementation and overexpression of the Arabidopsis thaliana tt19 mutant and wild type demonstrated that RsGSTF12 might play an indispensable role in anthocyanin accumulation in radish. Taken together, we provide compelling evidence that RsGSTF12 functions critically in how anthocyanins are sequestrated in radish, which may enrich our understanding of the mechanism of anthocyanin sequestration.

Glutathione S-transferase: a candidate gene for berry color in muscadine grapes (Vitis rotundifolia)

Muscadine grapes (Vitis rotundifolia Michx.) are a specialty crop cultivated in the southern United States. Muscadines (2n = 40) belong to the Muscadinia subgenus of Vitis, while other cultivated grape species belong to the subgenus Euvitis (2n = 38). The muscadine berry color locus was mapped to a 0.8 Mbp region syntenic with chromosome 4 of Vitis vinifera. In this study, we identified glutathione S-transferase4 as a likely candidate gene for anthocyanin transport within the berry color locus. PCR and Kompetitive allele-specific PCR genotyping identified a single intragenic SNP (C/T) marker corresponding to a proline to leucine mutation within the muscadine glutathione S-transferase4 (VrGST4) that differentiated black (CC and CT) from bronze (TT) muscadines in 126 breeding selections, 76 cultivars, and 359 progeny from 3 mapping populations. Anthocyanin profiling on a subset of the progeny indicated a dominant VrGST4 action. VrGST4 was expressed in skins of both black and bronze muscadines at similar levels. While nonsynonymous polymorphisms between black and bronze muscadines were discovered in VrGSTF12, another Type I GST-coding gene in the muscadine color locus, this gene was ruled out as a possible candidate for berry color because RNA sequencing indicated it is not expressed in berry skins at véraison from black or bronze genotypes. These results suggest that the bronze phenotype in muscadines is regulated by a mechanism distinct from the MybA gene cluster responsible for berry color variation in Vitis vinifera.

Genome-Wide Identification, Evolution and Expression Analysis of the Glutathione S-Transferase Supergene Family in Euphorbiaceae

Euphorbiaceae, a family of plants mainly grown in the tropics and subtropics, is also widely distributed all over the world and is well known for being rich in rubber, oil, medicinal materials, starch, wood and other economically important plant products. Glutathione S-transferases (GSTs) constitute a family of proteins encoded by a large supergene family and are widely expressed in animals, bacteria, fungi and plants, but with few reports of them in Euphorbiaceae plants. These proteins participate in and regulate the detoxification and oxidative stress response of heterogeneous organisms, resistance to stress, growth and development, signal transduction and other related processes. In this study, we identified and analyzed the whole genomes of four species of Euphorbiaceae, namely Ricinus communis, Jatropha curcas, Hevea brasiliensis, and Manihot esculenta, which have high economic and practical value. A total of 244 GST genes were identified. Based on their sequence characteristics and conserved domain types, the GST supergene family in Euphorbiaceae was classified into 10 subfamilies. The GST supergene families of Euphorbiaceae and Arabidopsis have been found to be highly conserved in evolution, and tandem repeats and translocations in these genes have made the greatest contributions to gene amplification here and have experienced strong purification selection. An evolutionary analysis showed that Euphorbiaceae GST genes have also evolved into new subtribes (GSTO, EF1BG, MAPEG), which may play a specific role in Euphorbiaceae. An analysis of expression patterns of the GST supergene family in Euphorbiaceae revealed the functions of these GSTs in different tissues, including resistance to stress and participation in herbicide detoxification. In addition, an interaction analysis was performed to determine the GST gene regulatory mechanism. The results of this study have laid a foundation for further analysis of the functions of the GST supergene family in Euphorbiaceae, especially in stress and herbicide detoxification. The results have also provided new ideas for the study of the regulatory mechanism of the GST supergene family, and have provided a reference for follow-up genetics and breeding work.

iTRAQ-based quantitative proteome analysis insights into cold stress of Winter Rapeseed (Brassica rapa L.) grown in the field

Winter rapeseed (Brassica rapa L.) is a major oilseed crop in Northern China, where its production was severely affected by chilling and freezing stress. However, not much is known about the role of differentially accumulated proteins (DAPs) during the chilling and freezing stress. In this study, isobaric tag for relative and absolute quantification (iTRAQ) technology was performed to identify DAPs under freezing stress. To explore the molecular mechanisms of cold stress tolerance at the cellular and protein levels, the morphological and physiological differences in the shoot apical meristem (SAM) of two winter rapeseed varieties, Longyou 7 (cold-tolerant) and Lenox (cold-sensitive), were explored in field-grown plants. Compared to Lenox, Longyou 7 had a lower SAM height and higher collar diameter. The level of malondialdehyde (MDA) and indole-3-acetic acid (IAA) content was also decreased. Simultaneously, the soluble sugars (SS) content, superoxide dismutase (SOD) activity, peroxidase (POD) activity, soluble protein (SP) content, and collar diameter were increased in Longyou 7 as compared to Lenox. A total of 6330 proteins were identified. Among this, 98, 107, 183 and 111 DAPs were expressed in L7 CK/Le CK, L7 d/Le d, Le d/Le CK and L7 d/L7 CK, respectively. Quantitative real-time PCR (RT-qPCR) analysis of the coding genes for seventeen randomly selected DAPs was performed for validation. These DAPs were identified based on gene ontology enrichment analysis, which revealed that glutathione transferase activity, carbohydrate-binding, glutathione binding, metabolic process, and IAA response were closely associated with the cold stress response. In addition, some cold-induced proteins, such as glutathione S-transferase phi 2(GSTF2), might play an essential role during cold acclimation in the SAM of Brassica rapa. The present study provides valuable information on the involvement of DAPs during cold stress responses in Brassica rapa L, and hence could be used for breeding experiments.

Flavonoid-based inhibitors of the Phi-class glutathione transferase from black-grass to combat multiple herbicide resistance

The evolution and growth of multiple-herbicide resistance (MHR) in grass weeds continues to threaten global cereal production. While various processes can contribute to resistance, earlier work has identified the phi class glutathione-S-transferase (AmGSTF1) as a functional biomarker of MHR in black-grass (Alopecurus myosuroides). This study provides further insights into the role of AmGSTF1 in MHR using a combination of chemical and structural biology. Crystal structures of wild-type AmGSTF1, together with two specifically designed variants that allowed the co-crystal structure determination with glutathione and a glutathione adduct of the AmGSTF1 inhibitor 4-chloro-7-nitro-benzofurazan (NBD-Cl) were obtained. These studies demonstrated that the inhibitory activity of NBD-Cl was associated with the occlusion of the active site and the impediment of substrate binding. A search for other selective inhibitors of AmGSTF1, using ligand-fishing experiments, identified a number of flavonoids as potential ligands. Subsequent experiments using black-grass extracts discovered a specific flavonoid as a natural ligand of the recombinant enzyme. A series of related synthetic flavonoids was prepared and their binding to AmGSTF1 was investigated showing a high affinity for derivatives bearing a O-5-decyl-α-carboxylate. Molecular modelling based on high-resolution crystal structures allowed a binding pose to be defined which explained flavonoid binding specificity. Crucially, high binding affinity was linked to a reversal of the herbicide resistance phenotype in MHR black-grass. Collectively, these results present a nature-inspired new lead for the development of herbicide synergists to counteract MHR in weeds.

Glutathione S-transferase: a versatile protein family

Glutathione-S transferase (GST) is a most ancient protein superfamily of multipurpose roles and evolved principally from gene duplication of an ancestral GSH binding protein. They have implemented in diverse plant functions such as detoxification of xenobiotic, secondary metabolism, growth and development, and majorly against biotic and abiotic stresses. The vital structural features of GSTs like highly divergent functional topographies, conserved integrated architecture with separate binding pockets for substrates and ligand, the stringent structural fidelity with high Tm values (50º-60º), and stress-responsive cis-regulatory elements in the promoter region offer this protein as most flexible plant protein for plant breeding approaches, biotechnological applications, etc. This review article summarizes the recent information of GST evolution, and their distribution and structural features with emphasis on the assorted roles of Ser and Cys GSTs with the signature motifs in their active sites, alongside their recent biotechnological application in the area of agriculture, environment, and nanotechnology have been highlighted.

Molecular analysis of somatic embryogenesis through proteomic approach and optimization of protocol in recalcitrant Musa spp

Somatic embryogenesis (SE) is a complex stress related process regulated by numerous biological factors. SE is mainly applicable to mass propagation and genetic improvement of plants through gene transfer technology and induced mutations. In banana, SE is highly genome dependent as the efficiency varies with cultivars. To understand the molecular mechanism of SE, a proteomics approach was carried out to identify proteins expressed during embryogenic calli (EC) induction, regeneration and germination of somatic embryos in the banana cultivar cv. Rasthali (AAB). In total, 70 spots were differentially expressed in various developmental stages of SE, of which 16 were uniquely expressed and 17 were highly abundant in EC compared to non-embryogenic calli and explants. Also, four spots were uniquely expressed in germinating somatic embryos. The functional annotation of identified proteins revealed that calcium signaling along with stress and endogenous hormones related proteins played a vital role in EC induction and germination of somatic embryos. Thus, based on this outcome, the callus induction media was modified and tested in five cultivars. Among them, cultivars Grand Naine (AAA), Monthan (ABB) and Ney Poovan (AB) showed a better response in tryptophan added media, whereas Red Banana (AAA) and Karpuravalli (ABB) showed maximum EC induction in kinetin and CaCl₂ supplemented media respectively. Simultaneously, germination media were modified to induce proteins responsible for germination. In cv. Rasthali, media supplemented with 10 mM CaCl₂ showed a maximum increase in germination (51.79%) over control plants. Thus, the present study revealed that media modification based on proteomic analysis can induce SE in recalcitrant cultivars and also enhance germination in cultivars amenable for SE.

Mutation of Mediator subunit CDK8 counteracts the stunted growth and salicylic acid hyperaccumulation phenotypes of an Arabidopsis MED5 mutant

The Mediator complex functions as a hub for transcriptional regulation. MED5, an Arabidopsis Mediator tail subunit, is required for maintaining phenylpropanoid homeostasis. A semidominant mutation (ref4-3) that causes a single amino acid substitution in MED5b functions as a strong suppressor of the pathway, leading to decreased soluble phenylpropanoid accumulation, reduced lignin content and dwarfism. By contrast, loss of MED5 results in increased concentrations of phenylpropanoids. We used a reverse genetic approach to identify suppressors of ref4-3 and found that ref4-3 requires CDK8, a kinase module subunit of Mediator, to repress plant growth. The genetic interaction between MED5 and CDK8 was further characterized using mRNA-sequencing (RNA-seq) and metabolite analysis. Growth inhibition and suppression of phenylpropanoid metabolism can be genetically separated in ref4-3 by elimination of CDK8 kinase activity; however, the stunted growth of ref4-3 is not dependent on the phosphorylation event introduced by the G383S mutation. In addition, rather than perturbation of lignin biosynthesis, misregulation of DJC66, a gene encoding a DNAJ protein, is involved in the dwarfism of the med5 mutants. Together, our study reveals genetic interactions between Mediator tail and kinase module subunits and enhances our understanding of dwarfing in phenylpropanoid pathway mutants.

Genome wide identification and comparative analysis of glutathione transferases (GST) family genes in Brassica napus

Glutathione transferases (GSTs) are multifunctional enzymes that play important roles in plant development and responses to biotic and abiotic stress. However, a systematic analysis of GST family members in Brassica napus has not yet been reported. In this study, we identified 179 full-length GST genes in B. napus, 44.2% of which are clustered on various chromosomes. In addition, we identified 141 duplicated GST gene pairs in B. napus. Molecular evolutionary analysis showed that speciation and whole-genome triplication played important roles in the divergence of the B. napus GST duplicated genes. Transcriptome analysis of 21 tissues at different developmental stages showed that 47.6% of duplicated GST gene pairs have divergent expression patterns, perhaps due to structural divergence. We constructed a GST gene coexpression network with genes encoding various transcription factors (NAC, MYB, WRKY and bZIP) and identified six modules, including genes expressed during late seed development (after 40 days; BnGSTU19, BnGSTU20 and BnGSTZ1) and in the seed coat (BnGSTF6 and BnGSTF12), stamen and anther (BnGSTF8), root and stem (BnGSTU21), leaves and funiculus, as well as during the late stage of pericarp development (after 40 days; BnGSTU12 and BnGSTF2) and in the radicle during seed germination (BnGSTF14, BnGSTU1, BnGSTU28, and BnGSTZ1). These findings lay the foundation for elucidating the roles of GSTs in B. napus.

Genome-wide identification and expression of the entire 52 glutathione S-transferase (GST) subfamily genes in the Cu2+-exposed marine copepods Tigriopus japonicus and Paracyclopina nana

In this study, the entire glutathione S-transferases (GSTs), the major phase II detoxification enzyme, were identified in two marine copepod species Tigriopus japonicus and Paracyclopina nana. The genome-wide identification of GSTs in T. japonicus and P. nana resulted in 32 and 20 GSTs in total, respectively. Among the identified GSTs, two specific classes of GSTs, specifically sigma and delta/epsilon GSTs were the dominant form of cytosolic GSTs in T. japonicus, while delta/epsilon and mu classes were dominant cytosolic GSTs in P. nana. In addition, Membrane-Associated Proteins in Eicosanoid and Glutathione metabolism (MAPEG) family were found in relatively higher proportion compared to other classes. Moreover, sigma, delta/epsilon, and microsomal GSTs have shown to expand through tandem duplication. To validate the detoxification function of the identified GSTs, both copepods were exposed to copper (Cu²⁺) and the reactive oxygen species (ROS) level and GST activity were measured. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in two marine copepod species and their important role in marine environmental ecotoxicology.

CtACO1 Overexpression Resulted in the Alteration of the Flavonoids Profile of Safflower

Background: Flavonoids with various structures play a vital role in plant acclimatization to varying environments as well as in plant growth, development, and reproduction. Exogenous applications of ethylene and 1-aminocyclopropane carboxylic acid (ACC), could affect the accumulation of flavonoids. Very few attempts have been made to investigate the effect of 1-aminocyclopropane carboxylic acid oxidase (ACO), a unique enzyme that catalyzes ACC to ethylene, on genes and metabolites in the flavonoid biosynthetic pathway. In this study, two ACOs in safflower (CtACOs) were cloned, and then transgenic safflower with overexpressed CtACO1 was generated through the Agrobacterium-mediated floral dipping method. Results: CtACO1 and CtACO2 were both characterized by the 2-oxoglutarate binding domain RxS and the ferrous iron binding site HxDxnH as ACOs from other plants. However, the transcript levels of CtACO1 in flowers at stages I, II, III, and IV were all higher than those of CtACO2. At the cellular level, by using electroporation transformation, CtACO1 was found to be localized at the cytomembrane in onion epidermal cells. CtACO1 overexpression had varying effects on genes involved in the ethylene and flavonoid biosynthetic pathways. The metabolites analysis showed that CtACO1 overexpression lines had a higher accumulation of quercetin and its glycosylated derivatives (quercetin 3-β-d-glucoside and rutin). In contrast, the accumulation of quinochalcones (hydroxysafflor yellow A and carthamin), kaempferol glycosylated derivatives (kaempferol-3-O-β-rutinoside and kaempferol-3-O-β-d-glucoside), apigenin, and luteolin in CtACO1 overexpression lines were decreased. Conclusion: This study confirmed the feasibility of applying the floral dipping method to safflower and showed a novel regulatory effect of CtACO1 in the flavonoid biosynthetic pathway. It provides hypothetical and practical groundwork for further research on regulating the overall metabolic flux of flavonoids in safflower, particularly hydroxysafflor yellow A and other quinochalcones, by using appropriate genetic engineering strategies.

RNA-Seq Transcriptome Analysis of Rice Primary Roots Reveals the Role of Flavonoids in Regulating the Rice Primary Root Growth

Flavonoids play important roles in root development and in its tropic responses, whereas the flavonoids-mediated changes of the global transcription levels during root growth remain unclear. Here, the global transcription changes in quercetin-treated rice primary roots were analyzed. Quercetin treatment significantly induced the inhibition of root growth and the reduction of H₂O₂ and O₂⁻ levels. In addition, the RNA-seq analysis revealed that there are 1243 differentially expressed genes (DEGs) identified in quercetin-treated roots, including 1032 up-regulated and 211 down-regulated genes. A gene ontology (GO) enrichment analysis showed that the enriched GO terms are mainly associated with the cell wall organization, response to oxidative stress, and response to hormone stimulus. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment pathway analysis showed that the enriched DEGs are involved in phenylpropanoid biosynthesis, glutathione metabolism, and plant hormone signal transduction. Moreover, the quercetin treatment led to an increase of the antioxidant enzyme activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) in rice roots. Also, the quercetin treatment altered the DR5:GUS expression pattern in the root tips. All of these data indicated that the flavonoids-mediated transcription changes of genes are related to the genes involved in cell wall remodeling, redox homeostasis, and auxin signaling, leading to a reduced cell division in the meristem zone and cell elongation in the elongation zone of roots.

Functional, Structural and Biochemical Features of Plant Serinyl-Glutathione Transferases

Glutathione transferases (GSTs) belong to a ubiquitous multigenic family of enzymes involved in diverse biological processes including xenobiotic detoxification and secondary metabolism. A canonical GST is formed by two domains, the N-terminal one adopting a thioredoxin (TRX) fold and the C-terminal one an all-helical structure. The most recent genomic and phylogenetic analysis based on this domain organization allowed the classification of the GST family into 14 classes in terrestrial plants. These GSTs are further distinguished based on the presence of the ancestral cysteine (Cys-GSTs) present in TRX family proteins or on its substitution by a serine (Ser-GSTs). Cys-GSTs catalyze the reduction of dehydroascorbate and deglutathionylation reactions whereas Ser-GSTs catalyze glutathione conjugation reactions and eventually have peroxidase activity, both activities being important for stress tolerance or herbicide detoxification. Through non-catalytic, so-called ligandin properties, numerous plant GSTs also participate in the binding and transport of small heterocyclic ligands such as flavonoids including anthocyanins, and polyphenols. So far, this function has likely been underestimated compared to the other documented roles of GSTs. In this review, we compiled data concerning the known enzymatic and structural properties as well as the biochemical and physiological functions associated to plant GSTs having a conserved serine in their active site.

Structure-Guided Mechanisms Behind the Metabolism of 2,4,6-Trinitrotoluene by Glutathione Transferases U25 and U24 That Lead to Alternate Product Distribution

The explosive xenobiotic 2,4,6-trinitrotoluene (TNT) is a major worldwide environmental pollutant and its persistence in the environment presents health and environmental concerns. The chemical structure of TNT dictates that biological detoxification pathways follow predominantly reductive transformation of the nitro groups, and as a result, TNT is notoriously recalcitrant to mineralization in the environment. Plant-based technologies to remediate this toxic pollutant rely on a solid understanding of the biochemical detoxification pathways involved. Toward this, two Arabidopsis Tau class glutathione transferases, GSTU24 and GSTU25, have been identified that catalyze the formation of three TNT-glutathionylated conjugates. These two GSTs share 79% identity yet only GSTU25 catalyzes the substitution of a nitro group for sulfur to form 2-glutathionyl-4,6-dinitrotoluene. The production of this compound is of interest because substitution of a nitro group could lead to destabilization of the aromatic ring, enabling subsequent biodegradation. To identify target amino acids within GSTU25 that might be involved in the formation of 2-glutathionyl-4,6-dinitrotoluene, the structure for GSTU25 was determined, in complex with oxidized glutathione, and used to inform site-directed mutagenesis studies. Replacement of five amino acids in GSTU24 established a conjugate profile and activity similar to that found in GSTU25. These findings contribute to the development of plant-based remediation strategies for the detoxification of TNT in the environment.

Proteomic analysis of the response of Funnelifor mismosseae/Medicago sativa to atrazine stress

BACKGROUND

Arbuscular mycorrhizal (AM) fungi form symbiotic associations with host plants can protect host plants against diverse biotic and abiotic stresses, and promote biodegradation of various contaminants. However, the molecular mechanisms of how the arbuscular mycorrhizal fungi and host plant association on atrazine stress were still poorly understood. To better characterize how arbuscular mycorrhizal fungi and host plant interactions increase atrazine stress, we performed physiological and proteomic analysis of Funneliformis mosseae (mycorrhizal fungi) and Medicago sativa (alfalfa) association under atrazine stress.

RESULTS

The results showed that in the Arbuscular mycorrhizal, protective enzymes were up regulated and the malondialdehyde content increased relative to those of non-mycorrhizal M.sativa. We also examined the atrazine degradation rates within the nutrient solution, and a 44.43% reduction was observed with the mycorrhizal M.sativa, with 30.83% of the reduction attributed to F. mosseae. The accumulation content in root and stem of mycorrhizal M.sativa were obviously increased 11.89% and 16.33% than those of non- mycorrhizal M.sativa. The activity of PPO, POD, CAT and SOD in mycorrhizal M.sativa were obviously higher than non mycorrhizal M.sativa under atrazine stess. We identified differential root proteins using isobaric tags for relative and absolute quantization coupled with liquid chromatography-mass spectrometry, with 533 proteins identified (276 unregulated and 257 downregulated). The differentially expressed proteins were further examined using GO, BLAST comparisons, and a literature inquiry and were classified into the categories of atrazine degradation (37.1%); atrazine stress response (28.6%); plant immune responses (14.3%); translation, synthesis, and processing (10%); and signal transduction and biological processes (10%). Furthermore, we identified glycosyl transferase, glutathione S-transferase, laccase, cytochrome P450 monooxygenase, peroxidase, and other proteins closely related to the degradation process.

CONCLUSIONS

Mycorrhizal Medicago showed improved atrazine degradation within the culturing medium and increased atrazine enrichment in the roots and stems. Additionally, AMF increased the plant root response to atrazine, with relevant enzymes up regulated and toxic effects alleviated. Overall, the findings of this study show that AMF played an important role in easing atrazine stress in plants and contributed to atrazine remediation and further contributed to the understanding of the molecular mechanism associated with atrazine stresses and potential mycorrhizal contributions in M.sativa.

Weed resistance to synthetic auxin herbicides

Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non-cropland areas since the first synthetic auxin herbicide (SAH), 2,4-D, was introduced to the market in the mid-1940s. The incidence of weed species resistant to SAHs is relatively low considering their long-term global application with 30 broadleaf, 5 grass, and 1 grass-like weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017; Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH-tolerant crops. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Antidiabetic and antiparasitic potentials: Inhibition effects of some natural antioxidant compounds on α-glycosidase, α-amylase and human glutathione S-transferase enzymes

The glutathione S-transferase (GST) was purified from fresh blood erythrocytes using affinity column chromatography. Also, α-amylase from porcine pancreas and α-glycosidase from Saccharomyces cerevisiae were used as target enzymes. In this study, these compounds were tested on α-amylase, α-glycosidase, and GST enzymes and demonstrated effective inhibitor compounds with K_i values in the range of 8.34-40.78 μM against GST, and 120.53-892.36 nM against α-glycosidase. Additionally, the phenolic molecules were tested for the inhibition of α-amylase enzyme which determined effective inhibition profile with IC₅₀ values in the range of 175.01-626.58 nM. Indeed, these molecules can be elective inhibitors of GST, α-glycosidase and α-amylase enzymes as antidiabetic and antiparasitic agents.

Protein-Ligand Fishing in planta for Biologically Active Natural Products Using Glutathione Transferases

Screening for natural products which bind to proteins in planta has been used to identify ligands of the plant-specific glutathione transferase (GST) tau (U) and phi (F) classes, that are present in large gene families in crops and weeds, but have largely undefined functions. When expressed as recombinant proteins in Escherichia coli these proteins have been found to tightly bind a diverse range of natural product ligands, with fatty acid-and porphyrinogen-derivatives associated with GSTUs and a range of heterocyclic compounds with GSTFs. With an interest in detecting the natural binding partners of these proteins in planta, we have expressed the two best characterized GSTs from Arabidopsis thaliana (At), AtGSTF2 and AtGSTU19, as Strep-tagged fusion proteins in planta. Following transient and stable expression in Nicotiana and Arabidopsis, respectively, the GSTs were recovered using Strep-Tactin affinity chromatography and the bound ligands desorbed and characterized by LC-MS. AtGSTF2 predominantly bound phenolic derivatives including S-glutathionylated lignanamides and methylated variants of the flavonols kaempferol and quercetin. AtGSTU19 captured glutathionylated conjugates of oxylipins, indoles, and lignanamides. Whereas the flavonols and oxylipins appeared to be authentic in vivo ligands, the glutathione conjugates of the lignanamides and indoles were artifacts formed during extraction. When tested for their binding characteristics, the previously undescribed indole conjugates were found to be particularly potent inhibitors of AtGSTU19. Such ligand fishing has the potential to both give new insight into protein function in planta as well as identifying novel classes of natural product inhibitors of enzymes of biotechnological interest such as GSTs.

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.

Effect of Patulin from Penicillium vulpinum on the Activity of Glutathione-S-Transferase and Selected Antioxidative Enzymes in Maize

The mycotoxin patulin (PAT) was purified from Penicillium vulpinum CM1 culture that has been isolated from a soil cultivated with maize. The effect of PAT and of a fungal culture filtrate on the activities of glutathione-S-transferase (GST) and some antioxidant enzymes viz. ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) was investigated in roots and shoots of 8-day-old maize seedlings. PAT and culture filtrate caused significant reduction effects in a dose-related manner on the total GST activity. Upon application of the high PAT concentration (25 μg·mL-1) and of the concentrated fungal filtrate (100%, v/v), the reduction in GST activity of roots was 73.8-76.0% and of shoots was 60-61.7%. Conversely, significant increases in the activities of antioxidant enzymes were induced. Application of 25 μg·PAT·mL-1 increased APX, GR, DHAR, and MDHAR activity of root by 2.40-, 2.00-, 1.24-, and 2.16-fold, respectively. In shoots, the enzymatic activity was increased by 1.57-, 1.45-, 1.45-, and 1.61-fold, respectively. Similar induction values of the enzymatic activity were obtained upon application of the concentrated fungal filtrate. This is the first report describing the response of GST and antioxidant enzyme activities of plant cells to PAT toxicity.

Current understanding of the pathways of flavonoid biosynthesis in model and crop plants

Flavonoids are a signature class of secondary metabolites formed from a relatively simple collection of scaffolds. They are extensively decorated by chemical reactions including glycosylation, methylation, and acylation. They are present in a wide variety of fruits and vegetables and as such in Western populations it is estimated that 20-50 mg of flavonoids are consumed daily per person. In planta they have demonstrated to contribute to both flower color and UV protection. Their consumption has been suggested to presenta wide range of health benefits. Recent technical advances allowing affordable whole genome sequencing, as well as a better inventory of species-by-species chemical diversity, have greatly advanced our understanding as to how flavonoid biosynthesis pathways vary across species. In parallel, reverse genetics combined with detailed molecular phenotyping is currently allowing us to elucidate the functional importance of individual genes and metabolites and by this means to provide further mechanistic insight into their biological roles. Here we provide an inventory of current knowledge of pathways of flavonoid biosynthesis in both the model plant Arabidopsis thaliana and a range of crop species, including tomato, maize, rice, and bean.

Plants under Stress: Involvement of Auxin and Cytokinin

Plant growth and development are critically influenced by unpredictable abiotic factors. To survive fluctuating changes in their environments, plants have had to develop robust adaptive mechanisms. The dynamic and complementary actions of the auxin and cytokinin pathways regulate a plethora of developmental processes, and their ability to crosstalk makes them ideal candidates for mediating stress-adaptation responses. Other crucial signaling molecules responsible for the tremendous plasticity observed in plant morphology and in response to abiotic stress are reactive oxygen species (ROS). Proper temporal and spatial distribution of ROS and hormone gradients is crucial for plant survival in response to unfavorable environments. In this regard, the convergence of ROS with phytohormone pathways acts as an integrator of external and developmental signals into systemic responses organized to adapt plants to their environments. Auxin and cytokinin signaling pathways have been studied extensively. Nevertheless, we do not yet understand the impact on plant stress tolerance of the sophisticated crosstalk between the two hormones. Here, we review current knowledge on the function of auxin and cytokinin in redirecting growth induced by abiotic stress in order to deduce their potential points of crosstalk.

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

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

De Novo transcriptome characterization of Dracaena cambodiana and analysis of genes involved in flavonoid accumulation during formation of dragon's blood

Dragon’s blood is a red resin mainly extracted from Dracaena plants, and has been widely used as a traditional medicine in East and Southeast Asia. The major components of dragon’s blood are flavonoids. Owing to a lack of Dracaena plants genomic information, the flavonoids biosynthesis and regulation in Dracaena plants remain unknown. In this study, three cDNA libraries were constructed from the stems of D. cambodiana after injecting the inducer. Approximately 266.57 million raw sequencing reads were de novo assembled into 198,204 unigenes, of which 34,873 unique sequences were annotated in public protein databases. Many candidate genes involved in flavonoid accumulation were identified. Differential expression analysis identified 20 genes involved in flavonoid biosynthesis, 27 unigenes involved in flavonoid modification and 68 genes involved in flavonoid transport that were up-regulated in the stems of D. cambodiana after injecting the inducer, consistent with the accumulation of flavonoids. Furthermore, we have revealed the differential expression of transcripts encoding for transcription factors (MYB, bHLH and WD40) involved in flavonoid metabolism. These de novo transcriptome data sets provide insights on pathways and molecular regulation of flavonoid biosynthesis and transport, and improve our understanding of molecular mechanisms of dragon’s blood formation in D. cambodiana.

Transcriptomic analysis reveals key early events of narciclasine signaling in Arabidopsis root apex

Histochemical staining and RNA-seq data demonstrated that the ROS- and plant hormone-regulated stress responses are the key early events of narciclasine signaling in Arabidopsis root cells. Narciclasine, an amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs, employs a broad range of functions on plant development and growth. However, its molecular interactions that modulate these roles in plants are not fully understood. To elucidate the global responses of Arabidopsis roots to short-term narciclasine exposure, we first measured the accumulation of H₂O₂ and O₂^- with histochemical staining, and then profiled the gene expression pattern in Arabidopsis root tips treated with 0.5 µM narciclasine across different exposure times by RNA-seq. Physiological measurements showed a significant increase in H₂O₂ began at 30-60 min of narciclasine treatment and O₂^- accumulated by 120 min. Compared with controls, 236 genes were upregulated and 54 genes were downregulated with 2 h of narciclasine treatment, while 968 genes were upregulated and 835 genes were downregulated with 12 h of treatment. The Gene Ontology analysis revealed that the differentially expressed genes were highly enriched during oxidative stress, including those involved in the "regulation of transcription", "response to oxidative stress", "plant-pathogen interaction", "ribonucleotide binding", "plant cell wall organization", and "ribosome biogenesis". Moreover, Kyoto Encyclopedia of Genes and Genomes pathway enrichment statistics suggested that carbohydrate metabolism, amino acid metabolism, amino sugar and nucleotide sugar metabolism, and biosynthesis of phenylpropanoid and secondary metabolites were significantly inhibited by 12 h of narciclasine exposure. Hence, our results demonstrate that hormones and H₂O₂ are important regulators of narciclasine signaling and help to uncover the factors involved in the molecular interplay between narciclasine and phytohormones in Arabidopsis root cells.

Identification and Comparative Analysis of H2O2-Scavenging Enzymes (Ascorbate Peroxidase and Glutathione Peroxidase) in Selected Plants Employing Bioinformatics Approaches

Among major reactive oxygen species (ROS), hydrogen peroxide (H2O2) exhibits dual roles in plant metabolism. Low levels of H2O2 modulate many biological/physiological processes in plants; whereas, its high level can cause damage to cell structures, having severe consequences. Thus, steady-state level of cellular H2O2 must be tightly regulated. Glutathione peroxidases (GPX) and ascorbate peroxidase (APX) are two major ROS-scavenging enzymes which catalyze the reduction of H2O2 in order to prevent potential H2O2-derived cellular damage. Employing bioinformatics approaches, this study presents a comparative evaluation of both GPX and APX in 18 different plant species, and provides valuable insights into the nature and complex regulation of these enzymes. Herein, (a) potential GPX and APX genes/proteins from 18 different plant species were identified, (b) their exon/intron organization were analyzed, (c) detailed information about their physicochemical properties were provided, (d) conserved motif signatures of GPX and APX were identified, (e) their phylogenetic trees and 3D models were constructed, (f) protein-protein interaction networks were generated, and finally (g) GPX and APX gene expression profiles were analyzed. Study outcomes enlightened GPX and APX as major H2O2-scavenging enzymes at their structural and functional levels, which could be used in future studies in the current direction.

An RNA-Seq-based reference transcriptome for Citrus

Previous RNA-Seq studies in citrus have been focused on physiological processes relevant to fruit quality and productivity of the major species, especially sweet orange. Less attention has been paid to vegetative or reproductive tissues, while most Citrus species have never been analysed. In this work, we characterized the transcriptome of vegetative and reproductive tissues from 12 Citrus species from all main phylogenetic groups. Our aims were to acquire a complete view of the citrus transcriptome landscape, to improve previous functional annotations and to obtain genetic markers associated with genes of agronomic interest. 28 samples were used for RNA-Seq analysis, obtained from 12 Citrus species: C. medica, C. aurantifolia, C. limon, C. bergamia, C. clementina, C. deliciosa, C. reshni, C. maxima, C. paradisi, C. aurantium, C. sinensis and Poncirus trifoliata. Four different organs were analysed: root, phloem, leaf and flower. A total of 3421 million Illumina reads were produced and mapped against the reference C. clementina genome sequence. Transcript discovery pipeline revealed 3326 new genes, the number of genes with alternative splicing was increased to 19,739, and a total of 73,797 transcripts were identified. Differential expression studies between the four tissues showed that gene expression is overall related to the physiological function of the specific organs above any other variable. Variants discovery analysis revealed the presence of indels and SNPs in genes associated with fruit quality and productivity. Pivotal pathways in citrus such as those of flavonoids, flavonols, ethylene and auxin were also analysed in detail.

Flavonoid transport mechanisms: how to go, and with whom

Subcellular flavonoid transport and its underlying regulatory mechanisms are still poorly understood, but are fascinating research frontiers in plant science. Recent studies support and further extend previous hypotheses indicating that vacuolar sequestration of flavonoids involves vesicle trafficking, membrane transporters, and glutathione S-transferase (GST). However, the question remains to be addressed of how three distinct but nonexclusive mechanisms are functionally integrated into diverse but redundant transport routes for vacuolar sequestration or extracellular secretion of flavonoids. In this review, I highlight recent progress in understanding flavonoid-transporting vesicle behavior and properties, GST and membrane transporter functions and mechanisms, and flavonoid transport substrate specificity and preference.

Production and transcriptional regulation of proanthocyanidin biosynthesis in forage legumes

Proanthocyanidins (PA), also known as condensed tannins, contribute to important forage legumes traits including disease resistance and forage quality. PA in forage plants has both positive and negative effects on feed digestibility and animal performance. The analytical methods and their applicability in measuring the contents of PA in forage plants are essential to studies on their nutritional effects. In spite of important breakthroughs in our understanding of the PA biosynthesis, important questions still remain to be answered such as the PA polymerization and transport. Recent advances in the understanding of transcription factor-mediated gene regulation mechanisms in anthocyanin and PA biosynthetic pathway in model plants suggest new approaches for the metabolic engineering of PA in forage plants. The present review will attempt to present the state-of-the-art of research in these areas and provide an update on the production and metabolic engineering of PA in forage plants. We hope that this will contribute to a better understanding of the ways in which PA production to manipulate the content of PA for beneficial effects in forage plants.

Low glutathione regulates gene expression and the redox potentials of the nucleus and cytosol in Arabidopsis thaliana

Reduced glutathione (GSH) is considered to exert a strong influence on cellular redox homeostasis and to regulate gene expression, but these processes remain poorly characterized. Severe GSH depletion specifically inhibited root meristem development, while low root GSH levels decreased lateral root densities. The redox potential of the nucleus and cytosol of Arabidopsis thaliana roots determined using roGFP probes was between -300 and -320 mV. Growth in the presence of the GSH-synthesis inhibitor buthionine sulfoximine (BSO) increased the nuclear and cytosolic redox potentials to approximately -260 mV. GSH-responsive genes including transcription factors (SPATULA, MYB15, MYB75), proteins involved in cell division, redox regulation (glutaredoxinS17, thioredoxins, ACHT5 and TH8) and auxin signalling (HECATE), were identified in the GSH-deficient root meristemless 1-1 (rml1-1) mutant, and in other GSH-synthesis mutants (rax1-1, cad2-1, pad2-1) as well as in the wild type following the addition of BSO. Inhibition of auxin transport had no effect on organ GSH levels, but exogenous auxin decreased the root GSH pool. We conclude that GSH depletion significantly increases the redox potentials of the nucleus and cytosol, and causes arrest of the cell cycle in roots but not shoots, with accompanying transcript changes linked to altered hormone responses, but not oxidative stress.

Cantharidin, a protein phosphatase inhibitor, strongly upregulates detoxification enzymes in the Arabidopsis proteome

Cantharidin, a potent inhibitor of plant serine/threonine protein phosphatases (PPPs), is highly phytotoxic and dramatically affects the transcriptome in Arabidopsis. To investigate the effect of cantharidin on the Arabidopsis proteome, a combination of two-dimensional difference gel electrophoresis (2-D DIGE) and matrix-assisted laser desorption ionization time-of-flight (MALDI/TOF) mass spectrometry was employed for protein profiling. Multivariate statistical analysis identified 75 significant differential spots corresponding to 59 distinct cantharidin-responsive proteins, which were representative of different biological processes, cellular components, and molecular functions categories. The majority of identified proteins localized in the chloroplast had a significantly decreased presence, especially proteins involved in photosynthesis. Detoxification enzymes, especially glutathione-S-transferases (GSTs), were the most upregulated group (ca. 1.5- to 3.3-fold). Given that the primary role of GSTs is involved in the process of detoxification of both xenobiotic and endobiotic compounds, the induction of GSTs suggests that cantharidin promoted inhibition of PPPs may lead to defense-like responses through regulation of GST enzymes as well as other metabolic pathways.

Structural and enzymatic insights into Lambda glutathione transferases from Populus trichocarpa, monomeric enzymes constituting an early divergent class specific to terrestrial plants

GSTs represent a superfamily of multifunctional proteins which play crucial roles in detoxification processes and secondary metabolism. Instead of promoting the conjugation of glutathione to acceptor molecules as do most GSTs, members of the Lambda class (GSTLs) catalyse deglutathionylation reactions via a catalytic cysteine residue. Three GSTL genes (Pt-GSTL1, Pt-GSTL2 and Pt-GSTL3) are present in Populus trichocarpa, but two transcripts, differing in their 5' extremities, were identified for Pt-GSTL3. Transcripts for these genes were primarily found in flowers, fruits, petioles and buds, but not in leaves and roots, suggesting roles associated with secondary metabolism in these organs. The expression of GFP-fusion proteins in tobacco showed that Pt-GSTL1 is localized in plastids, whereas Pt-GSTL2 and Pt-GSTL3A and Pt-GSTL3B are found in both the cytoplasm and the nucleus. The resolution of Pt-GSTL1 and Pt-GSTL3 structures by X-ray crystallography indicated that, although these proteins adopt a canonical GST fold quite similar to that found in dimeric Omega GSTs, their non-plant counterparts, they are strictly monomeric. This might explain some differences in the enzymatic properties of both enzyme types. Finally, from competition experiments between aromatic substrates and a fluorescent probe, we determined that the recognition of glutathionylated substrates is favoured over non-glutathionylated forms.

The still mysterious roles of cysteine-containing glutathione transferases in plants

Glutathione transferases (GSTs) represent a widespread multigenic enzyme family able to modify a broad range of molecules. These notably include secondary metabolites and exogenous substrates often referred to as xenobiotics, usually for their detoxification, subsequent transport or export. To achieve this, these enzymes can bind non-substrate ligands (ligandin function) and/or catalyze the conjugation of glutathione onto the targeted molecules, the latter activity being exhibited by GSTs having a serine or a tyrosine as catalytic residues. Besides, other GST members possess a catalytic cysteine residue, a substitution that radically changes enzyme properties. Instead of promoting GSH-conjugation reactions, cysteine-containing GSTs (Cys-GSTs) are able to perform deglutathionylation reactions similarly to glutaredoxins but the targets are usually different since glutaredoxin substrates are mostly oxidized proteins and Cys-GST substrates are metabolites. The Cys-GSTs are found in most organisms and form several classes. While Beta and Omega GSTs and chloride intracellular channel proteins (CLICs) are not found in plants, these organisms possess microsomal ProstaGlandin E-Synthase type 2, glutathionyl hydroquinone reductases, Lambda, Iota and Hemerythrin GSTs and dehydroascorbate reductases (DHARs); the four last classes being restricted to the green lineage. In plants, whereas the role of DHARs is clearly associated to the reduction of dehydroascorbate to ascorbate, the physiological roles of other Cys-GSTs remain largely unknown. In this context, a genomic and phylogenetic analysis of Cys-GSTs in photosynthetic organisms provides an updated classification that is discussed in the light of the recent literature about the functional and structural properties of Cys-GSTs. Considering the antioxidant potencies of phenolic compounds and more generally of secondary metabolites, the connection of GSTs with secondary metabolism may be interesting from a pharmacological perspective.

Spatial H2O2 signaling specificity: H2O2 from chloroplasts and peroxisomes modulates the plant transcriptome differentially

Hydrogen peroxide (H2O2) operates as a signaling molecule in eukaryotes, but the specificity of its signaling capacities remains largely unrevealed. Here, we analyzed whether a moderate production of H2O2 from two different plant cellular compartments has divergent effects on the plant transcriptome. Arabidopsis thaliana overexpressing glycolate oxidase in the chloroplast (Fahnenstich et al., 2008; Balazadeh et al., 2012) and plants deficient in peroxisomal catalase (Queval et al., 2007; Inzé et al., 2012) were grown under non-photorespiratory conditions and then transferred to photorespiratory conditions to foster the production of H2O2 in both organelles. We show that H2O2 originating in a specific organelle induces two types of responses: one that integrates signals independently from the subcellular site of H2O2 production and another that is dependent on the H2O2 production site. H2O2 produced in peroxisomes induces transcripts involved in protein repair responses, while H2O2 produced in chloroplasts induces early signaling responses, including transcription factors and biosynthetic genes involved in production of secondary signaling messengers. There is a significant bias towards the induction of genes involved in responses to wounding and pathogen attack by chloroplastic-produced H2O2, including indolic glucosinolates-, camalexin-, and stigmasterol-biosynthetic genes. These transcriptional responses were accompanied by the accumulation of 4-methoxy-indol-3-ylmethyl glucosinolate and stigmasterol.

The effects of redox controls mediated by glutathione peroxidases on root architecture in Arabidopsis thaliana

Glutathione peroxidases (GPXs) fulfil important functions in oxidative signalling and protect against the adverse effects of excessive oxidation. However, there has been no systematic characterization of the functions of the different GPX isoforms in plants. The roles of the different members of the Arabidopsis thaliana GPX gene (AtGPX) family were therefore investigated using gpx1, gpx2, gpx3, gpx4, gpx6, gpx7, and gpx8 T-DNA insertion mutant lines. The shoot phenotypes were largely similar in all genotypes, with small differences from the wild type observed only in the gpx2, gpx3, gpx7, and gpx8 mutants. In contrast, all the mutants showed altered root phenotypes compared with the wild type. The gpx1, gpx4, gpx6, gpx7, and gpx8 mutants had a significantly greater lateral root density (LRD) than the wild type. Conversely, the gpx2 and gpx3 mutants had significantly lower LRD values than the wild type. Auxin increased the LRD in all genotypes, but the effect of auxin was significantly greater in the gpx1, gpx4, and gpx7 mutants than in the wild type. The application of auxin increased GPX4 and GPX7 transcripts, but not GPX1 mRNAs in the roots of wild-type plants. The synthetic strigolactone GR24 and abscisic acid (ABA) decreased LRD to a similar extent in all genotypes, except gpx6, which showed increased sensitivity to ABA. These data not only demonstrate the importance of redox controls mediated by AtGPXs in the control of root architecture but they also show that the plastid-localized GPX1 and GPX7 isoforms are required for the hormone-mediated control of lateral root development.

A putative lambda class glutathione S-transferase enhances plant survival under salinity stress

In a survey of candidate genes located in the salinity tolerance locus of soybean, we identified a putative glutathione S-transferase (GST) gene (GmGSTL1) which was up-regulated in response to salt treatment. Phylogenetic analyses revealed that this putative GST belongs to the Lambda class, a plant-specific group with unknown functions. We expressed GmGSTL1 in heterologous systems, including tobacco BY-2 cells and Arabidopsis thaliana, to test its ability to protect the cell/plant against salinity stress. Compared with the control, we observed a marked reduction of reactive oxygen species (ROS) accumulation in transgenic cells under salt treatment, and their survival rate was also improved. Similarly, expression of GmGST1 in transgenic A. thaliana also alleviated stress symptoms under salt treatment. To address further the possible protective mechanisms of GmGSTL1, we identified two candidate flavonoid interactants (quercetin and kaemferol) of the GmGSTL1 protein from soybean leaf extract. Exogenous application of quercetin could reduce salinity-induced ROS accumulation in BY-2 cells and leaf chlorosis in A. thaliana.

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

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

Expression of OsMATE1 and OsMATE2 alters development, stress responses and pathogen susceptibility in Arabidopsis

Multidrug and Toxic compound Extrusion proteins (MATE) are a group of secondary active transporters with ubiquitous occurrences in all domains of life. This is a newly characterized transporter family with limited functional knowledge in plants. In this study, we functionally characterised two members of rice MATE gene family, OsMATE1 and OsMATE2 through expression in heterologous system, Arabidopsis. Expression of OsMATEs in Arabidopsis altered growth and morphology of transgenic plants. Genome-wide expression analysis revealed modulation of genes involved in plant growth, development and biotic stress in transgenic lines. Transgenic plants displayed sensitivity for biotic and abiotic stresses. Elevated pathogen susceptibility of transgenic lines was correlated with reduced expressions of defence related genes. Promoter and cellular localization studies suggest that both MATEs express in developing and reproductive organs and are plasma-membrane localised. Our results reveal that OsMATE1 and OsMATE2 regulate plant growth and development as well as negatively affect disease resistance.

Characterization of the glutathione S-transferase gene family through ESTs and expression analyses within common and pigmented cultivars of Citrus sinensis (L.) Osbeck

BACKGROUND

Glutathione S-transferases (GSTs) represent a ubiquitous gene family encoding detoxification enzymes able to recognize reactive electrophilic xenobiotic molecules as well as compounds of endogenous origin. Anthocyanin pigments require GSTs for their transport into the vacuole since their cytoplasmic retention is toxic to the cell. Anthocyanin accumulation in Citrus sinensis (L.) Osbeck fruit flesh determines different phenotypes affecting the typical pigmentation of Sicilian blood oranges. In this paper we describe: i) the characterization of the GST gene family in C. sinensis through a systematic EST analysis; ii) the validation of the EST assembly by exploiting the genome sequences of C. sinensis and C. clementina and their genome annotations; iii) GST gene expression profiling in six tissues/organs and in two different sweet orange cultivars, Cadenera (common) and Moro (pigmented).

RESULTS

We identified 61 GST transcripts, described the full- or partial-length nature of the sequences and assigned to each sequence the GST class membership exploiting a comparative approach and the classification scheme proposed for plant species. A total of 23 full-length sequences were defined. Fifty-four of the 61 transcripts were successfully aligned to the C. sinensis and C. clementina genomes. Tissue specific expression profiling demonstrated that the expression of some GST transcripts was 'tissue-affected' and cultivar specific. A comparative analysis of C. sinensis GSTs with those from other plant species was also considered. Data from the current analysis are accessible at http://biosrv.cab.unina.it/citrusGST/, with the aim to provide a reference resource for C. sinensis GSTs.

CONCLUSIONS

This study aimed at the characterization of the GST gene family in C. sinensis. Based on expression patterns from two different cultivars and on sequence-comparative analyses, we also highlighted that two sequences, a Phi class GST and a Mapeg class GST, could be involved in the conjugation of anthocyanin pigments and in their transport into the vacuole, specifically in fruit flesh of the pigmented cultivar.

The poplar Phi class glutathione transferase: expression, activity and structure of GSTF1

Glutathione transferases (GSTs) constitute a superfamily of enzymes with essential roles in cellular detoxification and secondary metabolism in plants as in other organisms. Several plant GSTs, including those of the Phi class (GSTFs), require a conserved catalytic serine residue to perform glutathione (GSH)-conjugation reactions. Genomic analyses revealed that terrestrial plants have around ten GSTFs, eight in the Populus trichocarpa genome, but their physiological functions and substrates are mostly unknown. Transcript expression analyses showed a predominant expression of all genes both in reproductive (female flowers, fruits, floral buds) and vegetative organs (leaves, petioles). Here, we show that the recombinant poplar GSTF1 (PttGSTF1) possesses peroxidase activity toward cumene hydroperoxide and GSH-conjugation activity toward model substrates such as 2,4-dinitrochlorobenzene, benzyl and phenetyl isothiocyanate, 4-nitrophenyl butyrate and 4-hydroxy-2-nonenal but interestingly not on previously identified GSTF-class substrates. In accordance with analytical gel filtration data, crystal structure of PttGSTF1 showed a canonical dimeric organization with bound GSH or 2-(N-morpholino)ethanesulfonic acid molecules. The structure of these protein-substrate complexes allowed delineating the residues contributing to both the G and H sites that form the active site cavity. In sum, the presence of GSTF1 transcripts and proteins in most poplar organs especially those rich in secondary metabolites such as flowers and fruits, together with its GSH-conjugation activity and its documented stress-responsive expression suggest that its function is associated with the catalytic transformation of metabolites and/or peroxide removal rather than with ligandin properties as previously reported for other GSTFs.

The flavonoid biosynthetic pathway in Arabidopsis: structural and genetic diversity

Flavonoids are representative plant secondary products. In the model plant Arabidopsis thaliana, at least 54 flavonoid molecules (35 flavonols, 11 anthocyanins and 8 proanthocyanidins) are found. Scaffold structures of flavonoids in Arabidopsis are relatively simple. These include kaempferol, quercetin and isorhamnetin for flavonols, cyanidin for anthocyanins and epicatechin for proanthocyanidins. The chemical diversity of flavonoids increases enormously by tailoring reactions which modify these scaffolds, including glycosylation, methylation and acylation. Genes responsible for the formation of flavonoid aglycone structures and their subsequent modification reactions have been extensively characterized by functional genomic efforts - mostly the integration of transcriptomics and metabolic profiling followed by reverse genetic experimentation. This review describes the state-of-art of flavonoid biosynthetic pathway in Arabidopsis regarding both structural and genetic diversity, focusing on the genes encoding enzymes for the biosynthetic reactions and vacuole translocation.

Gravity Persistent Signal 1 (GPS1) reveals novel cytochrome P450s involved in gravitropism

PREMISE

Gravity is an important environmental factor that affects growth and development of plants. In response to changes in gravity, directional growth occurs along the major axes and lateral branches of both shoots and roots. The gravity persistent signal (gps) mutants of Arabidopsis thaliana were previously identified as having an altered response to gravity when reoriented relative to the gravity vector in the cold, with the gps1 mutant exhibiting a complete loss of tropic response under these conditions.

METHODS

Thermal asymmetric interlaced (TAIL) PCR was used to identify the gene defective in gps1. Gene expression data, molecular modeling and computational substrate dockings, quantitative RT-PCR analyses, reporter gene fusions, and physiological analyses of knockout mutants were used to characterize the genes identified.

RESULTS

Cloning of the gene defective in gps1 and genetic complementation revealed that GPS1 encodes CYP705A22, a cytochrome P450 monooxygenase (P450). CYP705A5, a closely related family member, was identified as expressed specifically in roots in response to gravistimulation, and a mutation affecting its expression resulted in a delayed gravity response, increased flavonol levels, and decreased basipetal auxin transport. Molecular modeling coupled with in silico substrate docking and diphenylboric acid 2-aminoethyl ester (DBPA) staining indicated that these P450s are involved in biosynthesis of flavonoids potentially involved in auxin transport.

CONCLUSION

The characterization of two novel P450s (CYP705A22 and CYP705A5) and their role in the gravity response has offered new insights into the regulation of the genetic and physiological controls of plant gravitropism.

Identification of genes involved in indole-3-butyric acid-induced adventitious root formation in nodal cuttings of Camellia sinensis (L.) by suppression subtractive hybridization

The plant hormone auxin plays a key role in adventitious rooting. To increase our understanding of genes involved in adventitious root formation, we identified transcripts differentially expressed in single nodal cuttings of Camellia sinensis treated with or without indole-3-butyric acid (IBA) by suppressive subtractive hybridization (SSH). A total of 77 differentially expressed transcripts, including 70 up-regulated and 7 down-regulated sequences, were identified in tea cuttings under IBA treatment. Seven candidate transcripts were selected and analyzed for their response to IBA, and IAA by real time RT-PCR. All these transcripts were up regulated by at least two folds one day after IBA treatment. Meanwhile, IAA showed less positive effects on the expression of candidate transcripts. The full-length cDNA of a F-box/kelch gene was also isolated and found to be similar to a group of At1g23390 like genes. These unigenes provided a new source for mining genes related to adventitious root formation, which facilitate our understanding of relative fundamental metabolism.

The Arabidopsis phi class glutathione transferase AtGSTF2: binding and regulation by biologically active heterocyclic ligands

The plant-specific phi class of glutathione transferases (GSTFs) are often highly stress-inducible and expressed in a tissue-specific manner, suggestive of them having important protective roles. To date, these functions remain largely unknown, although activities associated with the binding and transport of reactive metabolites have been proposed. Using a sensitive and selective binding screen, we have probed the Arabidopsis thaliana GSTFs for natural product ligands from bacteria and plants. Uniquely, when overexpressed in bacteria, family members GSTF2 and GSTF3 bound a series of heterocyclic compounds, including lumichrome, harmane, norharmane and indole-3-aldehyde. When screened against total metabolite extracts from A. thaliana, GSTF2 also selectively bound the indole-derived phytoalexin camalexin, as well as the flavonol quercetin-3-O-rhamnoside. In each case, isothermal titration calorimetry revealed high-affinity binding (typically Kd<1 μM), which was enhanced in the presence of glutathione and by the other heterocyclic ligands. With GSTF2, these secondary ligand associations resulted in an allosteric enhancement in glutathione-conjugating activity. Together with the known stress responsiveness of GSTF2 and its association with membrane vesicles, these results are suggestive of roles in regulating the binding and transport of defence-related compounds in planta.