Family Of Herbicides Research Articles

Theoretical Study of Structural and Electronic Trends of the Sulfonylurea Herbicides Family.

The sulfonylurea herbicide family has been extensively studied using computational techniques. The most stable conformer structures of the 34 molecules analyzed in gaseous, aqueous, and octanol phases have been determined. The study employed CREST conformational search methods along with the CENSO script to explore all possible conformational structures. Additional evaluations conducted at the B3LYP-D3/6-311+G(d,p) level have enabled the identification of intramolecular stability patterns across the various compounds. It has been discovered that stability is primarily determined by two factors: intramolecular hydrogen bonding involving an NH group adjacent to the sulfonyl group with either N donors or the nearby carbonyl group and potential π-π interactions between the aromatic rings of the molecules. These have been characterized through QTAIM and NCI population analyses. Furthermore, with the goal of developing predictive models for the physicochemical properties of pesticides that include the sulfonylurea family, a statistical analysis among the different properties of the studied molecules has been conducted. Significant correlations have been found between various properties, predicting a promising future for the prediction of characteristics that could assist laboratories in selecting among different pesticides.

Very long chain fatty acid–inhibiting herbicides: Current uses, site of action, herbicide-resistant weeds, and future

Abstract The herbicides that inhibit very-long-chain fatty acid (VLCFA) elongases are primarily used for residual weed control in corn, barley, oat, sorghum, soybean, sugarcane, certain vegetable crops, and wheat production fields in the United States. They act primarily by inhibiting shoot development of susceptible species, preventing weed emergence and growth. The objectives of this review were to summarize 1) the chemical family of VLCFA-inhibiting herbicides and their use in the United States, 2) the VLCFA biosynthesis in plants and their site of action, 3) VLCFA-inhibitor resistant weeds and their mechanism of resistance, and 4) the future of VLCFA-inhibiting herbicides. After their reclassification as Group 15 herbicides to include shoot growth-inhibiting herbicides (Group 8), the VLCFA-inhibiting herbicides are currently represented by eight chemical families (benzofurans, thiocarbamates, α-chloroacetamides, α-oxyacetamides, azolyl-carboxamides, isoxazolines, α-thioacetamides, and oxiranes). On average, VLCFA-inhibiting herbicides are applied once a year to both corn and soybean crops in the United States with acetochlor and S-metolachlor being the most used VLCFA-inhibiting herbicides in corn and soybean production, respectively. The site of action of Group 15 herbicides results from inhibition of the VLCFA synthase, which is encoded by several fatty acid elongase (FAE1)-like genes in VLCFA elongase complex in an endoplasmic reticulum. The VLCFA synthase is a condensing enzyme, and relies on a conserved, reactive cysteinyl sulfur in its active site that performs a nucleophilic attack on either the natural substrate (fatty acyl-CoA) or the herbicide. As of August 2023, 13 weed species have been documented to be resistant to VLCFA inhibitors, including 11 monocot weeds and two dicot weeds (Palmer amaranth and waterhemp). The isoxazolines (pyroxasulfone and fenoxasulfone) are the most recently (2014) discovered VLCFA-inhibiting herbicides. Although the intensity of VLCFA-inhibitor-directed discovery efforts has decreased over the past decade, this biochemical pathway remains a viable mechanistic target for the discovery of herbicide premixes and a valuable component of them.

Combining crop-exposure matrices and land use data to estimate indices of environmental and occupational exposure to pesticides.

Exposure assessment represents a major challenge for studies on the relation between pesticides and health. We developed a method combining information from crop-exposure matrices (CEMs) and land use data, in order to compute indices of environmental and occupational pesticide exposure. We illustrate our approach using French data (1979-2010). We used CEMs for five crops (straw cereals, grain corn, corn fodder, potatoes, vineyards) that describe use (annual probability, frequency, intensity) of pesticide subgroups, chemical families, and active substances by region and time since 1960. We combined these data with land use data from agricultural censuses (1979, 1988, 2000, 2010) to compute indices of environmental and occupational pesticide exposure in cantons (small French administrative units). Indices of environmental exposure were calculated based on the area of each crop in the cantons, while indices of occupational exposure depended on combinations of crops in each farm from the cantons. To illustrate our approach, we selected a pesticide group (herbicides), chemical family of herbicides (phenoxyacetic acids), and active substance from the phenoxyacetic acids chemical family (2,4-D). The estimated proportion of the area of crops with CEMs and of farms sprayed with herbicides was close to 100% between 1979-2010, but the estimated average annual number of applications increased. There were decreasing time-trends for phenoxyacetic acids and 2,4-D over the same period for all indices of exposure. There was a high use of herbicides throughout France in 2010, except in the South coast. For phenoxyacetic acids and 2,4-D, the spatial distribution was heterogeneous for all indices of exposure, with the highest values in the Centre and North regions. Assessment of pesticide exposure is a key issue for epidemiological studies on their association with health outcomes. However, it presents some unique challenges, particularly for retrospective exposure and the investigation of chronic diseases. We present a method to compute indices of exposure by combining information from crop-exposure matrices for five crops and land use data. Specificities of environmental and occupational exposure are addressed using different methods. These methods are applied to pesticides used in agriculture in France for five crops (3 groups, 91 chemical families,197 activesubstances) to produce indices at a small geographic scale from 1979 to 2010 for the whole metropolitan France. Besides using these indices in French epidemiological studies, our approach could be relevant for other countries.

Computational molecular explanation of Soybean AHAS resistance from P197S mutation

The first enzyme in the pathway involving branched-chain amino is acetohydroxyacid synthase (AHAS, E.C. 2.2.1.6), which is inhibited by five commercial herbicide families. In this work a computational study of a point mutation of Proline-197-Serine of the Soybean AHAS enzyme, which was obtained by mutagenesis, explains the latter's S197 resistance to the commonly used Chlorsulfuron. Using protein-ligand docking and large-scale sampling and distributions from AlphaFold-generated the resistant and susceptible soybean AHAS protein structure. The computational approach here is scaled to screen for mutation probabilities of protein binding sites, similar to screening compounds for potential hits in therapeutic design using the docking software. P197 and S197 AHAS structures were found to be different even if only one amino acid was changed. The non-specific distribution of bindings in the S197 cavity after the P197S change has been rigorously calculated by RMSD analysis that it would require x20 more concentrations to fill the P197 site by the same amount. There is no previously performed detailed chlorsulfuron soybean P197S AHAS binding calculation. In the herbicide site of AHAS, several amino acids interact - a computational study could elucidate the optimal choice of point mutations for herbicidal resistance either individually or collectively by mutations one at a time and analyzing the effects with a set of herbicides individually. With a computational approach, enzymes involved in crop research and development could be analyzed more quickly, enabling faster discovery and development of herbicides.

Crystal Structure of the Commercial Herbicide, Amidosulfuron, in Complex with Arabidopsis thaliana Acetohydroxyacid Synthase

Amidosulfuron (AS) is from the commercial sulfonylurea herbicide family. It is highly effective against dicot broad-leaf weeds. This herbicide targets acetohydroxyacid synthase (AHAS), the first enzyme in the branched chain amino acid biosynthesis pathway. Here, we have determined the crystal structure of AS in complex with wildtype Arabidopsis thaliana AHAS (AtAHAS) and with the resistance mutant, S653T. In both structures, the cofactor, ThDP, is modified to a peracetate adduct, consistent with time-dependent accumulative inhibition. Compared to other AHAS-inhibiting herbicides of the sulfonylurea family, AS lacks a second aromatic ring. The replacement is an aryl sulfonyl group with a reduced number of interactions with the enzyme and relatively low affinity (Ki = 4.2 μM vs low nM when two heteroaromatic rings are present). This study shows that effective herbicides can have a relatively high Ki for plant AHAS but can still be a potent herbicide provided accumulative inhibition also occurs.

The differential binding and biological efficacy of auxin herbicides.

Auxin herbicides have been used for selective weed control for 75 years and they continue to be amongst the most widely used weed control agents globally. The auxin herbicides fall into five chemical classes, with two herbicides not classified, and in all cases it is anticipated that recognition in the plant starts with binding to the Transport Inhibitor Response 1 (TIR1) family of auxin receptors. There is evidence that some classes of auxins act selectively with certain clades of receptors, although a comprehensive structure-activity relationship has not been available. Using purified receptor proteins to measure binding efficacy we have conducted quantitative structure activity relationship (qSAR) assays using representative members of the three receptor clades in Arabidopsis, TIR1, AFB2 and AFB5. Complementary qSAR data for biological efficacy at the whole-plant level using root growth inhibition and foliar phytotoxicity assays have also been analyzed for each family of auxin herbicides, including for the afb5-1 receptor mutant line. Comparisons of all these assays highlight differences in receptor selectivity and some systematic differences between results for binding in vitro and activity in vivo. The results could provide insights into weed spectrum differences between the different classes of auxin herbicides, as well as the potential resistance and cross-resistance implications for this herbicide class. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Ethalfluralin induces developmental toxicity in zebrafish via oxidative stress and inflammation

Ethalfluralin, of dinitroaniline herbicide family, is an effective weed controller. Following residue detection in herbicide-treated fields, ethalfluralin was reported to interfere with early stages of implantation in some vertebrate species. However, the role of ethalfluralin in the development of zebrafish embryos has not been elucidated yet. Therefore, in the present study, we investigated the morphological and physiological changes that occur in the embryonic development of zebrafish due to ethalfluralin exposure. Results indicated that ethalfluralin decreased survival rate along with reduction in the hatching ratio and heartbeat. It was observed to cause edema in the heart and yolk sac, and apoptosis in the anterior region of the developing zebrafish larvae; as visualized through acridine orange and TUNEL staining. In addition, ethalfluralin increased the expression of the apoptosis-associated genes including tp53, cyc1, casp8, casp9, and casp3. The Seahorse Mito Stress analysis revealed that ethalfluralin slightly reduced mitochondrial respiration in live zebrafish embryos. Reactive oxygen species (ROS) production was also observed to be elevated in zebrafish larvae in response to ethalfluralin. Treatment with ethalfluralin decreased blood vessel formation in brain and intestine in flk1 transgenic zebrafish embryos. The decrease in angiogenesis related gene expression was specifically observed in vegfc, flt1, and kdrl, and in the intestinal vasculature related genes apoa4a, aqp3, fabp2, and vil1. Moreover, an increase in inflammatory genes such as cox2a, cox2b, cxcl-c1c, il8, mcl1a, mcl1b, and nf-κb was observed using real-time PCR analysis. Collectively, these results indicate that oxidative stress generated by exposure to ethalfluralin induced ROS generation, apoptosis, inflammation and anti-angiogenic effects, and therefore, ethalfluralin may be toxic to the development of zebrafish embryos.

NMR evidence for hydrogen bonding stabilized anti conformation of 1-methoxy-1-methyl-3-phenylurea and the concentration detection by SERS

Phenylurea-based herbicides have been widely used to control the plant growth. Due to their toxicity, strict regulations to limit their usage have been applied. Developing trace detection protocols of substituted phenylureas has attracted more attention, especially with the availability of a wide range of spectroscopic and analytical techniques. In this study, the conformational and structural properties of 1-methoxy-1-methyl-3-phenylurea (MMPU) which belongs to the family of phenylurea-based herbicides have been characterized. The anti-configuration, facilitated by the intramolecular hydrogen bonding between the oxygen atom of the methoxy moiety and the acidic amide proton, was observed using the nuclear magnetic resonance (NMR) spectroscopy through the Selective Nuclear Overhauser Effect (SelNOE) approach. The density functional theory (DFT) calculations suggested that the anti form is at least 9 kcal/mol more stable than the corresponding syn structure. Possible degradation pathways of such a class of herbicides can be explored when a firm understanding of their electronic and conformational behaviors is established. The detection of trace MMPU has been successfully developed using the surface-enhanced Raman scattering (SERS) spectroscopic tool. The most enhanced peak associated with the carbonyl group stretching vibration which appears nearly at 1600 cm−1 has presented a Raman enhancement factor of 3.24 × 105 and a micrommolar limit of detection.

Preparation of well-structured hybrid material through ion exchange of chloride by 2,4,5-trichlorophenoxyacetic herbicide in a layered double hydroxide

The [Zn2–Al–Cl] layered double hydroxide (LDH) was used to successfully exchange chloride ions by 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), as a model of the carboxylate herbicide family. The total exchange was obtained after 6 h of stirring with a 2,4,5-T/Cl molar ratio of 10 and a pH of 7. The characterization by various techniques (XRD, FTIR, TG-DTG and SEM) indicates that this exchange led to the production of a new stable hybrid LDH phase intercalated by the herbicide. The structural analysis of the material, based on the interlayer distance of 1.855 nm, indicates that the 2,4,5-T anion takes a vertical arrangement in a double layer. The cohesion of the structure is ensured by hydrogen bonds between the carboxylate group of the herbicide and the hydroxyl groups of the LDH sheets. The exchange causes a modification of the type of symmetry from a 3R stacking mode for [Zn2–Al–Cl] (space group R3‾m) to a 2H for [Zn2–Al-2,4,5-T] (space group P63/mmc). This result confirms the already proven use of LDH materials as efficient anion exchangers for the trapping and elimination of this type of pollutant from wastewater.

Elevated pulmonary levels of Axin2 in mice exposed to herbicide 2,4‐D with or without endotoxin

2,4-Dichlorophenoxyacetic acid (2,4-D), a member of the phenoxy family of herbicides is commonly used in agriculture for controlling broadleaf weeds but its uncontrolled and incoherent use has been linked to incidences of lung toxicity. The present study aimed to understand the molecular mechanisms behind the 2,4-D alone or in combination with endotoxin (lipopolysaccharide [LPS]) induced pulmonary toxicity. Blood and lung samples were collected from Swiss albino mice (n = 48) following chronic exposure to high (37 mg/kg; 1/10th of LD50 ) and low (18.5 mg/kg; 1/20th of LD50 ) doses of 2,4-D alone or in combination with endotoxin (80 µg/animal). Transcriptome analysis revealed Wnt Canonical signaling as one of the top dysregulated pathways in mice lung following exposure to 2,4-D with and without endotoxin (LPS) co-exposure. Global view of differentially expressed genes showed increased messenger RNA expression of Axin2 by 0.26, 2.58, 3.14, 2.59, and 2.97 folds following exposure to LPS, high dose alone or in combination with LPS and low dose alone or in combination with LPS, respectively. The microarray data were validated using quantitative polymerase chain reaction and immunohistochemistry. Furthermore, the plasma concentration of Axin2 was elevated in the high dose group as revealed by Sandwich ELISA. The data taken together suggest a role of Axin2 to activate the Canonical Wnt signaling pathway in 2,4-D and or endotoxin-induced lung damage in mice.

Trp548Met mutation of acetolactate synthase in rice confers resistance to a broad spectrum of ALS-inhibiting herbicides

Herbicide resistance in crop plants is valuable for integrated weed management in agriculture. Herbicide resistant rice, in particular, is important to management of weedy rice, a close relative of cultivated rice and a noxious weed prevalent in rice fields that remains challenging to farmers worldwide. Herbicide resistant plants can be obtained through transgenic approach or by mutagenesis of regular plant and screening of mutants with elevated resistance to herbicide. In this study, we conducted ethyl methyl sulfonate mutagenesis (EMS) to elite indica cultivar Huanghuazhan (HHZ) and screened for mutants resistant to imazapic, a herbicide that can inhibit the acetolactate synthase (ALS) in plants. We obtained three mutants of OsALS gene that have not been reported previously in rice. One of the mutants, with Trp548 changed to Met (W548M), was analyzed in more details in this study. This mutation had no negative effect on the plant physiology and morphology as well as rice yield. Compared with the imidazolinone-resistant mutant S627N (Ser627 changed to Asn) that has been deployed for Clearfield rice development, W548M mutant showed high levels of resistance to a broad spectrum of five families of ALS-inhibiting herbicides, in addition to a higher level of resistance to herbicides of the imidazolinone family. The herbicide-resistance was stably inherited by crossing into other rice lines. Thus, the W548M mutation provides a valuable resource for breeding of herbicide resistant rice and weed management.

Spatial Availability of Nitrogen and Pesticides in the Surface Layers of Agricultural Soils of Tropical Hydrosystems in the Wet Season: Case of the Béré Watershed in Côte d’Ivoire (West Africa)

The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems to the spatial availability of nitrogen and pesticides during the wet season, such as the Béré watershed (BW) in C?te d’Ivoire. For this purpose, after mapping the spatial distribution of the BW cropping systems based on the likelihood classification methodology of satellite images of the study area, 27 samples from the 0 - 20 cm horizon of the soil surface layers of the agricultural areas were taken during the wet and agricultural season of the year 2016. The Kjeldahl method has been used to evaluate the total nitrogen concentration and high-performance liquid chromatography (HPLC) chain made it possible for the analysis of pesticide residues in the soil solutions. Geostatistical analysis and processing of spatial data and physicochemical and agrochemical soil parameters revealed that two major agricultural areas stand out in the BW, namely the Béré upstream watershed (BUW) dominated at 32.65% by annual croppings (maize, cotton, rainfed or lowland rice, market gardening, etc.) and the Béré downstream watershed (BDW) by large areas of perennial croppings (cashew nuts, cocoa, etc.), i.e. 21.47%. Agricultural soils in BW are usually of the moderately desaturated ferralitic type with a low acid pH and a quite strong temperature, such as those of tropical soils’ characteristics. However, agricultural soils in the BUW are characterized by higher proportions of sand and coarse sand. The parameters such as total porosity, cation exchange capacity, clay, organic matter, silt, fine silt, coarse silt, and potassium ions, are higher in the soils of the agricultural area of the BDW. Moreover, soils in the agricultural areas of the BUW are less rich in total nitrogen (0.84 g·kg-1) in contrast to those of the BDW (1.2 g·kg-1). On the other hand, the median concentrations of total pesticides remain very high in the BUW (193.80 μg·kg-1) in front of those of the BDW (94.81 μg·kg-1). In addition, the biological family of herbicides was the most notable in BW. The chemical families of triazines (100% detection; 79.37 μg·kg-1) are the most important in the agricultural area of the BUW with the very significant presence of active molecules of pesticides such as simazine (92.86% detection; 13.17 μg·kg-1). However, in the BDW, urea substitute (100% detection; 44.02 μg·kg-1) dominate, including the active substance chlortoluron (84.62% detection; 10.12 μg·kg-1). The presence and abundance of nitrogen and pesticides in the soils of the agricultural areas of BW are strongly linked to the intensive use of these agrochemicals in cropping systems in recent decades in West African countries, even though most of the active molecules found are forbidden in several countries, especially in European countries. These are applied to tropical agricultural soils with physicochemical characteristics favorable to their retention in wet weather, as confirmed by the case of BW’s agricultural soils. Therefore, the BW’s water resources present worrying risks of contamination during rainy events that deserve to be assessed and monitored. Hence the need to take mitigating measures to this effect in order to preserve the quality of the environment.

Multiple mutations in the EPSPS and ALS genes of Amaranthus hybridus underlie resistance to glyphosate and ALS inhibitors

Amaranthus hybridus is one of the main weed species in Córdoba, Argentina. Until recently, this weed was effectively controlled with recurrent use of glyphosate. However, a population exhibiting multiple resistance (MR2) to glyphosate and imazamox appeared in a glyphosate resistant (GR) soybean field, with levels of resistance up to 93 and 38-fold higher to glyphosate and imazamox, respectively compared to the susceptible (S) population. In addition to imidazolinones, MR2 plants showed high resistance levels to sulfonylamino-carbonyl (thio) benzoates and moderate resistance to sulfonylureas and triazolopyrimidines. Multiple amino acid substitutions were found in both target genes, acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), responsible for conferring high herbicides resistance levels in this A. hybridus population. In the case of EPSPS, the triple amino acid substitution TAP-IVS was found. In addition, MR2 plants also showed increased EPSPS gene expression compared to susceptible plants. A Ser653Asn substitution was found in the ALS sequence of MR2, explaining the pattern of cross-resistance to the ALS-inhibitor herbicide families found at the ALS enzyme activity level. No other mutations were found in other conserved domains of the ALS gene. This is the first report worldwide of the target site resistance mechanisms to glyphosate and ALS inhibitors in multiple herbicide resistance Amaranthus hybridus.

Adsorption of Imazalil herbicide onto Moroccan agricultural soils: Kinetic and isotherm adsorption studies

Imazalil herbicide [1-[2-(2,4-dichlorophenyl)-2-prop-2-enoxyethyl] imidazole] belongs to the Enilconazole family of herbicides, this compound is largely utilized on agricultural field crops in Morocco. Soil properties greatly improve the adsorption of this chemical compound in soils, but there is a need to understand their effect on said soils. This current study evaluates the adsorption behavior of Imazalil using four agricultural soils from Morocco in batch systems and examines the impact of contact time and initial Imazalil concentration. The physico-chemical properties of soils were characterized by several analytical methods. The equilibrium isotherms of Imazalil removal by Moroccan soils were studied using batch tests. The obtained data revealed that the adsorbed amount of pollutant increases with the increasing the organic matter and organic carbon contents in soils. The adsorption kinetic process of different soils followed the pseudo second order kinetic model, and the adsorption mechanism of herbicide using different soils was controlled by intraparticle diffusion model. Isotherm adsorption experiments of Imazalil on four agricultural soils indicated that adsorption was best fitted by the Langmuir and Freundlich models. Our data suggest potential for reduced transfer of Imazalil from agricultural soils to groundwater in Morocco.

Relative activity comparison of aminocyclopyrachlor to pyridine carboxylic acid herbicides

AbstractThe pyridine carboxylic acid (PCA) herbicide family can exhibit differential activity within and among plant species, despite molecular resemblances. Aminocyclopyrachlor (AMCP), a pyrimidine carboxylic acid, is a recently discovered compound with similar use patterns to those of the PCA family; however, relative activity among PCAs and AMCP is not well understood. Therefore, the objective of this study was to quantify relative activity among aminopyralid, picloram, clopyralid, triclopyr, and AMCP in canola, squash, and okra using dose-response whole-plant bioassays. Clopyralid was less active than all other herbicides in all species and did not fit dose-response models. Aminopyralid and picloram performed similarly in squash (ED50= 21.1 and 23.3 g ae ha−1, respectively). Aminopyralid was 3.8 times and 1.7 times more active than picloram in canola (ED50= 60.3 and 227.7 g ha−1, respectively) and okra (ED50= 10.3 and 17.3 g ha−1, respectively). Triclopyr (ED50= 37.3 g ha−1) was more active than AMCP (ED50= 112.9 g ha−1) and picloram in canola. Aminocyclopyrachlor (ED50= 6.6 g ha−1) and triclopyr (ED50= 7.8 g ha−1) were more active in squash than aminopyralid and picloram. In okra, AMCP (ED50= 14.6 g ha−1) and aminopyralid (ED50= 10.3 g ha−1) performed similarly but were more active than triclopyr (ED50= 88.2 g ha−1). Herbicidal activity among AMCP and PCAs was vastly different despite molecular similarities that could be due to variable target-site sensitivity among species.

Prometryn induces apoptotic cell death through cell cycle arrest and oxidative DNA damage.

Prometryn is a slightly to moderately toxic herbicide belonging to the triazine family of herbicides, which are widely used in agriculture to control the growth of various weeds. Although many studies have shown that triazine herbicides have carcinogenic potential in humans, the cytotoxic effects of prometryn on human cells, and the mechanisms underlying these effects, are not yet fully understood. The lung is one of the most important organs where there is accumulation of environmental pollutants. The aim of this study was to determine the cytotoxic effects of prometryn on normal lung cells using the human bronchial epithelial cell line BEAS-2B. We found that treatment with high concentrations of prometryn arrested BEAS-2B cell growth in the S phase, while at low concentrations the cell cycle was not affected. Furthermore, we observed changes in the expression levels of cyclin-dependent kinase 2 (CDK2) and cyclin A that were consistent with the induction of cell cycle arrest in BEAS-2B cells exposed to prometryn. We also observed the increased formation of intracellular reactive oxygen species (ROS) in BEAS-2B cells, suggesting that this cell line is sensitive to prometryn. Finally, prometryn induced DNA double-strand breaks in BEAS-2B cells. In conclusion, prometryn affected key molecules involved in cell cycle regulation, induced oxidative stress, and induced DNA damage in BEAS-2B cells, which may shed light on the mechanism by which prometryn promotes lung cancer development.

Development of enzymes for robust aryloxyphenoxypropionate and synthetic auxin herbicide tolerance traits in maize and soybean crops.

Effective management of weedy species in agricultural fields is essential for maintaining favorable growing conditions and crop yields. The introduction of genetically modified crops containing herbicide tolerance traits has been a successful additional tool available to farmers to better control weeds. However, weed resistance challenges present a need for additional herbicide tolerance trait options. To help meet this challenge, a new trait that provides tolerance to an aryloxyphenoxypropionate (FOP) herbicide and members of the synthetic auxin herbicide family, such as 2,4-dichlorophenoxyacetic acid (2,4-D), was developed. Development of this herbicide tolerance trait employed an enzyme engineered with robust and specific enzymatic activity for these two herbicide families. This engineering effort utilized a microbial-sourced dioxygenase scaffold to generate variants with improved enzymatic parameters. Additional optimization to enhance in-plant stability of the enzyme enabled an efficacious trait that can withstand the higher temperature conditions often found in field environments. Optimized herbicide tolerance enzyme variants with enhanced enzymatic and temperature stability parameters enabled robust herbicide tolerance for two herbicide families in transgenic maize and soybeans. This herbicide tolerance trait for FOP and synthetic auxin herbicides such as 2,4-D could be useful in weed management systems, providing additional tools for farmers to control weeds. © 2019 Society of Chemical Industry.

How protoporphyrinogen IX oxidase inhibitors and transgenesis contribute to elucidate plant tetrapyrrole pathway

Several families of herbicides, especially diphenyl ether (DPE) and pyrimidinedione, target the plant tetrapyrrole biosynthesis pathways and in particular one key enzyme, protoporphyrinogen IX oxidase (PPO). When plants are treated with DPE or pyrimidinedione, an accumulation of protoporphyrin IX, the first photosensitizer of this pathway, is observed in cytosol where it becomes very deleterious under light. Indeed these herbicides trigger plant death in two distinct ways: (i) inhibition of chlorophylls and heme syntheses and (ii) a huge accumulation of protoporphyrin IX in cytosol. Recently, a strategy based on plant transgenesis that induces deregulation of the tetrapyrrole pathway by up- or down-regulation of genes encoding enzymes, such as glutamyl-[Formula: see text]RNA reductase, porphobilinogen deaminase and PPO, has been developed. Against all expectations, only transgenic crops overexpressing PPO showed resistance to DPE and pyrimidinedione. This herbicide resistance of transgenic crops leads to the hypothesis that the overall consumption of herbicides will be reduced as previously reported for glyphosate-resistant transgenic crops. In this review, after a rapid presentation of plant tetrapyrrole biosynthesis, we show how only PPO enzyme can be the target of DPE and how transgenic crops can be further resistant not only to herbicide but also to abiotic stress such as drought or chilling. Keeping in mind that this approach is mostly prohibited in Europe, we attempt to discuss it to interest the scientific community, from plant physiologists to chemists, who work on the interface of photosensitizer optimization and agriculture.

Commercial AHAS-inhibiting herbicides are promising drug leads for the treatment of human fungal pathogenic infections

The increased prevalence of drug-resistant human pathogenic fungal diseases poses a major threat to global human health. Thus, new drugs are urgently required to combat these infections. Here, we demonstrate that acetohydroxyacid synthase (AHAS), the first enzyme in the branched-chain amino acid biosynthesis pathway, is a promising new target for antifungal drug discovery. First, we show that several AHAS inhibitors developed as commercial herbicides are powerful accumulative inhibitors of Candida albicans AHAS (K i values as low as 800 pM) and have determined high-resolution crystal structures of this enzyme in complex with several of these herbicides. In addition, we have demonstrated that chlorimuron ethyl (CE), a member of the sulfonylurea herbicide family, has potent antifungal activity against five different Candida species and Cryptococcus neoformans (with minimum inhibitory concentration, 50% values as low as 7 nM). Furthermore, in these assays, we have shown CE and itraconazole (a P450 inhibitor) can act synergistically to further improve potency. Finally, we show in Candida albicans-infected mice that CE is highly effective in clearing pathogenic fungal burden in the lungs, liver, and spleen, thus reducing overall mortality rates. Therefore, in view of their low toxicity to human cells, AHAS inhibitors represent a new class of antifungal drug candidates.

Variability of CP4 EPSPS expression in genetically engineered soybean (Glycine max L. Merrill)

The expression of the CP4 EPSPS protein in genetically engineered (GE) soybean confers tolerance to the Roundup® family of agricultural herbicides. This study evaluated the variability of CP4 EPSPS expression using an enzyme-linked immunosorbent assay in soybean tissues collected across diverse germplasm and 74 different environments in Argentina, Brazil and the USA. Evaluated material included single and combined (stacked) trait products with other GE traits in entries with cp4 epsps gene at one or two loci. The highest level of CP4 EPSPS was observed in leaf tissues, intermediate in forage and seed, and lowest in root tissues. Varieties with two loci had approximately twice the level of CP4 EPSPS expression compared to one locus entries. Variable and non-directional level of CP4 EPSPS was observed with other factors like genetic background, trait stacking, growing region or season. The maximum and average CP4 EPSPS expression levels in seed provided large margins of exposure (MOE of approximately 4000 and 11,000, respectively), mitigating concerns over exposure to this protein in food and feed from soybean varieties tolerant to Roundup® herbicides.