Mesotrione: a new selective herbicide for use in maize

Isolation, identification, and degradation mechanism by multi-omics of mesotrione-degrading Amycolatopsis nivea La24

Mesotrione is a herbicide used in agricultural production; however, its stability and long-term residues pose ecological risks to soil health and subsequent crops. In this research, the strain Amycolatopsis nivea La24 was identified as capable of completely degrading 50 mg∙L-1 mesotrione within 48 h. It exhibited a broad adaptability to various environment and could degrade three sulfonylurea herbicides (nicosulfuron, chlorimuron-methyl, and cinosulfuron). Non-target metabonomic and mass spectrometry demonstrated that La24 strain broke down the mesotrione parent molecule by targeting the β-diketone bond and nitro group, resulting in the production of five possible degradation products. The differentially expressed genes were significantly enriched in fatty acid degradation, amino acid metabolism, and other pathways, and the differentially metabolites in glutathione metabolism, arginine/proline metabolism, cysteine/methionine metabolism, and other pathways. Additionally, it was confirmed by heterologous expression that nitroreductase was directly involved in the mesotrione degradation, and NDMA-dependent methanol dehydrogenase would increase the resistance to mesotrione. Finally, the intracellular response of La24 during mesotrione degradation was proposed. This work provides insight for a comprehensive understanding of the mesotrione biodegradation mechanism, significantly expands the resources for pollutant degradation, and offers the potential for a more sustainable solution to address herbicide pollution in soil.

Analyzing the response of rice to tefuryltrione herbicide: Haplotype variation and evolutionary dynamics of the HIS1 gene

Weeds pose multifaceted challenges in rice cultivation, leading to substantial economic losses through reduced yield and poor grain quality. Harnessing the natural genetic diversity in germplasm collections becomes crucial for identifying novel herbicide resistance loci in crops. A comprehensive analysis was conducted on 475 rice accessions from the KRICE depository, assessing their response to TFT (tefuryltrione) and probing the underlying HIS1 (HPPD INHIBITOR SENSITIVE 1) genotypic variations. The HIS1 gene, responsible for detoxifying benzobicyclon (BBC) and imparting broad-spectrum herbicide resistance, holds significant promise in rice breeding. This study explores the genetic landscape of HIS1 within Korean rice collection (KRICE), aiming to unveil genetic variations, haplotype diversity, and evolutionary relationships across diverse rice ecotypes. The indica ecotype showed the highest nucleotide diversity, while the wild and temperate japonica groups exhibited low diversity, hinting at selective sweeps and possible population expansion. Negative Tajima's D values in temperate japonica and wild groups indicate an excess of low-frequency mutations, potentially resulting from selective sweeps. In contrast, with positive Tajima's D values, admixture, indica, and aus groups suggest balancing selection. Furthermore, haplotype analysis uncovered 42 distinct haplotypes within KRICE, with four shared haplotypes between cultivated and wild accessions, four specific to cultivated accessions, and 34 specific to wild types. Phenotypic assessments of these haplotypes revealed that three haplotypes, viz., Hap_1 (predominant in japonica), Hap_2 (predominant in indica), and Hap_3 (specific to indica), displayed significant differences from aus-specific Hap_4 and indica-specific Hap_5. This study offers insights into genetic diversity, selective pressures, and ecotype-specific responses, ultimately paving the way for developing HPPD-inhibiting herbicide-resistant rice cultivars.

β-Triketones as Reactive Handles for Polymer Diversification via Dynamic Catalyst-Free Diketoenamine Click Chemistry

The spontaneous condensation of amines with β-triketones (TK), forming β,β'-diketoenamines (DKE) and releasing water as the sole byproduct, exhibits many of the hallmarks of "click" reactions. Such characteristics render TKs as a highly advantageous platform for efficient polymer diversification, even in biological contexts. Leveraging reversible addition-fragmentation chain transfer (RAFT) and photoiniferter polymerization of novel TK-containing vinylic monomers, we synthesized polymers containing pendent TKs with excellent control of molecular weights, even in excess of 106 g mol-1. Under mild, catalyst-free conditions, poly(β-triketone methacrylate) could be modified with a diverse scope of amines containing a plethora of functional groups. The high efficiency of this functionalization approach was further emphasized when grafting-to with poly(ethylene glycol)-amine resulting in bottlebrushes with molecular weights reaching 2.0 × 107 g mol-1. Critically, while the formed DKE linkages are stable under ambient conditions, they undergo catalyst-free, dynamic transamination at elevated temperatures, paving the way for associative covalent adaptable networks. Overall, we introduce pendent triketone moieties into methacrylate and acrylamide polymers, establishing a novel postpolymerization modification technique that facilitates catalyst-free ligation of amines under highly permissible conditions.

Design, Synthesis, and Biological Activity of Novel Triketone-Containing Phenoxy Nicotinyl Inhibitors of HPPD

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a crucial target enzyme in albino herbicides. The inhibition of HPPD activity interferes with the synthesis of carotenoids, blocking photosynthesis and resulting in bleaching and necrosis. To develop herbicides with excellent activity, a series of 3-hydroxy-2-(6-substituted phenoxynicotinoyl)-2-cyclohexen-1-one derivatives were designed via active substructure combination. The title compounds were characterized via infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopies, and high-resolution mass spectrometry. The structure of compound III-17 was confirmed via single-crystal X-ray diffraction. Preliminary tests demonstrated that some compounds had good herbicidal activity. Crop safety tests revealed that compound III-29 was safer than the commercial herbicide mesotrione in wheat and peanuts. Moreover, the compound exhibited the highest inhibitory activity against Arabidopsis thaliana HPPD (AtHPPD), with a half-maximal inhibitory concentration of 0.19 μM, demonstrating superior activity compared with mesotrione (0.28 μM) in vitro. A three-dimensional quantitative structure-activity relationship study revealed that the introduction of smaller groups to the 5-position of cyclohexanedione and negative charges to the 3-position of the benzene ring enhanced the herbicidal activity. A molecular structure comparison demonstrated that compound III-29 was beneficial to plant absorption and conduction. Molecular docking and molecular dynamics simulations further verified the stability of the complex formed by compound III-29 and AtHPPD. Thus, this study may provide insights into the development of green and efficient herbicides.

Metabolism of the 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor, Mesotrione, in Multiple-Herbicide-Resistant Palmer amaranth (Amaranthus palmeri)

Metabolic resistance to the maize-selective, HPPD-inhibiting herbicide, mesotrione, occurs via Phase I ring hydroxylation in resistant waterhemp and Palmer amaranth; however, mesotrione detoxification pathways post-Phase I are unknown. This research aims to (1) evaluate Palmer amaranth populations for mesotrione resistance via survivorship, foliar injury, and aboveground biomass, (2) determine mesotrione metabolism rates in Palmer amaranth populations during a time course, and (3) identify mesotrione metabolites including and beyond Phase I oxidation. The Palmer amaranth populations, SYNR1 and SYNR2, exhibited higher survival rates (100%), aboveground biomass (c.a. 50%), and lower injury (25-30%) following mesotrione treatment than other populations studied. These two populations also metabolized mesotrione 2-fold faster than sensitive populations, PPI1 and PPI2, and rapidly formed 4-OH-mesotrione. Additionally, SYNR1 and SYNR2 formed 5-OH-mesotrione, which is not produced in high abundance in waterhemp or naturally tolerant maize. Metabolite features derived from 4/5-OH-mesotrione and potential Phase II mesotrione-conjugates were detected and characterized by liquid chromatography-mass spectrometry (LCMS).

Agroecological transition: towards a better understanding of the impact of ecology-based farming practices on soil microbial ecotoxicology

Alternative farming systems have developed since the beginning of industrial agriculture. Organic, biodynamic, conservation farming, agroecology and permaculture, all share a grounding in ecological concepts and a belief that farmers should work with nature rather than damage it. As ecology-based agricultures rely greatly on soil organisms to perform the functions necessary for agricultural production, it is thus important to evaluate the performance of these systems through the lens of soil organisms, especially soil microbes. They provide numerous services to plants, including growth promotion, nutrient supply, tolerance to environmental stresses and protection against pathogens. An overwhelming majority of studies confirm that ecology-based agricultures are beneficial for soil microorganisms. However, three practices were identified as posing potential ecotoxicological risks: the recycling of organic waste products, plastic mulching, and pest and disease management with biopesticides. The first two because they can be a source of contaminants; the third because of potential impacts on non-target microorganisms. Consequently, developing strategies to allow a safe recycling of the increasingly growing organic matter stocks produced in cities and factories, and the assessment of the ecotoxicological impact of biopesticides on non-target soil microorganisms, represent two challenges that ecology-based agricultural systems will have to face in the future.

A naked-eye visible aluminium (III)-based complex fluorescence sensor for sensitive detection of mesotrione

Mesotrione, which is a kind of herbicide to control broad-leaved weeds, has been increasingly used due to its excellent selectivity, rapid process and low toxicity. However, the excessive application of mesotrione have led to widespread contamination. Herein, a turn-on competitive coordination-based fluorescent probe, 2-hydroxy-1-(9-purin)-methylidenehydrazinenaphthalene (HPM), has been successfully synthesized. HPM could effectively detect Al3+ in CH3OH/HEPES (1/9, v/v) with low limit of detection (LOD) being 0.2 µM via coordination. HPM also exhibited excellent imaging capabilities for Al3+ in living cells with low cytotoxicity. On the basis of the competitive coordination of HPM with Al3+, the [HPM-Al3+] complex could also serve as a potential fluorescence sensor for detecting mesotrione with the LOD of 0.2 µM. Furthermore, [HPM-Al3+] complex was applied for the detection of mesotrione in real samples and test paper. Finally, the mechanism of [HPM-Al3+] for sensing mesotrione was investigated deeply as well. This work designed a new convenient method for on-site detection of mesotrione without the large-scale equipment or complicated pre-treatment.

Crystal structure of the sodium salt of mesotrione: a triketone herbicide

The crystal structure of the sodium salt of mesotrione, namely, catena-poly[[sodium-μ3-2-[(4-methane-sulfonyl-2-nitro-phen-yl)carbon-yl]-3-oxo-cyclo-hex-1-en-1-olato] ethanol monosolvate], {[Na(C14H12NO7S)]C2H5OH}n, is described. The X-ray structural analysis results reveal that the coordination sphere is established by two chelating O atoms, the O atom of the coordinated ethanol mol-ecule, and an O atom from the methyl-sulfonyl group of a neighboring mol-ecule. Simultaneously, an O atom of the cyclo-hexane fragment serves as a bridge to a neighboring sodium ion, forming a flat Na-O-Na-O quadrangle, thereby forming a mono-periodic polymer. The structure displays O-H⋯O hydrogen bonds and C-H⋯O short contacts. Thermogravimetric analysis (TGA) data indicate that the sodium salt of mesotrione decomposes in four stages.

Discovery of Tetrazolamide-benzimidazol-2-ones as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is one of the most valuable herbicide targets due to its unique biological functions. In search of HPPD inhibitors with promising biological performance, we designed and synthesized a series of novel tetrazolamide-benzimidazol-2-ones using a structure-based drug design strategy. Among the synthesized compounds, 1-(2-chlorobenzyl)-3-methyl-N-(1-methyl-1H-tetrazol-5-yl)-2-oxo-2,3-dihydro-1H-benzo[d]imidazole-4-carboxamide, 25, IC50 = 10 nM, was identified to be the most outstanding HPPD inhibitor, which showed more than 36-fold increased Arabidopsis thaliana HPPD (AtHPPD) inhibition potency than mesotrione (IC50 = 363 nM). Our AtHPPD-25 complex indicated that one nitrogen atom on the tetrazole ring and the oxygen atom on the amide group formed a classical bidentate chelation interaction with the metal ion, the benzimidazol-2-one ring created a tight π-π stacking interaction with Phe381 and Phe424, and some hydrophobic interactions were also found between the ortho-Cl-benzyl group and surrounding residues. Compound 32 showed more than 80% inhibition against all four tested weeds at 150 g ai/ha by the postemergence application. Our results indicated that the tetrazolamide-benzimidazol-2-one scaffold may be a new lead structure for herbicide discovery.

Structural and functional characterization of triketone dioxygenase from Oryza Sativa

The transgenic expression of rice triketone dioxygenase (TDO; also known as HIS1) can provide protection from triketone herbicides to susceptible dicot crops such as soybean. Triketones are phytotoxic inhibitors of plant hydroxyphenylpyruvate dioxygenases (HPPD). The TDO gene codes for an iron/2-oxoglutarate-dependent oxidoreductase. We obtained an X-ray crystal structure of TDO using SeMet-SAD phasing to 3.16 Å resolution. The structure reveals that TDO possesses a fold like that of Arabidopsis thaliana 2-oxoglutarate‑iron-dependent oxygenase anthocyanidin synthase (ANS). Unlike ANS, this TDO structure lacks bound metals or cofactors, and we propose this is because the disordered flexible loop over the active site is sterically constrained from folding properly in the crystal lattice. A combination of mass spectrometry, nuclear magnetic resonance, and enzyme activity studies indicate that rice TDO oxidizes mesotrione in a series of steps; first producing 5-hydroxy-mesotrione and then oxy-mesotrione. Evidence suggests that 5-hydroxy-mesotrione is a much weaker inhibitor of HPPD than mesotrione, and oxy-mesotrione has virtually no inhibitory activity. Of the close homologues which have been tested, only corn and rice TDO have enzymatic activity and the ability to protect plants from mesotrione. Correlating sequence and structure has identified four amino acids necessary for TDO activity. Introducing these four amino acids imparts activity to a mesotrione-inactive TDO-like protein from sorghum, which may expand triketone herbicide resistance in new crop species.

Synergies of WO3 and Co3O4 intercalated ball milling exfoliated graphene 3D helix electrocatalyst: A highly sensitive electrochemical detection of mesotrione herbicide in vegetable samples

In the booming global population, monitoring of mesotrione (MTN) like agricultural pollutants is crucial for human safety. Herein, the research reports the synthesis of tungsten trioxide (WO3) and cobalt oxide (Co3O4) nanostructures intercalated ball milling exfoliated graphene (WO3/Co3O4/graphene) 3D helix electrocatalyst for the electrochemical detection of MTN herbicide. The proposed WO3/Co3O4/graphene sensor material achieved a wide range of MTN detection from 0.001 µM to 1885 µM. In addition, the estimated limit of sensing and sensitivity values are 0.42 nM and 0.802 µAµM-1 cm-2 respectively. The real sample experiment was accomplished in MTN-added vegetables (corn, sugar cane, tomato, green soybean) and environmental samples (sewage water, river water). At most, the recorded minimum MTN response recovery in vegetables and water samples is about 95% and 98% respectively. Furthermore, the designed sensor electrode achieved storage stability of 98.7% after three weeks.

Sense and Shoot: Unveiling the Electro-/Photocatalytic Potential of 2D White Graphene-Supported Perovskite Strontium Cobaltite from Detection to Remediation of Oxidative Stress Herbicide (Mesotrione)

In this research, we employed a strategy akin to "Feeding Two Birds with One Stone" aiming for the dual objectives of highly selective electrochemical detection and photocatalytic degradation of the environmentally hazardous herbicide mesotrione (MTN). We achieved this by utilizing hexagonal boron nitride (BN)-supported strontium cobaltite perovskite nanocomposites (SrCoO3/BN). The fabrication of the innovative bifunctional SrCoO3/BN nanocomposites involved a straightforward process of precipitation, followed by an annealing treatment and ultrasonication. The successful formation of these nanocomposites was corroborated through the application of diverse spectroscopic tools. Notably, as-prepared SrCoO3/BN nanocomposites exhibited a remarkable sensing platform for MTN, characterized by a notably low detection limit (11 nm), considerable sensitivity (3.782 μA μM-1 cm-2), and outstanding selectivity, alongside remarkable stability. Concurrently, these SrCoO3/BN nanocomposites demonstrated exceptional visible-light-driven photocatalytic efficacy for MTN degradation (99%) and complete mineralization. Our investigation systematically delved into the influence of operational parameters, including catalyst loading and the involvement of reactive oxidative species, in both the electrocatalytic and photocatalytic reactions. Drawing from these comprehensive studies, we have proposed plausible mechanisms for detecting and degrading MTN. Our findings pave the way for catalyst development, offering a unified solution for detecting and eliminating toxic organic compounds from the environment.

Ring Closure and Ring Opening as Useful Scaffold Hopping Tools in Agrochemistry

Ring closing acyclic parts of a molecular scaffold or the opposite manipulation, opening rings to produce pseudo-ring structures, is an important scaffold hopping manipulation. Analogues derived from biologically active compounds through the utilization of such strategies are often similar in shape and physicochemical properties and, therefore, likely to exhibit similar potency. This review will demonstrate how several different ring closure techniques, such as replacing carboxylic functions by cyclic peptide mimics, incorporating double bonds into aromatic rings, tying back ring substituents to a bicyclic structure, cyclizing adjacent ring substituents to an annulated ring, bridging annulated ring systems to tricyclic scaffolds, and exchanging gem-dimethyl groups by cycloalkyl rings, but also ring opening led to the discovery of highly active agrochemicals.

Investigating the effects of mesotrione/atrazine-based herbicide on honey bee foragers

A mixture of the herbicides mesotrione and atrazine (Calaris®) is a widely used herbicide in agriculture in several countries. However, the possible toxicological effects of this formulation on non-target organisms require investigation. In this study, the effects of acute oral exposure to Calaris® were evaluated in Apis mellifera foragers. The effect of seven different concentrations of Calaris® on survival and sucrose consumption was studied, while the recommended concentration for field use (FC) and its 10× dilution (0.1 FC) were used to assess overall locomotor activity, respiratory rate, flight, midgut morphology, oxidative and nitrosative stresses, and hemocyte counting. The exposure to FC or 0.1 FC decreased locomotor activity and induced damage to the midgut epithelium. Additionally, the two tested concentrations reduced superoxide dismutase activity, nitric oxide levels, and total hemocyte count. FC also increased malondialdehyde content and 0.1 FC increased respiratory rate and decreased the proportion of prohemocytes. Overall, our findings evidenced significant harmful effects on A. mellifera foragers resulting from the ingestion of the Calaris® herbicide.

Improving the Herbicide Resistance of Rice 4-Hydroxyphenylpyruvate Dioxygenase by DNA Shuffling Basis-Directed Evolution

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an ideal target for herbicide resistance genetic engineering. In this study, a mutant MFRR-2 with mesotrione resistance was screened from an Oryza sativa HPPD and mutant-Zea mays HPPD DNA shuffling library. The enzyme properties showed that although the stability of the mutant decreased in vitro, the enzyme activity of MFRR-2 at the optimum temperature of 25 °C was still equivalent to that of OsHPPD. Under 50 μM mesotrione treatment, MFRR-2 enzyme activity remained at approximately 90%, while the enzyme activity of OsHPPD decreased by approximately 50%. Surprisingly, Fe2+ was found to have an inhibitory effect on the enzyme activity. Then, the transgenic rice of the MFRR-2 gene showed approximately 1.5 times mesotrione resistance compared to OsHPPD transgenic rice. In conclusion, this study has conducted a beneficial exploration on the use of DNA shuffling for HPPD-directed evolution, and the mutant has potential application value for herbicide resistance genetic engineering.

Photoredox catalysis in alkene and alkyne alkylsulfonylations: the construction of Markovnikov selective α-sulfones

Photoredox alkene or alkyne alkylsulfonylation has been achieved with phthalimide esters and sulfinates providing unexpected α-sulfones. Mechanistic studies disclose that the preferential alkyl radical addition to the alkene or the Markovnikov hydrosulfonation of the alkyne should contribute to the formation of the β-alkylated α-sulfones. Moreover, the reaction is easy to operate covering quite large substrate scales including primary, secondary and tertiary alkyl groups and all sorts of terminal aryl alkenes or alkynes. Besides, the reaction was also suitable for the sulfonylation of several drug molecules.

β-triketone herbicide exposure cause tyrosine and fat accumulation in Caenorhabditis elegans

β-triketone herbicides have been efficiently employed as an alternate to atrazine. Triketones are 4-hydroxyphenylpyruvate dioxygenase (HPPD) enzyme inhibitors and exposure is reported to cause significant increase in plasma tyrosine levels. In this study, we have employed a non-target organism Caenorhabditis elegans to determine the impact of β-triketone exposures at recommended field doses (RfD). Our results indicate sulcotrione and mesotrione, negatively influence the survival, behavior, and reproduction of the organism at RfD. Additionally, we have traced the parallels regarding the impact of triketones on the tyrosine metabolism pathway, in C. elegans to those in mammalian models, wherein the expression of the tyrosine metabolism pathway genes are altered, directly influencing tyrosine catabolism leading to significant tyrosine accumulation in exposed organism. Further, we investigated the impact of sulcotrione and mesotrione exposure on fat deposition (triglyceride levels, Oil-Red-O staining and lipidomics) and the fatty acid metabolism pathway. In the exposed worms, the expression of enlongases and fatty acid desaturases were up-regulated along with an increase in the levels of triglycerides. Thus, the data indicates a positive association of β-triketone exposure to mis-regulation of the fatty acid metabolism pathway genes leading to fat accumulation in worms. Therefore, β-triketone might be a potential obesogen.

Study of two combined series of triketones with HPPD inhibitory activity by molecular modelling

Triketones are suitable compounds for 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibition and are important compounds for eliminating agricultural weeds. We report herein quantitative structure-activity relationship (QSAR) modelling and docking studies for a series of triketone-quinoline hybrids and 2-(aryloxyacetyl)cyclohexane-1,3-diones with the aim of proposing new chemical candidates that exhibit improved performance as herbicides. The QSAR models obtained were reliable and predictive (average r², q², and r²_pred of 0.72, 0.51, and 0.71, respectively). Guided by multivariate image analysis of the PLS regression coefficients and variable importance in projection scores, the substituent effects could be analysed, and a promising derivative with R¹ = H, R² = CN, and R³ = 5,7,8-triCl at the triketone-quinoline scaffold (P18) was proposed. Docking studies demonstrated that π-π stacking interactions and specific interactions between the substituents and amino acid residues in the binding site of the Arabidopsis thaliana HPPD (AtHPPD) enzyme support the desired bioactivity. In addition, compared to a benchmark commercial triketone (mesotrione), the proposed compounds are more lipophilic and less mobile in soil rich in organic matter and are less prone to contaminate groundwater.

Identification and Characterization of Mesotrione-Resistant Grain Sorghum [Sorghum bicolor (L.) Moench]: A Viable Option for Postemergence Grass Weed Control

Mesotrione is effective in controlling a wide spectrum of weeds in corn but not registered for postemergence use in sorghum because of crop injury. We screened a sorghum germplasm collection and identified two mesotrione-resistant sorghum genotypes (G-1 and G-10) and one susceptible genotype (S-1) in an in vitro plate assay. A mesotrione dose-response assay under greenhouse and field conditions confirmed that G-1 and G-10 are highly resistant compared to S-1. We found enhanced metabolism of mesotrione in G-1 and G-10 using HPLC assay, and a significant reduction in biomass accumulation was found in G-1 and G-10 plants pretreated with cytochrome P450 (CYP)-inhibitors malathion or piperonyl butoxide, indicating the involvement of CYPs in the metabolism of mesotrione. Genetic analyses using F₁ and F₂ progenies generated by crossing G-1 and G-10 separately with S-1 revealed that mesotrione resistance in sorghum is controlled by a single dominant gene along with several genes with minor effects.

Assessing the effects of β-triketone herbicides on HPPD from environmental bacteria using a combination of in silico and microbiological approaches

4-hydroxyphenylpyruvate dioxygenase (HPPD) is the molecular target of β-triketone herbicides in plants. This enzyme, involved in the tyrosine pathway, is also present in a wide range of living organisms, including microorganisms. Previous studies, focusing on a few strains and using high herbicide concentrations, showed that β-triketones are able to inhibit microbial HPPD. Here, we measured the effect of agronomical doses of β-triketone herbicides on soil bacterial strains. The HPPD activity of six bacterial strains was tested with 1× or 10× the recommended field dose of the herbicide sulcotrione. The selected strains were tested with 0.01× to 15× the recommended field dose of sulcotrione, mesotrione, and tembotrione. Molecular docking was also used to measure and model the binding mode of the three herbicides with the different bacterial HPPD. Our results show that responses to herbicides are strain-dependent with Pseudomonas fluorescens F113 HPPD activity not inhibited by any of the herbicide tested, when all three β-triketone herbicides inhibited HPPD in Bacillus cereus ATCC14579 and Shewanella oneidensis MR-1. These responses are also molecule-dependent with tembotrione harboring the strongest inhibitory effect. Molecular docking also reveals different binding potentials. This is the first time that the inhibitory effect of β-triketone herbicides is tested on environmental strains at agronomical doses, showing a potential effect of these molecules on the HPPD enzymatic activity of non-target microorganisms. The whole-cell assay developed in this study, coupled with molecular docking analysis, appears as an interesting way to have a first idea of the effect of herbicides on microbial communities, prior to setting up microcosm or even field experiments. This methodology could then largely be applied to other family of pesticides also targeting an enzyme present in microorganisms.

In vivo fluorescent screening for HPPD-targeted herbicide discovery

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD), playing a critical role in vitamin E and plastoquinone biosynthesis in plants, has been recognized as one of the most important targets for herbicide discovery for over 30 years. Structure-based rational design of HPPD inhibitors has received more and more research interest. However, a critical challenge in the discovery of new HPPD inhibitors is the common inconsistency between molecular-level HPPD-based bioevaluation and the weed control efficiency in fields, due to the unpredictable biological processes of absorption, distribution, metabolism, and excretion.

RESULTS

In this study, we developed a fluorescent-sensing platform of efficient in vivo screening for HPPD-targeted herbicide discovery. The refined sensor has good capability of in situ real-time fluorescence imaging of HPPD in living cells and zebrafish. More importantly, it enabled the direct visible monitoring of HPPD inhibition in plants in a real-time manner.

CONCLUSION

We developed a highly efficient in vivo fluorescent screening method for HPPD-targeted herbicide discovery. This discovery not only offers a promising tool to advance HPPD-targeted herbicide discovery, but it also demonstrates a general path to develop the highly efficient, target-based, in vivo screening for pesticide discovery. © 2022 Society of Chemical Industry.

Herbicidal characteristics and structural identification of a potential active compound produced by Streptomyces sp. KRA18-249

The KRA18-249 strain, isolated from a natural recreational forest near Jeongseon, Gangwon-do, when applied to plants induced signs of wilting within 24 h, leading to plant death. The isolated actinomycete was identified as Streptomyces gardneri based on 16S rRNA gene homogeneity analysis. The culture filtrate was solvent fractionated to obtain the active substance, and the active compound 249-Y1 was isolated from the purified fractions via a herbicide activity test using Digitaria ciliaris. NMR and ESI-MS analyses revealed that the molecular formula of 249-Y1 is C₂₀H₁₆O₆ [MW = 352.0947] and is an anthraquinone (rubiginone D2) produce by polyketide synthetase system. The active compound 249-Y1 showed strong (100%) herbicidal activity against several weeds at 500 μg mL^-1 concentration. Twisting symptoms began to appear within 24 h of treatment and intensified over time. The KRA18-249 strain produced the herbicidal compound under specific culture conditions, that is, at 200 rpm, 35 °C, for eight days at an initial pH of 10. We also found that 249-Y1 inhibited chlorophyll, but was not a radical generator. Overall, the secondary metabolite 249-Y1, produced by KRA18-249, can be used as a new biological agent for weed control.

Copper(I)-Catalyzed Cross-Coupling of Arylsulfonyl Radicals with Diazo Compounds: Assembly of Arylsulfones

A novel copper-catalyzed cross-coupling of arylsulfonyl radicals with diazo compounds is described for the synthesis of various arylsulfones under mild conditions. In this reaction, the cheap, environmentally friendly, and readily available inorganic K₂S₂O₅ is employed as the sulfur dioxide source for providing arylsulfonyl radicals. In addition, a radical mechanism involving the insertion of sulfur dioxide with aryl radicals followed by the coupling of arylsulfonyl radicals with copper carbenes is proposed.

Ectopic expression of a rice triketone dioxygenase gene confers mesotrione tolerance in soybean

BACKGROUND

Herbicide-resistant weeds pose a challenge to agriculture and food production. New herbicide tolerance traits in crops will provide farmers with more options to effectively manage weeds. Mesotrione, a selective pre- and post-emergent triketone herbicide used in corn production, controls broadleaf and some annual grass weeds via hydroxyphenylpyruvate dioxygenase (HPPD) inhibition. Recently, the rice HIS1 gene, responsible for native tolerance to the selective triketone herbicide benzobicyclon, was identified. Expression of HIS1 also confers a modest level of mesotrione resistance in rice. Here we report the use of the HIS1 gene to develop a mesotrione tolerance trait in soybean.

RESULTS

Conventional soybean is highly sensitive to mesotrione. Ectopic expression of a codon-optimized version of the rice HIS1 gene (TDO) in soybean confers a commercial level of mesotrione tolerance. In TDO transgenic soybean plants, mesotrione is rapidly and locally oxidized into noninhibitory metabolites in leaf tissues directly exposed to the herbicide. These metabolites are further converted into compounds similar to known classes of plant secondary metabolites. This rapid metabolism prevents movement of mesotrione from treated leaves into vulnerable emerging leaves. Minimizing the accumulation of the herbicide in vulnerable emerging leaves protects the function of HPPD and carotenoid biosynthesis more generally while providing tolerance to mesotrione.

CONCLUSIONS

Mesotrione has a favorable environmental and toxicological profile. The TDO-mediated soybean mesotrione tolerance trait described here provides farmers with a new option to effectively manage difficult-to-control weeds using familiar herbicide chemistry. This trait can also be adapted to other mesotrione-sensitive crops (e.g. cotton) for effective weed management. © 2022 Bayer Crop Science. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Virtual screening based on pharmacophore model for developing novel HPPD inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an important target for herbicide design. A multilayered virtual screening workflow was constructed by combining two pharmacophore models based on ligand and crystal complexes, molecular docking, molecular dynamics (MD), and biological activity determination to identify novel small-molecule inhibitors of HPPD. About 110, 000 compounds of Bailingwei and traditional Chinese medicine databases were screened. Of these, 333 were analyzed through docking experiments. Five compounds were selected by analyzing the binding pattern of inhibitors with amino acid residues in the active pocket. All five compounds could produce stable coordination with cobalt ion, and form favorable π-π interactions. MD simulation demonstrated that Phe381 and Phe424 made large contributions to the strength of binding. The enzyme activity experiment verified that compound-139 displayed excellent potency against AtHPPD (IC₅₀ = 0.742 μM), however, compound-5222 had inhibitory effect on human HPPD (IC₅₀ = 6 nM). Compound-139 exhibited herbicidal activity to some extent on different gramineous weeds. This work provided a strong insight into the design and development of novel HPPD inhibitor using in silico techniques.

Pyridylidene Amide Ru Complex for Selective Oxidation in Organic Synthesis

The ruthenium(II) bis(PYA) complex 1 (PYA = p-pyridylidene amide) is a powerful catalyst for the oxidation of sulfides to sulfones, of alkenes to carbonyl compounds, and of terminal alkynes to carboxylic acids by using NaIO₄ as the terminal oxidant. The catalytic system shows a broad functional group tolerance and rate differences between alkyne and sulfide oxidation that are sufficiently large to effectively achieve selective sulfide oxidation with exquisite selectivity.

Comparison of quintrione and quinclorac on mechanism of action

Quintrione is a new post-emergence herbicide developed for use in rice; however, the mechanism of action remains unclear. We determined the phytotoxicity of quintrione, and the contributions of hormone levels and lipid peroxidation to phytotoxicity, by comparing them to those induced by quinclorac. We also investigated 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity and carotenoid content following treatment with quintrione by comparing them to those induced by quinclorac and mesotrione. We found that quintrione and quinclorac both inhibited the growth of Echinochloa crusgalli var. zelayensis, but that quinclorac was a little more effective. At 24 h, quintrione and quinclorac significantly increased ethylene production and the contents of abscisic acid (ABA) and indole acetic acid (IAA) compared with the control. No significant differences were observed between quintrione and quinclorac on the three plant hormones. Quintrione and quinclorac also induced the formation of malondialdehyde (MDA), which is associated with lipid peroxidation, with no significant difference between them. Carotenoid content was reduced in E. crusgalli var. zelayensis following treatments with quintrione, quinclorac, and mesotrione. At 120 h, carotenoid contents were significantly higher following the quintrione and quinclorac treatments, in comparison with mesotrione treatment. There were no significant differences between quintrione and quinclorac in the inhibition of HPPD activity, and the effects of both were significantly less than the effect of mesotrione. In summary, E. crusgalli var. zelayensis was susceptible to both quintrione and quinclorac. The mechanism of action of quintrione, like that of quinclorac, was related to levels of plant hormones and lipid peroxidation; however, quintrione was a poor inhibitor of HPPD activity compared to mesotrione.

On the use of inhibitors of 4-hydroxyphenylpyruvate dioxygenase as a vector-selective insecticide in the control of mosquitoes

BACKGROUND

Blood-sucking insects incorporate many times their body weight of blood in a single meal. Because proteins are the major component of vertebrate blood, its digestion in the gut generates extremely high concentrations of free amino acids. Previous reports showed that the tyrosine degradation pathway plays an essential role in adapting these animals to blood feeding. Inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD), the rate-limiting step of tyrosine degradation, results in the death of insects after a blood meal. Therefore, it has been suggested that compounds that block the catabolism of tyrosine could act selectively on blood-feeding insects. Here, we evaluated the toxicity against mosquitoes of three HPPD inhibitors currently used as herbicides and in human health.

RESULTS

Of the compounds tested, nitisinone (NTBC) proved to be more potent than mesotrione (MES) and isoxaflutole (IFT) in Aedes aegypti. NTBC was lethal to Ae. aegypti in artificial feeding assays [median lethal dose (LD₅₀ ): 4.53 μm] and in topical application (LD₅₀ : 0.012 nmol/mosquito). NTBC was also lethal to Ae. aegypti populations that were resistant to neurotoxic insecticides, and to other mosquito species (Anopheles and Culex).

CONCLUSION

HPPD inhibitors, particularly NTBC, represent promising new drugs for mosquito control. Because they affect only blood-feeding organisms, they represent a safer and more environmentally friendly alternative to conventional neurotoxic insecticides. © 2021 Society of Chemical Industry.

Allelopathy and its application as a weed management tool: A review

Weeds are a serious threat to crop production as they interfere with the crop growth and development and result in significant crop losses. Weeds actually cause yield loss higher than any other pest in crop production. As a result, synthetic herbicides have been widely used for weed management. Heavy usage of synthetic herbicides, however, has resulted in public concerns over the impact of herbicides on human health and the environment. Due to various environmental and health issues associated with synthetic herbicides, researchers have been exploring alternative environmentally friendly means of controlling weed. Among them, incorporating allelopathy as a tool in an integrated weed management plan could meaningfully bring down herbicide application. Allelopathy is a biological phenomenon of chemical interaction between plants, and this phenomenon has great potential to be used as an effective and environmentally friendly tool for weed management in field crops. In field crops, allelopathy can be applied through intercropping, crop rotation, cover crops, mulching and allelopathic water extracts to manage weeds. Accumulating evidence indicates that some plant species possess potent allelochemicals that have great potential to be the ecofriendly natural herbicides. This review is intended to provide an overview of several allelopathic species that release some form of the potent allelochemical with the potential of being used in conventional or organic agriculture. Further, the review also highlights potential ways allelopathy could be utilized in conventional or organic agriculture and identify future research needs and prospects. It is anticipated that the phenomenon of allelopathy will be further explored as a weed management tool, and it can be a part of a sustainable, ecological, and integrated weed management system.

Improving the herbicide resistance of 4-hydroxyphenylpyruvate dioxygenase SpHPPD by directed evolution

Topramezone, a highly efficient 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitor herbicide, is an ideal target for herbicide-resistant genetic engineering. However, there is still a lack of HPPD gene that is highly resistant to topramezone. In previous studies, we obtained a topramezone-resistant HPPD (SpHPPDm) gene from Sphingobium sp. TPM-19, however, its resistance strength still could not meet the requirements for construction of herbicide-resistant crop. In this study, random mutagenesis (error-prone PCR) was employed to improve the topramezone resistance of SpHPPDm. Two mutants with improved resistance, K-28 (E322R) and K-113 (K249R, G327C), were screened from the random mutation library of SpHPPDm. The catalytic efficiency (k_cat/K_m) of mutants K-28 and K-113 only slightly decreased by approximately 2%. The half-maximal inhibitory concentration (IC₅₀) of topramezone increased by 58.5% and 195.5% for mutants K-28 and K-113, respectively. Furthermore, mutant K-113 also showed significantly improved resistance to mesotrione and DKN (the active ingredient of isoxaflutole) with the IC₅₀ increasing by 60.3% and 167.5%, respectively; while mutant K-28 only showed increased resistance to mesotrione with IC₅₀ increasing by 77.6%, but reduced resistance to DKN with IC₅₀ declining by 20.9%. Site-directed mutation assays revealed that G327C, but not K249R, contributed to topramezone resistance in mutant K-113. This study provides genetic resources for the genetic engineering of HPPD-inhibitor-resistant crops and a basis for further research on HPPD resistance mechanisms.

Resistance to a nonselective 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide via novel reduction-dehydration-glutathione conjugation in Amaranthus tuberculatus

Metabolic resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides is a threat in controlling waterhemp (Amaranthus tuberculatus) in the USA. We investigated resistance mechanisms to syncarpic acid-3 (SA3), a nonselective, noncommercial HPPD-inhibiting herbicide metabolically robust to Phase I oxidation, in multiple-herbicide-resistant (MHR) waterhemp populations (SIR and NEB) and HPPD inhibitor-sensitive populations (ACR and SEN). Dose-response experiments with SA3 provided ED₅₀ -based resistant : sensitive ratios of at least 18-fold. Metabolism experiments quantifying parent SA3 remaining in excised leaves during a time course indicated MHR populations displayed faster rates of SA3 metabolism compared to HPPD inhibitor-sensitive populations. SA3 metabolites were identified via LC-MS-based untargeted metabolomics in whole plants. A Phase I metabolite, likely generated by cytochrome P450-mediated alkyl hydroxylation, was detected but was not associated with resistance. A Phase I metabolite consistent with ketone reduction followed by water elimination was detected, creating a putative α,β-unsaturated carbonyl resembling a Michael acceptor site. A Phase II glutathione-SA3 conjugate was associated with resistance. Our results revealed a novel reduction-dehydration-GSH conjugation detoxification mechanism. SA3 metabolism in MHR waterhemp is thus atypical compared to commercial HPPD-inhibiting herbicides. This previously uncharacterized detoxification mechanism presents a unique opportunity for future biorational design by blocking known sites of herbicide metabolism in weeds.

Copper-Catalyzed N-Directed Distal C(sp3)-H Sulfonylation and Thiolation with Sulfinate Salts

We herein report a selective and catalytic C(sp³)-H functionalization approach to access amines bearing organo-sulfonyl and organo-thiol groups. This reaction proceeds through a cascade process of N-radical formation, alkyl radical formation via 1,5-HAT, and C-S bond formation, thereby offering a series of functionalized amines. This method could enable primary, secondary, and tertiary C(sp³)-H sulfonylation and thiolation and also exhibits good functional group tolerance.

Charge-transfer complex-based spectrophotometric method for the determination of mesotrione in environmental samples

A simple, accurate, sensitive, and selective spectrophotometric method has been developed for the determination of mesotrione. This method is based on the reaction of mesotrione with Fe(III) to form a charge transfer metal complex having λ_max at 348 nm. Beer's law was obeyed in the concentration range of 0.2-10.0 µg mL^-1 with limit of detection (LOD) and limit of quantification (LOQ) equal to 0.053 and 0.162 µg mL^-1, respectively. The percent recovery of mesotrione from different environmental and agricultural samples was found to be 95.00-106.50% at various levels. Notably, the developed method was successfully employed for the determination of mesotrione in environmental (pond water, canal water, tap water, and soil) and agricultural (maize grains) samples.

A three-component reaction of arynes, sodium sulfinates, and aldehydes toward 2-sulfonyl benzyl alcohol derivatives

A novel three-component reaction of arynes, sodium sulfinates, and aldehydes under mild reaction conditions is described. This transformation provides a direct synthetic approach to 2-sulfonyl benzyl alcohol derivatives, which could be rapidly converted to diverse arylsulfur compounds via the transformation of the corresponding hydroxyl groups. Various aryne precursors, sodium arenesulfinates, and aromatic aldehydes can be effectively converted to the desired products in 40-84% yields (29 examples).

Unravelling Phytotoxicity and Mode of Action of Tripyrasulfone, a Novel Herbicide

Tripyrasulfone is a novel herbicide post-emergence applied in paddy fields. In this study, tripyrasulfone phytotoxicity and its mode of action were investigated. Within 3-7 days after treatment (DAT), tripyrasulfone caused strong bleaching symptoms on newly developed leaves of Echinochloa crus-galli followed by necrosis prior to death within 14 DAT. By investigating pigment composition, photosynthetic activity and energy dissipation of E. crus-galli treated with tripyrasulfone, the accumulation of phytoene and significant decreases in total carotenoids were observed; the photosystem II complex (PSII) reaction center and PSII-PSI electron transport chain were damaged; and the non-photochemical energy quenching and reactive oxygen species were significantly increased. Based on the reversion of bleaching symptoms in treated Spirodela polyrrhiza by the addition of homogentisic acid, it was hypothesized that tripyrasulfone blocks the biosynthesis of HGA, possibly by the inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD). However, based on its chemical structure, tripyrasulfone may tend to be hydrolyzed in plants. Indeed, the hydrolyzed tripyrasulfone (HDT) inhibited the activity of HPPD from Arabidopsis thaliana produced by Escherichia coli, which was approximately 6 times less effective than mesotrione. Molecular docking showed that the HDT formed a stable bidentate interaction with the active center Fe²⁺ chelation of A. thaliana HPPD.

Recurrent Selection with Sub-Lethal Doses of Mesotrione Reduces Sensitivity in Amaranthus palmeri

Amaranthus palmeri, ranked as the most prolific and troublesome weed in North America, has evolved resistance to several herbicide sites of action. Repeated use of any one herbicide, especially at lower than recommended doses, can lead to evolution of weed resistance, and, therefore, a better understanding of the process of resistance evolution is essential for the management of A. palmeri and other difficult-to-control weed species. Amaranthus palmeri rapidly developed resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors such as mesotrione. The objective of this study was to test the potential for low-dose applications of mesotrione to select for reduced susceptibility over multiple generations in an A. palmeri population collected from an agricultural field in 2001. F₀ plants from the population were initially treated with sub-lethal mesotrione rates and evaluated for survival three weeks after treatment. All F₀ plants were controlled at the 1× rate (x = 105 g ai ha⁻¹). However, 2.5% of the F₀ plants survived the 0.5× treatment. The recurrent selection process using plants surviving various mesotrione rates was continued until the F₄ generation was reached. Based on the GR₅₀ values, the sensitivity index was determined to be 1.7 for the F₄ generation. Compared to F₀, HPPD gene expression level in the F₃ population increased. Results indicate that after several rounds of recurrent selection, the successive generations of A. palmeri became less responsive to mesotrione, which may explain the reduced sensitivity of this weed to HPPD-inhibiting herbicides. The results have significance in light of the recently released soybean and soon to be released cotton varieties with resistance to HPPD inhibitors.

Verbascoside from Verbena incompta is a plant root growth inhibitor

The use of biopesticides has expanded rapidly in recent years; however, their use in weed control is less advanced. Herein, we describe the development of a weed control agent by screening 208 plant extracts (104 species) for their plant growth-inhibition activities, which resulted in 142 active samples (from 89 plant species). Verbascoside, isolated from the shoots of Verbena incompta, was identified as a growth inhibitor against rice root (EC50, 1.75 m m), and its root growth-inhibition activity was also confirmed in radish, tomato, and Lotus japonicus. Verbascoside is composed of hydroxytyrosol (EC50,12.51 m m) and caffeic acid (EC50, 4.08 m m), 2 poorly water-soluble phenolic components with weak growth-inhibition activities, and 2 sugars, which are more soluble but inactive. The plant apparently developed a more active and highly soluble compound by condensing these 4 components. We conclude that a biopesticide containing verbascoside may be useful for weed-control purposes.

Discovery of novel benzofuran scaffold as 4-hydroxyphenylpyruvate dioxygenase inhibitors

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. This study sheds new light on the differences in molecular scaffold from commercialized HPPD inhibitors.

RESULTS

The compounds A1-A18 and B1-B27 were synthesized for in vitro and greenhouse experiments. The greenhouse experiment data indicated that compounds B14 and B18 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. In vitro testing indicated that the compounds were HPPD inhibitors. Moreover, molecular simulation results show that the compounds B14, B18, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on crop selectivity results, compounds B14 and B18 were selected for maize studies (injury≤10%), indicating its potential for weed control in maize fields.

CONCLUSION

These results showed that the pyrazole-benzofuran structure could be used as possible lead compounds for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Structure-Guided Discovery of Silicon-Containing Subnanomolar Inhibitor of Hydroxyphenylpyruvate Dioxygenase as a Potential Herbicide

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) has been recognized as one of the most promising targets in the field of herbicide innovation considering the severity of weed resistance currently. In a persistent effort to develop effective HPPD-inhibiting herbicides, a structure-guided strategy was carried out to perform the structural optimization for triketone-quinazoline-2,4-diones, a novel HPPD inhibitor scaffold first discovered in our lab. Herein, starting from the crystal structure of Arabidopsis thaliana (At)HPPD complexed with 6-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-1,5-dimethyl-3-(o-tolyl)quinazoline-2,4(1H,3H)-dione (MBQ), three subseries of quinazoline-2,4-dione derivatives were designed and prepared by optimizing the hydrophobic interactions between the side chain of the core structure at the R¹ position and the hydrophobic pocket at the active site entrance of AtHPPD. 6-(2-Hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-1,5-dimethyl-3-(3-(trimethylsilyl)prop-2-yn-1-yl)quinazoline-2,4(1H,3H)-dione (60) with the best inhibitory activity against AtHPPD was identified to be the first subnanomolar-range AtHPPD inhibitor (K_i = 0.86 nM), which significantly outperformed that of the lead compound MBQ (K_i = 8.2 nM). Further determination of the crystal structure of AtHPPD in complex with compound 60 (1.85 Å) and the binding energy calculation provided a molecular basis for the understanding of its high efficiency. Additionally, the greenhouse assay indicated that 6-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-1,5-dimethyl-3-propylquinazoline-2,4(1H,3H)-dione (28) and compound 60 showed acceptable crop safety against peanut and good herbicidal activity with a broad spectrum. Moreover, compound 28 also showed superior selectivity for wheat at the dosage of 120 g ai/ha and favorable herbicidal efficacy toward the gramineous weeds at the dosage of as low as 30 g ai/ha. We believe that compounds 28 and 60 have promising prospects as new herbicide candidates for wheat and peanut fields.

Assessing the Effects of β-Triketone Herbicides on the Soil Bacterial and hppd Communities: A Lab-to-Field Experiment

Maize cultivators often use β-triketone herbicides to prevent the growth of weeds in their fields. These herbicides target the 4-HPPD enzyme of dicotyledons. This enzyme, encoded by the hppd gene, is widespread among all living organisms including soil bacteria, which are considered as “non-target organisms” by the legislation. Within the framework of the pesticide registration process, the ecotoxicological impact of herbicides on soil microorganisms is solely based on carbon and nitrogen mineralization tests. In this study, we used more extensive approaches to assess with a lab-to-field experiment the risk of β-triketone on the abundance and the diversity of both total and hppd soil bacterial communities. Soil microcosms were exposed, under lab conditions, to 1× or 10× the recommended dose of sulcotrione or its commercial product, Decano^®. Whatever the treatment applied, sulcotrione was fully dissipated from soil after 42 days post-treatment. The abundance and the diversity of both the total and the hppd bacterial communities were not affected by the herbicide treatments all along the experiment. Same measurements were led in real agronomical conditions, on three different fields located in the same area cropped with maize: one not exposed to any plant protection products, another one exposed to a series of plant protection products (PPPs) comprising mesotrione, and a last one exposed to different PPPs including mesotrione and tembotrione, two β-triketones. In this latter, the abundance of the hppd community varied over time. The diversity of the total and the hppd communities evolved over time independently from the treatment received. Only slight but significant transient effects on the abundance of the hppd community in one of the tested soil were observed. Our results showed that tested β-triketones have no visible impact toward both total and hppd soil bacteria communities.

Effects of the novel HPPD-inhibitor herbicide QYM201 on enzyme activity and microorganisms, and its degradation in soil

QYM201 is a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicide recently registered in China for controlling grass and broadleaf weeds in wheat. It is a novel herbicide, and its potential harm to soil ecosystems has not yet been reported. This study investigates the influence of QYM201 on soil enzyme activity and microorganism quantities in two different soils at concentrations of 0.1, 1, and 5 mg kg^-1 soil. Results indicate that QYM201 initially inhibited soil protease, urease, and sucrase activity and this effect increased with concentration. During the later stages of incubation, inhibitory effects gradually weakened and by the end of the experiment (45 days), enzyme activity was restored to control levels. Catalase activity was stimulated by QYM201, with significant differences observed between the QYM201-treated groups and the control at the onset of exposure. This stimulation effect decreased during the later stages of the experiment. However, catalase activity was still significantly higher at the end of the experiment compared to the control. The effects of QYM201 on soil microorganisms differed. Initially, bacteria and actinomycetes quantities were decreased by QYM201 (10 days). As the incubation progressed, microorganism quantities in the lower concentration groups (0.1 and 1 mg kg^-1 soil) were restored to control levels, while those of the high concentration group (5 mg kg^-1 soil) did not fully recover. QYM201 did not significantly impact the quantity of fungi. The half-life and degradation rate constant (k) of QYM201 for the two studied soil types were 23.1 days and 16.1 days, and 0.030 and 0.043 day^-1, respectively.

Discovery of novel arylthioacetic acid derivatives as 4-hydroxyphenylpyruvate dioxygenase inhibitors

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. In a continuing effort to discover novel HPPD inhibitors, we adopted a bioisosterism strategy to design a series of novel arylthioacetic acid scaffold based on the previously discovered aryloxyacetic acid scaffold. This study sheds new light on the discovery of novel HPPD inhibitors.

RESULTS

The compounds A1-A30 and B1-B39 were prepared through an efficient synthetic route for in vitro and glasshouse experiments (herbicidal activities, herbicidal activity spectrum, and crop selectivity). Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD inhibitors, compounds A11 (K_i = 0.021 μmol L^-1 ) and B20 (K_i = 0.022 μmol L^-1 ), which exhibit similar activities to that of mesotrione (K_i = 0.020 μmol L^-1 ). The glasshouse experiments data indicated that compounds B34 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. Moreover, molecular simulation results show that the compounds B20, B34, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on herbicidal results, compound B34 was selected for crop selectivity studies (corn injury ≤ 10%), indicating its potential for weed control in corn fields.

CONCLUSION

These bioassay results showed that the compound B34 could be used as a possible lead compound for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Base-Mediated Denitrogenative Sulfonylation/Benzannulation of Conjugated N-Sulfonylhydrazones with 3-Formylchromones for the Construction of Polyfunctionalized Biaryl Sulfones

Base-promoted benzannulation of conjugated N-sulfonylhydrazones and 3-formylchromones for the synthesis of diverse biaryl sulfones is described. The approach facilitates new C-C and C-S bond formation via the cascade diazo formation/Michael addition/ring opening/denitrogenative sulfonylation/intramolecular cycloaddition/dehydration and introduces diverse functional groups onto biaryl sulfones. The synthesized compounds are converted to aryl sulfones bearing bioactive benzisoxazole and benzofuran frameworks. Moreover, the synthesized biaryl sulfones possess potent turn-on fluorescence sensing and UV absorbance properties.

In vivo and in vitro evidence for the inhibition of homogentisate solanesyltransferase by cyclopyrimorate

BACKGROUND

Cyclopyrimorate is a highly effective bleaching herbicide discovered by Mitsui Chemicals Agro, Inc. The target site was recently reported to be homogentisate solanesyltransferase (HST) in the plastoquinone (PQ) biosynthesis pathway on the basis of the number of intermediates in cyclopyrimorate-treated plants and in vitro HST assays. Here, the target site of cyclopyrimorate was further explored using both in vivo and in vitro experiments.

RESULTS

The cyclopyrimorate-dependent bleaching effect on Arabidopsis thaliana was reversed by decyl PQ, suggesting that this symptom is attributable to the inhibition of PQ biosynthesis. Furthermore, homogentisate (HGA), a substrate of HST, weakly reversed the bleaching effect of cyclopyrimorate in a dose-dependent manner. We expected that the weak reversal by HGA was due to competitive inhibition by cyclopyrimorate or des-morpholinocarbonyl cyclopyrimorate (DMC), a metabolite of cyclopyrimorate in plants that exhibit higher HST-inhibitory activity as compared to cyclopyrimorate. Kinetic analysis was therefore conducted using DMC. DMC inhibited HST competitively with respect to HGA, and was a mixed non-competitive inhibitor with respect to the other substrate, farnesyl diphosphate. Moreover, neither cyclopyrimorate nor DMC inhibited 2-methyl-6-phytyl-1,4-benzoquinone/2-methyl-6-solanesyl-1,4-benzoquinone methyltransferase, which is located downstream of HST in the PQ biosynthesis pathway.

CONCLUSIONS

The target site of cyclopyrimorate and DMC is HST, which is a novel target site for commercial herbicides. © 2019 Society of Chemical Industry.

Potential of TiO2 with Various Au Nanoparticles for Catalyzing Mesotrione Removal from Wastewaters under Sunlight

Nowadays, great focus is given to the contamination of surface and groundwater because of the extensive usage of pesticides in agriculture. The improvements of commercial catalyst TiO₂ activity using different Au nanoparticles were investigated for mesotrione photocatalytic degradation under simulated sunlight. The selected system was 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) that was studied by transmission electron microscopy and ultraviolet-visible (UV-Vis) spectroscopy. It was found that TiO₂ particles size was ~20 nm and ~50 nm, respectively. The Au nanoparticles were below 10 nm and were well distributed within the framework of TiO₂. For 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L), band gap energy was 2.45 eV. In comparison to the pure TiO₂, addition of Au nanoparticles generally enhanced photocatalytic removal of mesotrione. By examining the degree of mineralization, it was found that 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) system was the most efficient for the removal of the mesotrione and intermediates. The effect of tert-butanol, NaF and ethylenediaminetetraacetic acid disodium salt on the transformation rate suggested that the relative contribution of various reactive species changed in following order: h⁺ > ^●OH_ads > ^●OH_bulk. Finally, several intermediates that were formed during the photocatalytic treatment of mesotrione were identified.

Identification of key residues determining the binding specificity of human 4-hydroxyphenylpyruvate dioxygenase

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is the second enzyme of the tyrosine catabolic pathway. Its physiological function is to catalyze the conversion of 4-hydroxyphenylpyruvic acid to homogentisic acid, which displays different physiological effects in mammals and plants. Insights on the selective inhibition of human HPPD (hHPPD) by triketone inhibitors were furnished by the integrated application of molecular simulation and biological testing. The binding free energy of hHPPD and inhibitors was obtained through molecular dynamics (MD) simulations, and the result was in agreement with the inhibition experiment in vitro. The binding free energy contribution demonstrated that the formation of hHPPD-inhibitor complexes was mainly driven by van der Waals energy. Ser226, Asn241, Gln265, Phe336, Phe359 and Phe364 made great contributions to binding affinities of all the systems. Among the residues involved in the interaction between nitisinone (NTBC) and hHPPD, Tyr221 and Leu224, whose mutation into Ala caused significant decrease of NTBC binding ability, were two key residues in determining the selective binding affinity of inhibitor and hHPPD. This work provides valuable theoretical basis for rational design of highly selective inhibitors targeting hHPPD.

Herbicidal efficacy of harzianums produced by the biofertilizer fungus, Trichoderma brevicompactum

Herbicides are important tools for weed control in modern agriculture. In the search for potential herbicidal natural products from fungal species, harzianum A and B were identified from the biofertilizer fungus, Trichoderma brevicompactum. In the phytotoxicity assays on the dicot species Brassica chinensis, harzianum A and B reduced both shoot and root lengths at low concentrations and inhibited the seed germination at 2 μg mL⁻¹. In addition, harzianum A and B also exhibited phytotoxicity against monocots, Oryza sativa L. cv. Nipponbare and Echinochloa crusgalli L. Beauv.. Compared with a common herbicide, 2,4-dichlorophenoxyacetic acid, harzianum A and B performed similar activity in a pot assay, and were more effective in post-emergence than pre-emergence conditions. Harzianum A and B have potential as efficient herbicide for controlling important dicotyledon and monocotyledon weeds at low concentrations. They can be sprayed in liquid form in both pre- and post-emergence conditions. Our results confirmed the importance of these molecules for the development of new herbicides.

Role of Cytochrome P450 Enzymes in Plant Stress Response

Cytochrome P450s (CYPs) are the largest enzyme family involved in NADPH- and/or O₂-dependent hydroxylation reactions across all the domains of life. In plants and animals, CYPs play a central role in the detoxification of xenobiotics. In addition to this function, CYPs act as versatile catalysts and play a crucial role in the biosynthesis of secondary metabolites, antioxidants, and phytohormones in higher plants. The molecular and biochemical processes catalyzed by CYPs have been well characterized, however, the relationship between the biochemical process catalyzed by CYPs and its effect on several plant functions was not well established. The advent of next-generation sequencing opened new avenues to unravel the involvement of CYPs in several plant functions such as plant stress response. The expression of several CYP genes are regulated in response to environmental stresses, and they also play a prominent role in the crosstalk between abiotic and biotic stress responses. CYPs have an enormous potential to be used as a candidate for engineering crop species resilient to biotic and abiotic stresses. The objective of this review is to summarize the latest research on the role of CYPs in plant stress response.