HPPD Herbicide Research Articles

First Report on Resistance to HPPD Herbicides Mediated by Nontarget-Site Mechanisms in the Grass Leptochloa chinensis.

The emergence of 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicides as efficacious target-site herbicides has been noteworthy. In recent years, only four species of broadleaf weeds have developed resistance due to the long-term widespread use of HPPD herbicides. This study represents the first reported instance of a grass weed exhibiting resistance to HPPD inhibitors. We identified a new HPPD-resistant Chinese sprangletop [Leptochloa chinensis (L.) Nees] population (R population). At the recommended dose of tripyrasulfone, the inhibition rate of the R population was only half that of the sensitive population (S). The mechanism underlying resistance does not involve target-site resistance triggered by amino acid mutations or depend on disparities within the HPPD INHIBITOR SENSITIVE 1 (HIS1) gene. The impetus for resistance appears to be interlinked with the metabolic activities of cytochrome P450 monooxygenase (P450) and glutathione S-transferase (GST) family genes. Following RNA sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) validation, the study suggests that five P450 genes, CYP71C1, CYP74A2, CYP72A1, CYP84A1, and CYP714C2, alongside a single GST gene GSTF1, may be implicated in the process of metabolic detoxification.

Degradation, adsorption, and bioaccumulation of novel triketone HPPD herbicide tembotrione.

Tembotrione is a new triketone HPPD herbicide widely used in Europe, USA, and other areas. However, tembotrione is moderately to highly toxic to algae and daphnia in aquatic ecosystems. In this study, hydrolysis, photolysis, soil degradation, soil adsorption, and bioaccumulation of tembotrione were systematically studied. Hydrolysis experiment revealed that tembotrione was stable in acidic, neutral, and alkaline conditions with half-lives of 231-289 days. The photolysis half-lives of tembotrione were 112-158 days and 76-107 days in pH 4, 7, 9 buffer solutions and on three soils surface, respectively, which demonstrated that tembotrione could be persisted in soil and water. Meanwhile, tembotrione Kfoc was 128-196 mL/g, indicating that tembotrione was not easily adsorbed to soil, and the adsorption capacity increased with the decrease in pH. The half-lives of tembotrione in the test soil were 32-48 days, and high organic matter soil is conducive to microbial activity and accelerates the degradation of tembotrione. Moreover, bioaccumulation experiment demonstrated that tembotrione with a BCF of 0.664 to 0.724 had a low risk of exposure to zebrafish. This study is very helpful for the evaluation environmental risk and safe use of tembotrione.

Effect of pre- and post-emergence (HPPD-Inhibitors) herbicides on weed dynamics and yield of kharif Maize (Zea mays)

The research was conducted to determine the effect of new HPPD herbicides tembotrione, mesotrione, and topramezone on weed density, growth, and yield of maize. A field experiment was performed at the Agronomy farm of Lovely Professional University, Phagwara, Punjab, India, during the kharif season of the year 2022, in Randomized Complete Block Design (RCBD) with three replications and eight treatments of weed management including T1: Atrazine @1kg ha-1 PE, T2: Pyroxasulfone @127g ha-1 PE, T3: Pyroxasulfone @ 127g + Atrazine @ 1kg ha-1 PE (tank mixture), T4: Tembotrione @ 120g + Atrazine @ 1kg ha-1 + MSO Adjuvant at 20 DAS (Tank mixture), T5: Topramezone @ 25g + Atrazine @ 1kg ha-1 + MSO Adjuvant at 20 DAS (Tank mixture), T6: Mesotrione 2.27% w/w+ atrazine 22.7% w/w SC @ 3.5L ha- 1 at 20 DAS (Ready to use), T7: Control (Weedy check) and T8: Weed free. However, the application of PoE herbicide T5 reduced the weed density significantly compared to T3 but was statistically at par with T6 and T4. There was a significant effect of herbicides on reducing weed dry matter, T5 gave superior results compared to T3 and was statistically at par with T4 and T6. Among the PoE herbicide T5 was significantly higher compared to T3 and statistically at par with T4. Effect on yield and yield component, the number of grains per cob was significantly higher in T8 compared to T7.

The novel 4-hydroxyphenylpyruvate dioxygenase inhibitors in vivo and in silico approach: 3D-QSAR analysis, molecular docking, bioassay and molecular dynamics

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is not only an important target enzyme for the treatment of type I tyrosinemia, but also a new target for design bleaching herbicides, and it plays key role in the biosynthesis of tocopherol and plastoquinone. Thirty-six known active pyridine derivatives were collected, and comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) models based on common skeleton were constructed to obtain novel HPPD herbicides with higher activity. Two new HPPD inhibitors were rationally designed and synthesized according to the CoMFA and CoMSIA models and verified by enzyme activity, biological assays, and molecular docking. The promising compound W1 ((E)-5-(3-(4-bromophenyl)acryloyl)-6-hydroxy-2,3-dihydropyridin-4(1H)-one) showed better AtHPPD inhibitory activity, and the bioassay results revealed that some weeds showed bleaching symptoms. The good binding stability of W1 and protein was confirmed by molecular dynamics simulation in 100 ns. These results would be highly useful in the progress of new HPPD inhibitors discovery.

Discovery of novel HPPD inhibitors based on a combination strategy of pharmacophore, consensus docking and molecular dynamics

4-Hydroxyphenylpyruvate dioxygenase (HPPD), an Fe(II)/Co(II)-dependent non-heme oxygenase, is a vital enzyme in the tyrosine catabolic pathway and has been proved to be a very successful herbicides target with bleaching properties. In this process, pharmacophore modeling combined with consensus docking was used to discover new HPPD-inhibitors. A total of 322,686 compounds from Targetmol, Bailingwei, and ZINC were screened through a multilayered screening work. To avoid the defects existing in the single docking process, the consensus docking was employed to analyze the docking results. Five compounds with good performance were finally obtained, and all of them could produce stable coordination with cobalt ions and form good π-π interactions. Calculated binding free energy indicated that the van der Waals (vdW), lipophilic, and coulomb force interactions were the major components to the binding affinity. The enzyme activity confirmed that Flavokawain A and Silymarin displayed significant potency against AtHPPD in vitro. This work provides a worthful theoretical basis and an important lead skeleton for the reasonable devise of innovative HPPD herbicides.

Synthesis and herbicidal activity of new pyrazole ketone derivatives

A series of pyrazole derivatives was designed according to prodrug strategy. These compounds were synthesized via eight steps and their structures were confirmed by 1H NMR spectroscopy and MS. The preliminary herbicidal bioassay results indicated that the title pyrazole ketone compounds exhibited low herbicidal activity against six weeds at 150 g/ha, which is weaker than that of the commercial HPPD herbicide topramezone. The docking results showed that the binding mode of the key intermediate (3-(2-(2-fluorophenoxy)ethoxy)-2-methyl-4-(methylsulfonyl)phenyl)(5-hydroxy-1,3-dimethyl-1H-pyrazol-4-yl)methanone is the same as the reported inhibitor DAS689 in the complex.

Design, synthesis and herbicidal activity of 5-cyclopropyl-N-phenylisoxazole-4-carboxamides

4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors are a type of important herbicides, and they cause bleaching symptoms by indirectly inhibiting the biosynthesis of carotenoids. In this study, thirty isoxazolamide compounds were designed based on the structure of Isoxaflutole, a commercial HPPD herbicide. Starting from 1,1-dimethoxy-N,N-dimethyl-methanamine and methyl 3-cyclopropyl-3-oxo-propanoate, the title compounds were readily prepared and their structures were determined by MS and NMR analysis. In Petri dish tests, most of the title compounds showed strong inhibitory effect on the root and stem growth of both monocotyledon and dicotyledon weeds, and it was clearly different from the symptoms caused by HPPD inhibitors. However, several of them, especially I-17, showed characteristic bleaching symptoms of HPPD herbicides and good post-emergence herbicidal activity on tested weeds in glasshouse assay. These compounds are prodrugs, and compounds undergo conversion to the active entity diketonitrile (DKN) in plant and soil. The result of molecular docking analysis revealed that the DKN moiety of I-17 excellently binds to the active sites of HPPD. The 1,3-diketone can form bidentate interaction with FeII, and the benzene ring can form π-π interaction with Phe 360 and Phe 403. These results indicated that the title compounds bears other herbicidal mechanism except for HPPD inhibitor. Therefore, a lead compound for the discovery of novel multi-target herbicides is provided.

Synthesis and herbicidal activities of aryloxyacetic acid derivatives as HPPD inhibitors.

A series of aryloxyacetic acid derivatives were designed and synthesized as 4-hydoxyphenylpyruvate dioxygenase (HPPD) inhibitors. Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD (AtHPPD) inhibitors, in particular compounds I12 (Ki = 0.011 µM) and I23 (Ki = 0.012 µM), which exhibit similar activities to that of mesotrione, a commercial HPPD herbicide (Ki = 0.013 µM). Furthermore, the newly synthesized compounds show significant greenhouse herbicidal activities against tested weeds at dosages of 150 g ai/ha. In particular, II4 exhibited high herbicidal activity for pre-emergence treatment that was slightly better than that of mesotrione. In addition, compound II4 was safe for weed control in maize fields at a rate of 150 g ai/ha, and was identified as the most potent candidate for a novel HPPD inhibitor herbicide. The compounds described herein may provide useful guidance for the design of new HPPD inhibiting herbicides and their modification.

Synthesis and herbicidal activity of novel pyrazole aromatic ketone analogs as HPPD inhibitor.

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) has been a good target for herbicide discovery. In order to discover novel HPPD herbicides, a series of pyrazole aromatic ketone analogs were designed and synthesized. The 25 pyrazole aromatic ketone analogs synthesized were tested for herbicidal activity and compounds A1, A3, A4, A17, A20 and A25 displayed excellent herbicidal activity against Chenopodium serotinum, Stellaria media and Brassica juncea at 37.5g ha-1 . In addition, compounds A1, A5, A9, A10, A16, A17, A20 and A25 exhibited good crop selectivity for wheat, maize and rice at 150 g ha-1 . Inhibition activities against AtHPPD proved the compounds were HPPD inhibitors. The structure-activity relationship of these pyrazole aromatic ketone analogs was studied using molecular docking. These pyrazole aromatic ketone derivatives could be used as lead structures for development of HPPD herbicides against dicotyledonous weeds with further structure modification. © 2019 Society of Chemical Industry.

Identification of novel inhibitors of p-hydroxyphenylpyruvate dioxygenase using receptor-based virtual screening

Abstract p-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is a potential target for herbicide discovery, which catalyzes the conversion of p-hydroxyphenylpyruvate to homogentisate. Triketone HPPD inhibitors have been widely applied to weed control for many years. To discover potential HPPD inhibitors with novel scaffold, a virtual screening procedure combining pharmacophore model, molecular docking and molecular dynamics (MD) simulation was carried out. The crystal complex (PDB: 6ISD ) with sulcotrione was selected to establish the receptor-ligand pharmacophore model (CBP). The verified CBP model with key features and interactions was employed to seek structures with potential inhibitory from ZINC database. The best-fit compounds from pharmacophore screening (2050 compounds) were subsequently subjected to molecular docking with CDOCKER method to identify the binding affinity of inhibitors with amino acid residues in active pocket. Six compounds were obtained as the final hits with the Fe(Ш) coordination and π-π interaction with Phe381 and Phe424. MD results demonstrated that Phe424 made great contributions to binding affinities of all the systems. This work provided powerful insights into the design and development of novel HPPD inhibitor in silico techniques. ZINC000255329531 was identified as the most promising candidate due to its high HPPD inhibition effect (ΔGbind = 25.66 kcal mol−1), in comparison with the commercial triketone HPPD herbicide sulcotrione (ΔGbind = 18.94 kcal mol−1).

Characterization of 4-hydroxyphenylpyruvate dioxygenases, inhibition by herbicides and engineering for herbicide tolerance in crops

4-Hydroxyphenylpyruvate dioxgenase (HPPD) enzymes from rat and from several plants contained only about a single inhibitor-binding active site per dimer which matched the content of iron in the purified Arabidopsis thaliana and Avena sativa enzymes. The dimeric HPPDs were about 10 fold more catalytically active than the tetrameric P. fluorescens enzyme with kcat/KmHPP values ranging from 0.8 to 2.5 s-1 μM-1. Most were also highly sensitive to herbicides with, for example, Ki values for mesotrione ranging from 25 to 100 pM. Curiously HPPDs from cool climate grasses were much less herbicide-sensitive. When likewise expressed in Nicotinia tabacum, Avena sativa HPPD, Ki value of 11 nM for mesotrione, conferred far greater tolerance to mesotrione (CallistoTM) than did any of the more sensitive HPPDs. Targeted mutagenesis of the Avena HPPD led to the discovery of 4 mutations imparting improved inherent tolerance, defined as the ratio of Ki to KmHPP, by about 16 fold without any loss of catalytic activity. The Nicotinia line with the highest expression of this quadruple mutant exhibited substantial resistance even up to a 3 kg/ha post-emergence application of mesotrione. The maximum observed expression level of heterologous plant HPPDs in tobacco was ca. 0.35% of the total soluble protein whereas the endogenous tobacco HPPD constituted only ca. 0.00075%. At such high expression even HPPDs with impaired catalytic activity could be effective. A quintuple mutant Avena sativa HPPD conferred substantial tolerance across a broad range of HPPD herbicide chemistries despite being only ca. 5 % as catalytically active as the wild type enzyme. Testing various wild type and mutant HPPDs in tobacco revealed that tolerance to field rates of herbicide generally requires about two order of magnitude increases in both inherent herbicide tolerance and expression relative to endogenous levels. This double hurdle may explain why target-site based resistance to HPPD-inhibiting herbicides has been slow to evolve in weeds.

Inheritance of 4-hydroxyphenylpyruvate dioxygenase inhibitor herbicide resistance in an Amaranthus tuberculatus population from Iowa, USA

Waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) is a weed prevalent in the Midwest United States and can cause yield losses up to 74% in maize (Zea mays L.) and 56% in soybean (Glycine max (L.) Merr.). An important adaptive trait commonly found in waterhemp is the ability to evolve herbicide resistance and waterhemp populations have evolved resistance to six herbicide sites of action. In 2011, two waterhemp populations were discovered resistant to p-hydroxyphenylpyruvate-dioxygenase (HPPD, EC 1.13.11.27) inhibitor herbicides. We reciprocally crossed a known HPPD-resistant waterhemp population with a known HPPD-susceptible waterhemp population and then intermated the F1 families to established a pseudo-F2 generation. We challenged the parent, F1 and pseudo-F2 generations against four HPPD-inhibiting herbicide rates (mesotrione). Our results suggest the HPPD-resistance trait is polygenic. Furthermore, the number of genes involved with the herbicide resistance increase at higher herbicide rates. These data indicated at least one dominant allele at each major locus is required to confer HPPD herbicide resistance in waterhemp. Using different waterhemp populations and methodologies, this study confirms the reported “complex” HPPD resistance inheritance while providing new information in the response of HPPD-resistant waterhemp to HPPD herbicides.

Use of Hppd-inhibiting Herbicides for Control of Troublesome Weeds in the Midsouthern United States

Transgenic crops provide cotton and soybean producers additional weed control options for many of the most problematic weeds in mid southern US. production systems. The expected commercialization of 4-hydroxyphenylpyruvate dioxygenase (HPPD)-resistant soybean in 2017 and cotton in 2020 will provide producers the option to apply HPPD-inhibiting herbicides that will offer an alternative mechanism of action for previously hardto- control weeds. Experiments were conducted in 2010 and 2011 to determine the efficacy of HPPD-inhibiting herbicides applied pre emergence (PRE) or post emergence (POST) for control of problematic weeds of cotton and soybean in the mid southern US. PRE experiments were conducted to understand the length and degree of control of Palmer amaranth and barn yard grass that could be expected with HPPD-inhibiting herbicides compared with current standards on silt loam and clay soil textures. The HPPD herbicides evaluated included mesotrione, tembotrione, and isoxaflutole compared to several standards currently labeled in soybean. In the POST experiment, applications of isoxaflutole, tembotrione, glyphosate, and two rates of glufosinate applied alone and both HPPD herbicides combined with glyphosate or glufosinate were evaluated for control of Palmer amaranth, barn yard grass, hemp sesbania, and yellow nutsedge. When herbicides were applied PRE, the HPPD-inhibiting herbicides and the current standard treatments all provided greater than 90% control of Palmer amaranth 4 weeks after treatment (WAT) on both soil textures. Barn yard grass control with HPPD-inhibitors was generally weaker than the current standards with the exception of mesotrione which proved to be comparable to the standards 4 WAT. In the POST experiment, all treatments, except for glyphosate alone, provided excellent (>85%) control of Palmer amaranth less than 10 cm in height. Barn yard grass, yellow nutsedge, and hemp sesbania were effectively controlled with HPPDinhibiting herbicides with and without glufosinate or glyphosate.

The structure-activity relationships of the triketone class of HPPD herbicides†

The 2-benzoylcyclohexane-1,3-diones, the triketones, are a novel class of bleaching herbicides whose mode of action is the inhibition of the enzyme p-hydroxyphenylpyruvate dioxygenase. The structure–activity relationships of this chemical class are elucidated. An ortho-substituent on the aryl ring is an absolute requirement for herbicidal activity. Beyond that, the herbicidal activity of these compounds is best correlated with the overall electron deficiency of the benzoyl group induced by 2,4-disubstitution of the aryl ring, with the most electron-deficient analogs being the most active. Moreover, the degree of electron deficiency of the benzoyl group is outwardly manifested in the acidity of the molecule. The activity of these compounds is further enhanced through additional aromatic substitution in the 3-position of the aryl ring. The greater activity of these 2,3,4-trisubstituted aryl analogs over the 2,4-disubstituted aryl analogs is due to increased intrinsic activity. © 1998 Society of Chemical Industry

The discovery and structural requirements of inhibitors of p-hydroxyphenylpyruvate dioxygenase

The benzoylcyclohexane-1,3-diones, the triketones, are potent bleaching herbicides whose structure-activity relationships and physical properties are substantially different from classical bleaching herbicides, which affect phytoene desaturase. The first clue to their unique mechanism of action was the discovery that rats treated with a triketone were found to be tyrosinemic. Additionally, examination of the rat urine revealed the accumulation of p-hydroxyphenylpyruvate (HPP) and p-hydroxyphenyllactate. These results suggested that this chemically induced tyrosinemia was the result of the inhibition of p-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27), and this suggestion was confirmed when a triketone was shown to be a potent inhibitor of rat liver HPPD. In plants, HPPD is a component of the biosynthetic pathway to plastoquinone (PQ), which in turn is a key cofactor of phytoene desaturase. The expectation that triketone-treated plants should accumulate tyrosine while having reduced PQ levels was dramatically demonstrated in the meristematic tissue of ivyleaf morningglory. Plant HPPD, like the mammalian enzyme, was inhibited in vitro by triketones. These biochemical effects provide evidence that the triketone herbicidal mechanism of action is HPPD inhibition leading to a deficiency of PQ, a key cofactor for carotenoid biosynthesis. Other chemical classes of bleaching herbicides were also examined for their ability to elevate tyrosine and deplete PQ as a definitive means of establishing their mode of action and for delineating the structural and physical chemical requirements for an HPPD herbicide. Evidence is provided to support the claim that a 2-benzoylethen-1-ol substructure is the minimum substructure required for a potent HPPD inhibitor.