Multisite Mutagenesis of 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) Enhances Rice Resistance to HPPD Inhibitors and Its Carotenoid Contents.

While frequently used herbicides display limited efficacy against herbicide-resistant weeds, it becomes imperative to explore novel herbicides that ensure both effective weed management and environmental safety. Though 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitory herbicides like mesotrione are prevalent in maize weed management, their integration into rice production is hindered due to the inherent sensitivity of rice HPPD (OsHPPD). In this study, a mutant allele of OsHPPD featuring six amino acid substitutions, termed OsHPPD-6M, maintains enzymatic activity in 200 µm mesotrione while the wild type can only withstand 1 µm. Enzymatic assays in vitro indicated that the HPPD activity of OsHPPD-6M surpassed that of the WT by 2-fold through enhanced substrate-binding. Its overexpression in transgenic rice conferred greater tolerance to mesotrione, topramezone, and isoxaflutole by 36.7-, 41.6-, and 37.1-fold relative to that in the WT rice. Interestingly, these 6M-OE plants demonstrated substantially elevated contents of carotenoids compared to WT plants without a significant impact on agronomic traits.

Advances in Understanding the Toxicity of 4-Hydroxyphenylpyruvate Dioxygenase-Inhibiting Herbicides.

4-Hydroxyphenylpyruvate dioxygenase inhibiting herbicides (HIHs) represent a recent class (HRAC group 27) of herbicides that offer many advantages, such as broad-spectrum activity, crop selectivity, and low resistance rates. However, emerging studies have highlighted the potential toxicity of HIHs in the environment. This review aims to provide a comprehensive summary of the toxicity of HIHs toward nontarget organisms, including plants, microorganisms, animals, and humans. Furthermore, the present work discusses the ecological roles of these organisms in the environment and their significance in agriculture. By shedding light on the toxicity of HIHs, this study seeks to raise awareness among end users, including environmentalists, researchers, and farmers, regarding the potential ecological implications of these herbicides. Hopefully, this knowledge can contribute to informed decision-making and sustainable practices in green agriculture and environmental management.

New biomarkers for liver involvement by dengue infection in adult Vietnamese patients: a case-control study.

Liver injury with marked elevation of aspartate aminotransferase enzyme (AST) is commonly observed in dengue infection. To understand the pathogenesis of this liver damage, we compared the plasma levels of hepatic specific, centrilobular predominant enzymes (glutamate dehydrogenase, GLDH; glutathione S transferase-α, αGST), periportal enriched 4-hydroxyphenylpyruvate dioxygenase (HPPD), periportal predominant arginase-1 (ARG-1), and other non-specific biomarkers (paraoxonase-1, PON-1) in patients with different outcomes of dengue infection. This hospital-based study enrolled 87 adult dengue patients, stratified into three groups based on plasma AST levels (< 80, 80-400, > 400 U/L) in a 1:1:1 ratio (n = 40, n = 40, n = 40, respectively. The new liver enzymes in the blood samples from the 4th to 6th days of their illness were measured by commercial enzyme-linked immunosorbent assay (ELISA) or colorimetric kits. Based on the diagnosis at discharge days, our patients were classified as 40 (46%) dengue without warning signs (D), 35 (40.2%) dengue with warning signs (DWS), and 11 (12.6%) severe dengue (SD) with either shock (two patients) or AST level over 1000 U/L (nine patients), using the 2009 WHO classification. The group of high AST (> 400 U/L) also had higher ALT, GLDH, ARG-1, and HPPD than the other groups, while the high (> 400 U/L) and moderate (80-400 U/L) AST groups had higher ALT, αGST, ARG-1, and HPPD than the low AST group (< 80 U/L). There was a good correlation between AST, alanine aminotransferase enzyme (ALT), and the new liver biomarkers such as GLDH, αGST, ARG-1, and HPPD. Our findings suggest that dengue-induced liver damage initiates predominantly in the centrilobular area toward the portal area during the dengue progression. Moreover, these new biomarkers should be investigated further to explain the pathogenesis of dengue and to validate their prognostic utility.

Identification of novel dual-target 4-hydroxyphenylpyruvate dioxygenase & phytoene dehydrogenase inhibitors via multiple virtual screening.

Two important plant enzymes are 4-hydroxyphenylpyruvate dioxygenase (HPPD; EC 1.13.11.27), which is necessary for biosynthesis of plastoquinone and tocopherols, and phytoene dehydrogenase (PDS; EC 1.3.99.26), which plays an important role in colour rendering. Dual-target proteins that inhibit pigment synthesis will prevent resistant weeds and improve the spectral characteristics of herbicides. This study introduces virtual screening of pharmacophores based on the complex structure of the two targets. A three-dimensional database was established by screening 1,492,858 compounds based on the Lipinski principle. HPPD&PDS dual-target receptor-ligand pharmacophore models were then constructed, and nine potential dual-target inhibitors were obtained through pharmacophore modeling, molecular docking, and molecular dynamics simulations. Ultimately, ADMET prediction software yielded three compounds with high potential as dual-target herbicides. The obtained nine inhibitors were stable when combined with both HPPD and PDS proteins. This study offers guidance for the development of HPPD&PDS dual-target inhibitors with novel skeletons.

Physiological Basis for the Mechanism of Selectivity of Tripyrasulfone between Rice (Oryza sativa) and Barnyard Grass (Echinochloa crus-galli).

Tripyrasulfone is currently the only HPPD-inhibiting herbicide that possesses outstanding selectivity even for direct-seeded rice (Oryza sativa) when applied POST to control grass weeds; however, the underlying mechanisms remain unclear. In this study, the inhibitory effects of the real active HDT of tripyrasulfone on recombinant 4-hydroxyphenylpyruvate dioxygenase (HPPDs) from rice and barnyard grass (Echinochloa crus-galli) were similar, with consistent structural interactions and similar binding energies predicted by molecular docking. However, the HPPD expression level in rice was significantly greater than that in barnyard grass after tripyrasulfone treatment. Tripyrasulfone was rapidly taken up and hydrolyzed into HDT, which was similarly distributed within the whole plants of rice and barnyard grass at 24 h after treatment. Compared with barnyard grass, rice has more uniform epicuticular wax in the cuticle of its leaves, absorbing less tripyrasulfone and metabolizing much more tripyrasulfone. Overall, to a greater extent, the different sensitivities to tripyrasulfone between barnyard grass and rice resulted from metabolic variations.

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.

Design, synthesis and herbicidal activity of novel cyclohexanedione derivations containing pyrazole and pyridine groups as potential HPPD inhibitors.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27; HPPD) is one of the important target enzymes in the development of herbicides. To discover novel HPPD inhibitors with unique molecular, 39 cyclohexanedione derivations containing pyrazole and pyridine groups were designed and synthesized. The preliminary herbicidal activity test results showed that some compounds had obvious inhibitory effects on monocotyledon and dicotyledonous weeds. The herbicidal spectrums of the highly active compounds were further determined, and the compound G31 exhibited the best inhibitory rate over 90% against Plantago depressa Willd and Capsella bursa-pastoris at the dosages of 75.0 and 37.5 g ai/ha, which is comparable to the control herbicide mesotrione. Moreover, compound G31 showed excellent crop safety, with less than or equal to 10% injury rates to corn, sorghum, soybean and cotton at a dosage of 225 g ai/ha. Molecular docking and molecular dynamics simulation analysis revealed that the compound G31 could stably bind to Arabidopsis thaliana HPPD (AtHPPD). This study indicated that the compound G31 could be used as a lead molecular structure for the development of novel HPPD inhibitors, which provided an idea for the design of new herbicides with unique molecular scaffold.

4-Hydroxyphenylpyruvate Dioxygenase-Like predicts the prognosis and the immunotherapy response of cancers: a pan-cancer analysis.

The 4-Hydroxyphenylpyruvate Dioxygenase-Like (HPDL) protein plays a crucial role in safeguarding cells from oxidative stress by orchestrating metabolic reprogramming. New research suggests that HPDL is considerably increased in pancreatic ductal adenocarcinoma, although its impact on cancer immunotherapy is still unclear. Pancancer transcriptional data were obtained from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression datasets. The cBioPortal webtool was utilized to examine genomic changes in different cancer types. The prognostic significance of HPDL in pancancer was evaluated using univariate Cox regression analysis. Extensive utilization of the CTRP and PRISM databases was performed to forecast potential medications that specifically target HPDL in LUAD. In summary, studies were conducted to evaluate the impact of HPDL on the proliferation and movement of LUAD cells using loss-of-function experiments. HPDL is expressed excessively in a wide variety of cancer types, indicating its prognostic and predictive value. Moreover, we emphasized the strong correlation between HPDL and indicators of immune stimulation, infiltration of immune cells, and expression of immunoregulators. The remarkable finding of the HPDL was its capacity to precisely anticipate responses to cancer therapies using anti-PDL1 and anti-PD1 antibodies among individuals. Moreover, HPDL can function as a predictive marker for specific inhibitors in instances of cancer. Suppression of HPDL resulted in reduced growth and movement of LUAD cells. To summarize, our results suggest that HPDL acts as a prospective predictor of outcomes and a positive indication of response to immunotherapy in patients undergoing treatment with immune checkpoint inhibitors (ICIs).

Metabolic engineering of Synechocystis sp. PCC 6803 for the improved production of phenylpropanoids.

BACKGROUND: Phenylpropanoids are a large group of plant secondary metabolites with various biological functions, derived from aromatic amino acids. Cyanobacteria are promising host organisms for sustainable production of plant phenylpropanoids. We have previously engineered Synechocystis sp. PCC 6803 to produce trans-cinnamic acid (tCA) and p-coumaric acid (pCou), the first intermediates of phenylpropanoid pathway, by overexpression of phenylalanine- and tyrosine ammonia lyases. In this study, we aimed to enhance the production of the target compounds tCA and pCou in Synechocystis. RESULTS: We eliminated the 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity, which is a competing pathway consuming tyrosine and, possibly, phenylalanine for tocopherol synthesis. Moreover, several genes of the terminal steps of the shikimate pathway were overexpressed alone or in operons, such as aromatic transaminases, feedback insensitive cyclohexadienyl dehydrogenase (TyrC) from Zymomonas mobilis and the chorismate mutase (CM) domain of the fused chorismate mutase/prephenate dehydratase enzyme from Escherichia coli. The obtained engineered strains demonstrated nearly 1.5 times enhanced tCA and pCou production when HPPD was knocked out compared to the parental production strains, accumulating 138 ± 3.5 mg L-1 of tCA and 72.3 ± 10.3 mg L-1 of pCou after seven days of photoautotrophic growth. However, there was no further improvement when any of the pathway genes were overexpressed. Finally, we used previously obtained AtPRM8 and TsPRM8 Synechocystis strains with deregulated shikimate pathway as a background for the overexpression of synthetic constructs with ppd knockout. CONCLUSIONS: HPPD elimination enhances the tCA and pCou productivity to a similar extent. The use of PRM8 based strains as a background for overexpression of synthetic constructs, however, did not promote tCA and pCou titers, which indicates a tight regulation of the terminal steps of phenylalanine and tyrosine synthesis. This work contributes to establishing cyanobacteria as hosts for phenylpropanoid production.

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-oxoglutarate­iron-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.

Discovery and Development of 4-Hydroxyphenylpyruvate Dioxygenase as a Novel Crop Fungicide Target.

Plant pathogenic fungi pose a significant threat to crop yields and quality, and the emergence of fungicide resistance has further exacerbated the problem in agriculture. Therefore, there is an urgent need for efficient and environmentally friendly fungicides. In this study, we investigated the antifungal activity of (+)-Usnic acid and its inhibitory effect on crop pathogenic fungal 4-hydroxyphenylpyruvate dioxygenases (HPPDs) and determined the structure of Zymoseptoria tritici HPPD (ZtHPPD)-(+)-Usnic acid complex. Thus, the antifungal target of (+)-Usnic acid and its inhibitory basis toward HPPD were uncovered. Additionally, we discovered a potential lead fungicide possessing a novel scaffold that displayed remarkable antifungal activities. Furthermore, our molecular docking analysis revealed the unique binding mode of this compound with ZtHPPD, explaining its high inhibitory effect. We concluded that HPPD represents a promising target for the control of phytopathogenic fungi, and the new compound serves as a novel starting point for the development of fungicides and dual-purpose pesticides.

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.

Transcriptomic analysis of wheat reveals possible resistance mechanism mediated by Yr10 to stripe rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a catastrophic disease that threatens global wheat yield. Yr10 is a race-specific all-stage disease resistance gene in wheat. However, the resistance mechanism of Yr10 is poorly characterized. Therefore, to elucidate the potential molecular mechanism mediated by Yr10, transcriptomic sequencing was performed at 0, 18, and 48 h post-inoculation (hpi) of compatible wheat Avocet S (AvS) and incompatible near-isogenic line (NIL) AvS + Yr10 inoculated with Pst race CYR32. Respectively, 227, 208, and 4050 differentially expressed genes (DEGs) were identified at 0, 18, and 48 hpi between incompatible and compatible interaction. The response of Yr10 to stripe rust involved various processes and activities, as indicated by the results of Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Specifically, the response included photosynthesis, defense response to fungus, metabolic processes related to salicylic acid (SA) and jasmonic acid (JA), and activities related to reactive oxygen species (ROS). Ten candidate genes were selected for qRT-PCR verification and the results showed that the transcriptomic data was reliable. Through the functional analysis of candidate genes by the virus-induced gene silencing (VIGS) system, it was found that the gene TaHPPD (4-hydroxyphenylpyruvate dioxygenase) negatively regulated the resistance of wheat to stripe rust by affecting SA signaling, pathogenesis-related (PR) gene expression, and ROS clearance. Our study provides insight into Yr10-mediated resistance in wheat.

A Protocol for Activated Bioorthogonal Fluorescence Labeling and Imaging of 4-Hydroxyphenylpyruvate Dioxygenase in Plants.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays a crucial role in the synthesis of nutrients needed to maintain optimal plant growth. Its level is closely linked to the extent of abiotic stress experienced by plants. Moreover, it is also the target of commercial herbicides. Therefore, labeling of HPPD in plants not only enables visualization of its tissue distribution and cellular uptake, it also facilitates assessment of abiotic stress of plants and provides information needed for the development of effective environmentally friendly herbicides. In this study, we created a method for fluorescence labeling of HPPD that avoids interference with the normal growth of plants. In this strategy, a perylene-linked dibenzyl-cyclooctyne undergoes strain-promoted azide-alkyne cycloaddition with an azide-containing HPPD ligand. The activation-based labeling process results in a significant emission enhancement caused by the change in the fluorescent forms from an excimer to a monomer. Notably, this activated bioorthogonal strategy is applicable to visualizing HPPD in Arabidopsis thaliana, and assessing its response to multiple abiotic stresses. Also, it can be employed to monitor in vivo levels and locations of HPPD in crops. Consequently, the labeling strategy will be a significant tool in investigations of HPPD-related abiotic stress mechanisms, discovering novel herbicides, and uncovering unknown biological functions.

Determination of the Association between Mesotrione Sensitivity and Conformational Change of 4-Hydroxyphenylpyruvate Dioxygenase via Free-Energy Analyses.

One widely known herbicide target is 4-hydroxyphenylpyruvate dioxygenase (HPPD). Avena sativa HPPD is less sensitive to mesotrione (herbicide) than Arabidopsis thaliana HPPD. HPPD inhibitor-sensitivity is governed by the dynamic behavior of the C-terminal α-helix of HPPD (H11) in closed and open forms. However, the specific relationship between the plant inhibitor sensitivity and H11 dynamic behavior remains unclear. Herein, we determined the conformational changes in H11 to understand the inhibitor-sensitivity mechanism based on free-energy calculations using molecular dynamics simulations. The calculated free-energy landscapes revealed that Arabidopsis thaliana HPPD preferred the open form of H11 in the apo form and the closed-like form in complex with mesotrione, whereas Avena sativa HPPD exhibited the opposite tendency. We also identified some important residues involved in the dynamic behavior of H11. Therefore, inhibitor sensitivity is governed by indirect interactions due to the protein flexibility caused by the conformational changes of H11.

Identification of Potential Inhibitors for the Treatment of Alkaptonuria Using an Integrated In Silico Computational Strategy.

Alkaptonuria (AKU) is a rare genetic autosomal recessive disorder characterized by elevated serum levels of homogentisic acid (HGA). In this disease, tyrosine metabolism is interrupted because of the alterations in homogentisate dioxygenase (HGD) gene. The patient suffers from ochronosis, fractures, and tendon ruptures. To date, no medicine has been approved for the treatment of AKU. However, physiotherapy and strong painkillers are administered to help mitigate the condition. Recently, nitisinone, an FDA-approved drug for type 1 tyrosinemia, has been given to AKU patients in some countries and has shown encouraging results in reducing the disease progression. However, this drug is not the targeted treatment for AKU, and causes keratopathy. Therefore, the foremost aim of this study is the identification of potent and druggable inhibitors of AKU with no or minimal side effects by targeting 4-hydroxyphenylpyruvate dioxygenase. To achieve our goal, we have performed computational modelling using BioSolveIT suit. The library of ligands for molecular docking was acquired by fragment replacement of reference molecules by ReCore. Subsequently, the hits were screened on the basis of estimated affinities, and their pharmacokinetic properties were evaluated using SwissADME. Afterward, the interactions between target and ligands were investigated using Discovery Studio. Ultimately, compounds c and f were identified as potent inhibitors of 4-hydroxyphenylpyruvate dioxygenase.

Discovery of Bis-5-cyclopropylisoxazole-4-carboxamides as Novel Potential 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27; HPPD) represents a potential target for novel herbicide development. To discover the more promising HPPD inhibitor, we designed and synthesized a series of bis-5-cyclopropylisoxazole-4-carboxamides with different linkers using a multitarget pesticide design strategy. Among them, compounds b9 and b10 displayed excellent herbicidal activities versus Digitaria sanguinalis (DS) and Amaranthus retroflexus (AR) with the inhibition of about 90% at the concentration of 100 mg/L in vitro, which was better than that of isoxaflutole (IFT). Furthermore, compounds b9 and b10 displayed the best inhibitory effect versus DS and AR with the inhibition of about 90 and 85% at 90 g (ai)/ha in the greenhouse, respectively. The structure-activity relationship study showed that the flexible linker (6 carbon atoms) is responsible for increasing their herbicidal activity. The molecular docking analyses showed that compounds b9 and b10 could more closely bind to the active site of HPPD and thus exhibited a better inhibitory effect. Altogether, these results indicated that compounds b9 and b10 could be used as potential herbicide candidates targeting HPPD.

Insights into 4-hydroxyphenylpyruvate dioxygenase-inhibitor interactions from comparative structural biology.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays a key role in tyrosine metabolism and has been identified as a promising target for herbicide and drug discovery. The structures of HPPD complexed with different types of inhibitors have been determined previously. We summarize the structures of HPPD complexed with structurally diverse molecules, including inhibitors, natural products, substrates, and catalytic intermediates; from these structures, the detailed inhibitory mechanisms of different inhibitors were analyzed and compared, and the key structural factors determining the slow-binding behavior of inhibitors were identified. Further, we propose four subpockets that accommodate different inhibitor substructures. We believe that these analyses will facilitate in-depth understanding of the enzymatic reaction mechanism and enable the design of new inhibitors with higher potency and selectivity.

Discovery of Novel Pyrazole Derivatives with Improved Crop Safety as 4-Hydroxyphenylpyruvate Dioxygenase-Targeted Herbicides.

As one of the essential herbicide targets, 4-hydroxyphenylpyruvate dioxygenase (HPPD) has recently been typically used to produce potent new herbicides. In continuation with the previous work, several pyrazole derivatives comprising a benzoyl scaffold were designed and synthesized, and their inhibitory effects on Arabidopsis thaliana hydroxyphenylpyruvate dioxygenase (AtHPPD) and herbicidal activities were comprehensively evaluated in this study. Compound Z9 showed top-rank inhibitory activity to AtHPPD with an half-maximal inhibitory concentration (IC50) value of 0.05 µM, which was superior to topramezone (1.33 µM) and mesotrione (1.76 µM). Compound Z21 exhibited superior preemergence inhibitory activity against Echinochloa crusgalli, with stem and root inhibition rates of 44.3 and 69.6%, respectively, compared to topramezone (16.0 and 53.0%) and mesotrione (12.8 and 41.7%). Compounds Z5, Z15, Z20, and Z21 showed excellent postemergence herbicidal activities at a dosage of 150 g ai/ha, along with distinct bleaching symptoms and higher crop safety than topramezone and mesotrione, and they all were safe for maize, cotton, and wheat with injury rates of 0 or 10%. In addition, the molecular docking analysis also revealed that these compounds formed hydrophobic π-π interactions with Phe360 and Phe403 to AtHPPD. This study suggests that pyrazole derivatives containing a benzoyl scaffold could be used as new HPPD inhibitors to develop pre- and postemergence herbicides and be applied to additional crop fields.