Chelation of the Optimal Antifungal Pogostone Analogue with Copper(II) to Explore the Dual Antifungal and Antibacterial Agent.

In an ongoing effort to explore more potent antifungal pogostone (Po) analogues, we maintained the previously identified 3-acetyl-4-hydroxy-2-pyrone core motif while synthesizing a series of Po analogues with variations in the alkyl side chain. The in vitro bioassay results revealed that compound 21 was the most potent antifungal analogue with an EC50 value of 1.1 µg/mL against Sclerotinia sclerotiorum (Lib.) de Bary. Meanwhile, its Cu(II) complex 34 manifested significantly enhanced antibacterial activity against Xanthomonas campestris pv campestris (Xcc) with a minimum inhibitory concentration (MIC) value of 300 µg/mL compared with 21 (MIC = 700 µg/mL). Complex 34 exhibited a striking preventive effect against S. sclerotiorum and Xcc in rape leaves, with control efficacies of 98.8% (50 µg/mL) and 80.7% (1000 µg/mL), respectively. The 3D-QSAR models generated using Topomer comparative molecular field analysis indicated that a shorter alkyl chain (carbon atom number <8), terminal rings, or electron-deficient groups on the alkyl side chain are beneficial for antifungal potency. Further, bioassay results revealed that the component of 21 in complex 34 dominated the antifungal activity, but the introduction of Cu(II) significantly enhanced its antibacterial activity. The toxicological observations demonstrated that 21 could induce abnormal mitochondrial morphology, loss of mitochondrial membrane potential, and reactive oxygen species (ROS) accumulation in S. sclerotiorum. The enzyme assay results showed that 21 is a moderate promiscuous inhibitor of mitochondrial complexes II and III. Besides, the introduction of Cu(II) to 34 could promote the disruption of the cell membrane and intracellular proteins and the ROS level in Xcc compared with 21. In summary, these results highlight the potential of 34 as a dual antifungal and antibacterial biocide for controlling rape diseases or as a promising candidate for further optimization.

Synthesis of Pogostone-Inspired Dehydroacetic Acid Derivatives and Their Antifungal Activity against Sclerotinia sclerotiorum (Lib.) de Bary.

In an effort to exploit the natural antifungal pogostone, its simplified scaffold dehydroacetic acid (DHA) was used as a lead compound to semi-synthesize 56 DHA derivatives (I1-48, II, III, and IV1-6). Among them, compound IV4 exhibited the most potent antifungal activity with 11.0 µM EC50 against mycelial growth of Sclerotinia sclerotiorum (Lib.) de Bary whose sclerotia production was also completely suppressed at this concentration. Furthermore, IV4 could completely inhibit infection cushion formation of S. sclerotiorum on rape leaves and achieved a preventive efficacy of 90.2 % at 500 µM, which was on the same level as that of commercial boscalid at 30 µM (88.7 %). The results of physiological and ultrastructural studies indicated that IV4 might disrupt the cell membrane permeability or induce the imbalance of mitochondrial membrane potential homeostasis to exert the antifungal mode of action. Besides, the robust and predicative three-dimensional quantitative structure-activity relationship (3D-QSAR) models were developed and discussed herein.

Synthesis of 3,4-dihydroisoquinolin-1(2H)-one derivatives and their antioomycete activity against the phytopathogen Pythium recalcitrans.

In an effort to exploit the bioactive natural scaffold 3,4-dihydroisoquinolin-1(2H)-one for plant disease management, 59 derivatives of this scaffold were synthesized using the Castagnoli-Cushman reaction. The results of bioassay indicated that their antioomycete activity against Pythium recalcitrans was superior to the antifungal activity against the other 6 phytopathogens. Compound I23 showed the highest in vitro potency against P. recalcitrans with an EC50 value of 14 µM, which was higher than that of the commercial hymexazol (37.7 µM). Moreover, I23 exhibited in vivo preventive efficacy of 75.4% at the dose of 2.0 mg/pot, which did not show significant differences compared with those of hymexazol treatments (63.9%). When the dose was 5.0 mg per pot, I23 achieved a preventive efficacy of 96.5%. The results of the physiological and biochemical analysis, the ultrastructural observation and lipidomics analysis suggested that the mode of action of I23 might be the disruption of the biological membrane systems of P. recalcitrans. In addition, the established CoMFA and CoMSIA models with reasonable statistics in the three-dimensional quantitative structure-activity relationship (3D-QSAR) study revealed the necessity of the C4-carboxyl group and other structural requirements for activity. Overall, the above results would help us to better understand the mode of action and the SAR of these derivatives, and provide crucial information for further design and development of more potent 3,4-dihydroisoquinolin-1(2H)-one derivatives as antioomycete agents against P. recalcitrans.

Guaiacol as a natural melanin biosynthesis inhibitor to control northern corn leaf blight.

BACKGROUND: The natural 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis inhibitors (MBIs) are one of the promising approaches to the integrated management of plant diseases but have received scarce attention until now. Herein, to explore the natural DHN MBIs used in the control of northern corn leaf blight (NCLB), a library of 53 essential oil compounds was used to screen the MBIs against Exserohilum turcicum, the causal pathogen of NCLB, using tricyclazole as a reference compound. RESULTS: The results of morphological change in the colony, thermogravimetric analysis, ultraviolet-visible spectroscopy, and transmission electron microscopy confirmed that guaiacol could effectively inhibit the melanin production at 50 µg/mL under in vitro conditions. The in vitro bioassay results indicated that this inhibition effect was concentration-dependent and the minimum inhibition concentration of guaiacol was 50 µg/mL. The in vivo experimental results demonstrated that guaiacol significantly inhibited appressorium formation and penetration on corn leaf sheaths at the concentration of 500 µg/mL. The pot experiment results revealed that there were no differences between guaiacol (500 µg/mL) and tricyclazole (100 µg/mL) in control efficacy. The enzymatic assay suggested that guaiacol might exert the activity through inhibiting DHN polymerization to form melanins, which was distinct from tricyclazole. CONCLUSIONS: Taken together, this study screened out guaiacol as a natural MBI from 53 essential oil compounds and verified its effectiveness in the control of NCLB at 500 µg/mL. Above all, this research opened an avenue for exploring natural DHN MBIs in the integrated management of plant diseases. © 2022 Society of Chemical Industry.

Bioassay-Guided Isolation of Nematicidal Artemisinic Acid and Dihydroartemisinic Acid from Artemisia annua L. and Evaluation of Their Activity against Meloidogyne incognita.

The extract of Artemisia annua L. has been shown to possess the nematicidal activity but the potent constituents were unclear. Herein, two nematicidal sesquiterpenoid acids artemisinic acid (ArA) and dihydroartemisinic acid (DHArA) were isolated from the methanol extract of the aerial parts of A. annua L. by the bioassay-guided isolation method using Meloidogyne incognita second stage juveniles (J2s) as the screening target. The in vitro activity, control efficacy in the pot experiment, and toxic effects of these two natural compounds against M. incognita were evaluated. The in vitro results showed that the EC50/48h values of ArA and DHArA were 0.37 mM and 0.76 mM against J2s, respectively. In the pot experiment, ArA and DHArA at the dose of 5 mg (a.i.)/pot could achieve the same level of control efficacy compared with avermectins at 2 mg (a.i.)/pot. Microscopic observations indicated the obvious toxic symptoms of J2s after ArA- and DHArA-treatment, including the shrinking body, imperfect body wall, and undiscerning organs. The physiological and biochemical studies, together with the toxic symptoms, revealed that ArA and DHArA had great impacts on the membrane system of J2s. Additionally, ArA occurring the α, ß-unsaturated carbonyl was demonstrated to be reactive with glutathione (GSH) and cause the decrease of GSH content in J2s. Taken together, the present study suggests that ArA and DHArA or ArA- and DHArA-based extracts of A. annua L. have a substantial potential to be used as botanical agents for integrated disease management programs against root-knot nematodes in crop protection.

Fungal oxysterol-binding protein-related proteins promote pathogen virulence and activate plant immunity.

Oxysterol-binding protein-related proteins (ORPs) are a conserved class of lipid transfer proteins that are closely involved in multiple cellular processes in eukaryotes, but their roles in plant-pathogen interactions are mostly unknown. We show that transient expression of ORPs of Magnaporthe oryzae (MoORPs) in Nicotiana benthamina plants triggered oxidative bursts and cell death; treatment of tobacco Bright Yellow-2 suspension cells with recombinant MoORPs elicited the production of reactive oxygen species. Despite ORPs being normally described as intracellular proteins, we detected MoORPs in fungal culture filtrates and intercellular fluids from barley plants infected with the fungus. More importantly, infiltration of Arabidopsis plants with recombinant Arabidopsis or fungal ORPs activated oxidative bursts, callose deposition, and PR1 gene expression, and enhanced plant disease resistance, implying that ORPs may function as endogenous and exogenous danger signals triggering plant innate immunity. Extracellular application of fungal ORPs exerted an opposite impact on salicylic acid and jasmonic acid/ethylene signaling pathways. Brassinosteroid Insensitive 1-associated Kinase 1 was dispensable for the ORP-activated defense. Besides, simultaneous knockout of MoORP1 and MoORP3 abolished fungal colony radial growth and conidiation, whereas double knockout of MoORP1 and MoORP2 compromised fungal virulence on barley and rice plants. These observations collectively highlight the multifaceted role of MoORPs in the modulation of plant innate immunity and promotion of fungal development and virulence in M. oryzae.

An LRR-only protein promotes NLP-triggered cell death and disease susceptibility by facilitating oligomerization of NLP in Arabidopsis.

Necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs) constitute a superfamily of proteins toxic to dicot plants, but the molecular basis of this toxicity remains obscure. Using quantitative trait locus (QTL) analysis we investigated the genetic variation underlying ion leakage in Arabidopsis plants elicited with MoNLP1 derived from Magnaporthe oryzae. The QTL conditioning MoNLP1 toxicity was positionally cloned and further characterized to elucidate its mode of action. MoNLP1-triggered cell death varied significantly across > 250 Arabidopsis accessions and three QTLs were identified conferring the observed variation. The QTL on chromosome 4 was uncovered to encode a leucine-rich repeat (LRR)-only protein designated as NTCD4, which shares high sequence identity with a set of nucleotide-binding LRR proteins. NTCD4 was secreted into the apoplast and physically interacted with multiple NLPs. Apoplastic NTCD4 facilitated the oligomerization of NLP, which was closely associated with toxicity in planta. The natural genetic variation causing D3N change in NTCD4 reduced the secretion efficiency of NTCD4 and the infection of Botrytis cinerea on Arabidopsis plants. These observations demonstrate that the plant-derived NTCD4 is recruited by NLPs to promote toxicity via facilitating their oligomerization, which extends our understanding of a key step in the toxic mode of action of NLPs.

Mn-Fe Layered Double Hydroxide Intercalated with Ethylene-Diaminetetraacetate Anion: Synthesis and Removal of As(III) from Aqueous Solution around pH 2-11.

A novel adsorbent Mn-Fe layered double hydroxides intercalated with ethylenediaminete-traacetic (EDTA@MF-LDHs) was synthesized by a low saturation coprecipitation method. The behavior and mechanism of As(III) removed by EDTA@MF-LDHs were investigated in detail in comparison with the carbonate intercalated Mn-Fe layered double hydroxides (CO3@MF-LDHs). The results showed that EDTA@MF-LDHs had a higher removal efficiency for As(III) than As(V) with a broader pH range than CO3@MF-LDH. The large adsorption capacity of EDTA@MF-LDHs is related to its large interlayer spacing and the high affinity of its surface hydroxyl groups. The maximum adsorption capacity for As(III) is 66.76 mg/g at pH 7. The FT-IR and XPS characterization indicated that the removal mechanism of the As(III) on EDTA@MF-LDHs include surface complexation, redox, and ion exchange.

[Remediation Performance via the Passivation of a Porous Biomorph Genetic Composite of α-Fe2O3/Fe3O4/C Using a Bamboo Template on As(â ¤) Contaminated Soils].

Red soil from Guangxi, China was selected as the background soil, and a porous biomorphic genetic composite of α-Fe2O3/Fe3O4/C comprising a bamboo template (PBGC-Fe/C) was used as a passivator to remediate As(Ⅴ) contaminated soils. The performance of PBGC-Fe/C was characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The results showed that PBGC-Fe/C could improve the passivation effect of As(Ⅴ) from the contaminated soils compared with a single passivation material. Under the conditions of a 5% dose addition, 25% water content, and particle size of 100 mesh, the stability rates of PBGC-Fe/C on As(Ⅴ) contaminated soils with different concentrations of 500 mg·kg-1 and 1000 mg·kg-1 could reach 80.95% and 73.49%, respectively. The porous biomorphic genetic composite of bamboo charcoal provided a large number of adsorption sites for As(Ⅴ), and the acidity of the soil was favorable for the remediation of As(Ⅴ) via passivation. Moreover, PBGC-Fe/C could not only adsorb and fix As(Ⅴ), but also promoted the stabilization of As species. Chemical complexation and ion exchange played major roles in this passivation process.

[Passivation and Remediation Effects and Mechanisms of Plant Residual Modified Materials on Lead-Contaminated Soils].

The specific characteristics and mechanism of passivation of Pb in soil were studied using HAP/C composite (PBGC-HAP/C) as passivation, and using proportion of PBGC-HAP/C, particle size and type of passivator, soil moisture content, soil pH value of Pb, and particle size of the material as influencing factors. The results showed that with an increase in dosage of the passivator and passivation time, the passivation effect increases gradually. Reducing the particle size of the passivator is beneficial to improving the passivation effect. pH has a greater impact on passivation, with the passivation effect obviously rising with increased pH, and the passivation rate in an alkaline environment can reach above 99%. An increase in water content is beneficial to the improvement of the passivation effect, but the contribution is not significant. Through comparative analysis of the XPS, XRD, and FT-IR of materials before and after passivation, the results indicated that the passivation of PBGC-HAP/C to Pb is mainly through direct and indirect effects. Direct effects include physical adsorption, chemical complexation, electrostatic interaction, ion exchange, and precipitation; the indirect effect is mainly enhanced by increasing the pH value of the organic matter.

The Nep1-like protein family of Magnaporthe oryzae is dispensable for the infection of rice plants.

The necrosis- and ethylene-inducing protein 1 (Nep1)-like proteins (NLPs) are a class of microbe-associated molecular patterns widely distributed across diverse groups of plant-associated microorganisms. In spite of the cytotoxic activity in dicot plants, the role of most NLPs in the virulence of plant pathogens is still largely unknown. We showed that the MoNLP family of rice blast fungus varied very little in amino acid sequence, transient expression of three MoNLPs induced cell death and the production of reactive oxygen species in Nicotiana benthamiana, and the expression of MoNLPs was induced during infection of susceptible rice plants. To further investigate the biological role of the MoNLP family, a marker-free gene replacement vector was developed and used to knock out the whole family in Magnaporthe oryzae. Results showed no significant difference in disease levels caused by wild type and the quadruple ΔMoNLP mutant strains. Likewise, the sporulation and radial growth of the two strains were similar under various unfavorable cultural conditions including malnutrition and abiotic stresses. These observations demonstrated that the MoNLP family is dispensable for the fungal tolerance to the tested adverse cultural conditions, and more importantly, for the virulence of blast fungus on susceptible rice plants.

Iridium-catalyzed asymmetric ring-opening reactions of azabenzonorbornadiene with carboxylic acid nucleophiles.

Iridium-catalyzed asymmetric ring-opening reaction of N-substituted azabenzonorbornadienes with various carboxylic acids has been developed. The ring-opening reaction offered trans-1,2-dihydronaphthalene products containing an allylic carboxylate moiety in moderate yields (up to 89 %) with high enantioselectivities (up to 96 %). The trans-configuration of the products was confirmed by X-ray crystallography.