Proline suppresses apoptosis in the fungal pathogen Colletotrichum trifolii

The role of reactive oxygen species (ROS) in cell communication, control of gene expression, and oxygen sensing is well established. Inappropriate regulation of ROS levels can damage cells, resulting in a diseased state. In Colletotrichum trifolii, a fungal pathogen of alfalfa, the mutationally activated oncogenic fungal Ras (DARas) elevates levels of ROS, causing abnormal fungal growth and development and eventual apoptotic-like cell death but only when grown under nutrient-limiting conditions. Remarkably, restoration to the wild-type phenotype requires only proline. Here, we describe a generally unrecognized function of proline: its ability to function as a potent antioxidant and inhibitor of programmed cell death. Addition of proline to DARas mutant cells effectively quenched ROS levels and prevented cell death. Treating cells with inhibitors of ROS production yielded similar results. In addition, proline protected wild-type C. trifolii cells against various lethal stresses, including UV light, salt, heat, and hydrogen peroxide. These observations appear to be general because proline also protected yeast cells from lethal levels of the ROS-generating herbicide methyl viologen (paraquat), suggesting a common protective role for proline in response to oxidative stress. The ability of proline to scavenge intracellular ROS and inhibit ROS-mediated apoptosis may be an important and broad-based function of this amino acid in responding to cellular stress, in addition to its well established role as an osmolyte.

Antifungal properties of Schiff bases of chitosan, N-substituted chitosan and quaternized chitosan

Schiff bases of chitosan, N-substituted chitosan, and quaternized chitosan were synthesized and their antifungal properties were analyzed against Botrytis cinerea Pers. (B. cinerea pers.) and Colletotrichum lagenarium (Pass) Ell.et halst (C. lagenarium (Pass) Ell.et halst) based on the method of D. Jasso de Rodríguez and co-workers. The results showed that quaternized chitosan had better inhibitory properties than chitosan, Schiff bases of chitosan, and N-substituted chitosan.

Fungicide activity through activation of a fungal signalling pathway

Fungicides generally inhibit enzymatic reactions involved in fungal cellular biosynthesis. Here we report, for the first time, an example of fungicidal effects through hyperactivation of a fungal signal transduction pathway. The OSC1 gene, encoding a MAP kinase (MAPK) related to yeast Hog1, was isolated from the fungal pathogen Colletotrichum lagenarium that causes cucumber anthracnose. The osc1 knockout mutants were sensitive to high osmotic stress and showed increased resistance to the fungicide fludioxonil, indicating that Osc1 is involved in responses to hyperosmotic stress and sensitivity to fludioxonil. The Osc1 MAPK is phosphorylated under high osmotic conditions, indicating activation of Osc1 by high osmotic stress. Importantly, fludioxonil treatment also activates phosphorylation of Osc1, suggesting that improper activation of Osc1 by fludioxonil has negative effects on fungal growth. In the presence of fludioxonil, the wild-type fungus was not able to infect the host plant because of a failure of appressorium-mediated penetration, whereas osc1 mutants successfully infected plants. Analysis using a OSC1-GFP fusion gene indicated that Osc1 is rapidly translocated to the nucleus in appressorial cells after the addition of fludioxonil, suggesting that fludioxonil impairs the function of infection structures by activation of Osc1. Furthermore, fludioxonil activates Hog1-type MAPKs in the plant pathogenic fungi Cochliobolus heterostrophus and Botrytis cinerea. These results strongly suggest that fludioxonil acts as a fungicide, in part, through activation of the MAPK cascade in fungal pathogens.

Efficient microwave enhanced regioselective synthesis of a series of benzimidazolyl/triazolyl spiro [indole-thiazolidinones] as potent antifungal agents and crystal structure of spiro[3H-indole-3,2′-thiazolidine]-3′(1,2,4-triazol-3-yl)-2,4′(1H)-dione

A microwave-assisted three-component, regioselective one-pot cyclocondensation method has been developed for the synthesis of a series of novel spiro[indole-thiazolidinones] (6a-l) using an environmentally benign procedure at atmospheric pressure in open vessel. This rapid method produces pure products in high yields within few minutes in comparison to a conventional two-step procedure. The crystal structure of one representative compound has been determined by X-ray diffraction. The synthesized compounds have been screened 'in vitro' for antifungal activity against Rhizoctonia solani, Fusarium oxysporum and Collectotrichum capsici. All compounds have shown good activity against these pathogens.

Purification and characterization of a lipopeptide produced by Bacillus thuringiensis CMB26

AIMS

To isolate an antagonist for use in the biological control of phytopathogenic fungi including Colletotrichum gloeosporioides, then to purify and characterize the biocontrol agent produced by the antagonist.

METHODS AND RESULTS

Bacteria that exhibited antifungal activity against the causative agent pepper anthracnose were isolated from soil, with Bacillus thuringiensis CMB26 showing the strongest activity. A lipopeptide produced by B. thuringiensis CMB26 was precipitated by adjusting the pH 2 with 3 n HCl and extracted using chloroform/methanol (2:1, v/v) and reversed-phase HPLC. The molecular weight was estimated as 1447 Da by MALDI-TOF mass spectrometry. Scanning electron and optical microscopies showed that the lipopeptide has activity against Escherichia coli O157:ac88, larvae of the cabbage white butterfly (Pieris rapae crucivora) and phytopathogenic fungi. The lipopeptide had cyclic structure and the amino acid composition was L-Glu, D-Orn, L-Tyr, D-allo-Thr, D-Ala, D-Val, L-Pro, and L-Ile in a molar ratio of 3:1:2:1:1:2:1:1. The purified lipopeptide showed the same amino acid composition as fengycin, but differed slightly in fatty acid composition, in which the double bond was at carbons 13-14 (m/z 303, 316) and there was no methyl group.

CONCLUSION

A lipopeptide was purified and characterized from B. thuringiensis CMB26 and found to be similar to the lipopeptide fengycin. This lipopeptide can function as a biocontrol agent, and exhibits fungicidal, bactericidal, and insecticidal activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Compared with surfactin and iturin, the lipopeptide from B. thuringiensis CMB26 showed stronger antifungal activity against phytopathogenic fungi. This lipopeptide is a candidate for the biocontrol of pathogens in agriculture.

Selective lignin downregulation leads to constitutive defense response expression in alfalfa (Medicago sativa L.)

• Downregulation of hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) in alfalfa (Medicago sativa) reduces lignin levels and improves forage quality and saccharification efficiency for bioethanol production. However, the plants have reduced stature. It was previously reported that HCT-down-regulated Arabidopsis have impaired auxin transport, but this has recently been disproved. • To address the basis for the phenotypes of lignin-modified alfalfa, we measured auxin transport, profiled a range of metabolites including flavonoids and hormones, and performed in depth transcriptome analyses. • Auxin transport is unaffected in HCT antisense alfalfa despite increased flavonoid biosynthesis. The plants show increased cytokinin and reduced auxin levels, and gibberellin levels and sensitivity are both reduced. Levels of salicylic, jasmonic and abscisic acids are elevated, associated with massive upregulation of pathogenesis and abiotic stress-related genes and enhanced tolerance to fungal infection and drought. • We suggest that HCT downregulated alfalfa plants exhibit constitutive activation of defense responses, triggered by release of bioactive cell wall fragments and production of hydrogen peroxide as a result of impaired secondary cell wall integrity.

Secondary metabolites from endophytic Streptomyces aureofaciens CMUAc130 and their antifungal activity

Streptomyces aureofaciens CMUAc130 was isolated from the root tissue of Zingiber officinale Rosc. (Zingiberaceae). It was an antagonist of Colletotrichum musae and Fusarium oxysporum, the causative agents of anthracnose of banana and wilt of wheat, respectively. Evidence for the in vitro antibiosis of S. aureofaciens CMUAc130 was demonstrated by the zone of fungal-growth inhibition. Microscopic observations showed thickness and bulbous structures at the edges of the inhibited fungal hyphae. The culture filtrate and crude extract from this strain were all inhibitory to tested phytopathogenic fungi. The major active ingredients from the culture filtrate of S. aureofaciens CMUAc130 were purified by silica gel-column chromatography and identified to be (i) 5,7-dimethoxy-4-p-methoxylphenylcoumarin and (ii) 5,7-dimethoxy-4-phenylcoumarin by NMR and mass-spectral data, respectively. Bioassay studies showed that compounds (i) and (ii) had antifungal activities against tested fungi, and their MICs were found to be 120 and 150 microg ml(-1), respectively. This is the first report of compounds (i) and (ii) from micro-organisms as active ingredients for the control of phytopathogenic fungi.

ZmPep1, an ortholog of Arabidopsis elicitor peptide 1, regulates maize innate immunity and enhances disease resistance

ZmPep1 is a bioactive peptide encoded by a previously uncharacterized maize (Zea mays) gene, ZmPROPEP1. ZmPROPEP1 was identified by sequence similarity as an ortholog of the Arabidopsis (Arabidopsis thaliana) AtPROPEP1 gene, which encodes the precursor protein of elicitor peptide 1 (AtPep1). Together with its receptors, AtPEPR1 and AtPEPR2, AtPep1 functions to activate and amplify innate immune responses in Arabidopsis and enhances resistance to both Pythium irregulare and Pseudomonas syringae. Candidate orthologs to the AtPROPEP1 gene have been identified from a variety of crop species; however, prior to this study, activities of the respective peptides encoded by these orthologs were unknown. Expression of the ZmPROPEP1 gene is induced by fungal infection and treatment with jasmonic acid or ZmPep1. ZmPep1 activates de novo synthesis of the hormones jasmonic acid and ethylene and induces the expression of genes encoding the defense proteins endochitinase A, PR-4, PRms, and SerPIN. ZmPep1 also stimulates the expression of Benzoxazineless1, a gene required for the biosynthesis of benzoxazinoid defenses, and the accumulation of 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside in leaves. To ascertain whether ZmPep1-induced defenses affect resistance, maize plants were pretreated with the peptide prior to infection with fungal pathogens. Based on cell death and lesion severity, ZmPep1 pretreatment was found to enhance resistance to both southern leaf blight and anthracnose stalk rot caused by Cochliobolis heterostrophus and Colletotrichum graminicola, respectively. We present evidence that peptides belonging to the Pep family have a conserved function across plant species as endogenous regulators of innate immunity and may have potential for enhancing disease resistance in crops.

Colletotrichum higginsianum extracellular LysM proteins play dual roles in appressorial function and suppression of chitin-triggered plant immunity

The genome of the hemibiotrophic anthracnose fungus, Colletotrichum higginsianum, encodes a large repertoire of candidate-secreted effectors containing LysM domains, but the role of such proteins in the pathogenicity of any Colletotrichum species is unknown. Here, we characterized the function of two effectors, ChELP1 and ChELP2, which are transcriptionally activated during the initial intracellular biotrophic phase of infection. Using immunocytochemistry, we found that ChELP2 is concentrated on the surface of bulbous biotrophic hyphae at the interface with living host cells but is absent from filamentous necrotrophic hyphae. We show that recombinant ChELP1 and ChELP2 bind chitin and chitin oligomers in vitro with high affinity and specificity and that both proteins suppress the chitin-triggered activation of two immune-related plant mitogen-activated protein kinases in the host Arabidopsis. Using RNAi-mediated gene silencing, we found that ChELP1 and ChELP2 are essential for fungal virulence and appressorium-mediated penetration of both Arabidopsis epidermal cells and cellophane membranes in vitro. The findings suggest a dual role for these LysM proteins as effectors for suppressing chitin-triggered immunity and as proteins required for appressorium function.

Leaf oil body functions as a subcellular factory for the production of a phytoalexin in Arabidopsis

Oil bodies are intracellular structures present in the seed and leaf cells of many land plants. Seed oil bodies are known to function as storage compartments for lipids. However, the physiological function of leaf oil bodies is unknown. Here, we show that leaf oil bodies function as subcellular factories for the production of a stable phytoalexin in response to fungal infection and senescence. Proteomic analysis of oil bodies prepared from Arabidopsis (Arabidopsis thaliana) leaves identified caleosin (CLO3) and α-dioxygenase (α-DOX1). Both CLO3 and α-DOX1 were localized on the surface of oil bodies. Infection with the pathogenic fungus Colletotrichum higginsianum promoted the formation of CLO3- and α-DOX1-positive oil bodies in perilesional areas surrounding the site of infection. α-DOX1 catalyzes the reaction from α-linolenic acid (a major fatty acid component of oil bodies) to an unstable compound, 2-hydroperoxy-octadecatrienoic acid (2-HPOT). Intriguingly, a combination of α-DOX1 and CLO3 produced a stable compound, 2-hydroxy-octadecatrienoic acid (2-HOT), from α-linolenic acid. This suggests that the colocalization of α-DOX1 and CLO3 on oil bodies might prevent the degradation of unstable 2-HPOT by efficiently converting 2-HPOT into the stable compound 2-HOT. We found that 2-HOT had antifungal activity against members of the genus Colletotrichum and that infection with C. higginsianum induced 2-HOT production. These results defined 2-HOT as an Arabidopsis phytoalexin. This study provides, to our knowledge, the first evidence that leaf oil bodies produce a phytoalexin under a pathological condition, which suggests a new mechanism of plant defense.

Natural fungicides from Ruta graveolens L. leaves, including a new quinolone alkaloid

Bioassay-directed isolation of antifungal compounds from an ethyl acetate extract of Ruta graveolens leaves yielded two furanocoumarins, one quinoline alkaloid, and four quinolone alkaloids, including a novel compound, 1-methyl-2-[6'-(3' ',4' '-methylenedioxyphenyl)hexyl]-4-quinolone. The (1)H and (13)C NMR assignments of the new compound are reported. Antifungal activities of the isolated compounds, together with 7-hydroxycoumarin, 4-hydroxycoumarin, and 7-methoxycoumarin, which are known to occur in Rutaceae species, were evaluated by bioautography and microbioassay. Four of the alkaloids had moderate activity against Colletotrichum species, including a benomyl-resistant C. acutatum. These compounds and the furanocoumarins 5- and 8-methoxypsoralen had moderate activity against Fusarium oxysporum. The novel quinolone alkaloid was highly active against Botrytis cinerea. Phomopsis species were much more sensitive to most of the compounds, with P. viticola being highly sensitive to all of the compounds.

Plant growth-promoting traits of yeasts isolated from the phyllosphere and rhizosphere of Drosera spatulata Lab

Microorganisms can promote plant growth through direct and indirect mechanisms. Compared with the use of bacteria and mycorrhizal fungi, the use of yeasts as plant growth-promoting (PGP) agents has not been extensively investigated. In this study, yeast isolates from the phyllosphere and rhizosphere of the medicinally important plant Drosera spatulata Lab. were assessed for their PGP traits. All isolates were tested for indole-3-acetic acid-, ammonia-, and polyamine-producing abilities, calcium phosphate and zinc oxide solubilizing ability, and catalase activity. Furthermore, the activities of siderophore, 1-aminocyclopropane-1-carboxylate deaminase, and fungal cell wall-degrading enzymes were assessed. The antagonistic action of yeasts against pathogenic Glomerella cingulata was evaluated. The cocultivation of Nicotiana benthamiana with yeast isolates enhanced plant growth, indicating a potential yeast-plant interaction. Our study results highlight the potential use of yeasts as plant biofertilizers under controlled and field conditions.

Antifungal activity against plant pathogens of metabolites from the endophytic fungus Cladosporium cladosporioides

Bioassay-guided fractionation of Cladosporium cladosporioides (Fresen.) de Vries extracts led to the isolation of four compounds, including cladosporin, 1; isocladosporin, 2; 5'-hydroxyasperentin, 3; and cladosporin-8-methyl ether, 4. An additional compound, 5',6-diacetylcladosporin, 5, was synthesized by acetylation of compound 3. Compounds 1-5 were evaluated for antifungal activity against plant pathogens. Phomopsis viticola was the most sensitive fungus to the tested compounds. At 30 μM, compound 1 exhibited 92.7, 90.1, 95.4, and 79.9% growth inhibition against Colletotrichum acutatum , Colletotrichum fragariae , Colletotrichum gloeosporioides , and P. viticola, respectively. Compound 2 showed 50.4, 60.2, and 83.0% growth inhibition at 30 μM against Co. fragariae, Co. gloeosporioides, and P. viticola, respectively. Compounds 3 and 4 were isolated for the first time from Cl. cladosporioides. Moreover, the identification of essential structural features of the cladosporin nuclei has also been evaluated. These structures provide new templates for the potential treatment and management of plant diseases.

Antifungal New Oxepine-Containing Alkaloids and Xanthones from the Deep-Sea-Derived Fungus Aspergillus versicolor SCSIO 05879

Phytopathogenic fungi remain a continuous and huge threat in the agricultural fields. The agrochemical industry has made great development of the use of microbial natural products, which has been regarded as an effective strategy against phytopathogenic fungi. Antifungal bioassay-directed fractionation was used to isolate two new oxepine-containing alkaloids (1 and 2), two new 4-aryl-quinolin-2-one alkaloids (3 and 4), and four new prenylated xanthones (5-8) from the deep-sea-derived fungus Aspergillus versicolor SCSIO 05879. Extensive NMR spectroscopic analysis, quantum mechanical calculations, and X-ray single-crystal diffraction were used to elucidate their structures, including their absolute configurations. Versicoloids A and B, versicone A, and cottoquinazoline A showed antifungal activities against three phytopathogenic fungi. The antifungal activities of these bioactive compounds strongly depend on the fungal species. Especially versicoloids A and B showed strong fungicidal effect (MIC of 1.6 μg/mL) against Colletotrichum acutatum, compared with that of the positive control cycloheximide (MIC of 6.4 μg/mL). The results of antifungal experiments indicated that versicoloids A and B may be regarded as candidate agents of antifungal agrochemicals.

Isolation and identification of antifungal and antialgal alkaloids from Haplophyllum sieversii

Bioassay-guided fractionation of the hexane/ethyl acetate/water (H/EtOAc/H2O) crude extract of the aerial parts of Haplophyllum sieversii was performed because of preliminary screening data that indicated the presence of growth inhibitory components against Colletotrichum fragariae, Colletotrichum gloeosporioides, and Colletotrichum acutatum. Fractionation was directed using bioautographical methods resulting in the isolation of the bioactive alkaloids flindersine, anhydroevoxine, haplamine, and a lignan eudesmin. These four compounds were evaluated for activity against C. fragariae, C. gloeosporioides, C. acutatum, Botrytis cinerea, Fusarium oxysporum, and Phomopsis obscurans in a dose-response growth-inhibitory bioassay at 50.0, 100.0, and 150.0 microM. Of the four compounds tested, flindersine demonstrated the highest level of antifungal activity. Additionally, flindersine, eudesmin, and haplamine were screened against the freshwater phytoplanktons Oscillatoria perornata, Oscillatoria agardhii, Selenastrum capricornutum, and Pseudanabaena sp. (strain LW397). Haplamine demonstrated selective inhibition against the odor-producing cyanobacterium O. perornata compared to the activity against the green alga S. capricornutum, with lowest observed effect concentration values of 1.0 and 10.0 microM, respectively.

Mycogenic Selenium Nanoparticles as Potential New Generation Broad Spectrum Antifungal Molecules

The current challenges of sustainable agricultural development augmented by global climate change have led to the exploration of new technologies like nanotechnology, which has potential in providing novel and improved solutions. Nanotools in the form of nanofertilizers and nanopesticides possess smart delivery mechanisms and controlled release capacity for active ingredients, thus minimizing excess run-off to water bodies. This study aimed to establish the broad spectrum antifungal activity of mycogenic selenium nanoparticles (SeNPs) synthesized from Trichoderma atroviride, and characterize the bioactive nanoparticles using UV-Vis spectroscopy, dynamic light scattering (DLS), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and high-resolution transmission electron microscopy (HR-TEM). The synthesized nanoparticles displayed excellent in vitro antifungal activity against Pyricularia grisea and inhibited the infection of Colletotrichum capsici and Alternaria solani on chili and tomato leaves at concentrations of 50 and 100 ppm, respectively. The SEM-EDS analysis of the bioactive SeNPs revealed a spherical shape with sizes ranging from 60.48 nm to 123.16 nm. The nanoparticles also possessed the unique property of aggregating and binding to the zoospores of P. infestans at a concentration of 100 ppm, which was visualized using light microscope, atomic force microscopy, and electron microscopy. Thus, the present study highlights the practical application of SeNPs to manage plant diseases in an ecofriendly manner, due to their mycogenic synthesis and broad spectrum antifungal activity against different phytopathogens.

Nitric oxide has a regulatory effect in the germination of conidia of Colletotrichum coccodes

Nitric oxide (NO) was first detected in mammals and has since been found in plants and in micro-organisms such as bacteria. NO is an important signalling molecule involved in a number of critical signal transduction pathways. To date, NO has not been directly detected in fungi, and little research on NO and fungi has been completed. Here, the role of NO in the germination of Colletotrichum coccodes conidia was investigated. Conidia were germinated on microscope slides, treated with chemicals to block NO, to add NO, and/or to detect NO, and assessed for their stage of development over 24 h. NO was detected in germinating conidia at all stages of development. Exogenous NO delayed germination, while treatment with NO inhibitors accelerated germination, suggesting NO may have a regulatory effect in germination. The differential effect of the various inhibitors suggests the fungal isoform of nitric oxide synthase (NOS) may be biochemically similar to mammalian constitutive NOS.

Two novel antifungal peptides distinct with a five-disulfide motif from the bark of Eucommia ulmoides Oliv

Two antifungal peptides, named EAFP1 and EAFP2, have been purified from the bark of Eucommia ulmoides Oliv. Each of the sequences consists of 41 residues with a N-terminal blockage by pyroglutamic acid determined by automated Edman degradation in combination with the tandem mass spectroscopy and the C-terminal ladder sequencing analysis. The primary structurs all contain 10 cysteines, which are cross-linked to form five disulfide bridges with a pairing pattern (C1-C5, C2-C9, C3-C6, C4-C7, C8-C10). This is the first finding of a plant antifungal peptide with a five-disulfide motif. EAFP1 and EAFP2 show characteristics of hevein domain and exhibit chitin-binding properties similar to the previously identified hevein-like peptides. They exhibit relatively broad spectra of antifungal activities against eight pathogenic fungi from cotton, wheat, potato, tomato and tobacco. The inhibition activity of EAFP1 and EAFP2 can be effective on both chitin-containing and chitin-free fungi. The values of IC(50) range from 35 to 155 microg/ml for EAFP1 and 18 to 109 microg/ml for EAFP2. Their antifungal effects are strongly antagonized by calcium ions.

cAMP regulation of "pathogenic" and "saprophytic" fungal spore germination

We report on the elucidation of two separate pathways of spore germination in a plant pathogenic fungus Colletotrichum gloeosporioides f. sp. aeschynomene. Conidia of the fungus can germinate either from one side or from both sides, depending on external conditions. In shake culture that includes an extract made up from fresh peas, the unicellular conidium divides and one of the two cells develops a germ tube. On a solid surface this germ tube differentiates an appressorium. In rich medium without pea extract, germination is highly similar to Aspergillus spore germination: the conidium swells, forms a single germ tube and then divides and forms a second germ tube. Conidia that germinate in a rich medium do not form appressoria even on a solid surface and are non-pathogenic. In rich medium, cAMP stimulates germination in rich liquid cultures and induces appressoria formation on a hard surface. In pea extract cAMP induces swelling and formation of irregular germ tubes and appressoria. Our results suggest that plant surface signals induce pathogenic-specific spore germination in a cAMP-independent manner. cAMP is required for saprophytic germination and for appressorium formation.

Antifungal constituents of the essential oil fraction of Artemisia dracunculus L. Var. dracunculus

The isolation and structure elucidation of antifungal constituents of the steam-distilled essential oil fraction of Artemisia dracunculus are described. Antifungal activities of 5-phenyl-1,3-pentadiyne and capillarin against Colletrotichum fragariae, Colletrotichum gloeosporioides, and Colletrotichum acutatum are reported for the first time. The relative abundance of 5-phenyl-1,3-pentadiyne is about 11% of the steam-distilled oil, as determined by GC-MS. Methyleugenol was also isolated and identified as an antifungal constituent of the oil.

Banana fruit NAC transcription factor MaNAC5 cooperates with MaWRKYs to enhance the expression of pathogenesis-related genes against Colletotrichum musae

Plants respond to pathogen attack by the modulation of a large set of genes, which are regulated by different types of transcription factor (TF). NAC (NAM/ATAF/CUC) and WRKY are plant-specific families of TFs, and have received much attention as transcriptional regulators in plant pathogen defence. However, the cooperation between NAC and WRKY TFs in the disease response remains largely unknown. Our previous study has revealed that two banana fruit WRKY TFs, MaWRKY1 and MaWRKY2, are involved in salicylic acid (SA)- and methyl jasmonate (MeJA)-induced resistance against Colletotrichum musae via binding to promoters of pathogenesis-related (PR) genes. Here, we found that MaNAC1, MaNAC2 and MaNAC5 were up-regulated after C. musae infection, and were also significantly enhanced by SA and MeJA treatment. Protein-protein interaction analysis showed that MaNAC5 physically interacted with MaWRKY1 and MaWRKY2. More importantly, dual-luciferase reporter (DLR) assay revealed that MaNAC5, MaWRKY1 and MaWRKY2 were transcriptional activators, and individually or cooperatively activated the transcriptional activities of MaPR1-1, MaPR2, MaPR10c and MaCHIL1 genes. Collectively, our results indicate that MaNAC5 cooperates with MaWRKY1 and MaWRKY2 to regulate the expression of a specific set of PR genes in the disease response, and to contribute at least partially to SA- and MeJA-induced pathogen resistance.

Synthesis and Pesticidal Activities of New Quinoxalines

Natural products are a source of many novel compounds with biological activity for the discovery of new pesticides and pharmaceuticals. Quinoxaline is a fused N-heterocycle in many natural products and synthetic compounds, and seven novel quinoxaline derivatives were designed and synthesized via three steps. Pesticidal activities of title quinoxaline derivatives were bioassayed. Most of these compounds had herbicidal, fungicidal, and insecticidal activities. The compounds 2-(6-methoxy-2-oxo-3-phenylquinoxalin-1(2H)-yl)acetonitrile (3f) and 1-allyl-6-methoxy-3-phenylquinoxalin-2(1H)-one (3g) were the most active herbicides and fungicides. Mode-of-action studies indicated that 3f is a protoprophyrinogen oxidase-inhibiting herbicide. Compound 3f also possessed broad-spectrum fungicidal activity against the plant pathogen Colletotrichum species. Some of these compounds also had insecticidal activity. Molecular docking and DFT analysis can potentially be used to design more active compounds.

Inhibition of plant-pathogenic fungi by the barley cystatin Hv-CPI (gene Icy) is not associated with its cysteine-proteinase inhibitory properties

The recombinant barley cystatin Hv-CPI inhibited the growth of three phytopathogenic fungi (Botrytis cinerea, Colletotrichum graminicola, and Plectosphaerella cucumerina) and the saprotrophic fungus Trichoderma viride. Several mutants of barley cystatin were generated by polymerase chain reaction approaches and both their antifungal and their cysteine-proteinase inhibitory properties investigated. Point mutants R38-->G, Q63-->L, and Q63-->P diminished their capacity for inhibiting papain and cathepsin B, retaining their antifungal properties. However, mutant C68-->G was more active for papain and cathepsin B than the wild type. These results indicate that in addition to the consensus cystatin-reactive site, Q63-V64-V65-A66-G67, the A37-R38-F39-A40-V41 region, common to all cereal cystatins, and the C68 residue are important for barley cystatin activity. On the other hand, the K92-->P mutant is inactive as a fungicide, but still retains measurable inhibitory activity for papain and cathepsin B. Against B. cinerea, the antifungal effect of Hv-CPI and of its derived mutants does not always correlate with their activities as proteinase inhibitors, because the Q63-->P mutant is inactive as a cystatin, while still inhibiting fungal growth, and the K92-->P mutant shows the reciprocal effects. These data indicate that inhibition of plant-pathogenic fungi by barley cystatin is not associated with its cysteine-proteinase inhibitory activity. Moreover, these results are corroborated by the absence of inhibition of intra- and extramycelia-proteinase activities by barley cystatin and by other well-known inhibitors of cysteine-proteinase activity in the fungal zymograms of B. cinerea.

Antifungal activity of thiophenes from Echinops ritro

Extracts from 30 plants of the Greek flora were evaluated for their antifungal activity using direct bioautography assays with three Colletotrichum species. Among the bioactive extracts, the dichloromethane extract of the radix of Echinops ritro (Asteraceae) was the most potent. Bioassay-guided fractionation of this extract led to the isolation of eight thiophenes. Antifungal activities of isolated compounds together with a previously isolated thiophene from Echinops transiliensis were first evaluated by bioautography and subsequently evaluated in greater detail using a broth microdilution assay against plant pathogens Colletotrichum acutatum, Colletotrichum fragariae, Colletotrichum gloeosporioides, Botrytis cinerea, Fusarium oxysporum, Phomopsis viticola, and Phomopsis obscurans. 5'-(3-Buten-1-ynyl)-2,2'-bithiophen (1), alpha-terthienyl (2), and 2-[pent-1,3-diynyl]-5-[4-hydroxybut-1-ynyl]thiophene (5) at 3 and 30 microM were active against all three Colletotrichum species, F. oxysporum, P. viticola, and P. obscurans.

Activity of quinones on colletotrichum species

The antifungal activity of 1,4-naphthoquinones, 1,2-naphthoquinones, 1,4-benzoquinones, and anthraquinones from our natural products collection was tested by direct bioautography to identify natural products with potential use in agricultural fungal pathogen control. Quinones demonstrated good to moderate antifungal activity against Colletotrichum spp. Colletotrichum fragariae was the most sensitive species to quinone-based chemistry, Colletotrichum gloeosporioides had intermediate sensitivity, while Colletotrichum acutatum was the species least sensitive to these compounds.