Synthesis and molecular docking simulations of novel azepines based on quinazolinone moiety as prospective antimicrobial and antitumor hedgehog signaling inhibitors.

A series of novel azepine derivatives based on quinazolinone moiety was synthesized through the reaction of quinazolinone chalcones (2a-d) either with 2-amino aniline in acidic medium to give diazepines (3a-d) or with 2-aminophenol to offer oxazepine (4a-d). The structure of the synthesized compounds was confirmed via melting points, elemental analyses, and different spectroscopic techniques. Moreover, these newly compounds mode of action was investigated in-silico using molecular docking against the outer membrane protein A (OMPA), exo-1,3-beta-glucanase for their antimicrobial activity, and against Smoothened (SMO), transcription factor glioma-associated homology (SUFU/GLI-1), the main proteins of Hedgehog signaling pathway to inspect their anticancer potential. Our results showed that, diazepine (3a) and oxazepine (4a) offered the highest binding energy against the target OMPA/ exo-1,3-beta-glucanase proteins and exhibited the potent antimicrobial activities against E. coli, P. aeruginosa, S. aureus, B. subtilis, C. Albicans and A. flavus. As well, diazepine (3a) and oxazepine (4a) achieved the best results among the other compounds, in their binding energy against the target SMO, SUFU/GLI-1 proteins. The in-vitro cytotoxic study was done for them on panel of cancer cell lines HCT-116, HepG2, and MCF-7 and normal cell line WI-38. Conclusively, it was revealed that molecular docking in-silico simulations and the in-vitro experiments were agreed. As a result, our findings elucidated that diazepine (3a) and oxazepine (4a), have the potential to be used as antimicrobial agents and as possible cancer treatment medications.

Inhibitory effect of berberine hydrochloride against Candida albicans and the role of the HOG-MAPK pathway.

Berberine hydrochloride (BH), an active component of Coptis chinensis and other plant taxa, has broad antimicrobial activity and may be useful for the treatment of Candida infections. In this study, the mechanisms underlying the inhibitory effect of BH against Candida albicans were evaluated, with a focus on the high-osmolarity glycerol mitogen-activated protein kinase (HOG-MAPK) pathway, which regulates multiple physiological functions. BH (256 and 64 µg ml-1) significantly increased intracellular glycerol and ROS levels in C. albicans, inhibited germ tube and hyphal formation, and increased chitin and ß-1,3-glucan exposure on the cell wall. The inhibitory effect of BH was positively correlated with its concentration, and the inhibitory effect of 256 µg ml-1 BH was greater than that of 4 µg ml-1 fluconazole (FLC). Furthermore, RT-PCR analysis showed that 256 and 64 µg ml-1 BH altered the HOG-MAPK pathway in C. albicans. In particular, the upregulation of the core genes, SLN1, SSK2, HOG1, and PBS2 may affect the expression of key downstream factors related to glycerol synthesis and osmotic pressure (GPD1), ROS accumulation (ATP11 and SOD2), germ tube and hyphal formation (HWP1), and cell wall integrity (CHS3 and GSC1). BH affects multiple biological processes in C. albicans; thus, it can be an effective alternative to conventional azole antifungal agents.

Laminarans and 1,3-ß-D-glucanases.

The laminarans are biologically active water-soluble polysaccharide (1,3;1,6-ß-D-glucans) of brown algae. These polysaccharides are an attractive object for research due to its relatively simple structure, low toxicity, and various biological effects. 1,3-ß-D-glucanases are an effective tool for studying the structure of laminarans, and can also be used to obtain new biologically active derivatives. This review is to outline what is currently known about laminarans and enzymes that catalyze of their transformation. We focused on information about sources, structure and properties of laminarans and 1,3-ß-D-glucanases, methods of obtaining and structural elucidation of laminarans, and biological activity of laminarans and products of their enzymatic transformation. It has an increased focus on the immunomodulating and anticancer activity of laminarans and their derivatives.

Purification and biochemical characterization of a novel thermophilic exo-ß-1, 3-glucanase from the thermophile biomass-degrading fungus Thielavia terrestris Co3Bag1

Background: The aim of this work was to purify and characterize exo-ß-1,3-glucanase, namely, TtBgnA, from the thermophilic fungus Thielavia terrestris Co3Bag1 and to identify the purified enzyme. Results: The thermophilic biomass-degrading fungus T. terrestris Co3Bag1 displayed ß-1,3-glucanase activity when grown on 1% glucose. An exo-ß-1,3-glucanase, with an estimated molecular mass of 129 kDa, named TtBgnA, was purified from culture filtrates from T. terrestris Co3Bag1. The enzyme exhibited optimum activity at pH 6.0 and 70°C and half-lives (t1/2) of 54 and 37 min at 50 and 60°C, respectively. Substrate specificity analysis showed that laminarin was the best substrate studied for TtBgnA. When laminarin was used as the substrate, the apparent KM and Vmax values were determined to be 2.2 mg mL-1 and 10.8 U/mg, respectively. Analysis of hydrolysis products by thin-layer chromatography (TLC) revealed that TtBgnA displays an exo mode of action. Additionally, the enzyme was partially sequenced by tandem mass spectrometry (MS/MS), and the results suggested that TtBgnA from T. terrestris Co3Bag1 could be classified as a member of the GH-31 family. Conclusions: This report thus describes the purification and characterization of TtBgnA, a novel exo-ß-1,3-glucanase of the GH-31 family from the thermophilic fungus T. terrestris Co3Bag1. Based on the biochemical properties displayed by TtBgnA, the enzyme could be considered as a candidate for potential biotechnological applications.

Purification and characterization of a novel ß-1,3-glucanase from Arca inflata and its immune-enhancing effects.

A novel ß-1,3-glucanase from Arca inflata was purified using chromatography methods. It was determined as a glycoprotein comprising 23.65% carbohydrate content with O-linked glycan and showed specific activity of 90.01 ±â€¯1.2 U/mg against laminarin. The optimal pH and temperature for the activity of the glucanase were 6.0 and 40 °C, respectively. The affinity parameter of the glucanase using laminarin was determined as Kd = 13.09 µM. The activity of the glucanase was 27 ±â€¯2.6% enhanced by 2-mM Mn2+ ions and inhibited by 40-50% using 2-mM Zn2+, Cu2+, or Ba2+ ions. The glucanase showed an endo-type cleavage mode and hydrolyzed laminarin into glucoses, disaccharides, trioligosaccharides, and tetraoligosaccharides. Otherwise, the glucanase exhibited immune-enhancing effects via significantly increasing the phagocytic activity of macrophages and inducing the release of nitric oxide, tumor necrosis factor α, and interleukin-6 in RAW264.7 cells. It might be used as a bifunctional additive for the food industry.

Improved extraction of resveratrol and antioxidants from grape peel using heat and enzymatic treatments.

BACKGROUND: Resveratrol, an extensively recognized phytochemical that belongs to the stilbene family, is abundant in grape peel which is discarded as a by-product during grape juice processing. RESULTS: In this study, we established that pre-heating grape peel above 75 °C significantly improved the extractability of resveratrol and its glucoside piceid. In particular, thermal heating of grape peel at 95 °C for 10 min, followed by treatment with a mixture of exo-1,3-ß-glucanase and pectinases at 50 °C for 60 min, dramatically increased the conversion of piceid into resveratrol and the overall extractability of this phytochemical by 50%. Furthermore, thermal pre-treatment promoted a substantial increase in the total phenol, flavonoid, and anthocyanin concentrations in the grape peel extract. Ultimately, resveratrol-enriched grape peel extract significantly augmented the antioxidant response in vitro, possibly by attenuating the accumulation of intracellular reactive oxygen species via the Nrf2 signaling pathway. CONCLUSION: The method developed in this study for preparing grape peel extract introduces a potential low-cost green processing for the industrial fortification of food products with resveratrol and other health-beneficial antioxidants. © 2019 Society of Chemical Industry.

Expression of pathogenesis-related proteins in transplastomic tobacco plants confers resistance to filamentous pathogens under field trials.

Plants are continuously challenged by pathogens, affecting most staple crops compromising food security. They have evolved different mechanisms to counterattack pathogen infection, including the accumulation of pathogenesis-related (PR) proteins. These proteins have been implicated in active defense, and their overexpression has led to enhanced resistance in nuclear transgenic plants, although in many cases constitutive expression resulted in lesion-mimic phenotypes. We decided to evaluate plastid transformation as an alternative to overcome limitations observed for nuclear transgenic technologies. The advantages include the possibilities to express polycistronic RNAs, to obtain higher protein expression levels, and the impeded gene flow due to the maternal inheritance of the plastome. We transformed Nicotiana tabacum plastids to co-express the tobacco PR proteins AP24 and ß-1,3-glucanase. Transplastomic tobacco lines were characterized and subsequently challenged with Rhizoctonia solani, Peronospora hyoscyami f.sp. tabacina and Phytophthora nicotianae. Results showed that transplastomic plants expressing AP24 and ß-1,3-glucanase are resistant to R. solani in greenhouse conditions and, furthermore, they are protected against P.hyoscyami f.sp. tabacina and P. nicotianae in field conditions under high inoculum pressure. Our results suggest that plastid co- expression of PR proteins AP24 and ß-1,3-glucanase resulted in enhanced resistance against filamentous pathogens.

A novel chitosan formulation treatment induces disease resistance of harvested litchi fruit to Peronophythora litchii in association with ROS metabolism.

This study aimed to investigate the effects of a novel chitosan formulation (Kadozan) treatment on disease development, response of disease resistance, metabolism of reactive oxygen species (ROS) in Peronophthora litchii-inoculated "Wuye" litchis. Compared with P. litchii-inoculated litchis, Kadozan-treated P. litchii-inoculated litchis exhibited lower fruit disease index, higher lignin content, higher activities of disease resistance-related enzymes (CHI, GLU and PAL), lower O2- generating rate and malondialdehyde content, higher activities of ROS scavenging enzymes (SOD, CAT and APX), higher contents of ascorbic acid and glutathione, and higher levels of reducing power and DPPH radical scavenging activity. These results suggest that Kadozan can be used to inhibit the growth of P. litchii in harvested litchis owning to the enhancement of disease resistance and ROS scavenging capacity, and decreases in O2- accumulation and membrane lipid peroxidation. Kadozan treatment can be used as a facile and novel method for suppressing postharvest pathogenic disease of litchis.

Biochemical responses induced in galls of three Cynipidae species in oak trees.

Gall-making Cynipidae manipulate the leaves of host plant to form galls where offspring find shelter and food. The relationship between oak gallwasp and biochemical mechanisms of galls still requires a better understanding. So, in this research, protein and phenolic compound contents, as well as the activity of antioxidative enzymes and pathogenesis-related (PR) proteins were determined. Galls caused by asexual generation of Cynips quercusfolii L., Neuroterus numismalis (Fourc.) and N. quercusbaccarum L., as a model were used. All cynipid species modified the protein levels of gall tissues, but they cannot be treated as protein sinks. Significantly higher levels of phenols were observed in the galled leaves and galls of all cynipid species when compared with the control tissues. Peroxidase and polyphenol oxidase activity was usually low or showed no activity in galled tissues of all species. PR proteins, such as chitinase and ß-1,3-glucanase, had a similar activity profile. Their activity significantly increased in the leaves with galls of all cynipid species, especially those infested with C. quercusfolii. Data generated in this study clearly indicate that galling Cynipidae manipulate the biochemical machinery of the galls for their own needs. However, the pattern of the biochemical features of leaves with galls and galled tissues depends on gall-making species.

Molecular characterization and evolution of carnivorous sundew (Drosera rotundifolia L.) class V ß-1,3-glucanase.

MAIN CONCLUSION: A gene for ß-1,3-glucanase was isolated from carnivorous sundew. It is active in leaves and roots, but not in digestive glands. Analyses in transgenic tobacco suggest its function in germination. Ancestral plant ß-1,3-glucanases (EC 3.2.1.39) played a role in cell division and cell wall remodelling, but divergent evolution has extended their roles in plant defense against stresses to decomposition of prey in carnivorous plants. As available gene sequences from carnivorous plants are rare, we isolated a glucanase gene from roundleaf sundew (Drosera rotundifolia L.) by a genome walking approach. Computational predictions recognized typical gene features and protein motifs described for other plant ß-1,3-glucanases. Phylogenetic reconstructions suggest strong support for evolutionary relatedness to class V ß-1,3-glucanases, including homologs that are active in the traps of related carnivorous species. The gene is expressed in sundew vegetative tissues but not in flowers and digestive glands, and encodes for a functional enzyme when expressed in transgenic tobacco. Detailed analyses of the supposed promoter both in silico and in transgenic tobacco suggest that this glucanase plays a role in development. Specific spatiotemporal activity was observed during transgenic seed germination. Later during growth, the sundew promoter was active in marginal and sub-marginal areas of apical true leaf meristems of young tobacco plants. These results suggest that the isolated glucanase gene is regulated endogenously, possibly by auxin. This is the first report on a nuclear gene study from sundew.

Stimulating S-adenosyl-l-methionine synthesis extends lifespan via activation of AMPK.

Dietary restriction (DR), such as calorie restriction (CR) or methionine (Met) restriction, extends the lifespan of diverse model organisms. Although studies have identified several metabolites that contribute to the beneficial effects of DR, the molecular mechanism underlying the key metabolites responsible for DR regimens is not fully understood. Here we show that stimulating S-adenosyl-l-methionine (AdoMet) synthesis extended the lifespan of the budding yeast Saccharomyces cerevisiae The AdoMet synthesis-mediated beneficial metabolic effects, which resulted from consuming both Met and ATP, mimicked CR. Indeed, stimulating AdoMet synthesis activated the universal energy-sensing regulator Snf1, which is the S. cerevisiae ortholog of AMP-activated protein kinase (AMPK), resulting in lifespan extension. Furthermore, our findings revealed that S-adenosyl-l-homocysteine contributed to longevity with a higher accumulation of AdoMet only under the severe CR (0.05% glucose) conditions. Thus, our data uncovered molecular links between Met metabolites and lifespan, suggesting a unique function of AdoMet as a reservoir of Met and ATP for cell survival.

Cultural conditions on the production of extracellular enzymes by Trichoderma isolates from tobacco rhizosphere.

Twelve isolates of Trichoderma spp. isolated from tobacco rhizosphere were evaluated for their ability to produce chitinase and ß-1,3-glucanase extracellular hydrolytic enzymes. Isolates ThJt1 and TvHt2, out of 12 isolates, produced maximum activities of chitinase and ß-1,3-glucanase, respectively. In vitro production of chitinase and ß-1,3-glucanase by isolates ThJt1 and TvHt2 was tested under different cultural conditions. The enzyme activities were significantly influenced by acidic pH and the optimum temperature was 30°C. The chitin and cell walls of Sclerotium rolfsii, as carbon sources, supported the maximum and significantly higher chitinase activity by both isolates. The chitinase activity of isolate ThJt1 was suppressed significantly by fructose (80.28%), followed by glucose (77.42%), whereas the ß-1,3-glucanase activity of ThJt1 and both enzymes of isolate TvHt2 were significantly suppressed by fructose, followed by sucrose. Ammonium nitrate as nitrogen source supported the maximum activity of chitinase in both isolates, whereas urea was a poor nitrogen source. Production of both enzymes by the isolates was significantly influenced by the cultural conditions. Thus, the isolates ThJt1 and TvHt2 showed higher levels of chitinase and ß-1,3-glucanase activities and were capable of hydrolyzing the mycelium of S. rolfsii infecting tobacco. These organisms can be used therefore for assessment of their synergism in biomass production and biocontrol efficacy and for their field biocontrol ability against S. rolfsii and Pythium aphanidermatum infecting tobacco.

Feeding of Whitefly on Tobacco Decreases Aphid Performance via Increased Salicylate Signaling.

BACKGROUND: The feeding of Bemisia tabaci nymphs trigger the SA pathway in some plant species. A previous study showed that B. tabaci nymphs induced defense against aphids (Myzus persicae) in tobacco. However, the mechanism underlying this defense response is not well understood. METHODOLOGY/PRINCIPAL FINDINGS: Here, the effect of activating the SA signaling pathway in tobacco plants through B. tabaci nymph infestation on subsequent M. persicae colonization is investigated. Performance assays showed that B. tabaci nymphs pre-infestation significantly reduced M. persicae survival and fecundity systemically in wild-type (WT) but not salicylate-deficient (NahG) plants compared with respective control. However, pre-infestation had no obvious local effects on subsequent M. persicae in either WT or NahG tobacco. SA quantification results indicated that the highest accumulation of SA was induced by B. tabaci nymphs in WT plants after 15 days of infestation. These levels were 8.45- and 6.14-fold higher in the local and systemic leaves, respectively, than in controls. Meanwhile, no significant changes of SA levels were detected in NahG plants. Further, biochemical analysis of defense enzymes polyphenol oxidase (PPO), peroxidase (POD), ß-1,3-glucanase, and chitinase demonstrated that B. tabaci nymph infestation increased these enzymes' activity locally and systemically in WT plants, and there was more chitinase and ß-1, 3-glucanase activity systemically than locally, which was opposite to the changing trends of PPO. However, B. tabaci nymph infestation caused no obvious increase in enzyme activity in any NahG plants except POD. CONCLUSIONS/SIGNIFICANCE: In conclusion, these results underscore the important role that induction of the SA signaling pathway by B. tabaci nymphs plays in defeating aphids. It also indicates that the activity of ß-1, 3-glucanase and chitinase may be positively correlated with resistance to aphids.

Chemical products induce resistance to Xanthomonas perforans in tomato.

The bacterial spot of tomato, caused by Xanthomonas spp., is a very important disease, especially in the hot and humid periods of the year. The chemical control of the disease has not been very effective for a number of reasons. This study aimed to evaluate, under greenhouse conditions, the efficacy of leaf-spraying chemicals (acibenzolar-S-methyl (ASM) (0.025 g.L(-1)), fluazinam (0.25 g.L(-1)), pyraclostrobin (0.08 g.L(-1)), pyraclostrobin + methiran (0.02 g.L(-1) + 2.2 g.L(-1)), copper oxychloride (1.50 g.L(-1)), mancozeb + copper oxychloride (0.88 g.L(-1) + 0.60 g.L(-1)), and oxytetracycline (0.40 g.L(-1))) on control of bacterial spot. Tomatoes Santa Clara and Gisele cultivars were pulverized 3 days before inoculation with Xanthomonas perforans. The production of enzymes associated with resistance induction (peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase, ß-1,3-glucanase, and protease) was quantified from leaf samples collected 24 hours before and 24 hours after chemical spraying and at 1, 2, 4, 6, and 8 days after bacterial inoculation. All products tested controlled bacterial spot, but only ASM, pyraclostrobin, and pyraclostrobin + metiram increased the production of peroxidase in the leaves of the two tomato cultivars, and increased the production of polyphenol oxidase and ß-1,3-glucanase in the Santa Clara cultivar.

An Enzymatically Active ß-1,3-Glucanase from Ash Pollen with Allergenic Properties: A Particular Member in the Oleaceae Family.

Endo-ß-1,3-glucanases are widespread enzymes with glycosyl hydrolitic activity involved in carbohydrate remodelling during the germination and pollen tube growth. Although members of this protein family with allergenic activity have been reported, their effective contribution to allergy is little known. In this work, we identified Fra e 9 as a novel allergenic ß-1,3-glucanase from ash pollen. We produced the catalytic and carbohydrate-binding domains as two independent recombinant proteins and characterized them from structural, biochemical and immunological point of view in comparison to their counterparts from olive pollen. We showed that despite having significant differences in biochemical activity Fra e 9 and Ole e 9 display similar IgE-binding capacity, suggesting that ß-1,3-glucanases represent an heterogeneous family that could display intrinsic allergenic capacity. Specific cDNA encoding Fra e 9 was cloned and sequenced. The full-length cDNA encoded a polypeptide chain of 461 amino acids containing a signal peptide of 29 residues, leading to a mature protein of 47760.2 Da and a pI of 8.66. An N-terminal catalytic domain and a C-terminal carbohydrate-binding module are the components of this enzyme. Despite the phylogenetic proximity to the olive pollen ß-1,3-glucanase, Ole e 9, there is only a 39% identity between both sequences. The N- and C-terminal domains have been produced as independent recombinant proteins in Escherichia coli and Pichia pastoris, respectively. Although a low or null enzymatic activity has been associated to long ß-1,3-glucanases, the recombinant N-terminal domain has 200-fold higher hydrolytic activity on laminarin than reported for Ole e 9. The C-terminal domain of Fra e 9, a cysteine-rich compact structure, is able to bind laminarin. Both molecules retain comparable IgE-binding capacity when assayed with allergic sera. In summary, the structural and functional comparison between these two closely phylogenetic related enzymes provides novel insights into the complexity of ß-1,3-glucanases, representing a heterogeneous protein family with intrinsic allergenic capacity.

Sublethal heavy metal stress stimulates innate immunity in tomato.

Effect of sublethal heavy metal stress as plant biotic elicitor for triggering innate immunity in tomato plant was investigated. Copper in in vivo condition induced accumulation of defense enzymes like peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), and ß-1,3 glucanase along with higher accumulation of total phenol, antioxidative enzymes (catalase and ascorbate peroxidase), and total chlorophyll content. Furthermore, the treatment also induced nitric oxide (NO) production which was confirmed by realtime visualization of NO burst using a fluorescent probe 4,5-diaminofluorescein diacetate (DAF-2DA) and spectrophotometric analysis. The result suggested that the sublethal dose of heavy metal can induce an array of plant defense responses that lead to the improvement of innate immunity in plants.

Cloning and functional characterization of ß-1, 3-glucanase gene from Podophyllum hexandrum - a high altitude Himalayan plant.

Podophyllum hexandrum is a high-altitude medicinal plant exploited for its etoposides which are potential anticancer compounds. ß-1, 3-glucanase cDNA was cloned from the germinating seeds of Podophyllum (Ph-glucanase). Glucanases belong to pathogenesis related glycohydralase family of proteins, which also play an important role in endosperm weakening and testa rupture during seed germination. Analysis of cloned nucleotide sequence revealed Ph-glucanase with an open reading frame of 852bp encoding a protein of 283 amino acids with a molecular mass of 31kDa and pI of 4.39. In-silico structure prediction of Ph-glucanase showed homology with that of Hevea brasiliensis (3em5B). Structural stability and enhanced catalytic efficiency in harsh climatic conditions possibly due to the presence of glycosyl hydrolase motif (LGIVISESGWPSAG) and a connecting loop towards inner side and well exposed carbohydrate metabolism domain-COG5309, can readily hydrolyse cell wall sugar moieties. Seeds from the transgenic Arabidopsis plants over-expressing Ph-glucanase showed better germination performance against a wide range of temperatures and abscisic acid (ABA) stress. This can be attributed to the accumulation of Ph-glucanase at both transcript and protein levels during the seed germination in transgenic Arabidopsis. Results confirm that the cloned novel seed specific glucanase from a cold desert plant Podophyllum could be used for the manipulation of different plant species seeds against various harsh conditions.

Are cyclic lipopeptides produced by Bacillus amyloliquefaciens S13-3 responsible for the plant defence response in strawberry against Colletotrichum gloeosporioides?

UNLABELLED: The antagonistic strain Bacillus amyloliquefaciens strain S13-3 decreased the severity of strawberry anthracnose caused by Colletotrichum gloeosporioides. The foliar application of S13-3 triggered the expression of pathogenesis-related proteins, chitinase and ß-1,3-glucanase, in strawberry leaves. We identified lipopeptide antibiotics, including iturin A, fengycin, mixirin, pumilacidin and surfactin, produced and secreted by S13-3. Iturin A and surfactin elicited the gene expression of the pathogenesis-related proteins in strawberry leaves, suggesting that antagonistic strain S13-3 confers resistance to strawberry leaves through the production of lipopeptide antibiotics. In fact, iturin A and surfactin triggered induced systemic resistance on strawberry plants, resulting in the reduction of the severity of anthracnose disease caused by Colletotrichum gloeosporioides. The bifunctional activity of S13-3, which consists of the antagonistic effect and the induction of plant defence response by the antibiotics produced by it, may make S13-3 an innovative biological control agent against phytopathogens in strawberry. SIGNIFICANCE AND IMPACT OF THE STUDY: This study tries to determine whether biocontrol of phytopathogens by Bacillus amyloliquefaciens in strawberry can be connected to induced plant resistance. The results suggested that the antagonistic strain B. amyloliquefaciens S13-3 confers resistance to strawberry through the production of lipopeptide antibiotics.

An aboveground pathogen inhibits belowground rhizobia and arbuscular mycorrhizal fungi in Phaseolus vulgaris.

BACKGROUND: Induced aboveground plant defenses against pathogens can have negative effects on belowground microbial symbionts. While a considerable number of studies have utilized chemical elicitors to experimentally induce such defenses, there is surprisingly little evidence that actual aboveground pathogens affect root-associated microbes. We report here that an aboveground fungal pathogen of common bean (Phaseolus vulgaris) induces a defense response that inhibits both the belowground formation of root nodules elicited by rhizobia and the colonization with arbuscular mycorrhizal fungi (AMF). RESULTS: Foliage of plants inoculated with either rhizobia or AMF was treated with both live Colletotrichum gloeosporioides-a generalist hemibiotrophic plant pathogen-and C. gloeosporioides fragments. Polyphenol oxidase (PPO), chitinase and ß-1,3-glucanase activity in leaves and roots, as well as the number of rhizobia nodules and the extent of AMF colonization, were measured after pathogen treatments. Both the live pathogen and pathogen fragments significantly increased PPO, chitinase and ß-1,3-glucanase activity in the leaves, but only PPO activity was increased in roots. The number of rhizobia nodules and the extent of AMF colonization was significantly reduced in treatment plants when compared to controls. CONCLUSION: We demonstrate that aboveground fungal pathogens can affect belowground mutualism with two very different types of microbial symbionts-rhizobia and AMF. Our results suggest that systemically induced PPO activity is functionally involved in this above-belowground interaction. We predict that the top-down effects we show here can drastically impact plant performance in soils with limited nutrients and water; abiotic stress conditions usually mitigated by microbial belowground mutualists.

Effect of antagonistic yeast XL-1 on resistance-associated enzyme activities in postharvest cantaloupe.

The effect of the antagonistic yeast XL-1 on resistance-associated enzyme activities in postharvest cantaloupe was studied by inoculating the antagonistic yeast XL-1. Cantaloupes were sterilized, dried in air, and soaked in antagonistic yeast treatment liquid for 30 s. After drying in air, the cantaloupe was stored at room temperature (2°-5°C). The activities of resistance-associated enzymes in cantaloupe like polyphenol oxidase, ß-1,3-glucanase, peroxidase, and superoxide dismutase were measured every 7 days. Our results indicated that the antagonistic yeast XL-1 significantly improved the activity of ß-1,3-glucanase and chitinase to promote the disease resistance of postharvest cantaloupe.