Showing papers on "Phytoalexin published in 2007"

Resistance to Botrytis cinerea Induced in Arabidopsis by Elicitors Is Independent of Salicylic Acid, Ethylene, or Jasmonate Signaling But Requires PHYTOALEXIN DEFICIENT3

Abstract: Oligogalacturonides (OGs) released from plant cell walls by pathogen polygalacturonases induce a variety of host defense responses. Here we show that in Arabidopsis (Arabidopsis thaliana), OGs increase resistance to the necrotrophic fungal pathogen Botrytis cinerea independently of jasmonate (JA)-, salicylic acid (SA)-, and ethylene (ET)-mediated signaling. Microarray analysis showed that about 50% of the genes regulated by OGs, including genes encoding enzymes involved in secondary metabolism, show a similar change of expression during B. cinerea infection. In particular, expression of PHYTOALEXIN DEFICIENT3 (PAD3) is strongly up-regulated by both OGs and infection independently of SA, JA, and ET. OG treatments do not enhance resistance to B. cinerea in the pad3 mutant or in underinducer after pathogen and stress1, a mutant with severely impaired PAD3 expression in response to OGs. Similarly to OGs, the bacterial flagellin peptide elicitor flg22 also enhanced resistance to B. cinerea in a PAD3-dependent manner, independently of SA, JA, and ET. This work suggests, therefore, that elicitors released from the cell wall during pathogen infection contribute to basal resistance against fungal pathogens through a signaling pathway also activated by pathogen-associated molecular pattern molecules.

Different mechanisms for phytoalexin induction by pathogen and wound signals in Medicago truncatula

Abstract: Cell suspensions of the model legume Medicago truncatula accumulated the isoflavonoid phytoalexin medicarpin in response to yeast elicitor or methyl jasmonate (MJ), accompanied by decreased levels of isoflavone glycosides in MJ-treated cells. DNA microarray analysis revealed rapid, massive induction of early (iso)flavonoid pathway gene transcripts in response to yeast elicitor, but not MJ, and differential induction by the two elicitors of sets of genes encoding transcription factors, ABC transporters, and β-glucosidases. In contrast, both elicitors induced genes encoding enzymes for conversion of the isoflavone formononetin to medicarpin. Four MJ-induced β-glucosidases were expressed as recombinant enzymes in yeast, and three were active with isoflavone glucosides. The most highly induced β-glucosidase was nuclear localized and preferred flavones to isoflavones. The results indicate that the genetic and biochemical mechanisms underlying accumulation of medicarpin differ depending on the nature of the stimulus and suggest a role for MJ as a signal for rapid hydrolysis of preformed, conjugated intermediates for antimicrobial biosynthesis during wound responses.

Resveratrol in human hepatoma HepG2 cells: metabolism and inducibility of detoxifying enzymes.

Abstract: trans-Resveratrol is a polyphenol present in several plant species. Its chemopreventive properties against several diseases have been largely documented. To validate a model for the study of the factors influencing its biological fate at the hepatic level, the metabolism and the efflux of resveratrol were studied in the human hepatoblastoma cell line, HepG2. Comparative high-performance liquid chromatography analysis of cell culture media before and after deconjugation showed that resveratrol was rapidly conjugated; at the concentration of 10 microM, it was entirely metabolized at 8 h of incubation. Two main resveratrol metabolites, monosulfate and disulfate, were identified by atmospheric pressure chemical ionization-mass spectrometry, thanks to their quasi-molecular ion and their characteristic fragmentation. To correlate with the auto-induction of resveratrol metabolism evidenced in HepG2 cells after a pretreatment for 48 h with 10 microM resveratrol, the inducibility of phase II enzymes by resveratrol was studied by real-time quantitative reverse transcriptase-polymerase chain reaction and flow cytometry. Observed, in particular, were an increase in mRNA expression levels of three metabolizing enzymes, two isoforms of UDP-glucuronosyltransferases, UGT1A1 and UGT2B7 (5-fold increased), and a sulfotransferase, ST1E1, in cells pretreated for 24 h with 10 microM resveratrol. These results were correlated with an increase in protein expression, especially after 48 h of treatment. On the other hand, the intracellular resveratrol retention in cells treated with MK571 (3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid), a multidrug resistance-associated protein inhibitor, strongly suggests the involvement of this ABC transporter family in the efflux of resveratrol conjugates from human liver.

Modification of phenolic metabolism in soybean hairy roots through down regulation of chalcone synthase or isoflavone synthase

Abstract: Soybean hairy roots, transformed with the soybean chalcone synthase (CHS6) or isoflavone synthase (IFS2) genes, with dramatically decreased capacity to synthesize isoflavones were produced to determine what effects these changes would have on susceptibility to a fungal pathogen. The isoflavone and coumestrol concentrations were decreased by about 90% in most lines apparently due to gene silencing. The IFS2 transformed lines had very low IFS enzyme activity in microsomal fractions as measured by the conversion of naringenin to genistein. The CHS6 lines with decreased isoflavone concentrations had 5 to 20-fold lower CHS enzyme activities than the appropriate controls. Both IFS2 and CHS transformed lines accumulated higher concentrations of both soluble and cell wall bound phenolic acids compared to controls with higher levels found in the CHS6 lines indicating alterations in the lignin biosynthetic branch of the pathway. Induction of the soybean phytoalexin glyceollin, of which the precursor is the isoflavone daidzein, by the fungal pathogen Fusarium solani f. sp. glycines (FSG) that causes soybean sudden death syndrome (SDS) showed that the low isoflavone transformed lines did not accumulate glyceollin while the control lines did. The (iso)liquritigenin content increased upon FSG induction in the IFS2 transformed roots indicating that the pathway reactions before this point can control isoflavonoid synthesis. The lowest fungal growth rate on hairy roots was found on the FSG partially resistant control roots followed by the SDS sensitive control roots and the low isoflavone transformants. The results indicate the importance of phytoalexin synthesis in root resistance to the pathogen.

Constitutive expression of a grapevine stilbene synthase gene in transgenic hop (Humulus lupulus L.) yields resveratrol and its derivatives in substantial quantities.

Abstract: Resveratrol, a well-known phytoalexin and antioxidant, is produced by the action of stilbene synthase (STS) in some plant species. Hop (Humulus lupulus L.) plants of the Tettnang variety were transformed with a gene encoding for STS from grapevine. Under the control of the constitutive 35S cauliflower mosaic virus promoter, expression of the transgene resulted in accumulation of resveratrol and high levels of its glycosylated derivatives in leaves and inflorescences. Piceid, the predominant derivative, reached a concentration of up to 560 microg/g of fresh weight (f.w.) in hop cones, whereas no stilbenes were detected in nontransformed controls (wild-type). In transgenic plants the amounts of alpha- and beta-acids, naringenin chalcone, and prenylated flavonoids did not change significantly when compared with nontransformed plants. Transgenic plants showed normal morphology and flower development as did the nontransformed controls. The results clearly show that in hop constitutive expression of sts interferes neither with plant development nor with the biosynthesis of secondary metabolites relevant for the brewing industry. Since resveratrol is a well-known phytoalexin and antioxidant, sts transgenic hop plants could display enhanced pathogen resistance against microbial pathogens, exhibit new beneficial properties for health, and open new venues for metabolic engineering.

Interrelationship of phytoalexin production and disease resistance in selected peanut genotypes.

Abstract: In peanuts, a mechanism of resistance to fungal infection is reportedly due to the synthesis of stilbene phytoalexins, which are antibiotic, low molecular weight metabolites. The phytoalexin-associated response of different peanut genotypes to exogenous invasion in the field has not been investigated and may be useful for breeding resistant peanut cultivars. Five peanut genotypes, Georgia Green, Tifton 8, C-99R, GK-7 High Oleic, and MARC I, which differ in resistance to major peanut diseases, were investigated for their ability to produce phytoalexins under field conditions in South Georgia in 2001 and 2002. Five known peanut phytoalexins, trans-resveratrol, trans-arachidin-1, trans-arachidin-2, trans-arachidin-3, and trans-3‘-isopentadienyl-3,5,4‘-trihydroxystilbene, were quantitated. The phytoalexins were measured in peanuts of different pod maturity (yellow, orange, brown, and black) with or without insect pod damage (externally scarified or penetrated). Kernels from insect-damaged pods of C-99R and Ti...

The Phytoalexins from Brassicaceae: Structure, Biological Activity, Synthesis and Biosynthesis

Abstract: The structures, biological activity, synthesis and biosynthesis of crucifer phytoalexins are reviewed.

Bioassays on the Activity of Resveratrol, Pterostilbene and Phosphorous Acid towards Fungi Associated with Esca of Grapevine

Abstract: An examination was carried out under laboratory conditions to determine whether resveratrol, pterostilbene and mixtures of each stilbene with phosphorous acid had an inhibitory activity against some fungi involved in esca: Phaeoacremonium aleophilum, Phaeomoniella chlamydospora, Libertella blepharis (anamorph of Eutypa lata), Fomitiporia punctata and Stereum hirsutum. An inhibition of mycelial growth by resveratrol was not found but there was a clear correlation between pterostilbene concentration and reduction of radial growth confirming the antifungal activity of this phytoalexin. Although phosphorous acid proved to be generally ineffective, an increase of antifungal activity of stilbenes in the mixtures was observed with all fungi except F. punctata. The possible relation between fungal phenol oxidase activity and inhibition by mixtures of stilbenes and phosphorous acid was discussed.

Efficient synthesis of brussalexin A, a remarkable phytoalexin from Brussels sprouts

Abstract: The synthesis of brussalexin A, the first phytoalexin containing an allyl thiolcarbamate group, and its selective inhibitory activity against fungal plant pathogens is described.

The effect of acetylation of capsidiol phytoalexin on fungitoxic activity

Abstract: Natural products have become increasingly sought after as ecologically safer alternatives to herbicides and pesticides, as well as a source of new medicines. However, the biological activity of these compounds is often affected by their stereochemistry, lipophilicity and other factors. Slight modifications can alter the bioactivity either positively or negatively. Capsidiol is the principal phytoalexin of Capsicum annuum. As part of a structure – activity investigation of this phytoalexin, acetyl-capsidiol was synthesized and tested in vitro for antifungal activity. Acetyl capsidiol was found to have a low inhibition effect on Aspergillus niger mycelial growth and spore germination. The results suggest that OH groups are indispensable for activity.

Phytoalexins from crucifers : probing detoxification pathways in Sclerotinia sclerotiorum

Abstract: This thesis investigates two aspects of phytoalexin metabolism by the phytopathogenic fungus Sclerotinia sclerotiorum (Lib) de Bary: (i) determination of detoxification pathways of structurally different molecules; (ii) design and synthesis of potential inhibitors of enzyme(s) involved in detoxification steps. First, the transformations of important cruciferous phytoalexins by the economically important stem rot fungus, S. sclerotiorum, were investigated. During these studies a number of new metabolic products were isolated, their chemical structures were determined using spectroscopic techniques, and further confirmed by synthesis. The metabolic products did not show detectable antifungal activity against S. sclerotiorum which indicated that these metabolic transformations were detoxification processes. Overall, the results of these transformations suggested that S. sclerotiorum produces various enzymes that can detoxify cruciferous phytoalexins via different pathways. While the detoxifications of strongly and moderately antifungal phytoalexins such as brassilexin, sinalexin, and 1-methoxybrassinin were fast and led to glucosylated products, the transformations of the weakly antifungal phytoalexins brassicanal A, spirobrassinin and 1-methoxyspirobrassinin were very slow and yielded nonglucosylated compounds. Next, the design of potentially selective inhibitors of the brassinin detoxification enzyme, BGT, was sought. Two sets of potential inhibitors of BGT were designed: (i) a group was based on the structure of brassinin, where the indole ring of brassinin was replaced with benzofuran, thianaphthene, 7-azaindole and pyrazolo[1,5a]pyridine and/or the position of side chain was changed from C-3 to C-2; and (ii) another group based on the structure of camalexin where the thiazole ring of camalexin was replaced with a phenyl group. The syntheses and chemical characterization of