Effects of Atmospheric CO2 Level on the Metabolic Response of Resistant and Susceptible Wheat to Fusarium graminearum Infection.

Rising atmospheric CO2 concentrations and associated climate changes are thought to have contributed to the steady increase of Fusarium head blight (FHB) on wheat. However, our understanding of precisely how elevated CO2 influences the defense response of wheat against Fusarium graminearum remains limited. In this study, we evaluated the metabolic profiles of susceptible (Norm) and moderately resistant (Alsen) spring wheat in response to whole-head inoculation with two deoxynivalenol (DON)-producing F. graminearum isolates (DON+), isolates 9F1 and Gz3639, and a DON-deficient (DON−) isolate (Gzt40) at ambient (400 ppm) and elevated (800 ppm) CO2 concentrations. The effects of elevated CO2 were dependent on both the Fusarium strain and the wheat variety, but metabolic differences in the host can explain the observed changes in F. graminearum biomass and DON accumulation. The complexity of abiotic and biotic stress interactions makes it difficult to determine if the observed metabolic changes in wheat are a result of CO2-induced changes in the host, the pathogen, or a combination of both. However, the effects of elevated CO2 were not dependent on DON production. Finally, we identified several metabolic biomarkers for wheat that can reliably predict FHB resistance or susceptibility, even as atmospheric CO2 levels rise

Structural characterization of novel extracellular liamocins (mannitol oils) produced by Aureobasidium pullulans strain NRRL 50380

Aureobasidium pullulans is a common, ubiquitous fungus, which is used industrially to produce the polysaccharide pullulan. We have previously shown that A. pullulans produces various heavier-than-water oils, first named here as liamocins, that accumulate in fermentations. Here we report the structural characterization of four liamocins, A1, A2, B1, and B2, produced by A. pullulans strain NRRL 50380 using a combination of MALDI-TOF/MS, quadrupole-TOF/MS, isotopic labeling, NMR, GC/MS, and classical carbohydrate analysis. The data showed that the liamocins are composed of a single mannitol headgroup partially O-acylated with three (for liamocin A1 and A2) or four (for liamocin B1 and B2) 3,5-dihydroxydecanoic ester groups. Liamocins A1 and B1 are non-acetylated, whereas A2 and B2 each contain a single 3′-O-acetyl group. Each of these compounds is characterized by pseudomolecular [M+Na]+ ions in the MALDI-TOF/MS spectra at m/z 763.22, 949.35, 805.22, and 991.37, respectively. The 186 Da mass difference between A-type and B-type liamocins corresponds to one O-linked 3,5-dihydroxydecanoate group. HMBC NMR showed that one 3,5-dihydroxydecanoate carbonyl group is ester linked to a primary hydroxyl on the mannitol. Other long range 13C–1H couplings across 1,5-ester bridges showed that the 3,5-dihydroxydecanoate groups form 1–5-linked polyester chains, similar in structure to the antibiotic substance exophilin A. Moreover, the MS analysis identified several non-conjugated poly-3,5-dihydroxydecanoate esters as minor components that are tentatively assigned as exophilins A1, A2, B1, and B2. The liamocins, and three of the exophilins, are new, previously unreported structures

Thiazolidine Peracetates: Carbohydrate Derivatives that Readily Assign <i>cis‑</i>,<i>trans</i>-2,3-Monosaccharides by Gas Chromatography–Mass Spectrometry Analysis

A novel group of carbohydrate derivatives is described that uniquely assign <i>cis</i>/<i>trans</i>-2,3-aldose stereoisomers at low nanomolar concentrations. Aldopentoses, aldohexoses, or component aldoses from hydrolysis of polysaccharides or oligosaccharides react with cysteamine in pyridine to give quantitative formation of thiazolidines, which are subsequently peracetylated in a one-pot reaction. The nonpolar thiazolidines peracetate (TPA) derivatives are analyzed by gas chromatography and electron impact mass spectrometry (GC/EI-MS), each aldose giving rise to two TPA geometric isomers. The quantitative ratio of these diastereomers is dependent upon whether the parent monosaccharide is <i>cis</i>-2,3-(Rib, Lyx, Man, All, Gul, and Tal), or <i>trans</i>-2,3-aldose (Xyl, Ara, Glc, Gal, Ido, and Alt). TPAs generate observed EI-MS fragment ions characteristic of C1–C2 and C3–C4 bond cleavage of the parent sugars. This has been used to estimate the extent of metabolic labeling of microbial cell-wall carbohydrates, especially into the defining anomeric carbons and during aldolase / ketolase -catalyzed rearrangements

Frost Grape Polysaccharide (FGP), an Emulsion-Forming Arabinogalactan Gum from the Stems of Native North American Grape Species Vitis riparia Michx.

A new arabinogalactan is described that is produced in large quantity from the cut stems of the North American grape species Vitis riparia (Frost grape). The sugar composition consists of l-arabinofuranose (l-Ara<i>f</i>, 55.2%) and d-galactopyranose (d-Gal<i>p</i> 30.1%), with smaller components of d-xylose (11.2%), d-mannose (3.5%), and glucuronic acid (GlcA, ∼2%), the latter linked via a galactosyl residue. Permethylation identified 3-linked Gal<i>p</i> residues, some substituted at the 2-position with Gal<i>p</i> or Man<i>p</i>, terminal Ara<i>f</i> and Xyl<i>p</i>, and an internal 3-substituted Ara<i>f</i>. NMR (HSQC, TOCSY, HMBC, DOSY) identified βGal<i>p</i> and three αAra<i>f</i> spin systems, in an Ara<i>f</i>-α1,3-Ara<i>f</i>-α1,2-Ara<i>f</i>-α1,2-Gal<i>p</i> structural motif. Diffusion-ordered NMR showed that the FGP has a molecular weight of 1–10 MDa. Unlike gum arabic, the FGP does not contain a hydroxyproline-rich protein (HPRP). FGP forms stable gels at >15% w/v and at 1–12% solutions are viscous and are excellent emulsifiers of flavoring oils (grapefruit, clove, and lemongrass), giving stable emulsions for ≥72 h. Lower concentrations (0.1% w/v) were less viscous, yet still gave stable grapefruit oil/water emulsions. Hence, FGP is a β1,3-linked arabinogalactan with potential as a gum arabic replacement in the food and beverage industries

Stereochemistry of Furfural Reduction by a Saccharomyces cerevisiae Aldehyde Reductase That Contributes to In Situ Furfural Detoxification▿

Ari1p from Saccharomyces cerevisiae, recently identified as an intermediate-subclass short-chain dehydrogenase/reductase, contributes in situ to the detoxification of furfural. Furfural inhibits efficient ethanol production by yeast, particularly when the carbon source is acid-treated lignocellulose, which contains furfural at a relatively high concentration. NADPH is Ari1p's best known hydride donor. Here we report the stereochemistry of the hydride transfer step, determined by using (4R)-[4-2H]NADPD and (4S)-[4-2H]NADPD and unlabeled furfural in Ari1p-catalyzed reactions and following the deuterium atom into products 2-furanmethanol or NADP+. Analysis of the products demonstrates unambiguously that Ari1p directs hydride transfer from the si face of NADPH to the re face of furfural. The singular orientation of substrates enables construction of a model of the Michaelis complex in the Ari1p active site. The model reveals hydrophobic residues near the furfural binding site that, upon mutation, may increase specificity for furfural and enhance enzyme performance. Using (4S)-[4-2H]NADPD and NADPH as substrates, primary deuterium kinetic isotope effects of 2.2 and 2.5 were determined for the steady-state parameters kcatNADPH and kcat/KmNADPH, respectively, indicating that hydride transfer is partially rate limiting to catalysis

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and β‑Isothapsenol

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and β-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and β-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, ¹H and ¹³C chemical shifts, and interconversion pathways

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and β‑Isothapsenol

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and β-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and β-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, ¹H and ¹³C chemical shifts, and interconversion pathways

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and β‑Isothapsenol

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and β-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and β-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, ¹H and ¹³C chemical shifts, and interconversion pathways

Discovery of the Aggregation Pheromone of the Brown Marmorated Stink Bug (<i>Halyomorpha halys</i>) through the Creation of Stereoisomeric Libraries of 1‑Bisabolen-3-ols

We describe a novel and straightforward route to all stereoisomers of 1,10-bisaboladien-3-ol and 10,11-epoxy-1-bisabolen-3-ol via the rhodium-catalyzed asymmetric addition of trimethylaluminum to diastereomeric mixtures of cyclohex-2-enones <b>1</b> and <b>2</b>. The detailed stereoisomeric structures of many natural sesquiterpenes with the bisabolane skeleton were previously unknown because of the absence of stereoselective syntheses of individual stereoisomers. Several of the bisabolenols are pheromones of economically important pentatomid bug species. Single-crystal X-ray crystallography of underivatized triol <b>13</b> provided unequivocal proof of the relative and absolute configurations. Two of the epoxides, (3<i>S</i>,6<i>S</i>,7<i>R</i>,10<i>S</i>)-10,11-epoxy-1-bisabolen-3-ol (<b>3</b>) and (3<i>R</i>,6<i>S</i>,7<i>R</i>,10<i>S</i>)-10,11-epoxy-1-bisabolen-3-ol (<b>4</b>), were identified as the main components of a male-produced aggregation pheromone of the brown marmorated stink bug, <i>Halyomorpha halys</i>, using GC analyses on enantioselective columns. Both compounds attracted female, male, and nymphal <i>H. halys</i> in field trials. Moreover, mixtures of stereoisomers containing epoxides <b>3</b> and <b>4</b> were also attractive to <i>H</i>. <i>halys</i>, signifying that the presence of additional stereoisomers did not hinder attraction of <i>H. halys</i> and relatively inexpensive mixtures can be used in monitoring, as well as control strategies. <i>H. halys</i> is a polyphagous invasive species in the U.S. and Europe that causes severe injury to fruit, vegetables, and field crops and is also a serious nuisance pest