Phylogenetic Analyses Reveal Monophyletic Origin of the Ergot Alkaloid Gene dmaW in Fungi

Ergot alkaloids are indole-derived mycotoxins that are important in agriculture and medicine. Ergot alkaloids are produced by a few representatives of two distantly related fungal lineages, the Clavicipitaceae and the Trichocomaceae. Comparison of the ergot alkaloid gene clusters from these two lineages revealed differences in the relative positions and orientations of several genes. The question arose: is ergot alkaloid biosynthetic capability from a common origin? We used a molecular phylogenetic approach to gain insights into the evolution of ergot alkaloid biosynthesis. The 4-γ,γ-dimethylallyltryptophan synthase gene, dmaW, encodes the first step in the pathway. Amino acid sequences deduced from dmaW and homologs were submitted to phylogenetic analysis, and the results indicated that dmaW of Aspergillus fumigatus (mitosporic Trichocomaceae) has the same origin as corresponding genes from clavicipitaceous fungi. Relationships of authentic dmaW genes suggest that they originated from multiple gene duplications with subsequent losses of original or duplicate versions in some lineages

Phylogenetic Analyses Reveal Monophyletic Origin of the Ergot Alkaloid Gene \u3cem\u3edmaW\u3c/em\u3e in Fungi

Ergot alkaloids are indole-derived mycotoxins that are important in agriculture and medicine. Ergot alkaloids are produced by a few representatives of two distantly related fungal lineages, the Clavicipitaceae and the Trichocomaceae. Comparison of the ergot alkaloid gene clusters from these two lineages revealed differences in the relative positions and orientations of several genes. The question arose: is ergot alkaloid biosynthetic capability from a common origin? We used a molecular phylogenetic approach to gain insights into the evolution of ergot alkaloid biosynthesis. The 4-γ,γ-dimethylallyltryptophan synthase gene, dmaW, encodes the first step in the pathway. Amino acid sequences deduced from dmaW and homologs were submitted to phylogenetic analysis, and the results indicated that dmaW of Aspergillus fumigatus (mitosporic Trichocomaceae) has the same origin as corresponding genes from clavicipitaceous fungi. Relationships of authentic dmaW genes suggest that they originated from multiple gene duplications with subsequent losses of original or duplicate versions in some lineages

Magnetic dichroism in the angular distribution of Fe 2p and 3p photoelectrons: Empirical support to Zeeman-like analysis

We report on the measurements and analysis of Fe 2p magnetic dichroism in the angular distribution of the photoelectrons from remanently magnetized Fe(100) surfaces with unpolarized, monochromatized, x rays of 1486 eV energy, and with linearly polarized synchrotron radiation of 800 eV energy. The analysis of the dichroic photoemission intensity in the two experiments verifies the applicability of the atomic photoionization model which provides a consistent understanding of the differences between photoemission experiments with unpolarized and linearly polarized radiation. A comparison of the Fe 2p and Fe 3p dichroism spectra allows us to discuss, on an empirical basis, the validity of a Zeeman-like interpretation of Fe 3p hole sublevels connected to the observed magnetic dichroism in photoemission

Partial Reconstruction of the Ergot Alkaloid Pathway by Heterologous Gene Expression in Aspergillus nidulans

Ergot alkaloids are pharmaceutically and agriculturally important secondary metabolites produced by several species of fungi. Ergot alkaloid pathways vary among different fungal lineages, but the pathway intermediate chanoclavine-I is evolutionarily conserved among ergot alkaloid producers. At least four genes, dmaW, easF, easE, and easC, are necessary for pathway steps prior to chanoclavine-I; however, the sufficiency of these genes for chanoclavine-I synthesis has not been established. A fragment of genomic DNA containing dmaW, easF, easE, and easC was amplified from the human-pathogenic, ergot alkaloid-producing fungus Aspergillus fumigatus and transformed into Aspergillus nidulans, a model fungus that does not contain any of the ergot alkaloid synthesis genes. HPLC and LC-MS analyses demonstrated that transformed A. nidulans strains produced chanoclavine-I and an earlier pathway intermediate. Aspergillus nidulans transformants containing dmaW, easF, and either easE or easC did not produce chanoclavine-I but did produce an early pathway intermediate and, in the case of the easC transformant, an additional ergot alkaloid-like compound. We conclude that dmaW, easF, easE, and easC are sufficient for the synthesis of chanoclavine-I in A. nidulans and expressing ergot alkaloid pathway genes in A. nidulans provides a novel approach to understanding the early steps in ergot alkaloid synthesis

Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review Letter

Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review Letter

Effect of S segregation on the surface magnetism of Fe(100)

Bulk impurities of the ferromagnetic transition metals segregate at the surface at moderate temperature and severely modify the surface magnetic properties. S segregation on Fe(100) produces a stable c(2x2) reconstruction at 600 degrees C. We have measured the change of the magnetic properties of Fe(100) due to the formation of the c(2x2)S surface by measuring the exchange coupling along a path perpendicular to the surface via the spin-wave stiffness and the relative change of the iron surface magnetic moment by photoemission magnetic dichroism experiments and spin-polarization measurements of the secondary yield. A stronger coupling between the c(2x2)S surface and the bulk then for the clean Fe(100) free surface is found. Changes of the Fe 3p core hole magnetic splitting show that the surface magnetic moment of Fe is reduced by up to 20% upon S segregation with respect to the clean surface. Strong magnetic dichroism of the electron states just below the Fermi level indicates a filling of the surface minority spin band in the c(2x2)S/Fe(100) surface relative to the clean Fe(100) surface

Local magnetic moment coupling of Gd on Fe(100) studied by magnetic dichroism in angular-dependent photoemission

We measured the magnetic linear dichroism in the angular distribution (MLDAD) of photoemission of thin Gd layers on Fe(100). At low photon energies large MLDAD asymmetries, up to 40%, in the (Formula presented) photoemission were observed. The line shape and the photon-energy dependence of the measured MLDAD are in good agreement with theoretical results. Analysis of the (Formula presented) and (Formula presented) magnetic signals indicates an antiferromagnetic coupling between Gd and Fe, confirming previous findings. We also demonstrate that the MLDAD plus-minus feature is governed by the orbital magnetic moment of the core hole state

Surface vs. bulk magnetic moments from photoemission dichroism

The value of the surface spin magnetic moment of Fe(100) is obtained by measuring the energy spread of the photoemission dichroism spectra of Fe3p core levels from bulk and surface. The bulk and surface signals have been resolved exploiting the photoemission diffraction effects in a linear magnetic dichroism of the angular distribution (LMDAD) experiment with soft X-rays. The LMDAD lineshape and energy width of the bulk contribution has been independently obtained from angular and from photon energy dependent experiments: it provides a gauge for determining the magnetic moment of the surface Fe3p atoms in the hypothesis of a linear dependance between energy width of dichroism and local spin magnetic moment

Proximity-induced ferromagnetism and chemical reactivity in few-layer VSe2 heterostructures

Among transition-metal dichalcogenides, mono and few-layers thick VSe2 has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of Fe/VSe2 heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk VSe2 do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the Fe/VSe2 interface and its relation with interfacial magnetic coupling