A pathogen effector FOLD diversified in symbiotic fungi.

Pathogenic fungi use secreted effector proteins to suppress immunity and support their infection, but effectors have also been reported from fungi that engage in nutritional symbioses with plants. Sequence-based effector comparisons between pathogens and symbiotic arbuscular mycorrhizal (AM) fungi are hampered by the huge diversity of effector sequences even within closely related microbes. To find sequence-divergent but structurally similar effectors shared between symbiotic and pathogenic fungi, we compared secreted protein structure models of the AM fungus Rhizophagus irregularis to known pathogen effectors. We identified proteins with structural similarity to known Fusarium oxysporum f. sp. lycopersici dual domain (FOLD) effectors, which occur in low numbers in several fungal pathogens. Contrastingly, FOLD genes from AM fungi (MycFOLDs) are found in enlarged and diversified gene families with higher levels of positive selection in their C-terminal domains. Our structure model comparison suggests that MycFOLDs are similar to carbohydrate-binding motifs. Different MycFOLD genes are expressed during colonisation of different hosts and MycFOLD-17 transcripts accumulate in plant intracellular arbuscules. The exclusive presence of MycFOLDs across unrelated plant-colonising fungi, their inducible expression, lineage-specific sequence diversification and transcripts in arbuscules suggest that FOLD proteins act as effectors during plant colonisation of symbiotic and pathogenic fungi.This work was funded by the Gatsby Charitable Foundation (GAT3395/GLD), the Royal Society (UF160413) and by an ERC starting grant (637537)

A pathogen effector <scp>FOLD</scp> diversified in symbiotic fungi

Summary: Pathogenic fungi use secreted effector proteins to suppress immunity and support their infection, but effectors have also been reported from fungi that engage in nutritional symbioses with plants. Sequence‐based effector comparisons between pathogens and symbiotic arbuscular mycorrhizal (AM) fungi are hampered by the huge diversity of effector sequences even within closely related microbes. To find sequence‐divergent but structurally similar effectors shared between symbiotic and pathogenic fungi, we compared secreted protein structure models of the AM fungus Rhizophagus irregularis to known pathogen effectors. We identified proteins with structural similarity to known Fusarium oxysporum f. sp. lycopersici dual domain (FOLD) effectors, which occur in low numbers in several fungal pathogens. Contrastingly, FOLD genes from AM fungi (MycFOLDs) are found in enlarged and diversified gene families with higher levels of positive selection in their C‐terminal domains. Our structure model comparison suggests that MycFOLDs are similar to carbohydrate‐binding motifs. Different MycFOLD genes are expressed during colonisation of different hosts and MycFOLD‐17 transcripts accumulate in plant intracellular arbuscules. The exclusive presence of MycFOLDs across unrelated plant‐colonising fungi, their inducible expression, lineage‐specific sequence diversification and transcripts in arbuscules suggest that FOLD proteins act as effectors during plant colonisation of symbiotic and pathogenic fungi

Advanced magnetic anisotropy determination through isothermal remanent magnetization of nanoparticles

International audienceWe propose a theoretical framework enabling the simulation of isothermal remanence magnetization (IRM) curves, based on the Stoner-Wohlfarth model combined with the Néel macrospin relaxation time description. We show how low temperature IRM curves, which have many advantages compared to hysteresis loops, can be efficiently computed for realistic assemblies of magnetic particles with both a size and anisotropy constant distribution, and a biaxial anisotropy. The IRM curves, which probe the irreversible switching provoked by an applied field, are shown to be complementary to other usual measurements (in particular low-field susceptibility curves where a thermal switching is involved). As an application, the experimental IRM curve of Co clusters embedded in a carbon matrix is analyzed. We demonstrate how powerful such an analysis can be, which in the present case allows us to put into evidence an anisotropy constant dispersion among the Co nanoparticles

Moiré induced organization of size-selected Pt clusters soft landed on epitaxial graphene

International audienceTwo-dimensional hexagonal arrays of Pt nanoparticles (1.5 nm diameter) have been obtained by deposition of preformed and size selected Pt nanoparticles on graphene. This original self-organization is induced, at room temperature, by the 2D periodic undulation (the moiré pattern) of graphene epitaxially grown on the Ir(111) surface. By means of complementary techniques (scanning tunneling microscopy, grazing incidence X ray scattering), the Pt clusters shapes and organization are characterized and the structural evolution during annealing is investigated. The soft-landed clusters remain quasi-spherical and a large proportion appears to be pinned on specific moiré sites. The quantitative determination of the proportion of organized clusters reveals that the obtained hexagonal array of the almost spherical nanoparticles is stable up to 650 K, which is an indication of a strong cluster-surface interaction

Organization and magnetic properties of FePt nanoparticles deposited on graphene/Ir moiré pattern

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Elaboration of nanomagnet arrays: organization and magnetic properties of mass-selected FePt nanoparticles deposited on epitaxially grown graphene on Ir(111)

International audienceThe moiré pattern created by the epitaxy of a graphene sheet on an iridium substrate can be used as a template for the growth of 2D atomic or cluster arrays. We observed for the first time a coherent organization of hard magnetic preformed FePt nanoparticles on the 2D lattice of graphene/Ir(111). Nanoparticles of 2 nm diameter have been mass-selected in gas phase and deposited with a low energy on the hexagonal moiré pattern. Their morphology and organization have been investigated using Grazing Incidence Small Angle X-ray Scattering, while their magnetic properties have been studied by X-ray Magnetic Circular Dichroism, both pointing to a FePt cluster/graphene surface specific interaction. The spatial coherence of the nanoparticles is preserved upon annealing up to 700°C where the hard magnetic phase of FePt is obtained

Magnetic hardness of graded interface exchange spring L10-FePt films with Co nanoinclusions

Hard-magnetic films with precisely tuned switching fields are of great interest for microsystems, when both the manipulation and the stability of the magnetization are brought into play. Here, we report on the exchange spring mechanism developed in compositionally-graded nanocomposite films of FePt integrating x per cent of Co nanoclusters (x varying from 0 to 50%), made from a combination of mass-selected cluster beam deposition (MS-LECBD) and e-beam evaporation. This technique offers a precise control over the nanoinclusion size (8 nm diameter) and its volume fraction in the host FePt matrix. The focus is put on the interplay between the local microstructure and the magnetic coercivity through a combinatorial approach that involves local determinations of composition, magnetization reversal from scanning magneto-optical Kerr effect and element-specific spin and orbital magnetic moments from X-ray magnetic circular dichroism. We show that Co-rich inclusions allow a fine tuning of the coercivity and that a consequent increase of effective magnetic spin moment at the Co edge is obtained in our system