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ID30A-3, a highly intense mini-beam facility for macromolecular crystallography at the ESRF, is described.., ID30A-3 (or MASSIF-3) is a mini-focus (beam size 18 µm × 14 µm) highly intense (2.0 × 1013 photons s−1), fixed-energy (12.81 keV) beamline for macromolecular crystallography (MX) experiments at the European Synchrotron Radiation Facility (ESRF). MASSIF-3 is one of two fixed-energy beamlines sited on the first branch of the canted undulator setup on the ESRF ID30 port and is equipped with a MD2 micro-diffractometer, a Flex HCD sample changer, and an Eiger X 4M fast hybrid photon-counting detector. MASSIF-3 is recommended for collecting diffraction data from single small crystals (≤15 µm in one dimension) or for experiments using serial methods. The end-station has been in full user operation since December 2014, and here its current characteristics and capabilities are described.

If there are no constraints on the process of speciation, then the number of species might be expected to match the number of available niches and this number might be indefinitely large. One possible constraint is the opportunity for allopatric divergence. In 1981, Felsenstein used a simple and elegant model to ask if there might also be genetic constraints. He showed that progress towards speciation could be described by the build-up of linkage disequilibrium among divergently selected loci and between these loci and those contributing to other forms of reproductive isolation. Therefore, speciation is opposed by recombination, because it tends to break down linkage disequilibria. Felsenstein then introduced a crucial distinction between "two-allele" models, which are subject to this effect, and "one-allele" models, which are free from the recombination constraint. These fundamentally important insights have been the foundation for both empirical and theoretical studies of speciation ever since.

Fluorescent base analogues (FBAs) have emerged as a powerful class of molecular reporters of location and environment for nucleic acids. In our overall mission to develop bright and useful FBAs for all natural nucleobases, herein we describe the synthesis and thorough characterization of bicyclic thymidine (bT), both as a monomer and when incorporated into DNA. We have developed a robust synthetic route for the preparation of the bT DNA monomer and the corresponding protected phosphoramidite for solid-phase DNA synthesis. The bT deoxyribonucleoside has a brightness value of 790 M−1cm−1 in water, which is comparable or higher than most fluorescent thymine analogues reported. When incorporated into DNA, bT pairs selectively with adenine without perturbing the B-form structure, keeping the melting thermodynamics of the B-form duplex DNA virtually unchanged. As for most fluorescent base analogues, the emission of bT is reduced inside DNA (4.5- and 13-fold in single- and double-stranded DNA, respectively). Overall, these properties make bT an interesting thymine analogue for studying DNA and an excellent starting point for the development of brighter bT derivatives.

Microbes that protect their hosts from pathogenic infection are widespread components of the microbiota of both plants and animals. It has been found that interactions between 'defensive' microbes and pathogens can be genotype-specific and even underlie the variation in host resistance to pathogenic infection. These observations suggest a dynamic co-evolutionary association between pathogens and defensive microbes, but direct evidence of co-evolution is lacking. We tested the hypothesis that defensive microbes and pathogens could co-evolve within host populations by co-passaging a microbe with host-defensive properties (Enterococcus faecalis) and a pathogen (Staphylococcus aureus) within Caenorhabditis elegans nematodes. Using both phenotypic and genomic analyses across evolutionary time, we found patterns of pathogen local adaptation and defensive microbe-pathogen co-evolution via fluctuating selection dynamics. Moreover, co-evolution with defensive microbes resulted in more rapid and divergent pathogen evolution compared to pathogens evolved independently in host populations. Taken together, our results indicate the potential for defensive microbes and pathogens to co-evolve, driving interaction specificity and pathogen evolutionary divergence in the absence of host evolution.

International audience; no abstract

Les agriculteurs et les forestiers désireux de réintroduire des pommiers sauvages dans le paysage rencontrent des difficultés pour se procurer des plants de pommiers véritablement sauvages. Les instances en charge de la conservation des ressources génétiques des arbres forestiers en France et en Europe s'inquiètent des conséquences de plantations forestières réalisées avec du matériel de provenance inconnue ou à base génétique trop étroite. Une thèse en cours d'achèvement et un projet qui la prolonge apportent des éléments de réponse à ces difficultés. La thèse met en lumière les mécanismes génétiques qui ont conduit à la différenciation des espèces de pommiers en Asie et en Europe et accompagné la domestication de cet arbre fruitier. Elle fournit des indications pour la conservation et l'utilisation des ressources génétiques des pommiers sauvages de France. Le projet a pour but d’étudier les hybridations entre pommiers sauvages et cultivés en Île-de-France mais son champ s'étend naturellement à l'ensemble du territoire national, notamment pour estimer la diversité et la spécificité éventuelle des ressources génétiques de pommiers sauvages. Cette étude permettra d'estimer quelles sont les meilleures populations sauvages pour la réimplantation des arbres en milieu agricole. Les données recueillies permettront aussi de préciser les précautions à respecter en matière de récolte et de transfert géographique des graines et plants. Des récoltes de greffons sont envisagées pour la constitution de vergers à graines conservatoires. Plus généralement, les résultats de la thèse et du projet permettront de jeter les bases d'une stratégie de conservation du pommier sauvage en France et de faciliter son élargissement à l'échelle paneuropéenne.

International audience