Laterites are deep weathering covers of the critical zone that occupy 80% of the total soil-mantle volume of the Earth’s landscape and significantly participate to the global geochemical budget of weathering and erosion, and greenhouse gas consumption. Despite their factual importance on Earth surface, the timing of their formation and evolution in response to climatic and geodynamic forcing are still obscure. RECA project will address both the topics of "Functioning and evolution of climate, oceans and major cycles" and "Continental Surfaces: critical zone and biosphere" from ANR Axis 1 – Challenge 1., by reconstructing the influence of climate change laterites formation. The originality of the RECA project is to combine chronometric, weathering and climatic proxies developed in the recent years in order to build a comprehensive and predictive scenario of laterite formation and evolution. We will concentrate our effort on geodynamically stable Guyana Shield and Central Amazonia regions, where laterites formed through the whole Cenozoic and can be associated with major geomorphological units. This ambitious multidisciplinary project proposes, for the first time, to perform absolute dating of lateritic duricrusts associated to five episodes of planation in the South American subcontinent. We will date mineralogically well-identified populations of iron oxides and oxyhydroxides (hematite, goethite) and clays (kaolinites) by using (U-Th)/He, (U-Th)/Ne and electron paramagnetic resonance spectroscopy, respectively. These recent methods are appropriates because they can be applied to the most common secondary minerals found in laterites and span geological time scales. The inherent complexity of weathering materials, which may contain different populations of a same secondary mineral related to distinct stages of lateritization will be taken into account. The timing of duricrust formation will then be related to paleoclimatic conditions (temperature, rainfall) derived from a combination of geochemical or mineralogical indices and proxies: (i) at global scale, through, e.g., the known continental drainage curves; (ii) at a more regional scale through the intensity of weathering, the ratio hematite/goethite or O and H isotope systems of kaolinite and iron oxides and oxyhydroxides. A second task will associate non-conventional Li, Si and Fe isotopic methods that will help to decipher the evolution of weathering processes linked to the various stages of laterite formation. Coupling weathering budget and the ages of weathering profiles will yield average weathering and erosion rates, allowing comparison with other weathering environments or paleo-environments at the Earth surface. To tackle this ambitious task, the RECA project gathers an international consortium made of skilled researchers in the identification of lateritic soils, dating methods, environmental mineralogy; "traditional" and "non-traditional" stable isotope geochemistry, and modeling approaches of the formation of weathering profiles. The synergy of the identified teams offers the highest level of guarantee to lift off the identified scientific and technical barriers, giving access to yet hidden information on soil formation as a response to climate change through geological times.

The liquid-liquid transition (LLT) is a rare and intriguing phenomenon is which a single-component liquid transforms into another one via a first-order transition. Owing to its counterintuitive nature, the LLT has intrigued scientists for several years and challenged our perception of the liquid state, for which the notion of polymorphism was long considered impossible. LLTs have been predicted from computer simulations of several systems, and heavily debated in the case of supercooled water. However, our theoretical understanding remains relatively primitive, and there is no theory at present able to predict whether a given system will exhibit a LLT. This is why the experimental realizations reported so far remain scarce, have been made rather accidentally and are often controversial. A recent breakthrough was made by the present proposer consortium, with the experimental discovery of such a LLT in compressed liquid sulfur, and the first-ever evidence of a liquid-liquid critical point (LLCP) ending the transition line. Such a LLCP has long been searched in water but to date impossible to reach by experiment. Located at about 2.15 GPa-1035 K, the LLCP in sulfur can be easily approached by experiment, which opens brand new perspectives to the field. The general objective of this project is to advance our understanding of LLTs, by obtaining accurate data sets from experiments and computer simulations that will form a solid basis to extract the systematics of LLTs, and aid the emergence of predictive theories. For this, we propose to study several systems which are representative of different types of materials, over a large range of pressure and temperature conditions (0-150 GPa, 300-3000 K), and using several x-ray and optical diagnostics available at the 3 partners’ sites. The first part of the project (Tasks 1 and 6) will focus on the two systems for which a LLT is now well established, phosphorus and sulfur. We will study for the first time the critical phenomena and universality class of the LLCP in sulfur using innovative small-angle x-ray scattering (SAXS) experiments in the diamond anvil cell (DAC). We will also determine whether a LLCP exists in phosphorus through x-ray measurements of the density jump along the LLT line. A better understanding of the microscopic nature of the low-density and high-density liquid phases and of the driving mechanism of the LLT in both S and P will be achieved through experiments and simulations. Finally, we will investigate their melting lines in the vicinity of the LLT and whether the two-state model is compatible with thermodynamic data for these two systems. In the second part of the project, we will extend our investigations to other systems which are promising candidates for a LLT, as suggested by computer simulations or previous experimental results. Specifically, we will focus on two network liquids (Task 2), B2O3 and AsS, the molecular liquids of nitrogen, carbon dioxide, hydrogen (Task 3), and the liquid alkali metals (Li, Na, K) (Task 4). For B2O3 and AsS, the LLT is expected below a few GPa and similar studies as those described above for sulfur and phosphorus will be carried out. For the molecular and alkali liquids, the expected location of the LLT resides at pressures from 20 to 150 GPa, which requires the use of smaller samples compressed in the DAC. The present proposers have developed new techniques in the framework of the ANR project MOFLEX which have made possible structural and vibrational studies of liquids composed of light elements in the DAC up to megabar pressures through x-ray diagnostics combined to Raman and Brillouin spectroscopies, which will be put to profit for this project. Additional technical developments (Task 5,) such as high P-T SAXS experiments, will be undertaken during the project to complement or enable new types of measurement under high P-T.

Magnetotactic bacteria (MTB) synthesize magnetite crystals within their cell. Although MTB may represent some of the oldest biomineralizing microbial organisms on Earth, their identification in the rock record has remained elusive. In the present proposal, we aim at testing and improving new chemical (trace elements) and isotopic (Fe) proxies for identification of MTB. Two main tasks will be achieved: (1) laboratory experiments to explore chemical and isotopic signatures of MTB strains under various culture conditions, (2) analysis of modern MTB in their environment to determine if the conclusions derived from laboratory experiments can be translated to natural systems. This multidisciplinary project, which gathers experts in biology, mineralogy, and elemental and isotope geochemistry, will pave the way for future geochemical studies of MTB search in the sedimentary record.

Symbiosis and mutualism are drivers of life diversification and sources of biological innovation in the microbial world. Recently, magnetotactic assemblies composed of a flagellated protist and ectosymbiotic bacteria biomineralizing magnetic crystals have been discovered. Their mutualistic symbiosis relies on a collective magnetotaxis coupled to a hydrogen-based syntrophy. This new form of cooperation challenges our view of magnetic biomineralization in prokaryotes and magnetoreception in eukaryotes, but it sill remains poorly understood. This project is based on the assumption that these magnetotactic symbioses emerged several times in the course of microbial eukaryotes evolution as an adaptation to anoxic environments. Thus, we propose to test this hypothesis by (1) characterizing the diversity and ecology of the magnetotactic holobionts, (2) identifying the functional bases of the symbiosis and (3) deciphering the origin and evolutionary history of the magnetotactic symbiosis.

BRCA2 tumour-suppressor protein is well known for its role in DNA repair by homologous recombination (HR). It facilitates the loading of RAD51 recombinase at DNA double-strand breaks. This function is executed by the C-terminal DNA binding domain (CTD) which binds single-stranded (ss)DNA, and the BRC repeats, which bind RAD51 and modulate its assembly onto ssDNA. However, our recent discovery of a new DNA binding domain in the N-terminal region of BRCA2 that can promote the HR activity of RAD51 in vitro raises the question of how the two DNA binding domains coordinate to ensure the HR activity of RAD51 and whether or not a disruption of either leads to a defective HR function in the cell. Mounting evidence from the literature suggests that the C-terminal and the N-terminal regions of BRCA2 interact in trans, which would shed light in the cooperation between the two DNA binding sites. Importantly, this process could regulate the activation of BRCA2 at DSBs. In the orthologue of BRCA2 in U. maydis, this regulation seems to be acted by DSS1, a protein that interacts with the C-terminal DNA binding domain precluding its DNA binding. Which is the active oligomeric form of human BRCA2 and whether DSS1 also regulates its oligomerisation and DNA binding capacities remains unclear. Here we propose an integrative approach that relies on the use of structural bioinformatics, biochemistry, structural biology and cell biology tools, together with phenotypic information from BRCA2 natural variants, to reveal new functional domains in the a priori "unstructured" N-terminal region of BRCA2, with a particular focus on the DNA binding domain recently identified.