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Société connectée, mais fragmentée : comment restaurer le sens du commun ?
No full textInternational audienceÀ l’heure où Elon Musk privatise l’espace public numérique en imposant ses propres règles sur X, créant une confusion majeure entre liberté et impunité, la question du commun et celle de « faire société » deviennent plus aiguës que jamais. Le commun, que nous entendons ici comme la capacité de s’entendre sur des règles de vie collective, est à la base de tout projet démocratique. Mais il n’est pas un acquis, il ne se décrète pas : il s’organise de manière sensible
Functional monocentricity with holocentric characteristics and chromosome-specific centromeres in a stick insect
No full textInternational audienceCentromeres are essential for chromosome segregation in eukaryotes, yet their specification is unexpectedly diverse among species and can involve major transitions such as those from localized to chromosome-wide centromeres between monocentric and holocentric species. How this diversity evolves remains elusive. We discovered within-cell variation in the recruitment of the major centromere protein CenH3, reminiscent of variation typically observed among species. While CenH3-containing nucleosomes are distributed in a monocentric fashion on autosomes and bind tandem repeat sequences specific to individual or groups of chromosomes, they show a longitudinal distribution and broad intergenic binding on the X chromosome, which partially recapitulates phenotypes known from holocentric species. Despite this variable CenH3 distribution among chromosomes, all chromosomes are functionally monocentric, marking the first instance of a monocentric species with chromosome-wide CenH3 deposition. Together, our findings illustrate a potential transitional state between mono- and holocentricity or toward CenH3-independent centromere determination and help to understand the rapid centromere sequence divergence between species
Introduction – Perspectives nouvelles sur John Williams (1) : héritages et postérités
No full textInternational audienc
Co-occurrence drives horizontal gene transfer among marine prokaryotes
No full textUnderstanding the drivers of horizontal gene transfer (HGT) is a key question in microbial evolution. While co-occurring taxa have long been appreciated to undergo HGT more often, this association is confounded with other factors, most notably their phylogenetic distance.To disentangle these factors, we analyzed 15,339 isolate and metagenome-assembled marine genomes. We identified HGT events across these genomes, and identified enrichments for functions previously shown to be prone to HGT. By mapping metagenomic reads from 1,862 ocean samples to these genomes, we also identified co-occurrence patterns and environmental associations. Although we observed an expected negative association between phylogenetic distance and HGT rates, we only detected the association between cooccurrence and phylogenetic distance when restricted to closely related taxa. This observation refines the previously reported trend to closely related taxa, rather than a consistent pattern across all taxonomic levels, at least within marine environments. In addition, we identified a significant association between co-occurrence and HGT, which remains even after controlling for phylogenetic distance and measured environmental variables. Overall, our findings demonstrate the significant influence of ecological associations in shaping marine bacterial evolution through HGT.</p
Genome-resolved biogeography of Phaeocystales, cosmopolitan bloom-forming algae
No full textInternational audiencePhaeocystales, comprising the genus Phaeocystis and an uncharacterized sister lineage, are nanoplanktonic haptophytes widespread in the global ocean. Several species form mucilaginous colonies and influence key biogeochemical cycles, yet their underlying diversity and ecological strategies remain underexplored. Here, we present new genomic data from 13 strains, including three high-quality reference genomes (N50 > 30 kbp), and integrate previous metagenome-assembled genomes to resolve a robust phylogeny. Divergence timing of P. antarctica aligns with Miocene cooling and Southern Ocean isolation. Genomic traits reveal metabolic flexibility, including mixotrophic nitrogen acquisition in temperate waters and gene expansions linked to polar nutrient adaptation. Concordantly, transcriptomic comparisons between temperate and polar Phaeocystis suggest Southern Ocean populations experience iron and B 12 limitation. We also identify signatures of horizontal gene transfer and endogenous giant virus/virophage insertions. Together, these findings highlight Phaeocystales as an ecologically versatile and geographically widespread lineage shaped by evolutionary innovation and adaptation to contrasting environmental stressors
Clé de répartition équitable des contrats islamiques d'investissement
No full textWe consider Islamic investment contracts, also known as Profit and Loss (PL) sharing contract, which may be mixed with an agency contract. Our aim is to determining both the profit sharing ratios and the induced expected payoff (at maturity) of each partner of the considered contracts according to its contribution to the project's overall success. To this end, we introduce the notion of {\em -fair} profit sharing ratios (, where is the number of partners) which is an equilibrium approach that considers the contributions of the counterparts of these contracts in terms of both capital and labour. We show several new results that elucidate the relationship between these profit-sharing ratios and various important economic factors, such as {\em investment risk}, {\em investment opportunity}, contribution factors to both {\em capital} and {\em labour}, providing accordingly a way of choosing the profit sharing ratios in connection with the real economy. The design of our approach allows all econometrics or stochastic diffusion models to be used to compute or approximate the quantities of interest. In practice, this work could help Islamic Finance institutions to better understand these contracts, while opening up new possibilities in the engineering and the industry of Islamic Finance
Multi‐Level Investigation in Arabidopsis of the Growth‐Stimulating Effects of a Protein Hydrolysate Biostimulant
No full textInternational audienceABSTRACT Biostimulant use is a promising agricultural strategy to maintain yield while decreasing mineral fertilisers and pesticides. Whereas the positive effect of protein hydrolysates (PH) on growth and yield has already been described, the underlying processes are not well understood. To better identify and characterise the physiological and molecular targets of PH, we first carried out in vitro experiments using the model species Arabidopsis thaliana . PH stimulated Arabidopsis root growth in a dose‐dependent manner, with high concentrations inhibiting growth. After having determined a stimulating PH concentration, we performed metabolomic and transcriptomic analyses. We observed that PH application increased amino acid levels in the plants, including a high level of glutamine, although it was only present in trace amounts in PH. These results suggest that amino acids are taken up and metabolized in the plant. PH also had a profound impact on the Arabidopsis transcriptome, with genes involved in nitrate and amino acid transport and assimilation showing a clear up‐ and down‐regulation, respectively. For example, the expression of the high‐affinity nitrate transporter NRT2.1 ( NITRATE TRANSPORTER 2 ) was decreased, and consistently high‐affinity nitrate uptake and the development of lateral roots were diminished. The PH contained high levels of branched amino acids, which are known to induce the TOR kinase activity, a major driver of growth. Finally, high‐throughput phenotyping also showed that PH supply increased shoot growth. In conclusion, our findings show that PH has a clear and robust effect on Arabidopsis growth, but also on the transcriptome, metabolite levels, and physiological processes like nitrogen metabolism
Bacillus paralicheniformis strain H12 from saline soil for the management of gray mold in cherry tomatoes
No full textInternational audienceFungal phytopathogens cause severe yield loss, endangering vital crops such as cherry tomatoes. This study was undertaken to investigate and identify Bacillus species that possess broad-spectrum antifungal activity, specifically, to select a biocontrol agent against gray mold disease caused by Botrytis cinerea affecting cherry tomato, and investigating its safety features (antibiotic resistance, hemolysis, and virulence genes). Out of 82 Bacillus strains isolated from different regions in Algeria, 41 strains exhibited antifungal activity, while 28 strains demonstrated broad-spectrum activity. In vitro studies showed that each isolate produced at least one lytic enzyme (chitinase, glucanase, amylase, protease, or lipase). The most promising strains were all classified within the Bacillus subtilis group based on 16 S rRNA sequencing. The biocontrol potential of B. paralicheniformis H12 strain, which exhibited the highest inhibition index against B. cinerea, was tested in vivo. The assays showed that H12 strain significantly decreased the gray mold decay in cherry tomatoes and resulted in less weight loss (weight loss rate 2.76%) compared to the control group (5.04%). The genome of H12 consisted of 4,283,563 bp, with 4,226 coding DNA sequences, and a GC content of 45.87%. Genome mining unveiled diverse biosynthetic gene clusters related to antimicrobial properties. Furthermore, H12 was categorized as non-hemolytic and sensitive to different antibiotic families. These findings highlight the potential of B. subtilis group species as a potential biocontrol agent. Specifically, they provide valuable insight into the genomic features of the B. paralicheniformis strain H12 from saline soil (sabkha) as a prospective candidate for agricultural application
Analyse croisée de données métabarcoding et métagénomiques sur des microbiotes d'hôtes animaux
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Entry and exit of Fragilariopsis cylindrus diatoms from the polar night: evidence for chromatin-mediated genome control
No full textInternational audienceAbstract Regulation of the epigenome landscape plays a crucial role in adaptation to environmental changes. However, the molecular mechanisms by which epigenome landscapes are established and tuned to adjust the cellular status to environmental cues remain poorly understood, especially in unicellular photosynthetic eukaryotes. Polar microalgae must adapt to extreme variations in light and temperature for survival and therefore represent excellent models to understand the diversity of gene regulatory mechanisms, yet chromatin-based mechanisms have never been explored in these organisms. In this study, we combined genome-wide profiling of histone and DNA modifications with transcriptomic analyses of the marine polar diatom Fragilariopsis cylindrus upon entry and exit of a 3-month-long polar night. We show that, in agreement with its established role in transcription facilitation, histone H2B monobiquitination (H2Bub) is modulated at active genes upon prolonged darkness to light re-exposure. In contrast, histone H3 lysine 27 trimethylation (H3K27me3) and DNA cytosine methylation (CG methylation), two modifications typically associated with the silencing of genes or transposable elements (TEs), remained stable throughout the transitions, reinforcing their role in transcriptional repression, particularly at TEs but also at a few genes. We further demonstrate that H3K27me3 and DNA methylation are physically associated at TEs, probably reflecting a dual locking system enabling F.cylindrus cells to cope with the invasive nature of these genetic elements under extreme environmental conditions. These findings enhance our understanding of genome and epigenome regulation in diatoms in response to environmental variability and open new avenues for exploring the role played by chromatin-level regulation in the unique evolutionary history of polar unicellular eukaryotes