Diatom molecular research comes of age: Model species for studying phytoplankton biology and diversity

Diatoms are the world’s most diverse group of algae, comprising at least 100,000 species. Contributing;20% of annual global carbon fixation, they underpin major aquatic food webs and drive global biogeochemical cycles. Over the past two decades, Thalassiosira pseudonana and Phaeodactylum tricornutum have become the most important model systems for diatom molecular research, ranging from cell biology to ecophysiology, due to their rapid growth rates, small genomes, and the cumulative wealth of associated genetic resources. To explore the evolutionary divergence of diatoms, additional model species are emerging, such as Fragilariopsis cylindrus and Pseudo-nitzschia multistriata. Here, we describe how functional genomics and reverse genetics have contributed to our understanding of this important class of microalgae in the context of evolution, cell biology, and metabolic adaptations. Our review will also highlight promising areas of investigation into the diversity of these photosynthetic organisms, including the discovery of new molecular pathways governing the life of secondary plastid-bearing organisms in aquatic environments

Multisignal control of expression of the LHCX protein family in the marine diatom Phaeodactylum tricornutum

Diatoms are phytoplanktonic organisms that grow successfully in the ocean where light conditions are highly variable. Studies of the molecular mechanisms of light acclimation in the marine diatom Phaeodactylum tricornutum show that carotenoid de-epoxidation enzymes and LHCX1, a member of the light-harvesting protein family, both contribute to dissipate excess light energy through non-photochemical quenching (NPQ). In this study, we investigate the role of the other members of the LHCX family in diatom stress responses. Our analysis of available genomic data shows that the presence of multiple LHCX genes is a conserved feature of diatom species living in different ecological niches. Moreover, an analysis of the levels of four P. tricornutum LHCX transcripts in relation to protein expression and photosynthetic activity indicates that LHCXs are differentially regulated under different light intensities and nutrient starvation, mostly modulating NPQ capacity. We conclude that multiple abiotic stress signals converge to regulate the LHCX content of cells, providing a way to fine-tune light harvesting and photoprotection. Moreover, our data indicate that the expansion of the LHCX gene family reflects functional diversification of its members which could benefit cells responding to highly variable ocean environments

Light-driven processes: key players of the functional biodiversity in microalgae

International audienc

Herpes-Virus Infection in Patients with Langerhans Cell Histiocytosis: A Case-Controlled Sero-Epidemiological Study, and In Situ Analysis

BACKGROUND: Langerhans cell histiocytosis (LCH) is a rare disease that affects mainly young children, and which features granulomas containing Langerhans-type dendritic cells. The role of several human herpesviruses (HHV) in the pathogenesis of LCH was suggested by numerous reports but remains debated. Epstein-barr virus (EBV, HHV-4), & Cytomegalovirus (CMV, HHV-5) can infect Langerhans cells, and EBV, CMV and HHV-6 have been proposed to be associated with LCH based on the detection of these viruses in clinical samples. METHODOLOGY: We have investigated the prevalence of EBV, CMV and HHV-6 infection, the characters of antibody response and the plasma viral load in a cohort of 83 patients and 236 age-matched controls, and the presence and cellular localization of the viruses in LCH tissue samples from 19 patients. PRINCIPAL FINDINGS: The results show that prevalence, serological titers, and viral load for EBV, CMV and HHV-6 did not differ between patients and controls. EBV was found by PCR in tumoral sample from 3/19 patients, however, EBV small RNAs EBERs -when positive-, were detected by in situ double staining in bystander B CD20+ CD79a+ lymphocytes and not in CD1a+ LC. HHV-6 genome was detected in the biopsies of 5/19 patients with low copy number and viral Ag could not be detected in biopsies. CMV was not detected by PCR in this series. CONCLUSIONS/SIGNIFICANCE: Therefore, our findings do not support the hypothesis of a role of EBV, CMV, or HHV-6 in the pathogenesis of LCH, and indicate that the frequent detection of Epstein-barr virus (EBV) in Langerhans cell histiocytosis is accounted for by the infection of bystander B lymphocytes in LCH granuloma. The latter observation can be attributed to the immunosuppressive micro environment found in LCH granuloma

Expansion of Regulatory T Cells in Patients with Langerhans Cell Histiocytosis

Frederic Geissmann and colleagues find that Langerhans cell accumulation in Langerhans cell histiocytosis results from survival rather than uncontrolled proliferation, and is associated with the expansion of regulatory T cells

The Cyst Nematode SPRYSEC Protein RBP-1 Elicits Gpa2- and RanGAP2-Dependent Plant Cell Death

Plant NB-LRR proteins confer robust protection against microbes and metazoan parasites by recognizing pathogen-derived avirulence (Avr) proteins that are delivered to the host cytoplasm. Microbial Avr proteins usually function as virulence factors in compatible interactions; however, little is known about the types of metazoan proteins recognized by NB-LRR proteins and their relationship with virulence. In this report, we demonstrate that the secreted protein RBP-1 from the potato cyst nematode Globodera pallida elicits defense responses, including cell death typical of a hypersensitive response (HR), through the NB-LRR protein Gpa2. Gp-Rbp-1 variants from G. pallida populations both virulent and avirulent to Gpa2 demonstrated a high degree of polymorphism, with positive selection detected at numerous sites. All Gp-RBP-1 protein variants from an avirulent population were recognized by Gpa2, whereas virulent populations possessed Gp-RBP-1 protein variants both recognized and non-recognized by Gpa2. Recognition of Gp-RBP-1 by Gpa2 correlated to a single amino acid polymorphism at position 187 in the Gp-RBP-1 SPRY domain. Gp-RBP-1 expressed from Potato virus X elicited Gpa2-mediated defenses that required Ran GTPase-activating protein 2 (RanGAP2), a protein known to interact with the Gpa2 N terminus. Tethering RanGAP2 and Gp-RBP-1 variants via fusion proteins resulted in an enhancement of Gpa2-mediated responses. However, activation of Gpa2 was still dependent on the recognition specificity conferred by amino acid 187 and the Gpa2 LRR domain. These results suggest a two-tiered process wherein RanGAP2 mediates an initial interaction with pathogen-delivered Gp-RBP-1 proteins but where the Gpa2 LRR determines which of these interactions will be productive

Etude des Mécanismes de Régulation de la photosynthèse chez Bradyrhizobium

Les Bradyrhizobium nodulant les tiges de certaines légumineuses tropicales du genre Aeschynomene présentent la particularité d être photosynthétiques. La synthèse de leur photosystème présente une régulation originale par la lumière impliquant l action d un bactériophytochrome. Par ailleurs, deux facteurs de transcription homologues à PpsR, régulateur clé de l'expression des gènes photosynthétiques chez les bactéries pourpres, ont été identifiés chez ces Bradyrhizobium. Ce travail a consisté tout d'abord à déterminer le rôle, les propriétés et les mécanismes d'action de ces deux PpsR. En combinant des approches biochimiques et génétiques, il a pu être révélé un mécanisme extrêmement sophistiqué de régulation des gènes photosynthétiques résultant d'une compétition entre les deux PpsR: PpsR1 exerce un rôle activateur modulé par les conditions redox et PpsR2, joue un rôle répresseur modulé par la lumière via l action du bactériophytochrome. L'analyse de la séquence du génome de deux Bradyrhizobium photosynthétiques (ORS278 et BTAi1) a révélé par ailleurs la présence d'un autre bactériophytochrome spécifique à chaque souche. Les propriétés biophysiques et fonctionnelles de ces 2 bactériophytochromes ont été caractérisées soulignant la modularité et l'adaptabilité de cette famille de capteur de lumière. Enfin de nouveaux régulateurs de photosynthèse ont pu être identifié grâce au criblage d'une banque de 9500 mutants d ORS278 testée sous différentes conditions de lumièreBacteria able to form nitrogen-fixing nodules on the stem of some tropical aquatic leguminous belonging to the Aeschynomene genus display the very rare property to be photosynthetic. Photosystem synthesis is unexpectedly control by light via the action of a bacteriophytochrome. In addition, these bacteria possess two transcriptional factors homologous to PpsR considered as the master chief regulator of photosystem synthesis in purple bacteria. The first objective of this work was to describe the role, the properties and the mode of action of both PpsRs. By combined biochemical and genetical approaches, we described here a very sophisticated mechanism of regulation of photosystem synthesis involving the competition between both PpsRs: PpsR1 acts as an activator and its action is modulated by redox conditions whereas PpsR2 acts as a repressor which action is antagonised by the bacteriophytochrome. Furthermore, the sequence genome analysis of two photosynthetic Bradyrhizobium (ORS278 and BTAi1) has revealed the additional presence of a specific bacteriophytochrome in each strain. The biophysical and functional properties of these bacteriophytochromes were characterised highlighting the modularity and adaptability of this light sensor family. Finally new photosystem synthesis regulators were identified thank to the screening of a mutant library of ORS278 strain cultivated under different light conditionsMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

L’orthophonie au regard des sciences sociales

International audienc

L'orthophonie au regard des sciences sociales

International audienc

L'orthophonie au regard des sciences sociales

International audienc