Balancing the risks of hydraulic failure and carbon starvation: a twig scale analysis in declining Scots pine

Understanding physiological processes involved in drought‐induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought‐exposed trees. However, little is known about the specific responses of leaves and supporting twigs, despite their critical role in balancing carbon acquisition and water loss. Comparing healthy (non‐defoliated) and unhealthy (defoliated) Scots pine at the same site, we measured the physiological variables involved in regulating carbon and water resources. Defoliated trees showed different responses to summer drought compared with non‐defoliated trees. Defoliated trees maintained gas exchange while non‐defoliated trees reduced photosynthesis and transpiration during the drought period. At the branch scale, very few differences were observed in non‐structural carbohydrate concentrations between health classes. However, defoliated trees tended to have lower water potentials and smaller hydraulic safety margins. While non‐defoliated trees showed a typical response to drought for an isohydric species, the physiology appears to be driven in defoliated trees by the need to maintain carbon resources in twigs. These responses put defoliated trees at higher risk of branch hydraulic failure and help explain the interaction between carbon starvation and hydraulic failure in dying trees.     

Functional characterization of terpene synthases and chemotypic variation in three lavender species of section Stoechas

Lavandula pedunculata (Mill.) Cav. subsp. lusitanica, Lavandula stoechas L. subsp. stoechas and Lavandula viridis l'Hér. are three lavender taxa that belong to the botanical section Stoechas and are widely used as aromatherapy, culinary herb or folk medicine in many Mediterranean regions. The analysis of their bioactive volatile constituents revealed the presence of 124 substances, the most abundant being the bicyclic monoterpenes fenchone, camphor and 1,8‐cineole that give these three species their respective chemotypes. Most noteworthy was fenchone which, with its reduced form fenchol, made 48% of the total volatile constituents of L. pedunculata while present at 2.9% in L. stoechas and undetectable in L. viridis. In order to provide a molecular explanation to the differences in volatile compounds of these three species, two monoterpene synthases (monoTPS) and one sesquiterpene synthase (sesquiTPS) were cloned in L. pedunculata and functionally characterized as fenchol synthase (LpFENS), α‐pinene synthase (LpPINS) and germacrene A synthase (LpGEAS). The two other lavender species contained a single orthologous gene for each of these three classes of TPS with similar enzyme product specificities. Expression profiles of FENS and PINS genes matched the accumulation profile of the enzyme products unlike GEAS. This study provides one of the rare documented cases of chemotype modification during plant speciation via changes in the level of plant TPS gene expression, and not functionality.     

Production of phthiocerol dimycocerosates protects Mycobacterium tuberculosis from the cidal activity of reactive nitrogen intermediates produced by macrophages and modulates the early immune response to infection

The growth of Mycobacterium tuberculosis mutants unable to synthesize phthiocerol dimycocerosates (DIMs) was recently shown to be impaired in mouse lungs. However, the precise role of these molecules in the course of infection remained to be determined. Here, we provide evidence that the attenuation of a DIM-deficient strain takes place during the acute phase of infection in both lungs and spleen of mice, and that this attenuation results in part from the increased sensitivity of the mutant to the cidal activity of reactive nitrogen intermediates released by activated macrophages. We also show that the DIM-deficient mutant, the growth and survival of which were not impaired within resting macrophages and dendritic cells, induced these cells to secrete more tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 than the wild-type strain. Although purified DIM molecules by themselves had no effect on the activation of macrophages and dendritic cells in vitro, we found that the proper localization of DIMs in the cell envelope of M. tuberculosis is critical to their biological effects. Thus, our findings suggest that DIM production contributes to the initial growth of M. tuberculosis by protecting it from the nitric oxide-dependent killing of macrophages and modulating the early immune response to infection.     

Unusual microbial mat‐related structural diversity 2.1 billion years ago and implications for the Francevillian biota

The 2.1‐billion‐year‐old (Ga) Francevillian series in Gabon hosts some of the oldest reported macroscopic fossils of various sizes and shapes, stimulating new debates on the origin, evolution and organization of early complex life. Here, we document ten representative types of exceptionally well‐preserved mat‐related structures, comprising “elephant‐skin” textures, putative macro‐tufted microbial mats, domal buildups, flat pyritized structures, discoidal microbial colonies, horizontal mat growth patterns, wrinkle structures, “kinneyia” structures, linear patterns and nodule‐like structures. A combination of petrographic analyses, scanning electron microscopy, Raman spectroscopy and organic elemental analyses of carbon‐rich laminae and microtexture, indicate a biological origin for these structures. The observed microtextures encompass oriented grains, floating silt‐sized quartz grains, concentrated heavy minerals, randomly oriented clays, wavy‐crinkly laminae and pyritized structures. Based on comparisons with modern analogues, as well as an average δ¹³C organic matter (C_org) composition of ?32.94 ± 1.17‰ (1 standard deviation, SD) with an outlier of ?41.26‰, we argue that the mat‐related structures contain relicts of multiple carbon pathways including heterotrophic recycling of photosynthetically derived C_org. Moreover, the relatively close association of the macroscopic fossil assemblages to the microbial mats may imply that microbial communities acted as potential benthic O₂ oases linked to oxyphototrophic cyanobacterial mats and grazing grounds. In addition, the mat's presence likely improved the preservation of the oldest large colonial organisms, as they are known to strongly biostabilize sediments. Our findings highlight the oldest community assemblage of microscopic and macroscopic biota in the aftermath of the “Great Oxidation Event,” widening our understanding of biological organization during Earth's middle age.     

Molecular Genetics of Alcohol Dependence and Related Endophenotypes

Alcohol dependence is a worldwide public health problem, and involves both environmental and genetic vulnerability factors. The heritability of alcohol dependence is rather high, ranging between 50% and 60%, although alcohol dependence is a polygenic, complex disorder.     

Sequence polymorphism-based identification and quantification of Vibrio nigripulchritudo at the species and subspecies level targeting an emerging pathogen for cultured shrimp in New Caledonia

In a previous study, we demonstrated the existence of an emerging cluster of Vibrio nigripulchritudo that proved to be associated with shrimp mortality events in New Caledonia. Using sequence polymorphisms evidenced in this previous MultiLocus Sequence Typing study, we developed two new quantitative PCR assays permitting the detection and quantification of V. nigripulchritudo at the genospecies level using SYBR Green I chemistry and at the emerging cluster level using Fluorescence Resonance Energy Transfer technology with hybridization probes. The use of this molecular diagnostic tool evidenced the colonization of the shrimp pond ecosystem by the pathogenic cluster at least at the onset of the disease. This new tool will allow better investigation of the dynamics of this bacterial pathogen in the shrimp farm ecosystem.     

Identification of a new family of genes involved in beta-1,2-mannosylation of glycans in Pichia pastoris and Candida albicans

Structural studies of cell wall components of the pathogenic yeast Candida albicans have demonstrated the presence of beta-1,2-linked oligomannosides in phosphopeptidomannan and phospholipomannan. During C. albicans infection, beta-1,2-oligomannosides play an important role in host/pathogen interactions by acting as adhesins and by interfering with the host immune response. Despite the importance of beta-1,2-oligomannosides, the genes responsible for their synthesis have not been identified. The main reason is that the reference species Saccharomyces cerevisiae does not synthesize beta-linked mannoses. On the other hand, the presence of beta-1,2-oligomannosides has been reported in the cell wall of the more genetically tractable C. albicans relative, P. pastoris. Here we present the identification, cloning, and characterization of a novel family of fungal genes involved in beta-mannose transfer. Employing in silico analysis, we identified a family of four related new genes in P. pastoris and subsequently nine homologs in C. albicans. Biochemical, immunological, and structural analyses following deletion of four genes in P. pastoris and deletion of four genes acting specifically on C. albicans mannan demonstrated the involvement of these new genes in beta-1,2-oligomannoside synthesis. Phenotypic characterization of the strains deleted in beta-mannosyltransferase genes (BMTs) allowed us to describe the stepwise activity of Bmtps and acceptor specificity. For C. albicans, despite structural similarities between mannan and phospholipomannan, phospholipomannan beta-mannosylation was not affected by any of the CaBMT1-4 deletions. Surprisingly, depletion in mannan major beta-1,2-oligomannoside epitopes had little impact on cell wall surface beta-1,2-oligomannoside antigenic expression.