Écologie et Biologie des Interactions

Rates of biodiversity loss are higher in freshwater ecosystems than in most terrestrial or marine ecosystems, making freshwater conservation a priority. However, prioritization methods are impeded by insufficient knowledge on the distribution and conservation status of freshwater taxa, particularly invertebrates. We evaluated the extinction risk of the world's 590 freshwater crayfish species using the IUCN Categories and Criteria and found 32% of all species are threatened with extinction. The level of extinction risk differed between families, with proportionally more threatened species in the Parastacidae and Astacidae than in the Cambaridae. Four described species were Extinct and 21% were assessed as Data Deficient. There was geographical variation in the dominant threats affecting the main centres of crayfish diversity. The majority of threatened US and Mexican species face threats associated with urban development, pollution, damming and water management. Conversely, the majority of Australian threatened species are affected by climate change, harvesting, agriculture and invasive species. Only a small proportion of crayfish are found within the boundaries of protected areas, suggesting that alternative means of long-term protection will be required. Our study highlights many of the significant challenges yet to come for freshwater biodiversity unless conservation planning shifts from a reactive to proactive approach.

Horizontal transfer (HT) of genetic material is central to the architecture and evolution of prokaryote genomes. Within eukaryotes, the majority of HTs reported so far are transfers of transposable elements (TEs). These reports essentially come from studies focusing on specific lineages or types of TEs. Because of the lack of large-scale survey, the amount and impact of HT of TEs (HTT) in eukaryote evolution, as well as the trends and factors shaping these transfers, are poorly known. Here, we report a comprehensive analysis of HTT in 195 insect genomes, representing 123 genera and 13 of the 28 insect orders. We found that these insects were involved in at least 2,248 HTT events that essentially occurred during the last 10 My. We show that DNA transposons transfer horizontally more often than retrotransposons, and unveil phylogenetic relatedness and geographical proximity as major factors facilitating HTT in insects. Even though our study is restricted to a small fraction of insect biodiversity and to a recent evolutionary timeframe, the TEs we found to be horizontally transferred generated up to 24% (2.08% on average) of all nucleotides of insect genomes. Together, our results establish HTT as a major force shaping insect genome evolution.

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

Root high plasticity is an adaptation to its changing environment. Water deficit impairs growth, leading to sugar accumulation in leaves, part of which could be available to roots via sucrose (Suc) phloem transport. Phloem loading is widely described in Arabidopsis (Arabidopsis thaliana), while unloading in roots is less understood. To gain information on leaf-to-root transport, a soil-based culture system was developed to monitor root system architecture in two dimensions. Under water deficit (50% of soil water-holding capacity), total root length was strongly reduced but the depth of root foraging and the shape of the root system were less affected, likely to improve water uptake. (14)CO2 pulse-chase experiments confirmed that water deficit enhanced carbon (C) export to the roots, as suggested by the increased root-to-shoot ratio. The transcript levels of AtSWEET11 (for sugar will eventually be exported transporter), AtSWEET12, and AtSUC2 (for Suc carrier) genes, all three involved in Suc phloem loading, were significantly up-regulated in leaves of water deficit plants, in accordance with the increase in C export from the leaves to the roots. Interestingly, the transcript levels of AtSUC2 and AtSWEET11 to AtSWEET15 were also significantly higher in stressed roots, underlying the importance of Suc apoplastic unloading in Arabidopsis roots and a putative role for these Suc transporters in Suc unloading. These data demonstrate that, during water deficit, plants respond to growth limitation by allocating relatively more C to the roots to maintain an efficient root system and that a subset of Suc transporters is potentially involved in the flux of C to and in the roots.

This review summarizes the available data related to the effects of air pollution on pollen grains from different plant species. Several studies carried out either on in situ harvested pollen or on pollen exposed in different places more or less polluted are presented and discussed. The different experimental procedures used to monitor the impact of pollution on pollen grains and on various produced external or internal subparticles are listed. Physicochemical and biological effects of artificial pollution (gaseous and particulate) on pollen from different plants, in different laboratory conditions, are considered. The effects of polluted pollen grains, subparticles, and derived aeroallergens in animal models, in in vitro cell culture, on healthy human and allergic patients are described. Combined effects of atmospheric pollutants and pollen grains-derived biological material on allergic population are specifically discussed. Within the notion of "polluen," some methodological biases are underlined and research tracks in this field are proposed.

We constructed an experimental model system to study the effects of grazing by a common soil amoeba, Acanthamoeba castellanii, on the composition of bacterial communities in the rhizosphere of Arabidopsis thaliana. Amoebae showed distinct grazing preferences for specific bacterial taxa, which were rapidly replaced by grazing tolerant taxa in a highly reproducible way. The relative proportion of active bacteria increased although bacterial abundance was strongly decreased by amoebae. Specific bacterial taxa had disappeared already two days after inoculation of amoebae. The decrease in numbers was most pronounced in Betaproteobacteria and Firmicutes. In contrast, Actinobacteria, Nitrospira, Verrucomicrobia and Planctomycetes increased. Although other groups, such as betaproteobacterial ammonia oxidizers and Gammaproteobacteria did not change in abundance, denaturing gradient gel electrophoresis with specific primers for pseudomonads (Gammaproteobacteria) revealed both specific changes in community composition as well as shifts in functional genes (gacA) involved in bacterial defence responses. The resulting positive feedback on plant growth in the amoeba treatment confirms that bacterial grazers play a dominant role in structuring bacteria-plant interactions. This is the first detailed study documenting how rapidly protozoan grazers induce shifts in rhizosphere bacterial community composition.

The regulation of source-to-sink sucrose transport is associated with AtSUC and AtSWEET sucrose transporters’ gene expression changes in plants grown hydroponically under different physiological conditions. Source-to-sink transport of sucrose is one of the major determinants of plant growth. Whole-plant carbohydrates’ partitioning requires the specific activity of membrane sugar transporters. In Arabidopsis thaliana plants, two families of transporters are involved in sucrose transport: AtSUCs and AtSWEETs. This study is focused on the comparison of sucrose transporter gene expression, soluble sugar and starch levels and long distance sucrose transport, in leaves and sink organs (mainly roots) in different physiological conditions (along the plant life cycle, during a diel cycle, and during an osmotic stress) in plants grown hydroponically. In leaves, the AtSUC2, AtSWEET11, and 12 genes known to be involved in phloem loading were highly expressed when sucrose export was high and reduced during osmotic stress. In roots, AtSUC1 was highly expressed and its expression profile in the different conditions tested suggests that it may play a role in sucrose unloading in roots and in root growth. The SWEET transporter genes AtSWEET12, 13, and 15 were found expressed in all organs at all stages studied, while differential expression was noticed for AtSWEET14 in roots, stems, and siliques and AtSWEET9, 10 expressions were only detected in stems and siliques. A role for these transporters in carbohydrate partitioning in different source–sink status is proposed, with a specific attention on carbon demand in roots. During development, despite trophic competition with others sinks, roots remained a significant sink, but during osmotic stress, the amount of translocated [U-14C]-sucrose decreased for rosettes and roots. Altogether, these results suggest that source–sink relationship may be linked with the regulation of sucrose transporter gene expression.

The unparalleled biodiversity found in the American tropics (the Neotropics) has attracted the attention of naturalists for centuries. Despite major advances in recent years in our understanding of the origin and diversification of many Neotropical taxa and biotic regions, many questions remain to be answered. Additional biological and geological data are still needed, as well as methodological advances that are capable of bridging these research fields. In this review, aimed primarily at advanced students and early-career scientists, we introduce the concept of "trans-disciplinary biogeography," which refers to the integration of data from multiple areas of research in biology (e.g., community ecology, phylogeography, systematics, historical biogeography) and Earth and the physical sciences (e.g., geology, climatology, palaeontology), as a means to reconstruct the giant puzzle of Neotropical biodiversity and evolution in space and time. We caution against extrapolating results derived from the study of one or a few taxa to convey general scenarios of Neotropical evolution and landscape formation. We urge more coordination and integration of data and ideas among disciplines, transcending their traditional boundaries, as a basis for advancing tomorrow's ground-breaking research. Our review highlights the great opportunities for studying the Neotropical biota to understand the evolution of life.

In plants, the transport of sugars from the site of biosynthesis to the site of utilization or storage relies on sugar transporters located in different subcellular compartments and different vascular cell types. The SWEET sugar transporter family is one such class and is represented by 17 members in Arabidopsis. AtSWEET1 was the first plant SWEET transporter to be characterized; it acts as a glucose uniporter in multiple systems (Chen et al., 2010Chen L.Q. Hou B.H. Lalonde S. Takanaga H. Hartung M.L. Qu X.Q. Guo W.J. Kim J.G. Underwood W. Chaudhuri B. Sugar transporters for intercellular exchange and nutrition of pathogens.Nature. 2010; 468: 527-532Crossref PubMed Scopus (939) Google Scholar). AtSWEET11 and AtSWEET12 were subsequently identified as key players in sucrose efflux from phloem parenchyma cells, a prerequisite for phloem loading by import into the sieve element–companion cell complex (Chen et al., 2012Chen L.Q. Qu X.Q. Hou B.H. Sosso D. Osorio S. Fernie A.R. Frommer W.B. Sucrose efflux mediated by SWEET proteins as a key step for phloem transport.Science. 2012; 335: 207-211Crossref PubMed Scopus (811) Google Scholar), whereas AtSWEET16 and AtSWEET17 probably export fructose out of the vacuole and contribute significantly to the regulation of fructose levels in Arabidopsis (Chardon et al., 2013Chardon F. Bedu M. Calenge F. Klemens P.A. Spinner L. Clement G. Chietera G. Léran S. Ferrand M. Lacombe B. et al.Leaf fructose content is controlled by the vacuolar transporter SWEET17 in Arabidopsis.Curr. Biol. 2013; 23: 697-702Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar, Klemens et al., 2013Klemens P.A. Patzke K. Deitmer J. Spinner L. Le Hir R. Bellini C. Bedu M. Chardon F. Krapp A. Neuhaus H.E. Overexpression of the vacuolar sugar carrier AtSWEET16 modifies germination, growth, and stress tolerance in Arabidopsis.Plant Physiol. 2013; 163: 1338-1352Crossref PubMed Scopus (187) Google Scholar, Guo et al., 2014Guo W.J. Nagy R. Chen H.Y. Pfrunder S. Yu Y.C. Santelia D. Frommer W.B. Martinoia E. SWEET17, a facilitative transporter, mediates fructose transport across the tonoplast of Arabidopsis roots and leaves.Plant Physiol. 2014; 164: 777-789Crossref PubMed Scopus (173) Google Scholar). The identification of the SWEET proteins as sucrose transporters has raised a number of questions. In particular, since AtSWEET11 and AtSWEET12 are expressed in most Arabidopsis organs (Chen et al., 2012Chen L.Q. Qu X.Q. Hou B.H. Sosso D. Osorio S. Fernie A.R. Frommer W.B. Sucrose efflux mediated by SWEET proteins as a key step for phloem transport.Science. 2012; 335: 207-211Crossref PubMed Scopus (811) Google Scholar), what roles might they play beyond phloem loading? The AtSWEET11 and AtSWEET12 proteins were shown to localize to the plasma membrane and to be expressed in a subset of leaf phloem parenchyma cells (Chen et al., 2012Chen L.Q. Qu X.Q. Hou B.H. Sosso D. Osorio S. Fernie A.R. Frommer W.B. Sucrose efflux mediated by SWEET proteins as a key step for phloem transport.Science. 2012; 335: 207-211Crossref PubMed Scopus (811) Google Scholar). By using transcriptional fusions and performing in situ hybridization experiments on flower stem sections, we confirmed the expression of these genes in the phloem tissues of Arabidopsis flower stems (Figure 1A–1D), but we also demonstrated that both genes are expressed in cells associated with the xylem vessels, and that SWEET11 is also in xylem cells close or adjacent to the cambium region (Figure 1A–1D), suggesting that they have some other role in addition to being the missing link in sucrose phloem loading as suggested by Chen et al., 2012Chen L.Q. Qu X.Q. Hou B.H. Sosso D. Osorio S. Fernie A.R. Frommer W.B. Sucrose efflux mediated by SWEET proteins as a key step for phloem transport.Science. 2012; 335: 207-211Crossref PubMed Scopus (811) Google Scholar. This is supported by the fact that under our conditions, the AtSWEET11 and AtSWEET12 proteins were both capable of transporting glucose and fructose as well as sucrose. Their substrate flexibility was demonstrated by heterologous expression in Xenopus laevis oocytes (Figure 1E) and supported by the complementation of the yeast strain EBY.VW4000 (Supplemental Figure 1), which is deficient in hexose transport. Since cold treatment is known to induce sugar accumulation, we analyzed the behavior of the different mutant lines after a week at 4°C. Interestingly, under long-day conditions, the single sweet11-1 accumulated twice as much glucose and four times more fructose than the wild-type after cold treatment (Figure 1F). This result supports a role in hexose transport, as has been observed for other SWEET proteins such as AtSWEET1, AtSWEET16, and AtSWEET17 (Chen et al., 2010Chen L.Q. Hou B.H. Lalonde S. Takanaga H. Hartung M.L. Qu X.Q. Guo W.J. Kim J.G. Underwood W. Chaudhuri B. Sugar transporters for intercellular exchange and nutrition of pathogens.Nature. 2010; 468: 527-532Crossref PubMed Scopus (939) Google Scholar, Chardon et al., 2013Chardon F. Bedu M. Calenge F. Klemens P.A. Spinner L. Clement G. Chietera G. Léran S. Ferrand M. Lacombe B. et al.Leaf fructose content is controlled by the vacuolar transporter SWEET17 in Arabidopsis.Curr. Biol. 2013; 23: 697-702Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar, Klemens et al., 2013Klemens P.A. Patzke K. Deitmer J. Spinner L. Le Hir R. Bellini C. Bedu M. Chardon F. Krapp A. Neuhaus H.E. Overexpression of the vacuolar sugar carrier AtSWEET16 modifies germination, growth, and stress tolerance in Arabidopsis.Plant Physiol. 2013; 163: 1338-1352Crossref PubMed Scopus (187) Google Scholar, Guo et al., 2014Guo W.J. Nagy R. Chen H.Y. Pfrunder S. Yu Y.C. Santelia D. Frommer W.B. Martinoia E. SWEET17, a facilitative transporter, mediates fructose transport across the tonoplast of Arabidopsis roots and leaves.Plant Physiol. 2014; 164: 777-789Crossref PubMed Scopus (173) Google Scholar). Under long-day conditions, the glucose and fructose contents of the wild-type doubled when the temperature was reduced to 4°C, whereas those of the double mutant did not increase in response to the same cooling (Figure 1F and Supplemental Figure 2A). This is probably because the double mutant had already high levels of cytosolic monosaccharides at 22°C (Supplemental Figure 2A), which were sensed by the cells and prevented further sugar accumulation. However, under short-day conditions, the double mutant accumulated much greater levels of all three sugars than the wild-type in response to cold treatment (Figure 1G and Supplemental Figure 2B), suggesting that cold acclimation is differentially regulated under short- and long-day conditions. Soluble sugars and sucrose in particular are known to act as osmoprotectants and can thus help to maintain cellular integrity and function (Ruan et al., 2010Ruan Y.L. Jin Y. Yang Y.J. Li G.J. Boyer J.S. Sugar input, metabolism, and signaling mediated by invertase: roles in development, yield potential, and response to drought and heat.Mol. Plant. 2010; 3: 942-955Abstract Full Text Full Text PDF PubMed Scopus (539) Google Scholar). Therefore, we sought to determine whether the enhanced sugar accumulation had any effect on the freezing tolerance of the mutants and we measured the electrical conductivity of the plants' leaves, which is a highly reproducible way of quantifying the freezing tolerance of individual plant lines (Nagele and Heyer, 2013Nagele T. Heyer A.G. Approximating subcellular organisation of carbohydrate metabolism during cold acclimation in different natural accessions of Arabidopsis thaliana.New Phytol. 2013; 198: 777-787Crossref PubMed Scopus (89) Google Scholar). The double mutant sweet11-1sweet12-1 released only 28% of its total electrolytes, whereas the wild-type released 43%; no significant difference was observed between the wild-type and the single mutants (Figure 1H). Thus, the double mutant exhibited greater freezing tolerance than the wild-type and both single mutants. The cold-related phenotype is supported by the down-regulation of SWEET11 and SWEET12 expression by cold treatment as shown in Supplemental Figure 2C. Interestingly, when the plants were grown under long-day conditions, the flower stem of the sweet11-1 single mutant was slightly but significantly thinner than that of the wild-type (Figure 1I). Although the sweet12-1 single mutant was not distinguishable from the wild-type, the double mutant had a substantially thinner flower stem (Figure 1I). The reduction in stem diameter observed for the sweet11-1 and sweet11-1sweet12-1 mutants were coupled with a reduction in the phloem and xylem areas (Figure 1J and 1K), which was proportional in that the phloem/xylem ratio remained constant (Supplemental Figures 3 and 4A and 4B). The reduction in phloem and xylem poles could be explained by a reduced number of cells (Figure 1L and 1M and Supplemental Figure 4C). For sweet11-1, the number of cells per phloem pole as well as the number of certain xylem cell categories were slightly but not significantly reduced compared with wild-type (Figure 1L and Supplemental Figure 4C). In the double mutant, we also observed a reduced circular diameter of xylem vessels, which likely contributed to reducing the xylem pole size (Figure 1N). The defects in vascular development are supported by the expression of both AtSWEET11 and AtSWEET12 in the phloem and xylem cells. In addition, the decreased number of xylem cells as well as the smaller diameter of xylem vessels observed in the double mutant likely contribute to increase the resistance to ambient low temperatures. Indeed, it is known that xylem in the floral stem of Arabidopsis shares strong structure–function relationships with the xylem of woody plants for which it has been established that xylem vessels of small diameter are less sensitive to cavitation caused by freezing (Pittermann and Sperry, 2003Pittermann J. Sperry J.S. Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers.Tree Physiol. 2003; 23: 907-914Crossref PubMed Scopus (199) Google Scholar). Both the developmental phenotype and increased freezing tolerance of the double mutant were reminiscent of the eskimo1 mutant phenotype (Lefebvre et al., 2011Lefebvre V. Fortabat M.-N. Ducamp A. North H.M. Maia-Grondard A. Trouverie J. Boursiac Y. Mouille G. Durand-Tardif M. ESKIMO1 disruption in Arabidopsis alters vascular tissue and impairs water transport.PLoS One. 2011; 6: e16645Crossref PubMed Scopus (56) Google Scholar). Although the xylem phenotypes we observed in the sweet11-1 and sweet11-1sweet12-1 mutants were less dramatic than the esk1 xylem phenotype, this observation prompted us to analyze the chemical composition of the cell walls. Using Fourier-transformed infrared spectroscopy, we analyzed the cell walls of the xylem cell in flower stem cross sections (Figure 1O and Supplemental Figures 4A and 5). We showed that the spectra for the sweet12-1 mutant exhibited significantly lower absorbance at wavenumbers between 1800 and 1700 cm−1 than observed for the wild-type (Figure 1O and Supplemental Figure 4C). Absorbances in this region of the spectrum typically correspond to ester linkages, esterified pectins or C=O stretching on acetyl groups (1730 cm−1). The absorbances for the single sweet11-1, sweet12-1, and double sweet11-1sweet12-1 mutants also differed significantly from those for the wild-type in two other regions of the spectrum: the first between 1693 and 1530 cm−1, and the second between 1130 and 1330 cm−1. Based on previous IR analyses of plant cell walls, the first of these two regions corresponds to the COOH groups of pectic polysaccharides, which are also known as acidic pectins, and the second has been assigned to C=O and C–O vibrations in pectic rhamnogalacturonan I and rhamnogalacturonan II or O-acetyl moieties found in plant cell wall polymers (1230, 1240, 1245 cm−1) (Figure 1O and Supplemental Figure 4B, 4C, and 4D). Although pectins are not abundant in secondary cell walls, pectin methylesterification appears to be a prerequisite for lignin modification during secondary cell wall deposition in xylem cells. In addition, some Arabidopsis mutants have been shown to exhibit defects in secondary cell wall formation associated with a deficiency in pectin content (Pelloux et al., 2007Pelloux J. Rusterucci C. Mellerowicz E.J. New insights into pectin methylesterase structure and function.Trends Plant Sci. 2007; 12: 267-277Abstract Full Text Full Text PDF PubMed Scopus (569) Google Scholar). A final set of differences was observed at around 890 cm−1 and 1369 cm−1; these regions are associated with crystalline polysaccharide components such as cellulose (β-linked glucan polymers at 898 cm−1) or deformation of C–H linkages in the methyl group of O-acetyl moieties (1369 cm−1). All three mutants exhibited significantly weaker absorbances than the wild-type in this region, suggesting that they have lower levels of crystalline cellulose and a modified xylan acetylation. When compared with each other, single and double mutants showed very similar average absorbance profiles (Supplemental Figure 5A, 5E–5G). Few significant differences could be observed. sweet11-1 exhibited significantly higher absorbances at wave numbers between 1700 and 1800 cm−1 and lower absorbances at 1450 and 1680 cm−1 compared with sweet12-1 (Supplemental Figure 5A and 5E). Compared with the double mutant, sweet11-1 showed significantly lower absorbances between wave numbers 1735 and 1600 cm−1, and sweet12-1 showed significantly lower absorbances at wave numbers between 1740 and 1800 cm−1 (Supplemental Figure 5A, 5F, and 5G). In conclusion, the xylem cell walls of both sweet single mutants and the double mutant exhibited severe chemical modifications. The overall phenotypical characteristics of single and double mutants as well as the fact that the double mutant phenotype differs from that of each single mutant suggest that SWEET 11 and SWEET 12 proteins play a synergistic role in the regulation of sugar transport. Two important issues that currently remain unclear are how the pools of carbohydrate skeletons required for the synthesis of these secondary cell wall components are transported to this non-photosynthetic tissue, and how the depletion of sugar precursors in the xylem cells would affect the development and structure of the secondary cell wall. The results presented herein support the hypothesis that, in addition to their contribution to phloem loading in source leaves, the AtSWEET11 and AtSWEET12 proteins act as sugar exporters that deliver carbon-containing skeletons to developing xylem cells in order to support secondary cell wall formation. In addition, due to their expression in both the phloem and xylem of the flower stem, we cannot exclude the possibility that they may contribute, together with additional SWEET proteins or sugar transporters, to the transport of sugar from the phloem to nourish adjacent stem tissues. This work was supported by the Swedish Research Council for Agriculture (FORMAS), the Swedish Foundation for Strategic Research (SSF) the Swedish Research Council for Research and Innovation for Sustainable Growth (VINNOVA), the K. & A. Wallenberg Foundation and the Carl Trygger Foundation (to C.B.) and by the Deutsche Forschungsgemeinschaft (FOR1061) (to E.N.).

Since the preindustrial era, the average surface ocean pH has declined by 0.1 pH units and is predicted to decline by an additional 0.3 units by the year 2100. Although subtle, this decreasing pH has profound effects on the seawater saturation state of carbonate minerals and is thus predicted to impact on calcifying organisms. Among these are the scleractinian corals, which are the main builders of tropical coral reefs. Several recent studies have evaluated the physiological impact of low pH, particularly in relation to coral growth and calcification. However, very few studies have focused on the impact of low pH at the global molecular level. In this context we investigated global transcriptomic modifications in a scleractinian coral (Pocillopora damicornis) exposed to pH 7.4 compared to pH 8.1 during a 3-week period. The RNAseq approach shows that 16% of our transcriptome was affected by the treatment with 6% of upregulations and 10% of downregulations. A more detailed analysis suggests that the downregulations are less coordinated than the upregulations and allowed the identification of several biological functions of interest. In order to better understand the links between these functions and the pH, transcript abundance of 48 candidate genes was quantified by q-RT-PCR (corals exposed at pH 7.2 and 7.8 for 3 weeks). The combined results of these two approaches suggest that pH≥7.4 induces an upregulation of genes coding for proteins involved in calcium and carbonate transport, conversion of CO2 into HCO3(-) and organic matrix that may sustain calcification. Concomitantly, genes coding for heterotrophic and autotrophic related proteins are upregulated. This can reflect that low pH may increase the coral energy requirements, leading to an increase of energetic metabolism with the mobilization of energy reserves. In addition, the uncoordinated downregulations measured can reflect a general trade-off mechanism that may enable energy reallocation.

In plants, the root is a typical sink organ that relies exclusively on the import of sugar from the aerial parts. Sucrose is delivered by the phloem to the most distant root tips and, en route to the tip, is used by the different root tissues for metabolism and storage. Besides, a certain portion of this carbon is exuded in the rhizosphere, supplied to beneficial microorganisms and diverted by parasitic microbes. The transport of sugars toward these numerous sinks either occurs symplastically through cell connections (plasmodesmata) or is apoplastically mediated through membrane transporters (MST, mononsaccharide tranporters, SUT/SUC, H+/sucrose transporters and SWEET, Sugar will eventually be exported transporters) that control monosaccharide and sucrose fluxes. Here, we review recent progresses on carbon partitioning within and outside roots, discussing membrane transporters involved in plant responses to biotic and abiotic factors.

Chlamydia spp. are strictly intracellular pathogens that grow inside a vacuole, called an inclusion. They possess genes encoding proteins homologous to components of type III secretion machineries, which, in other bacterial pathogens, are involved in delivery of bacterial proteins within or through the membrane of eukaryotic host cells. Inc proteins are chlamydial proteins that are associated with the inclusion membrane and are characterized by the presence of a large hydrophobic domain in their amino acid sequence. To investigate whether Inc proteins and other proteins exhibiting a similar hydropathic profile might be secreted by a type III system, we used a heterologous secretion system. Chimeras were constructed by fusing the N-terminal part of these proteins with a reporter, the Cya protein of Bordetella pertussis, and these were expressed in various strains of Shigella flexneri. We demonstrate that these hybrid proteins are secreted by the type III secretion system of S. flexneri, thereby providing evidence that IncA, IncB and IncC are secreted by a type III mechanism in chlamydiae. Moreover, we show that three other proteins from Chlamydia pneumoniae, all of which have in common the presence of a large hydrophobic domain, are also secreted by S. flexneri type III secretion machinery.

Genetic changes conferring adaptation to a new environment may induce a fitness cost in the previous environment. Although this prediction has been verified in laboratory conditions, few studies have tried to document this cost directly in natural populations. Here, we evaluated the pleiotropic effects of insecticide resistance on putative fitness components of the mosquito Culex pipiens. Experiments using different larval densities were performed during the summer in two natural breeding sites. Two loci that possess alleles conferring organophosphate (OP) resistance were considered: ace-1 coding for an acetylcholinesterase (AChE1, the OP target) and Ester, a ''super locus" including two closely linked loci coding for esterases A and B. Resistance ace-1 alleles coding for a modified AChE1 were associated with a longer development time and shorter wing length. The pleiotropic effects of two resistance alleles Ester1 and Ester4 coding for the overproduced esterases A1 and A4-B4, respectively, were more variable. Both A1 and A4-B4 reduced wing length, although only A1 was associated with a longer preimaginal stage. The fluctuating asymmetry (FA) of the wing did not respond to the presence or to the interaction of resistance alleles at the two loci at any of the density levels tested. Conversely, the FA of one wing section decreased when larval density increased. This may be the consequence of selection against less developmentally stable individuals. The results are discussed in relation to the local evolution of insecticide resistance genes.

Standardised terminology in science is important for clarity of interpretation and communication. In invasion science - a dynamic and rapidly evolving discipline - the proliferation of technical terminology has lacked a standardised framework for its development. The result is a convoluted and inconsistent usage of terminology, with various discrepancies in descriptions of damage and interventions. A standardised framework is therefore needed for a clear, universally applicable, and consistent terminology to promote more effective communication across researchers, stakeholders, and policymakers. Inconsistencies in terminology stem from the exponential increase in scientific publications on the patterns and processes of biological invasions authored by experts from various disciplines and countries since the 1990s, as well as publications by legislators and policymakers focusing on practical applications, regulations, and management of resources. Aligning and standardising terminology across stakeholders remains a challenge in invasion science. Here, we review and evaluate the multiple terms used in invasion science (e.g. 'non-native', 'alien', 'invasive' or 'invader', 'exotic', 'non-indigenous', 'naturalised', 'pest') to propose a more simplified and standardised terminology. The streamlined framework we propose and translate into 28 other languages is based on the terms (i) 'non-native', denoting species transported beyond their natural biogeographic range, (ii) 'established non-native', i.e. those non-native species that have established self-sustaining populations in their new location(s) in the wild, and (iii) 'invasive non-native' - populations of established non-native species that have recently spread or are spreading rapidly in their invaded range actively or passively with or without human mediation. We also highlight the importance of conceptualising 'spread' for classifying invasiveness and 'impact' for management. Finally, we propose a protocol for classifying populations based on (i) dispersal mechanism, (ii) species origin, (iii) population status, and (iv) impact. Collectively and without introducing new terminology, the framework that we present aims to facilitate effective communication and collaboration in invasion science and management of non-native species.

Insects are major contributors to our understanding of the interaction between transposable elements (TEs) and their hosts, owing to seminal discoveries, as well as to the growing number of sequenced insect genomes and population genomics and functional studies. Insect TE landscapes are highly variable both within and across insect orders, although phylogenetic relatedness appears to correlate with similarity in insect TE content. This correlation is unlikely to be solely due to inheritance of TEs from shared ancestors and may partly reflect preferential horizontal transfer of TEs between closely related species. The influence of insect traits on TE landscapes, however, remains unclear. Recent findings indicate that, in addition to being involved in insect adaptations and aging, TEs are seemingly at the cornerstone of insect antiviral immunity. Thus, TEs are emerging as essential insect symbionts that may have deleterious or beneficial consequences on their hosts, depending on context.

The alpha-proteobacteria Wolbachia are the most widespread endosymbionts in arthropods and nematodes. Mainly maternally inherited, these so-called sex parasites have selected several strategies that increase their vertical dispersion in host populations. However, the lack of congruence between the Wolbachia and their host phylogenies suggests frequent horizontal transfers. One way that could be used for horizontal Wolbachia transfers between individuals is predation. The aim of this study was to test whether horizontal passage of Wolbachia is possible when an uninfected terrestrial isopod eats an infected one. After having eaten Armadillidium vulgare harbouring Wolbachia, the predator-recipients (the two woodlice A. vulgare and Porcellio dilatatus dilatatus) that were initially Wolbachia-free were tested positive for the presence of Wolbachia both by quantitative PCR and Fluorescence in situ Hybridization (FISH). Even if the titers were low compared to vertically infected individuals, this constitutes the first demonstration of Wolbachia occurrence in various organs of an initially uninfected host after eating an infected one.

BACKGROUND: Woodlice are recognized as keystone species in terrestrial ecosystems due to their role in the decomposition of organic matter. Thus, they contribute to lignocellulose degradation and nutrient cycling in the environment together with other macroarthropods. Lignocellulose is the main component of plants and is composed of cellulose, lignin and hemicellulose. Its digestion requires the action of multiple Carbohydrate-Active enZymes (called CAZymes), typically acting together as a cocktail with complementary, synergistic activities and modes of action. Some invertebrates express a few endogenous lignocellulose-degrading enzymes but in most species, an efficient degradation and digestion of lignocellulose can only be achieved through mutualistic associations with endosymbionts. Similar to termites, it has been suspected that several bacterial symbionts may be involved in lignocellulose degradation in terrestrial isopods, by completing the CAZyme repertoire of their hosts. RESULTS: To test this hypothesis, host transcriptomic and microbiome shotgun metagenomic datasets were obtained and investigated from the pill bug Armadillidium vulgare. Many genes of bacterial and archaeal origin coding for CAZymes were identified in the metagenomes of several host tissues and the gut content of specimens from both laboratory lineages and a natural population of A. vulgare. Some of them may be involved in the degradation of cellulose, hemicellulose, and lignin. Reconstructing a lignocellulose-degrading microbial community based on the prokaryotic taxa contributing relevant CAZymes revealed two taxonomically distinct but functionally redundant microbial communities depending on host origin. In parallel, endogenous CAZymes were identified from the transcriptome of the host and their expression in digestive tissues was demonstrated by RT-qPCR, demonstrating a complementary enzyme repertoire for lignocellulose degradation from both the host and the microbiome in A. vulgare. CONCLUSIONS: Our results provide new insights into the role of the microbiome in the evolution of terrestrial isopods and their adaptive radiation in terrestrial habitats.

Polyethylene (PE), one of the most prominent synthetic polymers used worldwide, is very poorly biodegradable in the natural environment. Consequently, PE represents by itself more than half of all plastic wastes. PE biodegradation is achieved through the combination of abiotic and biotic processes. Several microorganisms have been shown to grow on the surface of PE materials, among which are the species of the Rhodococcus genus, suggesting a potent ability of these microorganisms to use, at least partly, PE as a potent carbon source. However, most of them, if not all, fail to induce a clear-cut degradation of PE samples, showing that bottlenecks to reach optimal biodegradation clearly exist. To identify the pathways involved in PE consumption, we used in the present study a combination of RNA-sequencing and lipidomic strategies. We show that short-term exposure to various forms of PE, displaying different molecular weight distributions and oxidation levels, lead to an increase in the expression of 158 genes in a Rhodococcus representative, R. ruber. Interestingly, one of the most up-regulated pathways is related to alkane degradation and β-oxidation of fatty acids. This approach also allowed us to identify metabolic limiting steps, which could be fruitfully targeted for optimized PE consumption by R. ruber.

BACKGROUND: Ambrosia artemisiifolia is a North American native that has become one of the most problematic invasive plants in Europe and Asia. We studied its worldwide population genetic structure, using both nuclear and chloroplast microsatellite markers and an unprecedented large population sampling. Our goals were (i) to identify the sources of the invasive populations; (ii) to assess whether all invasive populations were founded by multiple introductions, as previously found in France; (iii) to examine how the introductions have affected the amount and structure of genetic variation in Europe; (iv) to document how the colonization of Europe proceeded; (v) to check whether populations exhibit significant heterozygote deficiencies, as previously observed. PRINCIPAL FINDINGS: We found evidence for multiple introductions of A. artemisiifolia, within regions but also within populations in most parts of its invasive range, leading to high levels of diversity. In Europe, introductions probably stem from two different regions of the native area: populations established in Central Europe appear to have originated from eastern North America, and Eastern European populations from more western North America. This may result from differential commercial exchanges between these geographic regions. Our results indicate that the expansion in Europe mostly occurred through long-distance dispersal, explaining the absence of isolation by distance and the weak influence of geography on the genetic structure in this area in contrast to the native range. Last, we detected significant heterozygote deficiencies in most populations. This may be explained by partial selfing, biparental inbreeding and/or a Wahlund effect and further investigation is warranted. CONCLUSIONS: This insight into the sources and pathways of common ragweed expansion may help to better understand its invasion success and provides baseline data for future studies on the evolutionary processes involved during range expansion in novel environments.

Glioblastoma (GBM) is considered by the WHO classification to represent the most malignant grade of the astrocytic tumors. However, a subset of GBM includes recognizable areas with oligodendroglial features, suggesting that some GBM may also have an oligodendroglial origin. The aim of this study was to analyze the molecular profile of GBM associated with an oligodendroglial component (GBMO). We analyzed a series of 25 GBMO. Loss of heterozygosity (LOH) on 1p and 19q, known as common markers of oligodendroglial tumors, were observed in 40% and 60% of cases, respectively; 72% of the tumors displayed one or both of these markers. All but 4 tumors (84%) showed alterations known to be preferentially involved in the progression of astrocytic tumors to GBM, such as EGFR amplification (44%), P16 deletion (48%), LOH on 10q (64%), PTEN (20%), and TP53 (24%) mutations. Therefore, GBMO displayed all the genetic aberrations found in "standard" GBM with a comparable incidence, but differed from GBM by having a higher rate of LOH on 1p and 19q. These results suggest that GBMO might represent a subgroup of tumors of oligodendroglial origin that is distinct from the "standard" GBM in terms of tumorigenesis pathway.