Genome-wide annotation and functional identification of aphid GLUT-like sugar transporters

Background

Phloem feeding insects, such as aphids, feed almost continuously on plant phloem sap, a liquid diet that contains high concentrations of sucrose (a disaccharide comprising of glucose and fructose). To access the available carbon, aphids hydrolyze sucrose in the gut lumen and transport its constituent monosaccharides, glucose and fructose. Although sugar transport plays a critical role in aphid nutrition, the molecular basis of sugar transport in aphids, and more generally across all insects, remains poorly characterized. Here, using the latest release of the pea aphid, Acyrthosiphon pisum, genome we provide an updated gene annotation and expression profile of putative sugar transporters. Finally, gut expressed sugar transporters are functionally expressed in yeast and screened for glucose and fructose transport activity.

Results

In this study, using a de novo approach, we identified 19 sugar porter (SP) family transporters in the A. pisum genome. Gene expression analysis, based on 214, 834 A. pisum expressed sequence tags, supports 17 sugar porter family transporters being actively expressed in adult female aphids. Further analysis, using quantitative PCR identifies 4 transporters, A. pisum sugar transporter 1, 3, 4 and 9 (ApST1, ApST3, ApST4 and ApST9) as highly expressed and/or enriched in gut tissue. When expressed in a Saccharomyces cerevisiae hexose transporter deletion mutant (strain EBY.VW4000), only ApST3 (previously characterized) and ApST4 (reported here) transport glucose and fructose resulting in functional rescue of the yeast mutant. Here we characterize ApST4, a 491 amino acid protein, with 12 predicted transmembrane regions, as a facilitative glucose/fructose transporter. Finally, phylogenetic reconstruction reveals that ApST4, and related, as yet uncharacterized insect transporters are phylogenetically closely related to human GLUT (SLC2A) class I facilitative glucose/fructose transporters.

Conclusions

The gut enhanced expression of ApST4, and the transport specificity of its product is consistent with ApST4 functioning as a gut glucose/fructose transporter. Here, we hypothesize that both ApST3 (reported previously) and ApST4 (reported here) function at the gut interface to import glucose and fructose from the gut lumen.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-647) contains supplementary material, which is available to authorized users.     

ISOLATED GRAPTOLITES FROM THE LITUIGRAPTUS CONVOLUTUS BIOZONE (SILURIAN, LLANDOVERY) OF DALARNA, SWEDEN

Abstract:  Isolated material of 13 graptolite species from the Aeronian (middle Llandovery) Lituigraptus convolutus Biozone is described. A considerable amount of late astogenetic peridermal thickening is revealed in Normalograptus scalaris and Rivagraptus bellulus . As a result, in the former, thecal morphology is modified from climacograptid to pseudoglyptograptid; in both species, the virgella becomes robust. In Metaclimacograptus minimus and Me. sp., it is shown that the dorsal metathecal wall forms the genicular hood, whereas in N. nikolayevi , the infragenicular wall of the succeeding theca forms the distal thecal apertural margin. Pribylograptus argutus exhibits typical pribylograptid thecae along the length of the available rhabdosome fragments. Characters differentiating Campograptus lobiferus from C. harpago include the greater dorso-ventral width and more rapid increase in dorso-ventral width of the former and the greater recurving of distal thecae and presence of thecal spines/processes on all thecae of the latter. Lituigraptus convolutus has rastritiform thecae proximally; thecal apertures throughout the rhabdosome are crescentic and laterally expanded.     

Population genetic structure in Myrtus communis L. in a chronically fragmented landscape in the Mediterranean: can gene flow counteract habitat perturbation?

Ancient managed landscapes provide ideal opportunities to assess the consequences of habitat fragmentation on the patterns of genetic diversity and gene flow in long-lived plant species. Using amplified fragment length polymorphism (AFLP) and allozyme markers, we quantified seed-mediated gene flow and population genetic diversity and structure in 14 populations of Myrtus communis (myrtle), a common endozoochorous shrub species of forest patches in lowland agricultural Mediterranean areas. Overall, allozyme diversity for myrtle was low (P₉₅   =   25%; A   =   1.411; H_e = 0.085) compared to other known populations, and a significant portion of populations (57%) had lower levels of allelic diversity and/or heterozygosity than expected at random, as shown by simulated resampling of the whole diversity of the landscape. We found significant correlations between allozyme variability and population size and patch isolation, but no significant inbreeding in any population. Genetic differentiation among populations for both allozyme and AFLP markers was significant (Φ_ST = 0.144 and Φ_ST = 0.142, respectively) but an isolation-by-distance pattern was not detected. Assignment tests on AFLP data indicated a high immigration rate in the populations ( ca. 20–22%), likely through effective seed dispersal across the landscape by birds and mammals. Our results suggest that genetic isolation is not the automatic outcome of habitat destruction since substantial levels of seed-mediated gene flow are currently detectable. However, even moderate rates of gene flow seem insufficient in this long-lived species to counteract the genetic erosion and differentiation imposed by chronic habitat destruction.     

Litterfall of epiphytic macrolichens in Nothofagus forests of northern Patagonia,Argentina: Relation to stand age and precipitation

Abstract: The objective of this study was to analyse how stand age and precipitation influence abundance and diversity of epiphytic macrolichens in southern beech Nothofagus forests, estimated by lichen litter sampling. Five sites of Nothofagus dombeyi (Mirbel) Oersted were selected in Nahuel Huapi National Park, Argentina. At each site, lichen fragments from the forest floor were collected at 12.5 m² plots in pairs of young and mature N. dombeyi forest. Additionally, two sites with multi‐aged subalpine Nothofagus pumilio (Poepp. et Endl.) Krasser forest were investigated in a similar manner. Average litterfall biomass per stand varied from less than 1 kg ha^?1 in a young low‐precipitation stand to a maximum of 20 kg ha^?1 in a mature high‐precipitation stand. In places with higher precipitation, litterfall biomass in N. dombeyi forest was considerably higher in old stands as compared with young ones. In places with less than 2000 mm of precipitation, differences in biomass were less pronounced. Old humid stands contained about twice as many taxa in the litter as old low‐precipitation stands and young stands in general. Mature stands in low‐precipitation sites only contained 17% of the litter biomass as compared with mature stands in high‐precipitation sites. Epiphytic lichen composition changed from predominating fruticose lichens (Usnea spp. and Protousnea spp.) in low‐precipitation stands to Pseudocyphellaria spp., Nephroma spp. and other foliose lichens, in the high‐precipitation stands. There were no clear differences in the proportion of fruticose and foliose lichens between young and old stands. Fruticose lichens dominated litter biomass in both N. pumilio sites.     

Photosynthetic responses of soybean (Glycine max L.) to heat‐induced electrical signalling are predominantly governed by modifications of mesophyll conductance for CO2

In recent years, the effect of heat‐induced electrical signalling on plant photosynthetic activity has been demonstrated for many plant species. However, the underlying triggers of the resulting transient inhibition of photosynthesis still remain unknown. To further investigate on this phenomenon, we focused in our present study on soybean (Glycine max L.) on the direct effect of signal transmission in the leaf mesophyll on conductance for CO₂ diffusion in the mesophyll (g_m) and detected a drastic decline in g_m following the electrical signal, whereas the photosynthetic electron transport rate (ETR) was only marginally affected. In accordance with the drop in net photosynthesis (A_N), energy dispersive X‐ray analysis (EDXA) revealed a shift of K, Mg, O and P on leaf chloroplasts. Control experiments under elevated CO₂ conditions proved the transient reduction of A_N, ETR, the chloroplast CO₂ concentration (C_c) and g_m to be independent of the external CO₂ regime, whereas the effect of the electrical signal on stomatal conductance for CO₂ (g_s) turned out much less distinctive. We therefore conclude that the effect of electrical signalling on photosynthesis in soybean is triggered by its immediate effects on g_m.     

The innate immune receptor MDA5 limits rotavirus infection but promotes cell death and pancreatic inflammation

Melanoma differentiation‐associated protein 5 (MDA5) mediates the innate immune response to viral infection. Polymorphisms in IFIH1, the gene coding for MDA5, correlate with the risk of developing type 1 diabetes (T1D). Here, we demonstrate that MDA5 is crucial for the immune response to enteric rotavirus infection, a proposed etiological agent for T1D. MDA5 variants encoded by minor IFIH1 alleles associated with lower T1D risk exhibit reduced activity against rotavirus infection. We find that MDA5 activity limits rotavirus infection not only through the induction of antiviral interferons and pro‐inflammatory cytokines, but also by promoting cell death. Importantly, this MDA5‐dependent antiviral response is specific to the pancreas of rotavirus‐infected mice, similar to the autoimmunity associated with T1D. These findings imply that MDA5‐induced cell death and inflammation in the pancreas facilitate progression to autoimmune destruction of pancreatic β‐cells.     

Nine new polymorphic microsatellite loci for the amplification of archived otolith DNA of Atlantic cod,Gadus morhua L.

Nine out of 22 microsatellite primers tested were successfully amplified on three samples of cod Gadus morhua L. (two contemporary and one archived otolith samples). All loci were polymorphic (5–23 alleles/locus). The average observed heterozygosity across loci and samples was 0.625, ranging from 0.294 to 0.895 at each locus. All loci were under Hardy–Weinberg equilibrium, except PGmo56 that showed significant excess of heterozygotes in all studied samples. The isolated loci were suitable for degraded DNA and therefore useful for conducting a long‐term temporal study with DNA obtained from archived otoliths of cod.     

Subalpine grassland carbon dioxide fluxes indicate substantial carbon losses under increased nitrogen deposition,but not at elevated ozone concentration

Ozone (O₃) and nitrogen (N) deposition affect plant carbon (C) dynamics and may change ecosystem C‐sink/‐source properties. We studied effects of increased background [O₃] (up to [ambient] × 2) and increased N deposition (up to +50 kg ha^?1 a^?1) on mature, subalpine grassland during the third treatment year. During 10 days and 13 nights, distributed evenly over the growth period of 2006, we measured ecosystem‐level CO₂ exchange using a static cuvette. Light dependency of gross primary production (GPP) and temperature dependency of ecosystem respiration rates (R_eco) were established. Soil temperature, soil water content, and solar radiation were monitored. Using R_eco and GPP values, we calculated seasonal net ecosystem production (NEP), based on hourly averages of global radiation and soil temperature. Differences in NEP were compared with differences in soil organic C after 5 years of treatment. The high [O₃] had no effect on aboveground dry matter productivity (DM), but seasonal mean rates of both R_eco and GPP decreased ca. 8%. NEP indicated an unaltered growing season CO₂–C balance. High N treatment, with a +31% increase in DM, mean R_eco increased ca. 3%, but GPP decreased ca. 4%. Consequently, seasonal NEP yielded a 53.9 g C m^?2 (±22.05) C loss compared with control. Independent of treatment, we observed a negative NEP of 146.4 g C m^?2 (±15.3). Carbon loss was likely due to a transient management effect, equivalent to a shift from pasture to hay meadow and a drought effect, specific to the 2006 summer climate. We argue that this resulted from strongly intensified soil microbial respiration, following mitigation of nutrient limitation. There was no interaction between O₃ and N treatments. Thus, during the 2006 growing season, the subalpine grassland lost >2% of total topsoil organic C as respired CO₂, with increased N deposition responsible for one‐third of that loss.     

Extensive Pollen Flow but Few Pollen Donors and High Reproductive Variance in an Extremely Fragmented Landscape

Analysing pollen movement is a key to understanding the reproductive system of plant species and how it is influenced by the spatial distribution of potential mating partners in fragmented populations. Here we infer parameters related to levels of pollen movement and diversity of the effective pollen cloud for the wind-pollinated shrub Pistacia lentiscus across a highly disturbed landscape using microsatellite loci. Paternity analysis and the indirect KinDist and Mixed Effect Mating models were used to assess mating patterns, the pollen dispersal kernel, the effective number of males (N_ep) and their relative individual fertility, as well as the existence of fine-scale spatial genetic structure in adult plants. All methods showed extensive pollen movement, with high rates of pollen flow from outside the study site (up to 73–93%), fat-tailed dispersal kernels and large average pollination distances (δ = 229–412 m). However, they also agreed in detecting very few pollen donors (N_ep = 4.3–10.2) and a large variance in their reproductive success: 70% of males did not sire any offspring among the studied female plants and 5.5% of males were responsible for 50% of pollinations. Although we did not find reduced levels of genetic diversity, the adult population showed high levels of biparental inbreeding (14%) and strong spatial genetic structure (S_p = 0.012), probably due to restricted seed dispersal and scarce safe sites for recruitment. Overall, limited seed dispersal and the scarcity of successful pollen donors can be contributing to generate local pedigrees and to increase inbreeding, the prelude of genetic impoverishment.