AhpF and other NADH:peroxiredoxin oxidoreductases, homologues of low Mr thioredoxin reductase.

A group of bacterial flavoproteins related to thioredoxin reductase contain an additional approximately 200-amino-acid domain including a redox-active disulfide center at their N-termini. These flavoproteins, designated NADH:peroxiredoxin oxidoreductases, catalyze the pyridine-nucleotide-dependent reduction of cysteine-based peroxidases (e.g. Salmonella typhimurium AhpC, a member of the peroxiredoxin family) which in turn reduce H2O2 or organic hydroperoxides. These enzymes catalyze rapid electron transfer (kcat > 165 s-1) through one tightly bound FAD and two redox-active disulfide centers, with the N-terminal-most disulfide center acting as a redox mediator between the thioredoxin-reductase-like part of these proteins and the peroxiredoxin substrates. A chimeric protein with the first 207 amino acids of S. typhimurium AhpF attached to the N-terminus of Escherichia coli thioredoxin reductase exhibits very high NADPH:peroxiredoxin oxidoreductase and thioredoxin reductase activities. Catalytic turnover by NADH:peroxiredoxin oxidoreductases may involve major domain rotations, analogous to those proposed for bacterial thioredoxin reductase, and cycling of these enzymes between two electron-reduced (EH2) and four electron-reduced (EH4) redox states.     

Sequential Reductive Dechlorination of meta-Chlorinated Polychlorinated Biphenyl Congeners in Sediment Microcosms by Two Different Chloroflexi Phylotypes

Three species within a deeply branching cluster of the Chloroflexi are the only microorganisms currently known to anaerobically transform polychlorinated biphenyls (PCBs) by the mechanism of reductive dechlorination. A selective PCR primer set was designed that amplifies the 16S rRNA genes of a monophyletic group within the Chloroflexi including Dehalococcoides spp. and the o-17/DF-1 group. Assays for both qualitative and quantitative analyses by denaturing gradient gel electrophoresis and most probable number-PCR, respectively, were developed to assess sediment microcosm enrichments that reductively dechlorinated PCBs 101 (2,2′,4,5,5′-CB) and 132 (2,2′,3,3′,4,6′-CB). PCB 101 was reductively dechlorinated at the para-flanked meta position to PCB 49 (2,2′,4,5′-CB) by phylotype DEH10, which belongs to the Dehalococcoides group. This same species reductively dechlorinated the para- and ortho-flanked meta-chlorine of PCB 132 to PCB 91 (2,2′,3′,4,6′-CB). However, another phylotype designated SF1, which is more closely related to the o-17/DF-1 group, was responsible for the subsequent dechlorination of PCB 91 to PCB 51 (2,2′,4,6′-CB). Using the selective primer set, an increase in 16S rRNA gene copies was observed only with actively dechlorinating cultures, indicating that PCB-dechlorinating activities by both phylotype DEH10 and SF1 were linked to growth. The results suggest that individual species within the Chloroflexi exhibit a limited range of congener specificities and that a relatively diverse community of species within a deeply branching group of Chloroflexi with complementary congener specificities is likely required for the reductive dechlorination of different PCBs congeners in the environment.     

Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.     

T-cell-mediated inflammation does not contribute to the maintenance of airway dysfunction in mice.

T-cell-mediated airway inflammation is considered to be critical in the pathogenesis of airway hyperresponsiveness (AHR). We have described a mouse model in which chronic allergen exposure results in sustained AHR and aspects of airway remodeling and here sought to determine whether eliminating CD4(+) and CD8(+) cells, at a time when airway remodeling had occurred, would attenuate this sustained AHR. Sensitized BALB/c mice were subjected to either brief or chronic periods of allergen exposure and studied 24 h after brief or 4 wk after chronic allergen exposure. In both models, mice received three treatments with anti-CD4 and -CD8 monoclonal antibodies during the 10 days before outcome measurements. Outcomes included in vivo airway responsiveness to intravenous methacholine, CD4(+) and CD8(+) cell counts of lung and spleen using flow cytometric analysis, and airway morphometry using a computer-based image analysis system. Compared with saline control mice, brief allergen challenge resulted in AHR, which was eliminated by antibody treatment. Chronic allergen challenge resulted in sustained AHR and indexes of airway remodeling. This sustained AHR was not reversed by antibody treatment, even though CD4(+) and CD8(+) cells were absent in lung and spleen. These results indicate that T-cell-mediated inflammation is critical for development of AHR associated with brief allergen exposure, but is not necessary to maintain sustained AHR.     

Over-invasion in a freshwater ecosystem: newly introduced virile crayfish (Orconectes virilis) outcompete established invasive signal crayfish (Pacifastacus leniusculus)

Biological invasions are a key threat to freshwater biodiversity, and identifying determinants of invasion success is a global conservation priority. The establishment of introduced species is predicted to be hindered by pre-existing, functionally similar invasive species. Over a five-year period we, however, find that in the River Lee (UK), recently introduced non-native virile crayfish (Orconectes virilis) increased in range and abundance, despite the presence of established alien signal crayfish (Pacifastacus leniusculus). In regions of sympatry, virile crayfish had a detrimental effect on signal crayfish abundance but not vice versa. Competition experiments revealed that virile crayfish were more aggressive than signal crayfish and outcompeted them for shelter. Together, these results provide early evidence for the potential over-invasion of signal crayfish by competitively dominant virile crayfish. Based on our results and the limited distribution of virile crayfish in Europe, we recommend that efforts to contain them within the Lee catchment be implemented immediately.     

A dynamic leaf gas‐exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies

Rising atmospheric [CO₂], c_a, is expected to affect stomatal regulation of leaf gas‐exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas‐exchange that include maintaining a constant leaf internal [CO₂], c_i, a constant drawdown in CO₂ (c_a ? c_i), and a constant c_i/c_a. These strategies can result in drastically different consequences for leaf gas‐exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas‐exchange responses to varying c_a. The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas‐exchange responses to c_a. To assess leaf gas‐exchange regulation strategies, we analyzed patterns in c_i inferred from studies reporting C stable isotope ratios (δ¹³C) or photosynthetic discrimination (?) in woody angiosperms and gymnosperms that grew across a range of c_a spanning at least 100 ppm. Our results suggest that much of the c_a‐induced changes in c_i/c_a occurred across c_a spanning 200 to 400 ppm. These patterns imply that c_a ? c_i will eventually approach a constant level at high c_a because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant c_i. Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low c_a, when additional water loss is small for each unit of C gain, and increasingly water‐conservative at high c_a, when photosystems are saturated and water loss is large for each unit C gain.     

Climatic drivers of leaf traits and genetic divergence in the tree Annona crassiflora: a broad spatial survey in the Brazilian savannas

The Cerrado is the largest South American savanna and encompasses substantial species diversity and environmental variation. Nevertheless, little is known regarding the influence of the environment on population divergence of Cerrado species. Here, we searched for climatic drivers of genetic (nuclear microsatellites) and leaf trait divergence in Annona crassiflora, a widespread tree in the Cerrado. The sampling encompassed all phytogeographic provinces of the continuous area of the Cerrado and included 397 individuals belonging to 21 populations. Populations showed substantial genetic and leaf trait divergence across the species' range. Our data revealed three spatially defined genetic groups (eastern, western and southern) and two morphologically distinct groups (eastern and western only). The east‐west split in both the morphological and genetic data closely mirrors previously described phylogeographic patterns of Cerrado species. Generalized linear mixed effects models and multiple regression analyses revealed several climatic factors associated with both genetic and leaf trait divergence among populations of A. crassiflora. Isolation by environment (IBE) was mainly due to temperature seasonality and precipitation of the warmest quarter. Populations that experienced lower precipitation summers and hotter winters had heavier leaves and lower specific leaf area. The southwestern area of the Cerrado had the highest genetic diversity of A. crassiflora, suggesting that this region may have been climatically stable. Overall, we demonstrate that a combination of current climate and past climatic changes have shaped the population divergence and spatial structure of A. crassiflora. However, the genetic structure of A. crassiflora reflects the biogeographic history of the species more strongly than leaf traits, which are more related to current climate.     

Host Plant Physiology and Mycorrhizal Functioning Shift across a Glacial through Future [CO2] Gradient

Rising atmospheric carbon dioxide concentration ([CO₂]) may modulate the functioning of mycorrhizal associations by altering the relative degree of nutrient and carbohydrate limitations in plants. To test this, we grew Taraxacum ceratophorum and Taraxacum officinale (native and exotic dandelions) with and without mycorrhizal fungi across a broad [CO₂] gradient (180–1,000 µL L⁻¹). Differential plant growth rates and vegetative plasticity were hypothesized to drive species-specific responses to [CO₂] and arbuscular mycorrhizal fungi. To evaluate [CO₂] effects on mycorrhizal functioning, we calculated response ratios based on the relative biomass of mycorrhizal (M_Bio) and nonmycorrhizal (NM_Bio) plants (R_Bio = [M_Bio − NM_Bio]/NM_Bio). We then assessed linkages between R_Bio and host physiology, fungal growth, and biomass allocation using structural equation modeling. For T. officinale, R_Bio increased with rising [CO₂], shifting from negative to positive values at 700 µL L⁻¹. [CO₂] and mycorrhizal effects on photosynthesis and leaf growth rates drove shifts in R_Bio in this species. For T. ceratophorum, R_Bio increased from 180 to 390 µL L⁻¹ and further increases in [CO₂] caused R_Bio to shift from positive to negative values. [CO₂] and fungal effects on plant growth and carbon sink strength were correlated with shifts in R_Bio in this species. Overall, we show that rising [CO₂] significantly altered the functioning of mycorrhizal associations. These symbioses became more beneficial with rising [CO₂], but nonlinear effects may limit plant responses to mycorrhizal fungi under future [CO₂]. The magnitude and mechanisms driving mycorrhizal-CO₂ responses reflected species-specific differences in growth rate and vegetative plasticity, indicating that these traits may provide a framework for predicting mycorrhizal responses to global change.Atmospheric carbon dioxide concentration ([CO₂]) has more than doubled over the past 20,000 years, rising from a minimum value of approximately 180 µL L⁻¹ during the Last Glacial Maximum (LGM; Augustin et al., 2004) to a current value of 401 µL L⁻¹. Due to ongoing fossil fuel emissions, [CO₂] is expected to reach 700 to 1,000 µL L⁻¹ by the end of this century (IPCC, 2013). Rising [CO₂] has greatly impacted plant physiology since the LGM (Sage and Coleman, 2001; Ainsworth and Rogers, 2007; Gerhart and Ward, 2010), likely altering interactions between plants and their microbial symbionts over geologic and contemporary time scales.Mycorrhizal associations are ancient plant-fungal symbioses (Remy et al., 1994) where host plants and their fungal partners exchange photosynthetically derived carbohydrates for soil nutrients (Smith and Read, 2008). These associations play a critical role in modern ecosystems via their effects on plant physiology, species coexistence, carbon and nutrient cycling, and net primary productivity (Hodge and Fitter, 2010; Clemmensen et al., 2015; Lin et al., 2015). Temporal changes in [CO₂] since the LGM have likely influenced the functioning of mycorrhizal associations along a continuum from mutualism to parasitism, hereafter referred to as the M-P continuum (Johnson et al., 1997), by altering plant carbohydrate production and nutrient demand. Previous mycorrhizal-CO₂ studies have focused mainly on the effects of modern versus future conditions (Alberton et al., 2005; Mohan et al., 2014), and little is known about mycorrhizal responses to low [CO₂] of the past (Treseder et al., 2003; Procter et al., 2014). Assessing mycorrhizal responses to a broad, temporal [CO₂] gradient is critical to establish a baseline for how these symbioses functioned prior to anthropogenic forcing, which will provide insight into potential constraints on mycorrhizal responses to future conditions (Ogle et al., 2015). In addition, rising [CO₂] is known to cause nonlinear shifts in plant physiology and growth (Gerhart and Ward, 2010); therefore, nonlinear shifts in mycorrhizal functioning also are likely to occur. Characterizing such responses is critical to accurately predict how these symbioses will impact plant physiology and growth in the future and requires experimentation that manipulates mycorrhizal associations at both low and elevated [CO₂]. Furthermore, to fully understand the physiological mechanisms driving plant responses to mycorrhizal fungi, linkages between host plant physiology and mycorrhizal functioning across the full M-P continuum need to be assessed. A broad [CO₂] gradient will likely generate both mutualistic and parasitic symbioses and provide insight into physiological traits that vary with mycorrhizal functioning.In this study, we examined arbuscular mycorrhizal (AM) associations in two closely related C₃ plant species, Taraxacum ceratophorum and Taraxacum officinale (native and exotic common dandelions; Asteraceae), across a glacial through future [CO₂] gradient. AM fungi are the predominant, ancestral type of mycorrhizal fungi (Smith and Read, 2008), and approximately 80% of modern plant species form AM associations (Brundrett, 2009). These fungi are primarily associated with increased phosphorus (P) uptake (Johnson, 2010), and past studies show that as much as 90% of plant P is acquired via fungal symbionts (Pearson and Jakobsen, 1993; Smith et al., 2009). AM fungi also can increase nitrogen (N) uptake, especially NH₄⁺, although the fungal contribution to plant N uptake is challenging to measure and highly variable among studies (e.g. 0%–74% of total plant N; Hodge and Storer, 2015). In exchange for these nutrients, plants allocate an estimated 5% to 10% of their carbohydrates to AM fungi (Bryla and Eissenstat, 2005).The net effect of AM fungi on plants is often measured in terms of plant growth, with some associations promoting faster growth rates and larger, more competitive plants (mutualism), while other associations restrict plant growth, resulting in smaller, less competitive plants (parasitism; Johnson et al., 1997). Where an interaction falls along the M-P continuum is highly dependent on physiological tradeoffs and resource limitations in the host. In general, nutrient availability is thought to be the primary driver of mycorrhizal functioning, with AM fungi increasing plant growth when nutrients, especially P, are more limiting than carbohydrates (Johnson et al., 2015). Changes in [CO₂] will likely modulate nutrient effects on AM associations by altering the relative degree of nutrient and carbohydrate limitations in plants (Fig. 1; Johnson, 2010). More specifically, there is strong evidence that low [CO₂] during the LGM produced major carbon (C) limitations within C₃ plants, and modern plants grown at glacial [CO₂] generally exhibit greater than 50% reductions in growth and photosynthetic rates relative to modern [CO₂] (Polley et al., 1993; Tissue et al., 1995; Sage and Coleman, 2001; Beerling, 2005; Gerhart and Ward, 2010; Gerhart et al., 2012). Furthermore, the majority of C₃ plants show some level of increased photosynthetic rates, leaf carbohydrate levels, and biomass when grown at future [CO₂] (Ainsworth and Rogers, 2007; Prior et al., 2011). However, plants may require more nutrients in order to maintain high rates of photosynthesis and growth at elevated [CO₂] (Campbell and Sage, 2006; Lewis et al., 2010). Thus, rising [CO₂] may cause mycorrhizal associations to shift along the M-P continuum by reducing plant carbohydrate limitation while simultaneously increasing plant nutrient limitation.Open in a separate windowFigure 1.[CO₂] is predicted to mediate nutrient effects on mycorrhizal associations by altering relative resource limitation in host plants. Specifically, the mycorrhizal response ratio (R_Bio) is predicted to increase with rising [CO₂] due to simultaneous increases in plant carbohydrate production and plant nutrient limitation. R_Bio is calculated from the biomass of mycorrhizal (M_Bio) and nonmycorrhizal (NM_Bio) plants (R_Bio = [M_Bio − NM_Bio]/NM_Bio). The dashed line represents a neutral association (no difference in plant size). R_Bio may be negative (solid line) or marginally positive (dotted line) at low [CO₂], depending on mycorrhizal effects on plant physiological responses to a CO₂-limiting environment.Most mycorrhizal-CO₂ studies compared the effects of current (340–400 µL L⁻¹) and future (540–750 µL L⁻¹) [CO₂] (Alberton et al., 2005; Mohan et al., 2014), but very few studies included more than two [CO₂] treatments, preventing the assessment of potential nonlinear patterns. These studies indicate that AM fungi generally increase plant growth at elevated [CO₂] and that rising [CO₂] promotes stronger mutualism (Mohan et al., 2014). However, the functioning of mycorrhizal associations at low [CO₂] of the past remains unclear. One possibility is that AM fungi reduce plant growth at low [CO₂] because these symbionts are a major sink for carbohydrates that are expensive to produce when CO₂ is limiting (Gerhart and Ward, 2010; Gerhart et al., 2012). Studies that show reduced AM fungal abundance in soils exposed to preindustrial [CO₂] provide tentative support for this hypothesis (Treseder et al., 2003; Procter et al., 2014). Alternatively, some plants may partially compensate for low [CO₂] by increasing their investment in the photosynthetic machinery, including the enzyme Rubisco (Sage and Coleman, 2001; Becklin et al., 2014). This strategy enhances CO₂ uptake but comes at the cost of greater demand for N (Sage and Coleman, 2001). P limitation also has been shown to restrict the rate of ribulose bisphosphate regeneration, with subsequent effects on photosynthesis under preindustrial [CO₂] (Campbell and Sage, 2006). Thus, by alleviating nutrient limitations on plant physiology, AM fungi may promote plant growth even under low [CO₂].Characterizing CO₂ effects on AM associations is critical for understanding the unique properties of these symbioses as well as for predicting how these interactions respond to both past and future environments. Here, we examined mycorrhizal responses across a glacial through future [CO₂] gradient in a controlled-environment experiment. We predicted that mycorrhizal associations would become more beneficial (i.e. have a larger positive effect on plant growth) with rising [CO₂] (Fig. 1). We further hypothesized two possible outcomes for mycorrhizal functioning under low [CO₂] of the past: (1) AM fungi will exacerbate carbohydrate constraints and restrict plant growth under low [CO₂], resulting in parasitic mycorrhizal associations when CO₂ is limiting (Fig. 1, solid line); and (2) fungal effects on nutrient uptake will alleviate nutrient constraints on plant physiological responses to low [CO₂], resulting in mutualistic mycorrhizal associations under glacial conditions (Fig. 1, dotted line). Additionally, studies indicate that many C₃ plants respond nonlinearly to rising [CO₂], with stronger responses to changes in [CO₂] below the modern value compared with above (Gerhart and Ward, 2010). These nonlinear shifts in plant physiology and growth will likely alter plant resource limitations and mycorrhizal functioning across a broad [CO₂] gradient. Thus, we further predicted that plants will be most responsive to increases from glacial to modern [CO₂], resulting in nonlinear shifts in plant physiology, plant growth, and mycorrhizal functioning across the full [CO₂] gradient. To better understand the mechanisms that alter plant responses to mycorrhizal fungi and overall patterns of plant productivity with rising [CO₂], we conducted detailed studies of plant physiology, intraradical fungal growth, and plant biomass allocation in mycorrhizal plants. We then tested for causal relationships among these traits and overall plant responses to mycorrhizal fungi using structural equation modeling (Fig. 2).Open in a separate windowFigure 2.A, Piecewise structural equation models describing [CO₂] effects on R_Bio via changes in plant and fungal traits. B, Model results for T. ceratophorum indicate that both direct and indirect effects of [CO₂] on plant traits contributed to shifts in R_Bio. C, Model results for T. officinale indicate that primarily direct effects of [CO₂] on plant traits contributed to shifts in R_Bio. In B and C, boxes represent measured traits and solid arrows indicate significant pathways in the model (P < 0.05). Black and red arrows indicate positive and negative correlations, respectively. The thickness of solid arrows was scaled to reflect the magnitude of the standardized regression coefficients. r² values for each component model and standardized pathway coefficients are listed in Supplemental Table S4.     

A review of the biology,ecology and control of saddle gall midge,Haplodiplosis marginata (Diptera: Cecidomyiidae) with a focus on phenological forecasting

Saddle gall midge Haplodiplosis marginata (Diptera: Cecidomyiidae) is a pest of cereals across Europe. The occasional nature of this pest has resulted in limited and sporadic research activity. There remain important gaps in knowledge due either to a genuine lack of research or to previous research being difficult to access. These knowledge gaps make the development of effective control options difficult. Here, we review the existing literature in an attempt to consolidate the information on H. marginata from research which spans several decades and encompasses many different countries. The current distribution and pest status of this insect are updated, along with the methods of cultural and chemical control available to growers. The biology and life history of the insect are described in detail and the ecological processes governing them are discussed. A forecasting model is presented which allows the emergence of this pest in the UK to be predicted from degree day data, and the potential application of this model in management decisions is discussed. Finally, the areas in most need of further research are identified, along with suggestions of how this information can be used to help develop effective and sustainable management solutions for this pest.     

Metabolomics and lipidomics reveal perturbation of sphingolipid metabolism by a novel anti-trypanosomal 3-(oxazolo[4,5-<Emphasis Type="Italic">b</Emphasis>]pyridine-2-yl)anilide

Introduction

Trypanosoma brucei is the causative agent of human African trypanosomiasis, which is responsible for thousands of deaths every year. Current therapies are limited and there is an urgent need to develop new drugs. The anti-trypanosomal compound, 3-(oxazolo[4,5-b]pyridine-2-yl)anilide (OXPA), was initially identified in a phenotypic screen and subsequently optimized by structure–activity directed medicinal chemistry. It has been shown to be non-toxic and to be active against a number of trypanosomatid parasites. However, nothing is known about its mechanism of action.

Objective

Here, we have utilized an untargeted metabolomics approach to investigate the biochemical effects and potential mode of action of this compound in T. brucei.

Methods

Total metabolite extracts were analysed by HILIC-chromatography coupled to high resolution mass spectrometry.

Results

Significant accumulation of ceramides was observed in OXPA-treated T. brucei. To further understand drug-induced changes in lipid metabolism, a lipidomics method was developed which enables the measurement of hundreds of lipids with high throughput and precision. The application of this LC–MS based approach to cultured bloodstream-form T. brucei putatively identified over 500 lipids in the parasite including glycerophospholipids, sphingolipids and fatty acyls, and confirmed the OXPA-induced accumulation of ceramides. Labelling with BODIPY-ceramide further confirmed the ceramide accumulation following drug treatment.

Conclusion

These findings clearly demonstrate perturbation of ceramide metabolism by OXPA and indicate that the sphingolipid pathway is a promising drug target in T. brucei.