Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga

In freshwaters, algal species are exposed to different inorganic nitrogen (N_i) sources whose incorporation varies in biochemical energy demand. We hypothesized that due to the lesser energy requirement of ammonium ()‐use, in contrast to nitrate ()‐use, more energy remains for other metabolic processes, especially under CO₂‐ and phosphorus (P_i) limiting conditions. Therefore, we tested differences in cell characteristics of the green alga Chlamydomonas acidophila grown on or under covariation of CO₂ and P_i‐supply in order to determine limitations, in a full‐factorial design. As expected, results revealed higher carbon fixation rates for ‐grown cells compared to growth with under low CO₂ conditions. ‐grown cells accumulated more of the nine analyzed amino acids, especially under P_i‐limited conditions, compared to cells provided with . This is probably due to a slower protein synthesis in cells provided with . In contrast to our expectations, compared to ‐grown cells ‐grown cells had higher photosynthetic efficiency under P_i‐limitation. In conclusion, growth on the N_i‐source did not result in a clearly enhanced C_i‐assimilation, as it was highly dependent on P_i and CO₂ conditions (replete or limited). Results are potentially connected to the fact that C. acidophila is able to use only CO₂ as its inorganic carbon (C_i) source.     

Different ways to die in a changing world: Consequences of climate change for tree species performance and survival through an ecophysiological perspective

Anthropogenic activities such as uncontrolled deforestation and increasing greenhouse gas emissions are responsible for triggering a series of environmental imbalances that affect the Earth's complex climate dynamics. As a consequence of these changes, several climate models forecast an intensification of extreme weather events over the upcoming decades, including heat waves and increasingly severe drought and flood episodes. The occurrence of such extreme weather will prompt profound changes in several plant communities, resulting in massive forest dieback events that can trigger a massive loss of biodiversity in several biomes worldwide. Despite the gravity of the situation, our knowledge regarding how extreme weather events can undermine the performance, survival, and distribution of forest species remains very fragmented. Therefore, the present review aimed to provide a broad and integrated perspective of the main biochemical, physiological, and morpho‐anatomical disorders that may compromise the performance and survival of forest species exposed to climate change factors, particularly drought, flooding, and global warming. In addition, we also discuss the controversial effects of high CO₂ concentrations in enhancing plant growth and reducing the deleterious effects of some extreme climatic events. We conclude with a discussion about the possible effects that the factors associated with the climate change might have on species distribution and forest composition.     

Deeply conserved susceptibility in a multi‐host,multi‐parasite system

Variation in susceptibility is ubiquitous in multi‐host, multi‐parasite assemblages, and can have profound implications for ecology and evolution in these systems. The extent to which susceptibility to parasites is phylogenetically conserved among hosts can be revealed by analysing diverse regional communities. We screened for haemosporidian parasites in 3983 birds representing 40 families and 523 species, spanning ~ 4500 m elevation in the tropical Andes. To quantify the influence of host phylogeny on infection status, we applied Bayesian phylogenetic multilevel models that included a suite of environmental, spatial, temporal, life history and ecological predictors. We found evidence of deeply conserved susceptibility across the avian tree; host phylogeny explained substantial variation in infection status, and results were robust to phylogenetic uncertainty. Our study suggests that susceptibility is governed, in part, by conserved, latent aspects of anti‐parasite defence. This demonstrates the importance of deep phylogeny for understanding present‐day ecological interactions.     

The cystathionine‐β‐synthase domains on the guanosine 5′’‐monophosphate reductase and inosine 5′‐monophosphate dehydrogenase enzymes from Leishmania regulate enzymatic activity in response to guanylate and adenylate nucleotide levels

The Leishmania guanosine 5′‐monophosphate reductase (GMPR) and inosine 5′‐monophosphate dehydrogenase (IMPDH) are purine metabolic enzymes that function maintaining the cellular adenylate and guanylate nucleotide. Interestingly, both enzymes contain a cystathionine‐β‐synthase domain (CBS). To investigate this metabolic regulation, the Leishmania GMPR was cloned and shown to be sufficient to complement the guaC (GMPR), but not the guaB (IMPDH), mutation in Escherichia coli. Kinetic studies confirmed that the Leishmania GMPR catalyzed a strict NADPH‐dependent reductive deamination of GMP to produce IMP. Addition of GTP or high levels of GMP induced a marked increase in activity without altering the K_m values for the substrates. In contrast, the binding of ATP decreased the GMPR activity and increased the GMP K_m value 10‐fold. These kinetic changes were correlated with changes in the GMPR quaternary structure, induced by the binding of GMP, GTP, or ATP to the GMPR CBS domain. The capacity of these CBS domains to mediate the catalytic activity of the IMPDH and GMPR provides a regulatory mechanism for balancing the intracellular adenylate and guanylate pools.     

ER arrival sites for COPI vesicles localize to hotspots of membrane trafficking

COPI‐coated vesicles mediate retrograde membrane traffic from the cis‐Golgi to the endoplasmic reticulum (ER) in all eukaryotic cells. However, it is still unknown whether COPI vesicles fuse everywhere or at specific sites with the ER membrane. Taking advantage of the circumstance that the vesicles still carry their coat when they arrive at the ER, we have visualized active ER arrival sites (ERAS) by monitoring contact between COPI coat components and the ER‐resident Dsl tethering complex using bimolecular fluorescence complementation (BiFC). ERAS form punctate structures near Golgi compartments, clearly distinct from ER exit sites. Furthermore, ERAS are highly polarized in an actin and myosin V‐dependent manner and are localized near hotspots of plasma membrane expansion. Genetic experiments suggest that the COPI?Dsl BiFC complexes recapitulate the physiological interaction between COPI and the Dsl complex and that COPI vesicles are mistargeted in dsl1 mutants. We conclude that the Dsl complex functions in confining COPI vesicle fusion sites.     

Thermal performance of the Chagas disease vector,Triatoma infestans,under thermal variability

Vector-borne diseases (VBD) are particularly susceptible to climate change because most of the diseases’ vectors are ectotherms, which themselves are susceptible to thermal changes. The Chagas disease is one neglected tropical disease caused by the protozoan parasite, Trypanosoma cruzi. One of the main vectors of the Chagas disease in South America is Triatoma infestans, a species traditionally considered to be restricted to domestic or peridomestic habitats, but sylvatic foci have also been described along its distribution. The infestation of wild individuals, together with the projections of environmental changes due to global warming, urge the need to understand the relationship between temperature and the vector’s performance. Here, we evaluated the impact of temperature variability on the thermal response of T. infestans. We acclimated individuals to six thermal treatments for five weeks to then estimate their thermal performance curves (TPCs) by measuring the walking speed of the individuals. We found that the TPCs varied with thermal acclimation and body mass. Individuals acclimated to a low and variable ambient temperature (18°C ± 5°C) exhibited lower performances than those individuals acclimated to an optimal temperature (27°C ± 0°C); while those individuals acclimated to a low but constant temperature (18°C ± 0°C) did not differ in their maximal performance from those at an optimal temperature. Additionally, thermal variability (i.e., ± 5°C) at a high temperature (30°C) increased performance. These results evidenced the plastic response of T. infestans to thermal acclimation. This plastic response and the non-linear effect of thermal variability on the performance of T. infestans posit challenges when predicting changes in the vector’s distribution range under climate change.     

ENPP1 affects insulin action and secretion: evidences from in vitro studies

The aim of this study was to deeper investigate the mechanisms through which ENPP1, a negative modulator of insulin receptor (IR) activation, plays a role on insulin signaling, insulin secretion and eventually glucose metabolism. ENPP1 cDNA (carrying either K121 or Q121 variant) was transfected in HepG2 liver-, L6 skeletal muscle- and INS1E beta-cells. Insulin-induced IR-autophosphorylation (HepG2, L6, INS1E), Akt-Ser(473), ERK1/2-Thr(202)/Tyr(204) and GSK3-beta Ser(9) phosphorylation (HepG2, L6), PEPCK mRNA levels (HepG2) and 2-deoxy-D-glucose uptake (L6) was studied. GLUT 4 mRNA (L6), insulin secretion and caspase-3 activation (INS1E) were also investigated. Insulin-induced IR-autophosphorylation was decreased in HepG2-K, L6-K, INS1E-K (20%, 52% and 11% reduction vs. untransfected cells) and twice as much in HepG2-Q, L6-Q, INS1E-Q (44%, 92% and 30%). Similar data were obtained with Akt-Ser(473), ERK1/2-Thr(202)/Tyr(204) and GSK3-beta Ser(9) in HepG2 and L6. Insulin-induced reduction of PEPCK mRNA was progressively lower in untransfected, HepG2-K and HepG2-Q cells (65%, 54%, 23%). Insulin-induced glucose uptake in untransfected L6 (60% increase over basal), was totally abolished in L6-K and L6-Q cells. GLUT 4 mRNA was slightly reduced in L6-K and twice as much in L6-Q (13% and 25% reduction vs. untransfected cells). Glucose-induced insulin secretion was 60% reduced in INS1E-K and almost abolished in INS1E-Q. Serum deficiency activated caspase-3 by two, three and four folds in untransfected INS1E, INS1E-K and INS1E-Q. Glyburide-induced insulin secretion was reduced by 50% in isolated human islets from homozygous QQ donors as compared to those from KK and KQ individuals. Our data clearly indicate that ENPP1, especially when the Q121 variant is operating, affects insulin signaling and glucose metabolism in skeletal muscle- and liver-cells and both function and survival of insulin secreting beta-cells, thus representing a strong pathogenic factor predisposing to insulin resistance, defective insulin secretion and glucose metabolism abnormalities.     

Zinc to cadmium replacement in the A. thaliana SUPERMAN Cys₂ His₂ zinc finger induces structural rearrangements of typical DNA base determinant positions

Among heavy metals, whose toxicity cause a steadily increasing of environmental pollution, cadmium is of special concern due to its relatively high mobility in soils and potential toxicity at low concentrations. Given their ubiquitous role, zinc fingers domains have been proposed as mediators for the toxic and carcinogenic effects exerted by xenobiotic metals. To verify the structural effects of zinc replacement by cadmium in zinc fingers, we have determined the high resolution structure of the single Cys₂His₂ zinc finger of the Arabidopsis thaliana SUPERMAN protein (SUP37) complexed to the cadmium ion by means of UV–vis and NMR techniques. SUP37 is able to bind Cd(II), though with a dissociation constant higher than that measured for Zn(II). Cd‐SUP37 retains the ββα fold but experiences a global structural rearrangement affecting both the relative orientation of the secondary structure elements and the position of side chains involved in DNA recognition: among them Ser17 side chain, which we show to be essential for DNA binding, experiences the largest displacement. © 2011 Wiley Periodicals, Inc. Biopolymers 95: 801‐810, 2011.