Determinants of serum levels of surfactant proteins A and B and Clara cell protein CC16

Increased leakage of surfactant proteins A and B (SP-A and SP-B) and Clara cell secretory protein (CC16) from the air spaces into the circulation occurs in a range of respiratory conditions. However, circulating levels depend not only on the rate of entry into the circulation, but also on the rate of clearance. In order to clarify the role of the kidney in the clearance of these proteins, serum levels were related to markers of glomerular filtration in 54 non-smoking patients with varying degrees of renal dysfunction, none of whom had respiratory disease or were receiving dialysis at the time of sampling. Serum SP-A was related to SP-B (r=0.53, p<0.001) and to CC16 (r=0.33, p<0.02). Similarly, SP-B was related to CC16 (r=0.39, p<0.004). Stepwise multiple linear regression analysis suggested that serum SP-A and SP-B are influenced by age (～20 and ～25% of variance, respectively), whereas CC16 is determined by renal function and, to a lesser extent, by body weight (～63% of variance in total). We conclude that CC16 is cleared from blood by the renal route, whereas SP-A and SP-B are not. Serum SP-A and SP-B are influenced by age, which we speculate reflects increased damage to the alveolocapillary barrier.     

The homologous recombination system of Ustilago maydis

Homologous recombination is a high fidelity, template-dependent process that is used in repair of damaged DNA, recovery of broken replication forks, and disjunction of homologous chromosomes in meiosis. Much of what is known about recombination genes and mechanisms comes from studies on baker's yeast. Ustilago maydis, a basidiomycete fungus, is distant evolutionarily from baker's yeast and so offers the possibility of gaining insight into recombination from an alternative perspective. Here we have surveyed the genome of U. maydis to determine the composition of its homologous recombination system. Compared to baker's yeast, there are fundamental differences in the function as well as in the repertoire of dedicated components. These include the use of a BRCA2 homolog and its modifier Dss1 rather than Rad52 as a mediator of Rad51, the presence of only a single Rad51 paralog, and the absence of Dmc1 and auxiliary meiotic proteins.     

Differential frequency of NKG2C/<Emphasis Type="Italic">KLRC2</Emphasis> deletion in distinct African populations and susceptibility to Trachoma: a new method for imputation of <Emphasis Type="Italic">KLRC2</Emphasis> genotypes from SNP genotyping data

NKG2C is an activating receptor that is preferentially expressed on natural killer (NK) cells. The gene encoding NKG2C (killer cell lectin-like receptor C2, KLRC2) is present at different copy numbers in the genomes of different individuals. Deletion at the NKG2C locus was investigated in a case–control study of 1522 individuals indigenous to East- and West-Africa and the association with the ocular Chlamydia trachomatis infection and its sequelae was explored. The frequency of homozygous KLRC2 deletion was 13.7 % in Gambians and 4.7 % in Tanzanians. A significantly higher frequency of the deletion allele was found in West-Africans from the Gambia and Guinea-Bissau (36.2 % p = 2.105 × 10^?8, 26.8 % p = 0.050; respectively) in comparison to East-African Tanzanians where the frequency of the deletion is comparable to other human populations (20.9 %). We found no evidence for an association between the numbers of KLRC2 gene copies and the clinical manifestations of trachoma (follicular trachoma or conjunctival scarring). A new method for imputation of KLRC2 genotypes from single nucleotide polymorphism (SNP) data in 2621 individuals from the Gambia further confirmed these results. Our data suggest that NKG2C does not play a major role in trachomatous disease. We found that the deletion allele is present at different frequencies in different populations but the reason behind these differences is currently not understood. The new method offers the potential to use SNP arrays from genome wide association studies to study the frequency of KLRC2 deletion in other populations and its association with other diseases.     

Rice grain zinc concentrations as affected by genotype, native soil-zinc availability, and zinc fertilization

The development of rice (Oryza sativa L.) cultivars with a higher Zn content in their grains has been suggested as a way to alleviate Zn malnutrition in human populations subsisting on rice in their daily diets. This study was conducted to evaluate the effects of native soil Zn status and fertilizer application on Zn concentrations in grains of five rice genotypes that had previously been identified as either high or low in grain Zn. Genotypes were grown in field trials at four sites ranging in native soil-Zn status from severely deficient to high in plant available Zn. At each site a −Zn plot was compared to a +Zn plot fertilized with 15 kg Zn ha⁻¹. Results showed that native soil Zn status was the dominant factor to determine grain Zn concentrations followed by genotype and fertilizer. Depending on soil-Zn status, grain Zn concentrations could range from 8 mg kg⁻¹ to 47 mg kg⁻¹ in a single genotype. This strong location effect will need to be considered in estimating potential benefits of Zn biofortification. Our data furthermore showed that it was not possible to simply compensate for low soil Zn availability by fertilizer applications. In all soils fertilizer Zn was taken up as seen by a 50–200% increase in total plant Zn content. However, in more Zn deficient soils this additional Zn supply improved straw and grain yield and increased straw Zn concentrations by 43–95% but grain Zn concentrations remained largely unchanged with a maximum increase of 6%. Even in soils with high Zn status fertilizer Zn was predominantly stored in vegetative tissue. Genotypic differences in grain Zn concentrations were significant in all but the severely Zn deficient soil, with genotypic means ranging from 11 to 24 mg kg⁻¹ in a Zn deficient soil and from 34 to 46 mg kg⁻¹ in a high Zn upland soil. Rankings of genotypes remained largely unchanged from Zn deficient to high Zn soils, which suggests that developing high Zn cultivars through conventional breeding is feasible for a range of environments. However, it may be a challenge to develop cultivars that respond to Zn fertilizer with higher grain yield and higher grain Zn concentrations when grown in soils with low native Zn status.     

3-Hydroxypropionyl-Coenzyme A Dehydratase and Acryloyl-Coenzyme A Reductase,Enzymes of the Autotrophic 3-Hydroxypropionate/4-Hydroxybutyrate Cycle in the Sulfolobales

A 3-hydroxypropionate/4-hydroxybutyrate cycle operates in autotrophic CO₂ fixation in various Crenarchaea, as studied in some detail in Metallosphaera sedula. This cycle and the autotrophic 3-hydroxypropionate cycle in Chloroflexus aurantiacus have in common the conversion of acetyl-coenzyme A (CoA) and two bicarbonates via 3-hydroxypropionate to succinyl-CoA. Both cycles require the reductive conversion of 3-hydroxypropionate to propionyl-CoA. In M. sedula the reaction sequence is catalyzed by three enzymes. The first enzyme, 3-hydroxypropionyl-CoA synthetase, catalyzes the CoA- and MgATP-dependent formation of 3-hydroxypropionyl-CoA. The next two enzymes were purified from M. sedula or Sulfolobus tokodaii and studied. 3-Hydroxypropionyl-CoA dehydratase, a member of the enoyl-CoA hydratase family, eliminates water from 3-hydroxypropionyl-CoA to form acryloyl-CoA. Acryloyl-CoA reductase, a member of the zinc-containing alcohol dehydrogenase family, reduces acryloyl-CoA with NADPH to propionyl-CoA. Genes highly similar to the Metallosphaera CoA synthetase, dehydratase, and reductase genes were found in autotrophic members of the Sulfolobales. The encoded enzymes are only distantly related to the respective three enzyme domains of propionyl-CoA synthase from C. aurantiacus, where this trifunctional enzyme catalyzes all three reactions. This indicates that the autotrophic carbon fixation cycles in Chloroflexus and in the Sulfolobales evolved independently and that different genes/enzymes have been recruited in the two lineages that catalyze the same kinds of reactions.In the thermoacidophilic autotrophic crenarchaeum Metallosphaera sedula, CO₂ fixation proceeds via a 3-hydroxypropionate/4-hydroxybutyrate cycle (8, 23, 24, 28) (Fig. ​(Fig.1).1). A similar cycle may operate in other autotrophic members of the Sulfolobales and in mesophilic Crenarchaea (Cenarchaeum sp. and Nitrosopumilus sp.) of marine group I. The cycle uses elements of the 3-hydroxypropionate cycle that was originally discovered in the phototrophic bacterium Chloroflexus aurantiacus (11, 16, 17, 19, 20, 32, 33). It involves the carboxylation of acetyl-coenzyme A (CoA) to malonyl-CoA by the biotin-dependent acetyl-CoA carboxylase. Malonyl-CoA is reduced via malonate semialdehyde to 3-hydroxypropionate (1), which is further reductively converted to propionyl-CoA (3). Propionyl-CoA is carboxylated to (S)-methylmalonyl-CoA by a propionyl-CoA carboxylase that is similar or identical to acetyl-CoA carboxylase. In fact, only one copy of the genes for the acetyl-CoA/propionyl-CoA carboxylase subunits is present in most Archaea, suggesting that this is a promiscuous enzyme that acts on both acetyl-CoA and propionyl-CoA (24). (S)-Methylmalonyl-CoA is epimerized to (R)-methylmalonyl-CoA, followed by carbon rearrangement to succinyl-CoA by coenzyme B₁₂-dependent methylmalonyl-CoA mutase.Open in a separate windowFIG. 1.Proposed 3-hydroxypropionate/4-hydroxybutyrate cycle in M. sedula and other members of the Sulfolobales. Enzymes are the following: 1, acetyl-CoA carboxylase; 2, malonyl-CoA reductase (NADPH); 3, malonate semialdehyde reductase (NADPH); 4, 3-hydroxypropionyl-CoA synthetase (3-hydroxypropionate-CoA ligase, AMP forming); 5, 3-hydroxypropionyl-CoA dehydratase; 6, acryloyl-CoA reductase (NADPH); 7, propionyl-CoA carboxylase; 8, methylmalonyl-CoA epimerase; 9, methylmalonyl-CoA mutase; 10, succinyl-CoA reductase (NADPH); 11, succinate semialdehyde reductase (NADPH); 12, 4-hydroxybutyryl-CoA synthetase (4-hydroxybutyrate-CoA ligase, AMP-forming); 13, 4-hydroxybutyryl-CoA dehydratase; 14, crotonyl-CoA hydratase; 15, (S)-3-hydroxybutyryl-CoA dehydrogenase (NAD⁺); 16, acetoacetyl-CoA β-ketothiolase. The two steps of interest are highlighted.In Chloroflexus succinyl-CoA is converted to (S)-malyl-CoA, which is cleaved by (S)-malyl-CoA lyase to acetyl-CoA (thus regenerating the CO₂ acceptor molecule) and glyoxylate (16). Glyoxylate is assimilated into cell material by a yet not completely resolved pathway (37). In Metallosphaera succinyl-CoA is converted via 4-hydroxybutyrate to two molecules of acetyl-CoA (8), thus regenerating the starting CO₂ acceptor molecule and releasing another acetyl-CoA for biosynthesis. Hence, the 3-hydroxypropionate/4-hydroxybutyrate cycle (Fig. ​(Fig.1)1) can be divided into two parts. The first part transforms one acetyl-CoA and two bicarbonates into succinyl-CoA, and the second part converts succinyl-CoA to two acetyl-CoA molecules.The reductive conversion of 3-hydroxypropionate to propionyl-CoA requires three enzymatic steps: activation of 3-hydroxypropionate to its CoA ester, dehydration of 3-hydroxypropionyl-CoA to acryloyl-CoA, and reduction of acryloyl-CoA to propionyl-CoA. In C. aurantiacus these three steps are catalyzed by a single large trifunctional enzyme, propionyl-CoA synthase (2). This 200-kDa fusion protein consists of a CoA ligase, a dehydratase, and a reductase domain. Attempts to isolate a similar enzyme from M. sedula failed. Rather, a 3-hydroxypropionyl-CoA synthetase was found (3), suggesting that the other two reactions may also be catalyzed by individual enzymes.Here, we purified the missing enzymes 3-hydroxypropionyl-CoA dehydratase and acryloyl-CoA reductase from M. sedula, identified the coding genes in the genome of M. sedula and other members of the Sulfolobales, produced recombinant enzymes as proof of function, and studied the enzymes in some detail. A comparison with the respective domains of propionyl-CoA synthase from C. aurantiacus indicates that the conversion of 3-hydroxypropionate to propionyl-CoA via the 3-hydroxypropionate route has evolved independently in these two phyla.     

Biogeographic context is related to local scale tree demography,co-occurrence and functional differentiation

Identifying the drivers of community structure and dynamics is a major pursuit in ecology. Emphasis is typically placed on the importance of local scale interactions when attempting to explain these fundamental ecological patterns. However, regional scale phenomena are also important predictors. The importance of regional scale context should be more evident in assemblages where multiple species are close to their range margins. Here, we test the importance of regional scale context using data from a temperate forest plot that contains two species groups – one near its northern range limit and one near its southern range limit. We show the proximity of species to their southern or northern range margins is linked to local scale co-occurrence, similarity in gene expression responses to a key environmental driver, demographic performance and inter-specific variation in conspecific negative density dependence. In sum, many of the key local scale patterns and processes of interest to community ecologists are linked to biogeographic context that is frequently ignored.     

Impact of active transport and transpiration on nickel and cadmium accumulation in the leaves of the Ni-hyperaccumulator Leptoplax emarginata: a biophysical approach

Aims

The primary aim of this study was to investigate the impact of active nickel and cadmium transport, transpiration and shoot biomass production on Ni and Cd accumulation in the leaves of the Ni-hyperaccumulator Leptoplax emarginata. A secondary objective was to observe the effects of various concentrations of nickel and cadmium in solutions on the plant growth and ecophysiological characteristics of these plants. Finally, the study sought to identify possible nickel and cadmium concentration gradients in solution as a function of the root distance.

Methods

The Intact Plant Transpiration Stream Concentration Factor (TSCF=xylem/solution solute concentration ratio) was determined for both Ni and Cd and for the selected intact transpiring Ni-hyperaccumulator Leptoplax emarginata, cultivated on two contrasting fertilized and Ni-Cd-contaminated sandy porous media (rhizotrons with central root compartments, linked to Mariotte tubes operated at ?1?kPa). IPTSCF_Ni and IPTSCF_Cd were calculated as the ratios between the hyperaccumulator plant’s nickel or cadmium mass in the leaves and the nickel or cadmium concentration in solution by the volume of water transpired during the period of culture. Plant growth characteristics and gas exchanges were also recorded.

Results

IPTSCF values were much greater than 1 (IPTSCF_Ni?=?5.2?±?0.9 and IPTSCF_Cd?=?4.4?±?0.6) whatever the amount of available Ni and Cd. This characterized a predominantly active plant metal uptake. Moreover, biological regulation was reported: plant growth and transpiration were significantly lower for hyperaccumulator plants cultivated in sand which was rich in available Ni and Cd, than for hyperaccumulator plants cultivated in topsoil, poor in available Ni and Cd. In the soil rhizosphere, capillary flow was related to transpiration and a depletion pattern was developed for Ni and sometimes for Cd.

Conclusions

Overall, the Intact Plant Transpiration Stream Concentration Factor appeared to be a relevant metal bioconcentration factor taking into account the predominant type of metal transport from roots to leaves, plant growth and transpiration coupling and metal availability. IPTSCF_Ni and IPTSCF_Cd values were much greater than 1 and similar whatever the amount of available Ni and Cd. This characterized a predominantly active plant combining Ni and Cd uptake and biological regulations dependent of the Ni and Cd concentrations in solution.     

Characteristics of protectant synthesis of infective juveniles of Steinernema carpocapsae and importance of glycerol as a protectant for survival of the nematodes during osmotic dehydration

Two hypotheses on the synthesis of the protectants glycerol and trehalose of the infective juveniles (IJs) of Steinernema carpocapsae during osmotic dehydration were tested and utilised to evaluate the function and importance of glycerol on survival of the nematodes during osmotic dehydration. This was achieved by comparing the changes in survival, morphology, behaviour and levels of glycerol, trehalose and permeated compounds of the IJs dehydrated in seven hypertonic solutions at two temperature regimes: (1) 5 °C for 15 days; and (2) 23 °C for 1 day followed by 5 °C for another 14 days. The results substantiate both hypotheses tested: (1) the permeability of the IJs to various compounds, such as sucrose or ethylene glycol, when they are dehydrated in hypertonic solutions of these compounds; and (2) suppression of the synthesis of protectant glycerol but not trehalose when IJs are dehydrated at low temperature. The results also showed that: (1) although trehalose was the preferred dehydration protectant, glycerol played an important role in rapidly balancing the osmotic pressure when IJs were exposed in hypertonic solutions; (2) the presence of glycerol was essential for the IJs to survive and function properly even under moderate osmotic dehydration, especially when IJs were dehydrated in salt solutions; and (3) some exogenous compounds permeated into IJs during osmotic dehydration such as ethylene glycol, may function in the same way as glycerol and significantly improve the survival and function of the IJs. The results indicate that each of the protectants glycerol and trehalose has a specific function and neither is replaceable by the other.