Regulation of invertase levels in Avena stem segments by gibberellic Acid, sucrose, glucose, and fructose

Gibberellic acid and sucrose play significant roles in the increases in invertase and growth in Avena stem segments. About 80% of invertase is readily solubilized, whereas the rest is in the cell wall fraction. The levels of both types of invertase change in a similar manner in the response to gibberellic acid and sucrose treatment. The work described here was carried out with only the soluble enzyme. In response to a treatment, the level of invertase activity typically follows a pattern of increase followed by decrease; the increase in activity is approximately correlated with the active growth phase, whereas the decrease in activity is initiated when growth of the segments slows. A continuous supply of gibberellic acid retards the decline of enzyme activity. When gibberellic acid was pulsed to the segments treated with or without sucrose, the level of invertase activity increased at least twice as high in the presence of sucrose as in its absence, but the lag period is longer with sucrose present. Cycloheximide treatments effectively abolish the gibberellic acid-promoted growth, and the level of enzyme activity drops rapidly. Decay of invertase activity in response to cycloheximide treatment occurs regardless of gibberellic acid or sucrose treatment or both, and it is generally faster when the inhibitor is administered at the peak of enzyme induction than when given at its rising phase. Pulses with sucrose, glucose, fructose, or glucose + fructose elevate the level of invertase significantly with a lag of about 5 to 10 hours. The increase in invertase activity elicited by a sucrose pulse is about one-third that caused by a gibberellic acid pulse given at a comparable time during mid-phase of enzyme induction, and the lag before the enzyme activity increases is nearly twice as long for sucrose as for gibberellic acid. Moreover, the gibberellic acid pulse results in about three times more growth than the sucrose pulse. Our studies support the view that gibberellic acid, as well as substrate (sucrose) and end products (glucose and fructose), play a significant role in regulating invertase levels in Avena stem tissue, and that such regulation provides a mechanism for increasing the level of soluble saccharides needed for gibberellic acid-promoted growth.     

Effects of elevated CO2 on the tolerance of photosynthesis to acute heat stress in C3, C4, and CAM species

Determining the effect of elevated CO(2) on the tolerance of photosynthesis to acute heat stress (AHS) is necessary for predicting plant responses to global warming because photosynthesis is heat sensitive and AHS and atmospheric CO(2) will increase in the future. Few studies have examined this effect, and past results were variable, which may be related to methodological variation among studies. In this study, we grew 11 species that included cool and warm season and C(3), C(4), and CAM species at current or elevated (370 or 700 ppm) CO(2) and at species-specific optimal growth temperatures and at 30°C (if optimal ≠ 30°C). We then assessed thermotolerance of net photosynthesis (P(n)), stomatal conductance (g(st)), leaf internal [CO(2)], and photosystem II (PSII) and post-PSII electron transport during AHS. Thermotolerance of P(n) in elevated (vs. ambient) CO(2) increased in C(3), but decreased in C(4) (especially) and CAM (high growth temperature only), species. In contrast, elevated CO(2) decreased electron transport in 10 of 11 species. High CO(2) decreased g(st) in five of nine species, but stomatal limitations to P(n) increased during AHS in only two cool-season C(3) species. Thus, benefits of elevated CO(2) to photosynthesis at normal temperatures may be partly offset by negative effects during AHS, especially for C(4) species, so effects of elevated CO(2) on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.     

Richness and Composition of Niche-Assembled Viral Pathogen Communities

The pathogen and parasite community that inhabits every free-living organism can control host vital rates including lifespan and reproductive output. To date, however, there have been few experiments examining pathogen community assembly replicated at large-enough spatial scales to inform our understanding of pathogen dynamics in natural systems. Pathogen community assembly may be driven by neutral stochastic colonization and extinction events or by niche differentiation that constrains pathogen distributions to particular environmental conditions, hosts, or vectors.Here, we present results from a regionally-replicated experiment investigating the community of barley and cereal yellow dwarf viruses (B/CYDV''s) in over 5000 experimentally planted individuals of six grass species along a 700 km latitudinal gradient along the Pacific coast of North America (USA) in response to experimentally manipulated nitrogen and phosphorus supplies. The composition of the virus community varied predictably among hosts and across nutrient-addition treatments, indicating niche differentiation among virus species. There were some concordant responses among the viral species. For example, the prevalence of most viral species increased consistently with perennial grass cover, leading to a 60% increase in the richness of the viral community within individual hosts (i.e., coinfection) in perennial-dominated plots. Furthermore, infection rates of the six host species in the field were highly correlated with vector preferences assessed in laboratory trials. Our results reveal the importance of niche differentiation in structuring virus assemblages. Virus species distributions reflected a combination of local host community composition, host species-specific vector preferences, and virus responses to host nutrition. In addition, our results suggest that heterogeneity among host species in their capacity to attract vectors or support pathogens between growing seasons can lead to positive covariation among virus species.     

Absence of male reproductive skew,along with high frequency of polyandry and conspecific brood parasitism in the lekking Houbara bustard Chlamydotis undulata undulata

Behavioural studies have led to the perception that lekking species experience a high male reproductive skew as a consequence of females’ selective mate choice. In addition, observations suggest that females copulate only once and therefore polyandry seems unlikely as females are supposed to choose the best male available. In order to analyse the mating strategy of the Houbara bustard, an endangered lekking species under reinforcement in eastern Morocco, we used microsatellite data to perform paternity analyses. None of our observations followed common expectations under a lek mating system: we found no male reproductive skew suggesting no apparent selective female mate choice and no apparent male benefit from lekking. In contrast, a high level of polyandry (60 % of the nests) was recorded suggesting that sperm competition may operate. In addition, we present another case of conspecific brood parasitism in a lekking species and this was an unexpected alternative strategy for a species presenting high parental cost and low fecundity. The increasing number of studies contradicting common assumptions on lekking species suggests that alternative breeding strategies such as males pursuing an off‐lek mating strategy, female polyandry and even conspecific brood parasitism might be more widespread in lekking species than previously thought.     

Analysis of the putative regulatory region of the gastric inhibitory polypeptide receptor gene in food-dependent Cushing's syndrome

Gastric inhibitory polypeptide (GIP)-dependent Cushing's syndrome (CS) results from the ectopic expression of non-mutated GIP receptor (hGIPR) in the adrenal cortex. We evaluated whether mutations or polymorphisms in the regulatory region of the GIPR gene could lead to this aberrant expression. We studied 9.0kb upstream and 1.3kb downstream of the GIPR gene putative promoter (pProm) by sequencing leukocyte DNA from controls and from adrenal tissues of GIP- and non-GIP-dependent CS patients. The putative proximal promoter region (800 bp) and the first exon and intron of the hGIPR gene were sequenced on adrenal DNA from nine GIP-dependent CS, as well as on leukocyte DNA of nine normal controls. Three variations found in this region were found in all patients and controls; at position -4/-5, an insertion of a T was seen in four out of nine patients and in five out of nine controls. Transient transfection studies conducted in rat GC and mouse Y1 cells showed that the TT allele confers loss of 40% in the promoter activity. The analysis of the 8-kb distal pProm region revealed eight distal single nucleotide polymorphisms (SNPs) without probable association with the disease, since frequencies in patients and controls were very similar. In conclusion, mutations or SNPs in the regulatory region of the GIPR gene are unlikely to underlie GIP-dependent CS.     

Thermal difference spectra: a specific signature for nucleic acid structures

We show that nucleic acid structures may be conveniently and inexpensively characterized by their UV thermal difference spectra. A thermal difference spectrum (TDS) is obtained for a nucleic acid by simply recording the ultraviolet absorbance spectra of the unfolded and folded states at temperatures above and below its melting temperature (T_m). The difference between these two spectra is the TDS. The TDS has a specific shape that is unique for each type of nucleic acid structure, a conclusion that is based on a comparison of >900 spectra from 200 different sequences. The shape of the TDS reflects the subtleties of base stacking interactions that occur uniquely within each type of nucleic acid structure. TDS provides a simple, inexpensive and rapid method to obtain structural insight into nucleic acid structures, which is applicable to both DNA and RNA from short oligomers to polynucleotides. TDS complements circular dichroism as a tool for the structural characterization of nucleic acids in solution.     

Inactivation of Adhesion and Invasion of Food-Borne Listeria monocytogenes by Bacteriocin-Producing Bifidobacterium Strains of Human Origin

Three bacteriocin-producing bifidobacterial isolates from newborns were identified as Bifidobacterium thermacidophilum (two strains) and B. thermophilum (one strain). This study was undertaken to evaluate the ability of these strains to compete with food-borne Listeria monocytogenes for adhesion and invasion sites on Caco-2 and HT-29 cells. The bifidobacteria adhered at levels ranging from 4% to 10% of the CFU added, but none of the bifidobacteria were able to invade cells. The abilities of Listeria to adhere to and to invade cells varied widely depending on the strain tested. Three groups of Listeria were identified based on invasiveness: weakly invasive, moderately invasive, and highly invasive strains. One strain from each group was tested in competition with bifidobacteria. B. thermacidophilum RBL70 was the most effective in blocking invasion of Listeria, and the decreases in invasion ranged from 38% to 90%. For all three bifidobacterial strains, contact between the cell monolayer and the bifidobacteria for 1 h before exposure to Listeria increased the degree of inhibition. Finally, visualization of competition for adhesion sites on cells by fluorescent in situ hybridization suggested that the two bacteria tended to adhere in close proximity.     

The design of linear peptides that fold as monomeric beta-sheet structures.

Current knowledge about the determinants of beta-sheet formation has been notably improved by the structural and kinetic analysis of model peptides, by mutagenesis experiments in proteins and by the statistical analysis of the protein structure database (Protein Data Bank; PDB). In the past year, several peptides comprising natural and non-natural amino acids have been designed to fold as monomeric three-stranded beta-sheets. In all these cases, the design strategy has involved both the statistical analysis of the protein structure database and empirical information obtained in model beta-hairpin systems and in proteins. Only in one case was rotamer analysis performed to check for the compatibility of the sidechain packing. It is foreseeable that, in future designs, algorithms exploring the sequence and conformational space will be employed. For the design of small proteins (less than 30 amino acids), questions remain about the demonstration of two-state behavior, the formation of a well-defined network of mainchain hydrogen bonds and the quantification of the structured populations.     

New in vitro colonic fermentation model for Salmonella infection in the child gut

In this study, a new in vitro continuous colonic fermentation model of Salmonella infection with immobilized child fecal microbiota and Salmonella serovar Typhimurium was developed for the proximal colon. This model was then used to test the effects of two amoxicillin concentrations (90 and 180 mg day⁻¹) on the microbial composition and metabolism of the gut microbiota and on Salmonella serovar Typhimurium during a 43-day fermentation. Addition of gel beads (2%, v/v) colonized with Salmonella serovar Typhimurium in the reactor resulted in a high and stable Salmonella concentration (log 7.5 cell number mL⁻¹) in effluent samples, and a concomitant increase of Enterobacteriaeceae, Clostridium coccoides–Eubacterium rectale and Atopobium populations and a decrease of bifidobacteria. During amoxicillin treatments, Salmonella concentrations decreased while microbial balance and activity were modified in agreement with in vivo data, with a marked decrease in C. coccoides–E. rectale and an increase in Enterobacteriaceae . After interruption of antibiotic addition, Salmonella concentration again increased to reach values comparable to that measured before antibiotic treatments, showing that our model can be used to simulate Salmonella shedding in children as observed in vivo . This in vitro model could be a useful tool for developing and testing new antimicrobials against enteropathogens.     

Reference-free detection of isolated SNPs

Detecting single nucleotide polymorphisms (SNPs) between genomes is becoming a routine task with next-generation sequencing. Generally, SNP detection methods use a reference genome. As non-model organisms are increasingly investigated, the need for reference-free methods has been amplified. Most of the existing reference-free methods have fundamental limitations: they can only call SNPs between exactly two datasets, and/or they require a prohibitive amount of computational resources. The method we propose, discoSnp, detects both heterozygous and homozygous isolated SNPs from any number of read datasets, without a reference genome, and with very low memory and time footprints (billions of reads can be analyzed with a standard desktop computer). To facilitate downstream genotyping analyses, discoSnp ranks predictions and outputs quality and coverage per allele. Compared to finding isolated SNPs using a state-of-the-art assembly and mapping approach, discoSnp requires significantly less computational resources, shows similar precision/recall values, and highly ranked predictions are less likely to be false positives. An experimental validation was conducted on an arthropod species (the tick Ixodes ricinus) on which de novo sequencing was performed. Among the predicted SNPs that were tested, 96% were successfully genotyped and truly exhibited polymorphism.