Allocation of carbon and nitrogen as a function of the internal nitrogen status of a plant: Modelling allocation under non-steady-state situations

In this paper we model allocation of carbon and nitrogen to roots and leaves as a function of the nitrogen status of a plant. Under steady-state conditions, allocation of carbon and nitrogen to leaves is exponentially (positively) correlated with plant nitrogen concentration, whereas allocation to roots is correlated negatively, also in an exponential manner.Allocation functions derived under steady-state conditions are used to simulate biomass partitioning under non-steady-state nutrient conditions. Upon nitrogen deprivation, measured and simulated values are rather similar with time, suggesting that allocation functions derived under steady-state conditions also hold under non-steady-state conditions.     

Structure and Mode of Peptide Binding of Pheromone Receptor PrgZ

We present the crystal structure of the pheromone receptor protein PrgZ from Enterococcus faecalis in complex with the heptapeptide cCF10 (LVTLVFV), which is used in signaling between conjugative recipient and donor cells. Comparison of PrgZ with homologous oligopeptide-binding proteins (AppA and OppA) explains the high specificity of PrgZ for hydrophobic heptapeptides versus the promiscuity of peptide binding in the homologous proteins.     

New exocrine glands in the legionary ants of the genus Leptanilla (Hymenoptera,Formicidae, Leptanillinae)

Summary This paper reports the results of the first detailed study of the morphology of exocrine glands in two species of the ant subfamily Leptanillinae. Workers of Leptanilla escheri and L. japonica possess a large, unpaired sternal gland in the VIIth abdominal sternite, and an hypertrophied poison gland which is surrounded by a massive muscle layer. The sternal gland is absent in the queen of L. japonica, and the poison gland is highly degenerated. The queen is, however, endowed with a series of large, paired, intersegmental tergal and sternal glands, which occur between the IVth through the VIIth segments. The queen also posseses large spiracular plate glands.     

Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient

During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant bacteria can, unexpectedly, colonize environments where a lethal concentration of the antibiotic kanamycin is present. Colonizing bacteria establish an adaptively resistant population, which remains viable for over 24 h while exposed to the antibiotic. Quantitative analysis of multiple colonization events shows that collectively swimming bacteria need to exceed a critical population density in order to successfully colonize the antibiotic landscape. After colonization, bacteria are not dormant but show both growth and swimming motility under antibiotic stress. Our results highlight the importance of motility and population density in facilitating adaptive resistance, and indicate that adaptive resistance may be a first step to the emergence of genetically encoded resistance in landscapes of antibiotic gradients.     

Analysis of non-active engineered Bacillus thuringiensis crystal proteins

Abstract Crystal proteins of Bacillus thuringiensis are known for their insecticidal specificity. This specificity is, to a large extent, determined by the interaction of the proteins with high-affinity binding sites on the epithelial membrane of the midgut of sensitive insects. In particular, domain II of the three domains of the toxic moiety has been implicated in specificity. To determine which sequences of the protein are involved in binding, loops of domain II which terminate in the molecular apex of CryIA(b) were replaced by the corresponding regions of CryIE, a protein with different binding characteristics and insect specificity. In contrast to expression of the wild-type genes, expression of the mutant alleles in Escherichia coli resulted in the formation of biologically inactive, insoluble aggregates. Although these aggregates could be solubilized in vitro using urea, in contrast to the wild-type CryIA(b), the mutant proteins did not correctly refold as is shown by their increased protease sensitivity and lack of biological activity. The results indicate that engineering CryI proteins, based on the CryIIIA structure, is likely to prove difficult, particularly since the conformation of CryIIIA and CryI proteins might differ in domain II.     

AGC kinases and MAB4/MEL proteins maintain PIN polarity by limiting lateral diffusion in plant cells

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Molecular phylogeny of Malenchus and Filenchus (Nematoda: Tylenchidae)

The family Tylenchidae is phylogenetically important to understanding early‐branching Tylenchomorpha and to assess soil ecosystems. In this study, we focus on Malenchus and Filenchus as representatives of the Tylenchidae. Samples collected worldwide result in 58 new sequences, and light microscopy and transmission electron microscopy provide details on morphological features. For the first time, comprehensive morphological data are evaluated in the context of a molecular framework, thus highlighting the phylogenetic and evolutionary complexity of this structurally minimalistic group. Results show that the genus Filenchus is polyphyletic in both the 18S and 28S rDNA phylogeny, while Malenchus is polyphyletic and monophyletic in the 28S rDNA and the 18S rDNA, respectively. Ultrastructural study demonstrates specific aspects of lateral cuticular incisures, cuticular layering and the amphideal fovea are surprisingly congruent with the obtained molecular phylogenies, while classical characteristics such as cuticle annulations are evolutionary highly plastic and mosaic in distribution. The study also reveals the shortage of D2/D3 domain in 28S rDNA as a phylogenetic marker for early‐branching Tylenchomorpha.     

The Effectiveness of Percutaneous Vertebroplasty Is Determined by the Patient-Specific Bone Condition and the Treatment Strategy

PurposeVertebral fragility fractures are often treated by injecting bone cement into the collapsed vertebral bodies (vertebroplasty). The mechanisms by which vertebroplasty induces pain relief are not completely understood yet and recent debates cast doubt over the outcome of the procedure. The controversy is intensified by inconsistent results of randomized clinical trials and biomechanical studies that have investigated the effectiveness or the change in biomechanical response due to the reinforcement. The purpose of this study was to evaluate the effectiveness of vertebroplasty, by varying the relevant treatment parameters and (a) computationally predicting the improvement of the fracture risk depending on the chosen treatment strategy, and (b) identifying the determinants of a successful treatment.MethodsA Finite Element model with a patient-specific failure criterion and direct simulation of PMMA infiltration in four lumbar vertebrae was used to assess the condition of the bone under compressive load before and after the virtual treatment, simulating in a total of 12000 virtual treatments.ResultsThe results showed that vertebroplasty is capable of reducing the fracture risk by magnitudes, but can also have a detrimental effect. Effectiveness was strongly influenced by interactions between local bone quality, cement volume and injection location. However, only a moderate number of the investigated treatment strategies were able to achieve the necessary improvement for preventing a fracture.ConclusionsWe conclude that the effectiveness of vertebroplasty is sensitive to the patient’s condition and the treatment strategy.     

Ubiquitination by the Membrane-associated RING-CH-8 (MARCH-8) Ligase Controls Steady-state Cell Surface Expression of Tumor Necrosis Factor-related Apoptosis Inducing Ligand (TRAIL) Receptor 1

The eleven members of the membrane-associated RING-CH (MARCH) ubiquitin ligase family are relatively unexplored. Upon exogenous (over)expression, a number of these ligases can affect the trafficking of membrane molecules. However, only for MARCH-1 endogenous functions have been demonstrated. For the other endogenous MARCH proteins, no functions or substrates are known. We report here that TRAIL-R1 is a physiological substrate of the endogenous MARCH-8 ligase. Human TRAIL-R1 and R2 play a role in immunosurveillance and are targets for cancer therapy, because they selectively induce apoptosis in tumor cells. We demonstrate that TRAIL-R1 is down-regulated from the cell surface, with great preference over TRAIL-R2, by exogenous expression of MARCH ligases that are implicated in endosomal trafficking, such as MARCH-1 and -8. MARCH-8 attenuated TRAIL-R1 cell surface expression and apoptosis signaling by virtue of its ligase activity. This suggested that ubiquitination of TRAIL-R1 was instrumental in its down-regulation by MARCH-8. Indeed, in cells with endogenous MARCH expression, TRAIL-R1 was ubiquitinated at steady-state, with the conserved membrane-proximal lysine 273 as one of the potential acceptor sites. This residue was also essential for the interaction of TRAIL-R1 with MARCH-1 and MARCH-8 and its down-regulation by these ligases. Gene silencing identified MARCH-8 as the endogenous ligase that ubiquitinates TRAIL-R1 and attenuates its cell surface expression. These findings reveal that endogenous MARCH-8 regulates the steady-state cell surface expression of TRAIL-R1.