Ubiquitous urease affects soybean susceptibility to fungi

The soybean ubiquitous urease (encoded by GmEu4) is responsible for recycling metabolically derived urea. Additional biological roles have been demonstrated for plant ureases, notably in toxicity to other organisms. However, urease enzymatic activity is not related to its toxicity. The role of GmEu4 in soybean susceptibility to fungi was investigated in this study. A differential expression pattern of GmEu4 was observed in susceptible and resistant genotypes of soybeans over the course of a Phakopsora pachyrhizi infection, especially 24 h after infection. Twenty-nine adult, transgenic soybean plants, representing six independently transformed lines, were obtained. Although the initial aim of this study was to overexpress GmEu4, the transgenic plants exhibited GmEu4 co-suppression and decreased ureolytic activity. The growth of Rhizoctonia solani, Phomopsis sp., and Penicillium herguei in media containing a crude protein extract from either transgenic or non-transgenic leaves was evaluated. The fungal growth was higher in the protein extracts from transgenic urease-deprived plants than in extracts from non-transgenic controls. When infected by P. pachyrhizi uredospores, detached leaves of urease-deprived plants developed a significantly higher number of lesions, pustules and erupted pustules than leaves of non-transgenic plants containing normal levels of the enzyme. The results of the present work show that the soybean plants were more susceptible to fungi in the absence of urease. It was not possible to overexpress active GmEu4. For future work, overexpression of urease fungitoxic peptides could be attempted as an alternative approach.     

Adaptation mechanisms of bacteria during the degradation of polychlorinated biphenyls in the presence of natural and synthetic terpenes as potential degradation inducers

In this study, we examined the effect of polychlorinated biphenyls (PCBs) in the presence of natural and synthetic terpenes and biphenyl on biomass production, lipid accumulation, and membrane adaptation mechanisms of two PCB-degrading bacterial strains Pseudomonas stutzeri and Burkholderia xenovorans LB400. According to the results obtained, it could be concluded that natural terpenes, mainly those contained in ivy leaves and pine needles, decreased adaptation responses induced by PCBs in these strains. The adaptation processes under investigation included growth inhibition, lipid accumulation, composition of fatty acids, cis/trans isomerization, and membrane saturation. Growth inhibition effect decreased upon addition of these natural compounds to the medium. The amount of unsaturated fatty acids that can lead to elevated membrane fluidity increased in both strains after the addition of the two natural terpene sources. The cells adaptation changes were more prominent in the presence of carvone, limonene, and biphenyl than in the presence of natural terpenes, as indicated by growth inhibition, lipid accumulation, and cis/trans isomerization. Addition of biphenyl and carvone simultaneously with PCBs increased the trans/cis ratio of fatty acids in membrane fractions probably as a result of fluidizing effects of PCBs. This stimulation is more pronounced in the presence of PCBs as a sole carbon source. This suggests that PCBs alone have a stronger effect on bacterial membrane adaptation mechanisms than when added together with biphenyl or natural or synthetic terpenes.     

Neuropilin-1 regulates a new VEGF-induced gene, Phactr-1, which controls tubulogenesis and modulates lamellipodial dynamics in human endothelial cells

Recently, we identified a new Vascular Endothelial Growth Factor (VEGF)-A₁₆₅-induced gene Phactr-1, (Phosphatase Actin Regulator-1). We reported that Phactr-1 gene silencing inhibited tube formation in human umbilical endothelial cells (HUVECs) indicating a key role for Phactr-1 in tubulogenesis in vitro. In this study, we investigated the role of Phactr-1 in several cellular processes related to angiogenesis. We found that neuropilin-1 (NRP-1) and VEGF-R1 depletion inhibited Phactr-1 mRNA expression while NRP-2 and VEGF-R2 depletion had no effect. We described a new interaction site of VEGF-A₁₆₅ to VEGF-R1 in peptides encoded by exons 7 and 8 of VEGF-A₁₆₅. The specific inhibition of VEGF-A₁₆₅ binding on NRP-1 and VEGF-R1 by ERTCRC and CDKPRR peptides decreased the Phactr-1 mRNA levels in HUVECs indicating that VEGF-A₁₆₅-dependent regulation of Phactr-1 expression required both NRP-1 and VEGF-R1 receptors. In addition, upon VEGFA₁₆₅-stimulation Phactr-1 promotes formation and maintenance of cellular tubes through NRP-1 and VEGFR1. Phactr-1 was previously identified as protein phosphatase 1 (PP1) α-interacting protein that possesses actin-binding domains. We showed that Phactr-1 depletion decreased PP1 activity, disrupted the fine-tuning of actin polymerization and impaired lamellipodial dynamics. Taken together our results strongly suggest that Phactr-1 is a key component in the angiogenic process.     

Toxic effects of amyloid fibrils on cell membranes: the importance of ganglioside GM1

The interaction of amyloid aggregates with the cell plasma membrane is currently considered among the basic mechanisms of neuronal dysfunction in amyloid neurodegeneration. We used amyloid oligomers and fibrils grown from the yeast prion Sup35p, responsible for the specific prion trait [PSI(+)], to investigate how membrane lipids modulate fibril interaction with the membranes of cultured H-END cells and cytotoxicity. Sup35p shares no homology with endogenous mammalian polypeptide chains. Thus, the generic toxicity of amyloids and the molecular events underlying cell degeneration can be investigated without interference with analogous polypeptides encoded by the cell genome. Sup35 fibrils bound to the cell membrane without increasing its permeability to Ca(2+). Fibril binding resulted in structural reorganization and aggregation of membrane rafts, with GM1 clustering and alteration of its mobility. Sup35 fibril binding was affected by GM1 or its sialic acid moiety, but not by cholesterol membrane content, with complete inhibition after treatment with fumonisin B1 or neuraminidase. Finally, cell impairment resulted from caspase-8 activation after Fas receptor translocation on fibril binding to the plasma membrane. Our observations suggest that amyloid fibrils induce abnormal accumulation and overstabilization of raft domains in the cell membrane and provide a reasonable, although not unique, mechanistic and molecular explanation for fibril toxicity.     

Solution structure of the immunodominant domain of protective antigen GNA1870 of Neisseria meningitidis

GNA1870, a 28-kDa surface-exposed lipoprotein of Neisseria meningitidis recently discovered by reverse vaccinology, is one of the most potent antigens of Meningococcus and a promising candidate for a universal vaccine against a devastating disease. Previous studies of epitope mapping and genetic characterization identified residues critical for bactericidal response within the C-terminal domain of the molecule. To elucidate the conformation of protective epitopes, we used NMR spectroscopy to obtain the solution structure of the immunodominant 18-kDa C-terminal portion of GNA1870. The structure consists of an eight-stranded antiparallel beta-barrel overlaid by a short alpha-helix with an unstructured N-terminal end. Residues previously shown to be important for antibody recognition were mapped on loops facing the same ridge of the molecule. The sequence similarity of GNA1870 with members of the bacterial transferrin receptor family allows one to predict the folding of this class of well known bacterial antigens, providing the basis for the rational engineering of high affinity B cell epitopes.     

Redox regulation of beta-actin during integrin-mediated cell adhesion

Redox sensitivity of actin toward an exogenous oxidative stress has recently been reported. We report here the first evidence of in vivo actin redox regulation by a physiological source of reactive oxygen species, specifically those species generated by integrin receptors during cell adhesion. Actin oxidation takes place via the formation of a mixed disulfide between cysteine 374 and glutathione; this modification is essential for spreading and for cytoskeleton organization. Impairment of actin glutathionylation, either through GSH depletion or expression of the C374A redox-insensitive mutant, greatly affects cell spreading and the formation of stress fibers, leading to inhibition of the disassembly of the actinomyosin complex. These data suggest that actin glutathionylation is essential for cell spreading and cytoskeleton organization and that it plays a key role in disassembly of actinomyosin complex during cell adhesion.     

Molecular variability of Spodoptera frugiperda (Lepidoptera: Noctuidae) populations associated to maize and cotton crops in Brazil

The molecular variability among 10 populations of Spodoptera frugiperda (J.E. Smith), collected from maize, Zea mays L., or cotton Gossypium hirsutum L. crops located at distinctive geographical regions in Brazil, was assessed through random amplification of polymorphic DNA (RAPD)-polymerase chain reaction (PCR). In total, 208 RAPD markers were evaluated, and 98% of them were polymorphic. The mean genetic similarity was 0.6621 and 0.2499 by the Simple Matching and Jaccard matrices, respectively. In general, the unweighted pair-group method with arithmetic average dendrograms separated the populations into clusters related to the geographical origin of the samples. No branch of the dendrograms underpinning a molecular association of S. frugiperda has been identified to either of the two host plants. The molecular variance analysis showed that 18 and 82% of the genetic variation was distributed among and within the groups of populations, respectively. The principal coordinate analysis reinforced the pattern of population clustering found with the unweighted pair-group method with arithmetic average method. These results suggest the occurrence of considerable gene flow between S. frugiperda populations from maize and cotton fields located in the same region in Brazil. Therefore, for an effective management of this pest, there is an urgent need for a better understanding of the gene flow of S. frugiperda populations associated to different host plants along the distribution range of this pest over time in a specific cropping system.     

Functional conservation of MADS-box factors controlling floral organ identity in rice and Arabidopsis

Studies on MADS-box genes in Arabidopsis and other higher eudicotyledonous flowering plants have shown that they are key regulators of flower development. Since Arabidopsis and monocotyledonous rice are distantly related plant species it is interesting to investigate whether the floral organ identity factors have been conserved in their functions, and if not, to understand the differences. Arabidopsis and rice are very suitable for these studies since they are both regarded as models for plant functional genomics. Both their genomes are sequenced and tools are available for the analysis of gene function. These developments have accelerated experiments and increased our knowledge on rice gene function. Therefore it is the right moment to perform a comparative analysis on MADS-box factors controlling floral organ identity as reported in this review.