Recent advances in systemic acquired resistance research — a review

Little is known about the signal transduction events that lead to the establishment of the broad-spectrum, inducible plant immunity called systemic acquired resistance (SAR). Salicylic acid (SA) accumulation has been shown to be essential for the expression of SAR and plays a key role in SAR signaling. Hydrogen peroxide has been proposed to serve as a second messenger of SA. However, our results do not support such a role in the establishment of SAR. Further elucidation of SAR signal transduction has been facilitated by the identification and characterization of mutants. The lesions simulating disease (lsd) resistance response mutant class exhibits spontaneous lesions similar to those that occur during the hypersensitive response. Interestingly, some lsd mutants lose their lesioned phenotype when SA accumulation is prevented by expression of the nahG gene (encoding salicylate hydroxylase), thereby providing evidence for a feedback loop in SAR signal transduction. Characterization of a mutant non-responsive to SAR activator treatments has provided additional evidence for common signaling components between SAR and gene-for-gene resistance.     

Enterococcal biofilm—A nidus for antibiotic resistance transfer?

Enterococci, which are on the WHO list of priority pathogens, are commonly encountered in hospital acquired infection and are becoming increasing significant due to the development of strains resistant to multiple antibiotics. Enterococci are also important microorganisms in the environment, and their presence is frequently used as an indicator of faecal pollution. Their success is related to their ability to survive within a broad range of habitats and the ease by which they acquire mobile genetic elements, including plasmids, from other bacteria. The enterococci are frequently present within a bacterial biofilm, which provides stability and protection to the bacterial population along with an opportunity for a variety of bacterial interactions. Enterococci can accept extrachromosomal DNA both from within its own species and from other bacterial species, and this is enhanced by the proximity of the donor and recipient strains. It is this exchange of genetic material that makes the role of biofilms such an important aspect of the success of enterococci. There remain many questions regarding the most suitable model systems to study enterococci in biofilms and regarding the transfer of genetic material including antibiotic resistance in these biofilms. This review focuses on some important aspects of biofilm in the context of horizontal gene transfer (HGT) in enterococci.     

Inducible resistance to Fas—mediated apoptosis in B cells

Apoptosis produced in B cells through Fas(APO-1,CD95) triggering is regulated by signals derived from other surface receptors:CD40 engagement produces upregulation of Fas expression and marked susceptibility to Fas-induced cell death,whereas antigen receptor engagement,or IL-4R engagement,inhibits Fas killing and in so doing induces a state of Fas-resistance,even in otherwise sensitive,CD40-stimulated targets.Surface immunoglobulin and IL-4R utilize at least partially distinct path ways to produce Fas-resistance that differentially depend on PKC and STAT6,respectively.Further,surface immunoglobulin signaling for inducible Fas-resistance bypasses Btk,requires NF-κB,and entails new macromolecular synthesis.Terminal effectors of B cell Fas-resistance include the known anti-apoptotic gene products,Bcl-XL and FLIP,and a novel anti-apoptotic gene that encodes FAIM (Fas Apoptosis Inhibitory Molecule).faim was identified by differential display and exists in two alternatively spliced forms;faim-S is broadly expressed,but faim-L expression is tissue-specific.The FAIM sequence is highly evolu tionarily conserved,suggesting an important role for this molecule throughout phylogeny.Inducible resistance to Fas killing is hypothesized to protect foreign antigen-specific B cells during potentially hazardous interactions with FasL-bearing T cells,whereas autoreactive B cells fail to become Fas-resistant and are deleted via Fas-dependent cytotoxicity.Inadvertent or aberrant acquisition of Fas-resistance may permit autoreactive B cells to escape Fas deletion,and malignant lymphocytes to impede anti-tumor immunity.     

Translation attenuation regulation of chloramphenicol resistance in bacteria — a review

The chloramphenicol (Cm)-inducible cat and cmlA genes are regulated by translation attenuation, a regulatory device that modulates mRNA translation. In this form of gene regulation, translation of the Cm^R coding sequence is prevented by mRNA secondary structure that sequesters its ribosome-binding site (RBS). A translated leader of nine codons precedes the secondary structure, and induction results when a ribosome becomes stalled at a specific site in the leader. Here we demonstrate that the site of ribosome stalling in the leader is selected by a cis effect of the nascent leader peptide on its translating ribosome.     

EU-OPENSCREEN—chemical tools for the study of plant biology and resistance mechanisms

EU-OPENSCREEN is an academic research infrastructure initiative in Europe for enabling researchers in all life sciences to take advantage of chemical biology approaches to their projects. In a collaborative effort of national networks in 16 European countries, EU-OPENSCREEN will develop novel chemical compounds with external users to address questions in, among other fields, systems and network biology (directed and selective perturbation of signalling pathways), structural biology (compound-target interactions at atomic resolution), pharmacology (early drug discovery and toxicology) and plant biology (response of wild or crop plants to environmental and agricultural substances). EU-OPENSCREEN supports all stages of a tool development project, including assay adaptation, high-throughput screening and chemical optimisation of the ‘hit’ compounds. All tool compounds and data will be made available to the scientific community. EU-OPENSCREEN integrates high-capacity screening platforms throughout Europe, which share a rationally selected compound collection comprising up to 300,000 (commercial and proprietary compounds collected from European chemists). By testing systematically this chemical collection in hundreds of assays originating from very different biological themes, the screening process generates enormous amounts of information about the biological activities of the substances and thereby steadily enriches our understanding of how and where they act.     

Insect immune resistance to parasitoids

Insect host-parasitoid interactions involve complex physiological, biochemical and genetic interactions. Against endoparasitoids, immune-competent hosts initiate a blood cell-mediated response that quickly destroys the intruders and envelops them in a multilayered melanotic capsule. During the past decade, considerable progress has been made in identifying some of the critical components of the host response, mainly because of the use of efficient molecular tools. This review examines some of the components of the innate immune response of Drosophila, an insect that has served as an exceptionally good experimental model for studying non-self recognition processes and immune cell signaling mechanisms. Topics considered in this review include hematopoiesis, proliferation and adhesion of hemocytes, melanogenesis and associated cytotoxic molecules, and the genetic aspects of the host-parasitoid interaction.     

Surface coating — No improvement of shear stress resistance of anchorage dependent mammalian cells

Summary The growth of adherent Baby Hamster Kidney cells (BHK 21) on surfaces coated with different substances (FCS, Con. A, PHA, cholesterol, collagen) was investigated. A positive influence on cell viability could only be observed when using a fetal calf serum (FCS) coat. To evaluate the effects of coating on shear stress sensitivity, experiments in a home made flow chamber were carried out. For comparison further investigations were conducted for several serum concentrations in the medium. The results demonstrate that the latter had a more beneficial effect on shear stress resistance than coating.     

A model for the coevolution of resistance and virulence in coupled host—parasitoid interactions

A coevolutionary model is developed of the interaction between a host and an internal parasitoid, where the outcome of parasitism depends upon the extent to which individual hosts invest in resistance mechanisms and individual parasitoids in countermeasures (virulence). The host and parasitoid are assumed to have coupled population dynamics (of Nicholson–Bailey form) and to be composed of a series of asexual clones with different levels of resistance and virulence. Investment in resistance and virulence mechanisms is assumed to be costly. The model has two main outcomes. First, if resistance is relatively costly compared to virulence, the host may be selected not to invest in resistance mechanisms despite parasitoid investment in virulence, in effect trading off the risks of parasitism against the savings in costs. A number of cases which appear to correspond to this result have been reported. Second, for most other feasible parameter values, an arms race occurs between host and parasitoid, until effective resistance becomes so costly that the host abandons defence. This abandonment is followed by a reduction in parasitoid virulence and the cycle begins again. These cycles may explain reports of persistent additive genetic variation in resistance and virulence, and may also contribute towards population dynamic stability.     

Is xylem cavitation resistance a relevant criterion for screening drought resistance among Prunus species?

Fruit trees are likely to suffer from the effects of severe drought in the future; however, sound criteria for evaluating the species' ability to survive these extreme conditions are largely missing. Here, we evaluated the feasibility of using xylem cavitation resistance as a tool for screening Prunus species for drought resistance. Ten different Prunus species were selected to cover a large range of water requirements, from hydrophilic to xerophilic types. Shoot cavitation resistance was evaluated with the new Cavitron technique. At this inter-specific level, cavitation resistance was related to species drought resistance, with xerophilic species being less vulnerable to cavitation. The Cavitron technique enabled species characterization that required a short time and small amounts of plant material. This technique could be used to evaluate the drought resistance of a limited number of fruit tree genotypes. Genotype screening on a larger scale, however, would likely require another approach. Out of a number of anatomical traits tested, a significant correlation was found between cavitation resistance and inter-vessel wall thickness across species. This anatomical trait is, therefore, suggested as a possible alternative to direct cavitation estimates and could be included as a screening criterion in breeding programs for drought resistance of Prunus genotypes.     

Oxidative stress programming in a rat model of postnatal early overnutrition — role of insulin resistance

Postnatal early overfeeding (EO) is related to later development of overweight and other metabolic disorders. As oxidative stress is implicated in most human diseases, as obesity and diabetes, we decided to study some parameters related to oxidative stress and insulin signaling in liver from EO animals in adult life. To induce EO, litter size was reduced to three pups per litter (SL: small litter) and groups with normal litter size (NL:10 pups per litter) were used as control. After weaning, rats had free access to standard diet and water. Body weight and food intake were monitored daily and offspring were killed at 180 days-old. Significant differences had P<.05 or less. As expected, SL rats had hyperphagia, higher body weight and higher visceral fat mass at weaning and adulthood. In liver, postnatal EO programmed for lower catalase (? 42%), superoxide dismutase (? 45%) and glutathione peroxidase (? 65%) activities. The evaluation of liver injury in adult SL group showed lower nitrite content (? 10%), higher liver and plasma malondialdehyde content (+ 25% and 1.1-fold increase, respectively). No changes of total protein bound carbonyl or Cu/Zn superoxide dismutase protein expression in liver were detected between the groups. Regarding insulin signaling pathway in liver, SL offspring showed lower IRβ (? 66%), IRS1 (? 50%), phospho-IRS1 (? 73%), PI3-K (? 30%) and Akt1 (? 58%). Indeed, morphological analysis showed that SL rats presented focal areas of inflammatory cell infiltrate and lipid drops in their cytoplasm characterizing a microsteatosis. Thus, we evidenced that postnatal EO can program the oxidative stress in liver, maybe contributing for impairment of the insulin signaling.