Induction of preference and performance after acclimation to novel hosts in a phytophagous spider mite: adaptive plasticity?

We examined induction of preference and performance on novel host plants for two laboratory populations of the polyphagous spider mite Tetranychus urticae, with one population adapted to bean and the other population adapted to tomato. We bred four isofemale lines of the bean population only and used them in all the assays. The bean population had a 30% lower fecundity on tomato than on bean, while the tomato population had equal fecundity on both host plants. Acclimation of adult females to the novel host plant for both populations increased acceptability of that novel host but did not increase rejection of the original host. The bean population experienced a 60% benefit and a 30% cost in terms of egg production for acclimating to tomato, thus exemplifying adaptive plasticity. The tomato population showed a 23% benefit for acclimating to bean but no cost. Mites from the bean population that were acclimated to tomato fed more on tomato than did mites that were not acclimated to tomato. When these mites were fed inhibitors of cytochrome P-450 detoxification enzymes, their performance was severely depressed (84%) on tomato but not on bean. However, mites that were fed inhibitors of P-450 enzymes did not reduce their acceptance of tomato as a host. Thus, performance on novel hosts (but not preference) in this species is likely correlated with the induction of detoxifying enzymes. Spider mites are known to form host races rapidly on novel hosts. Induction of preference and physiological acclimation via detoxification enzymes may enhance performance and, thus, strongly contribute to initial stages of host race formation.     

Identification of metaflothionein in Pleurodeles waltl

The characterization of metallothionein in the Urodele amphibian species Pleurodeles waltl was achieved. A simple and rapid method for identification of metallothionein, based on its strong affinity for cadmium (109Cd), was used. We were able to show that metallothionein is constitutively synthesized in liver, ovary and brain. The property of metallothionein to strongly bind essential (Zn, Cu) as well as toxic (Cd, Hg) metals is consistent with a dual role in cellular metabolism, ie. homeostatis and detoxification of heavy metal ions.     

The autoregulatory role of EsaR,a quorum-sensing regulator in Pantoea stewartii ssp. stewartii: evidence for a repressor function

Capsular polysaccharide synthesis and virulence in the plant pathogenic bacterium Pantoea stewartii ssp. stewartii requires the quorum-sensing regulatory proteins, EsaR and EsaI, and the diffusible inducer N-(3-oxo-hexanoyl)-L-homoserine lactone. Prior mutational studies suggested that EsaR might function as a repressor of quorum sensing in the control of capsular polysaccharide synthesis. Further, a lux box-like palindromic sequence coinciding with the putative -10 element of the esaR promoter suggested a possible negative autoregulatory role for EsaR. This report presents genetic evidence that EsaR represses the esaR gene under inducer-limiting conditions, and that addition of inducer promotes rapid, dose-dependent derepression. DNA mobility-shift assays and analyses by surface plasmon resonance refractometry show that EsaR binds target DNAs in a ligand-free state, and that inducer alters the binding characteristics of EsaR. Physical measurements indicate that the EsaR protein binds N-(3-oxo-hexanoyl)-L-homoserine lactone, in a 1:1 protein:ligand ratio, and that inducer binding enhances the thermal stability of the EsaR protein. These combined genetic and biochemical data establish that EsaR regulates its own expression by signal-independent repression and signal-dependent derepression. Additionally, we provide evidence that EsaR does not govern the expression of the linked esaI gene, thus EsaR has no role in controlling coinducer synthesis.     

The Rickettsia prowazekii invasion gene homolog (invA) encodes a Nudix hydrolase active on adenosine (5')-pentaphospho-(5')-adenosine

The genomic sequence of Rickettsia prowazekii, the obligate intracellular bacterium responsible for epidemic typhus, reveals an uncharacterized invasion gene homolog (invA). The deduced protein of 18,752 Da contains a Nudix signature, the specific motif found in the Nudix hydrolase family. To characterize the function of InvA, the gene was cloned and overexpressed in Escherichia coli. The expressed protein was purified to near homogeneity and subsequently tested for its enzymatic activity against a series of nucleoside diphosphate derivatives. The purified InvA exhibits hydrolytic activity toward dinucleoside oligophosphates (Np(n)N; n > or = 5), a group of cellular signaling molecules. At optimal pH 8.5, the enzyme actively degrades adenosine (5')-pentaphospho-(5')-adenosine into ATP and ADP with a K(m) of 0.1 mM and k(cat) of 1.9 s(-1). Guanosine (5')-pentaphospho-(5')-guanosine and adenosine-(5')-hexaphospho (5')-adenosine are also substrates. Similar to other Nudix hydrolases, InvA requires a divalent metal cation, Mg(2+) or Zn(2+), for optimal activity. These data suggest that the rickettsial invasion protein likely plays a role in controlling the concentration of stress-induced dinucleoside oligophosphates following bacterial invasion.     

The aged: medical and social aspects

Physical health is affected by physiological aging that impacts on all tissues and organs, notably sensorial systems (hearing, sight), the locomotory and the immunological systems (lowering of resistance to infections). There is an increase with age in the incidence of many cancers (particularly breast, prostate, and colon cancers) and cardiovascular diseases. Regular check-ups are useful in order to take appropriate measures in time. It is important that people maintain regular physical activity and a balanced diet even up to an advanced age and the elderly must learn to adapt themselves to the ever-changing abilities of their organism. It is possible to slow down the aging process through good hygiene and often to maintain autonomy until the end of life. Mental health is threatened by impairment of mental functions, depressive tendencies, and the risk of senile dementia that cannot be foreseen or avoided. It appears that keeping intellectually active and having a good level of education impact favorably on mental aging. Social health depends, for a large part, on the way society accepts and treats the elderly. They must be kept integrated into society and allowed to live at home for as long as possible. Any measures of rejection, discrimination, and exclusion should be opposed. The dignity of the elderly must be respected and activities giving them a feeling of usefulness should be encouraged. It is important to help families who care for their parents at home, to develop and evaluate healthcare networks, and encourage medical professionals and social services to work together. The change in the demographic structure of France is a considerable phenomenon requiring a long-term strategy and not only superficial and cosmetic measures.     

Immunoglobulin-free light chains elicit immediate hypersensitivity-like responses

Immunoglobulin (Ig)-free light chains IgLC are present in serum and their production is augmented under pathological conditions such as multiple sclerosis, rheumatoid arthritis and neurological disorders. Until now, no (patho)physiological function has been ascribed to circulating Ig light chains. Here we show that IgLCs can confer mast cell dependent hypersensitivity in mice. Antigenic stimulation results in plasma extravasation, cutaneous swelling and mast-cell degranulation. We show that IgLCs have a crucial role in development of contact sensitivity, which could be completely prevented by a novel IgLC antagonist. Although IgE and IgG(1) are central to the induction of immediate hypersensitivity reactions, our results show that IgLCs have similar activity. IgLCs may therefore be a novel factor in the humoral immune response to antigen exposure. Our findings open new avenues in investigating the pathogenesis of autoimmune diseases and their treatments.     

Photosynthetic characteristics and tolerance to photo-oxidation of transgenic rice expressing C4 photosynthesis enzymes

The photosynthetic characteristics of four transgenic rice lines over-expressing rice NADP-malic enzyme (ME), and maize phosphoenolpyruvate carboxylase (PC), pyruvate,orthophosphate dikinase (PK), and PC+PK (CK) were investigated using outdoor-grown plants. Relative to untransformed wild-type (WT) rice, PC transgenic rice exhibited high PC activity (25-fold increase) and enhanced activity of carbonic anhydrase (more than two-fold increase), while the activity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco) and its kinetic property were not significantly altered. The PC transgenic plants also showed a higher light intensity for saturation of photosynthesis, higher photosynthetic CO₂ uptake rate and carboxylation efficiency, and slightly reduced CO₂ compensation point. In addition, chlorophyll a fluorescence analysis indicates that PC transgenic plants are more tolerant to photo-oxidative stress, due to a higher capacity to quench excess light energy via photochemical and non-photochemical means. Furthermore, PC and CK transgenic rice produced 22–24% more grains than WT plants. Taken together, these results suggest that expression of maize C₄ photosynthesis enzymes in rice, a C₃ plant, can improve its photosynthetic capacity with enhanced tolerance to photo-oxidation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytoseiid predators suppress populations of Bemisia tabaci on cucumber plants with alternative food

Phytoseiids are known to attack whiteflies, but it is an open question whether they can be used for biological control of these pest insects. Preselection experiments in the laboratory showed that two out of five phytoseiid species tested, Euseius scutalis and Typhlodromips swirskii, stood out in terms of their ability to develop and reproduce on a diet of Bemisia tabaci immatures. In this paper, we show that both predators are able to suppress whitefly populations on isolated cucumber plants in a greenhouse. Predatory mites were released 2 weeks in advance of the release of B. tabaci. To enable their survival and promote their population growth, they were provided weekly with alternative food, that is, Typha sp. pollen. A few weeks after whitefly introduction, the numbers of adult whiteflies on plants with predators were consistently lower than on plants without predators, where B. tabaci populations grew exponentially. After 9 weeks, this amounted to a 16- to 21-fold difference in adult whitefly population size. This shows that the two phytoseiid species are promising biocontrol agents of B. tabaci on greenhouse cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Participation of yeast inosine 5'-monophosphate dehydrogenase in an in vitro complex with a fragment of the C-rich telomeric strand

As part of our investigation of the i-motif, an intercalated structure formed by C-rich nucleic acid sequences, we searched for proteins of Saccharomyces cerevisiae which could associate with a sequence of the C-rich telomeric strand, d((CCCACA)(3)CCC). A gel retardation assay of yeast protein extract, in conditions where the DNA fragment folds into an intramolecular i-motif, shows formation of one major retarded band. The retarding factor was further characterized by a differential affinity procedure using streptavidin beads coated (or not coated) with the biotin-labeled DNA fragment. Differentially bound proteins were isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and identified by mass spectroscopy and Edman degradation as Imd2p, Imd3p and Imd4p. These highly similar (>95%) proteins are analogs of the two human NAD-dependent inosine 5'-monophosphate dehydrogenases (IMPDH) which occur as tetramers. The mass of the protein, as determined by gel exclusion chromatography, is about 250 kDa and is compatible with an IMPDH tetramer, but other compositions, involving non-IMPDH components, are not excluded. We note that the genes coding for Imd2p and Imd3p are located close to the telomere, and could therefore be subject to silencing by the telomere position effect.