The effects of abiotic factors on induced volatile emissions in corn plants

Many plants respond to herbivory by releasing a specific blend of volatiles that is attractive to natural enemies of the herbivores. In corn (Zea mays), this induced odor blend is mainly composed of terpenoids and indole. The induced signal varies with plant species and genotype, but little is known about the variation due to abiotic factors. Here, we tested the effect of soil humidity, air humidity, temperature, light, and fertilization rate on the emission of induced volatiles in young corn plants. Each factor was tested separately under constant conditions for the other factors. Plants released more when standing in dry soil than in wet soil, whereas for air humidity, the optimal release was found at around 60% relative humidity. Temperatures between 22 degrees C and 27 degrees C led to a higher emission than lower or higher temperatures. Light intensity had a dramatic effect. The emission of volatiles did not occur in the dark and increased steadily with an increase in the light intensity. An experiment with an unnatural light-dark cycle showed that the release was fully photophase dependent. Fertilization also had a strong positive effect; the emission of volatiles was minimal when plants were grown under low nutrition, even when results were corrected for plant biomass. Changes in all abiotic factors caused small but significant changes in the relative ratios among the different compounds (quality) in the induced odor blends, except for air humidity. Hence, climatic conditions and nutrient availability can be important factors in determining the intensity and variability in the release of induced plant volatiles.     

Differential regulation of the chick dorsal thoracic dermal progenitors from the medial dermomyotome

The chick dorsal feather-forming dermis originates from the dorsomedial somite and its formation depends primarily on Wnt1 from the dorsal neural tube. We investigate further the origin and specification of dermal progenitors from the medial dermomyotome. This comprises two distinct domains: the dorsomedial lip and a more central region (or intervening zone) that derives from it. We confirm that Wnt1 induces Wnt11 expression in the dorsomedial lip as previously shown, and show using DiI injections that some of these cells, which continue to express Wnt11 migrate under the ectoderm, towards the midline, to form most of the dorsal dermis. Transplantation of left somites to the right side to reverse the mediolateral axis confirms this finding and moreover suggests the presence of an attractive or permissive environment produced by the midline tissues or/and a repellent or inadequate environment by the lateral tissues. By contrast, the dorsolateral dermal cells just delaminate from the surface of the intervening space, which expresses En1. Excision of the axial organs or the ectoderm, and grafting of Wnt1-secreting cells, shows that, although the two populations of dermal progenitors both requires Wnt1 for their survival, the signalling required for their specification differs. Indeed Wnt11 expression relies on dorsal neural tube-derived Wnt1, while En1 expression depends on the presence of the ectoderm. The dorsal feather-forming dermal progenitors thus appear to be differentially regulated by dorsal signals from the neural tube and the ectoderm, and derive directly and indirectly from the dorsomedial lip. As these two dermomyotomal populations are well known to also give rise to epaxial muscles, an isolated domain of the dermomyotome that contains only dermal precursors does not exist and none of the dermomyotomal domains can be considered uniquely as a dermatome.     

Glycosylation of the hepatitis C virus envelope protein E1 occurs posttranslationally in a mannosylphosphoryldolichol-deficient CHO mutant cell line

The addition of N-linked glycans to a protein is catalyzed by oligosaccharyltransferase, an enzyme closely associated with the translocon. N-glycans are believed to be transferred as the protein is being synthesized and cotranslationally translocated in the lumen of the endoplasmic reticulum. We used a mannosylphosphoryldolichol-deficient Chinese hamster ovary mutant cell line (B3F7 cells) to study the temporal regulation of N-linked core glycosylation of hepatitis C virus envelope protein E1. In this cell line, truncated Glc(3)Man(5)GlcNAc(2) oligosaccharides are transferred onto nascent proteins. Pulse-chase analyses of E1 expressed in B3F7 cells show that the N-glycosylation sites of E1 are slowly occupied until up to 1 h after protein translation is completed. This posttranslational glycosylation of E1 indicates that the oligosaccharyltransferase has access to this protein in the lumen of the endoplasmic reticulum for at least 1 h after translation is completed. Comparisons with the N-glycosylation of other proteins expressed in B3F7 cells indicate that the posttranslational glycosylation of E1 is likely due to specific folding features of this acceptor protein.     

A natural recessive resistance gene against potato virus Y in pepper corresponds to the eukaryotic initiation factor 4E (eIF4E)

We show here that the pvr2 locus in pepper, conferring recessive resistance against strains of potato virus Y (PVY), corresponds to a eukaryotic initiation factor 4E (eIF4E) gene. RFLP analysis on the PVY-susceptible and resistant pepper cultivars, using an eIF4E cDNA from tobacco as probe, revealed perfect map co-segregation between a polymorphism in the eIF4E gene and the pvr2 alleles, pvr2(1) (resistant to PVY-0) and pvr2(2) (resistant to PVY-0 and 1). The cloned pepper eIF4E cDNA encoded a 228 amino acid polypeptide with 70-86% nucleotide sequence identity with other plant eIF4Es. The sequences of eIF4E protein from two PVY-susceptible cultivars were identical and differed from the eIF4E sequences of the two PVY-resistant cultivars Yolo Y (YY) (pvr2(1)) and FloridaVR2 (F) (pvr2(2)) at two amino acids, a mutation common to both resistant genotypes and a second mutation specific to each. Complementation experiments were used to show that the eIF4E gene corresponds to pvr2. Thus, potato virus X-mediated transient expression of eIF4E from susceptible cultivar Yolo Wonder (YW) in the resistant genotype YY resulted in loss of resistance to subsequent PVY-0 inoculation and transient expression of eIF4E from YY (resistant to PVY-0; susceptible to PVY-1) rendered genotype F susceptible to PVY-1. Several lines of evidence indicate that interaction between the potyvirus genome-linked protein (VPg) and eIF4E are important for virus infectivity, suggesting that the recessive resistance could be due to incompatibility between the VPg and eIF4E in the resistant genotype.     

A prediction-based resampling method for estimating the number of clusters in a dataset

Background  

Microarray technology is increasingly being applied in biological and medical research to address a wide range of problems, such as the classification of tumors. An important statistical problem associated with tumor classification is the identification of new tumor classes using gene-expression profiles. Two essential aspects of this clustering problem are: to estimate the number of clusters, if any, in a dataset; and to allocate tumor samples to these clusters, and assess the confidence of cluster assignments for individual samples. Here we address the first of these problems.     

Biomimetic poly(methyl methacrylate)-based terpolymers: modulation of bacterial adhesion effect

Adherence of Staphylococcus aureus, responsible for major foreign body infections, was assessed onto functionalized poly(methyl methacrylate)-based terpolymers bearing sulfonate and carboxylate groups and onto poly(methyl methacrylate) as control. These terpolymers, have been synthesized by radical copolymerization of methyl methacrylate, methacrylic acid, and sodium styrene sulfonate by varying the ratio R = [COO(-)]/[COO(-) + SO(3)(-)] from 0 to 1 and keeping ionic monomer content between 7 and 18%. Adsorption of fibronectin onto poly(methyl methacrylate) was shown to dramatically promote bacterial adherence, whereas a strong inhibition of bacteria adherence was observed onto functionalized terpolymers containing both carboxylate and sulfonate groups. When terpolymers were predominantly functionalized by carboxylate groups, bacteria adherence was favored and reached values close to those obtained for poly(methyl methacrylate). These results have been related to the distribution of the anionic groups along the macromolecular chains, creating active sites responsible for specific interactions with fibronectin and inducing modifications of its conformation. The conformation of the adsorbed adhesive protein was then suggested to have an influence on the availability of its interaction sites to bacteria adhesins and therefore on modulation of bacteria adherence. Inhibition of Staphylococcus aureus adherence by functionalized poly(methyl methacrylate)-based terpolymers is of great interest in the field of biomedical implants and especially in the case of ophthalmic applications.     

A simple two-step approach for introducing a protected diaminedithiol chelator during solid-phase assembly of peptides

A simple synthetic strategy is described to incorporate a protected diaminedithiol (N(2)S(2)) chelator during Fmoc solid-phase synthesis of short peptides. The resulting constructs could be efficiently labeled with technetium-99m (99mTc). The chelator was assembled at the N-terminus of peptides in a two-step procedure where the deprotected terminal amino group was first reacted with di-Fmoc-diaminopropionic acid (Fmoc-DAP-[Fmoc]-OH). The two protected amino groups were then simultaneously deprotected and subsequently reacted with S-benzoylthiolglycolic acid (TGA) to generate a protected N(2)S(2) chelator. This metal binding site was introduced into di- and tripeptides. Each peptide construct was composed of a C-terminal lysine residue and an N-terminal diaminopropionic moiety modified to create the chelator site. The epsilon-amino group at the C-terminal lysine was further derivatized with a nitroimidazole group to facilitate cellular retention. The resulting constructs were then cleaved from the resin support, purified, and labeled with [99mTc]pertechnetate. Six constructs were prepared differing by a single amino acid inserted between the diaminopropionic acid and lysine residues. Optimal labeling yields of >70% were achieved around neutral pH and heating at 75 degrees C for 10 min. Purified 99mTc-labeled constructs were found to accumulate in Chinese hamster ovary (CHO) cells in vitro as a function of charge and hydrophobicity.     

Enhancement of the inducible NO synthase activation by retinoic acid is mimicked by RARalpha agonist in vivo

We have previously shown that all-trans retinoic acid (atRA), the active metabolite of vitamin A, enhances the activation of the inducible nitric oxide synthase (NOS II) pathway, a component of innate immunity, in rats in vivo. We investigated the relative contribution of retinoic acid receptor-alpha (RARalpha) and retinoid X receptors (RXRs) to NOS II activation triggered by LPS. Five-day supplementation with 10 mg/kg of either atRA or the RARalpha selective agonist Ro-40-6055, but not with 10 mg/kg of the pan-RXR agonist Ro-25-7386, enhanced the LPS-induced NOS II mRNA, protein expression in liver, and plasma nitrite/nitrate concentration. Both atRA and the RARalpha agonist (but not the RXR agonist) increased the number of peripheral T helper lymphocytes and plasma interferon-gamma concentration. Synergism between retinoids and LPS on NOS II activation within an organ coincided with synergism on interferon regulatory factor-1 mRNA expression but not with the level of expression of the RARalpha protein. These results suggest that, in vivo, atRA activates NOS II through RARalpha and contributes to characterizing the complex effect of retinoids on the host inflammatory/immune response.     

Cholesterol-dependent insertion of glycosylphosphatidylinositol-anchored enzyme

Evidence is now accumulating that the plasma membrane is organized in different lipid and protein subdomains. Thus, glycosylphosphatidylinositol (GPI)-anchored proteins are proposed to be clustered in membrane microdomains enriched in cholesterol and sphingolipids, called rafts.By a detergent-mediated method, alkaline phosphatase, a GPI-anchored enzyme, was efficiently inserted into the membrane of sphingolipids- and cholesterol-rich liposomes as demonstrated by flotation in sucrose gradients. We have determined the enzyme extraluminal orientation. Using defined lipid components to assess the possible requirements for GPI-anchored protein insertion, we have demonstrated that insertion into membranes was cholesterol-dependent as the cholesterol addition increased the enzyme incorporation in simple phosphatidylcholine liposomes.