Transcriptomic response of female adult moths to host and non-host plants in two closely related species.

BACKGROUND: Divergent selection has been shown to promote speciation in many taxa and especially in phytophagous insects. In the Ostrinia species complex, the European corn borer (ECB) and adzuki bean borer (ABB) are two sibling species specialized to different host plants. The first is a well-known maize pest, whereas the second is a polyphagous species associated with various dicotyledons. Their specialization to host plants is driven by morphological, behavioral and physiological adaptations. In particular, previous studies have shown that ECB and ABB display marked behavior with regard to plant choice during oviposition, involving specific preference and avoidance mechanisms. In this study, our goal was to identify the mechanisms underlying this host-plant specialization in adult females through an analysis of their gene expression. We assembled and annotated a de novo reference transcriptome and measured differences in gene expression between ECB and ABB females, and between environments. We related differentially expressed genes to host preference behavior, and highlighted the functional categories involved. We also conducted a specific analysis of chemosensory genes, which are considered to be good candidates for host recognition before oviposition. RESULTS: We recorded more differentially expressed genes in ECB than in ABB samples, and noticed that the majority of genes potentially involved in the host preference were different between the two species. At the functional level, the response to plant environment in adult females involved many processes, including the metabolism of carbohydrates, lipids, proteins, and amino acids; detoxification mechanisms and immunity; and the chemosensory repertoire (as expected). Until now, most of the olfactory receptors described in Ostrinia spp. had been tested for their putative role in pheromone recognition by males. Here we observed that one specific olfactory receptor was clearly associated with ECB's discrimination between maize and mugwort conditions, highlighting a potential new candidate involved in plant odor discrimination in adult females. CONCLUSIONS: Our results are a first step toward the identification of candidate genes and functions involved in chemosensory processes, carbohydrate metabolism, and virus and retrovirus dynamics. These candidates provide new avenues for research into understanding the role of divergent selection between different environments in species diversification.

Genome-wide nucleotide diversity of hatchery-reared Atlantic and Mediterranean strains of brown trout Salmo trutta compared to wild Mediterranean populations.

A genome-wide assessment of diversity is provided for wild Mediterranean brown trout Salmo trutta populations from headwater tributaries of the Orb River and from Atlantic and Mediterranean hatchery-reared strains that have been used for stocking. Double-digest restriction-site-associated DNA sequencing (dd-RADseq) was performed and the efficiency of de novo and reference-mapping approaches to obtain individual genotypes was compared. Large numbers of single nucleotide polymorphism (SNP) markers with similar genome-wide distributions were discovered using both approaches (196 639 v. 121 016 SNPs, respectively), with c. 80% of the loci detected de novo being also found with reference mapping, using the Atlantic salmon Salmo salar genome as a reference. Lower mapping density but larger nucleotide diversity (π) was generally observed near extremities of linkage groups, consistent with regions of residual tetrasomic inheritance observed in salmonids. Genome-wide diversity estimates revealed reduced polymorphism in hatchery strains (π = 0·0040 and π = 0·0029 in Atlantic and Mediterranean strains, respectively) compared to wild populations (π = 0·0049), a pattern that was congruent with allelic richness estimated from microsatellite markers. Finally, pronounced heterozygote deficiency was found in hatchery strains (Atlantic FIS = 0·18; Mediterranean FIS = 0·42), indicating that stocking practices may affect the genetic diversity in wild populations. These new genomic resources will provide important tools to define better conservation strategies in S. trutta.

Structure and magnetism of [M3](6/7+) metal chain complexes from density functional theory: analysis for copper and predictions for silver.

The ground-state electronic structure of the trinuclear complex Cu3(dpa)4Cl2 (1), where dpa is the anion of di(2-pyridyl)amine, has been investigated within the framework of density functional theory (DFT) and compared with that obtained for other known M3(dpa)4Cl2 complexes (M = Cr, Co, Ni) and for the still hypothetical Ag3(dpa)4Cl2 compound. Both coinage metal compounds display three singly occupied x2-y2-like (delta) orbitals oriented toward the nitrogen environment of each metal atom, generating antibonding M-(N4) interactions. All other metal orbital combinations are doubly occupied, resulting in no delocalized metal-metal bonding. This is at variance with the other known symmetric M3(dpa)4Cl2 complexes of the first transition series, which all display some delocalized bonding through the metal backbone, with formal bond multiplicity decreasing in the order Cr > Co > Ni. An antiferromagnetic coupling develops between the singly occupied MOs via a superexchange mechanism involving the bridging dpa ligands. This magnetic interaction can be considered as an extension to the three aligned Cu(II) atoms of the well-documented exchange coupling observed in carboxylato-bridged dinuclear copper compounds. Broken-symmetry calculations with approximate spin projection adequately reproduce the coupling constant observed for 1. Oxidation of 1 removes an electron from the magnetic orbital located on the central Cu atom and its ligand environment; 1+ displays a much weaker antiferromagnetic interaction coupling the terminal Cu-N4 moieties via four ligand pathways converging through the x2-y2 orbital of the central metal. The silver homologues of 1 and 1+ display similar electronic ground states, but the calculated magnetic couplings are stronger by factors of about 3 and 4, respectively, resulting from a better overlap between the metal centers and their equatorial ligand environment within the magnetic orbitals.

Zeaxanthin and menaquinone-7 biosynthesis in Sphingobacterium multivorum via the methylerythritol phosphate pathway.

Feeding of [1-(13)C]glucose, [U-(13)C(6)]glucose, [3-(13)C]alanine and [1-(13)C]acetate to Sphingobacterium multivorum showed that this bacterium utilizes the methylerythritol phosphate pathway for the biosynthesis of menaquinone-7 and zeaxanthin, a carotenoid of industrial importance. Differential incorporation of the labeled precursors gave some insight into the preferred carbon sources involved in isoprenoid biosynthesis.

Metal-metal bond length variability in Co(3)(dipyridylamide)(4)Cl(2): bond-stretch isomerism, crystal field effects, or spin transition process? A DFT study.

The unprecedented structural behavior of Co(3)(dipyridylamide)(4)Cl(2), characterized in two crystalline forms in which the tricobalt framework is either symmetric or highly nonsymmetric at room temperature is investigated by means of gradient-corrected DFT calculations. The isolated molecule is assigned a single energy minimum associated with a low-spin (doublet) electronic configuration. The optimal geometry closely reproduces the X-ray structure observed for the isomer displaying equivalent metal-metal distances. However, the ground-state potential energy surface is extremely shallow with respect to a distortion of the Co(3) framework. A "weak" distortion, similar to that observed for the unsymmetrical complex at low temperature (Deltad(Co-Co) = 0.08 A at 110 K) induces a destabilization of 1.1 kcal.mol(-1) only. The distortion observed at room temperature (Deltad(Co-Co) = 0.17 A) destabilizes the isolated complex by 4.2 kcal.mol(-1). These results are rationalized in terms of the "three-electron three-center" concept applied to the sigma-bonding electrons of the cobalt framework. A phenomenological model based upon the Heisenberg Hamiltonian successfully reproduces the calculated potential energy curve and assigns the relative stability of the symmetric structure to local forces (Pauli repulsion, ligand bite, etc.) distinct from delocalized sigma bonding. In view of these results, the two structures characterized from X-rays cannot be termed "bond-stretch isomers" according to the strict definition given by Parkin. To investigate the origin of the distorted form, an electric field was applied to the isolated molecule, but it did not shift the equilibrium position toward asymmetry, despite a strong polarization of the electron density. Finally, the quartet state of lowest energy ((4)A state) has an optimal structure that is distorted and that reproduces most of the distinctive features observed in the nonsymmetric structure. Despite the high relative energy calculated for this quartet state, we assign the occurrence of the nonsymmetric form and its extreme variability with temperature to a progressive population of this excited state as temperature increases.

Novel hopanoids from Frankia spp. and related soil bacteria. Squalene cyclization and significance of geological biomarkers revisited.

Three series of hopanoids, differing by their configurations at C-17 and C-21, have been identified in several Frankia spp. and other related soil bacteria. The widespread bacterial hopanoids of the 17beta(H),21beta(H) series were accompanied by their isomers of the 17beta(H),21alpha(H) (moretane) and 17alpha(H), 21beta(H) series. The latter series has not previously been found in living organisms and is considered to be a result of the abiotic isomerization of the thermodynamically less stable 17beta(H),21beta(H) hopanoids. This simultaneous presence of three isomeric hopanoid series highlights intriguing problems in the biogenesis of the bacteriohopane skeleton and partly questions the significance of hopanic biomarkers in sediments.

Structural diversity of the triterpenic hydrocarbons from the bacterium Zymomonas mobilis: the signature of defective squalene cyclization by the squalene/hopene cyclase.

Twelve polycyclic triterpenic hydrocarbons (alpha- and gamma-polypodatetraenes, dammara-20(21),24-diene, 17-isodammara-12,24-diene, eupha-7,24-diene, hop-17(21)-ene, neohop-13(18)-ene, 17-isodammara-20(21),24-diene, neohop-12-ene, fern-8-ene, diploptene and hop-21-ene) were detected in the hydrocarbon fraction from the bacterium Zymomonas mobilis. Some of them have never been reported from bacteria. These triterpenes were present in Z. mobilis in significant amounts, comparable to those of diploptene, which is usually the major triterpenic hydrocarbon in hopanoid-producing bacteria. The occurrence of such compounds confirms the lack of specificity of bacterial squalene cyclases and the possibility of alternative cyclization routes induced by the existence in the cyclization process of intermediate carbocations of sufficient lifetime.

Novel methylated triterpenoids of the gammacerane series from the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110.

The nitrogen-fixing, symbiotic root-nodule forming bacterium Bradyrhizobium japonicum USDA 110 contained gammacerane derivatives next to triterpenoids of the hopane series. Diploptene, diplopterol, 2 beta-methyldiplopterol, aminobacteriohopanetriol and adenosylhopane were accompanied by tetrahymanol and the corresponding novel methylated homologues 2 beta-methyltetrahymanol, 20 alpha-methyltetrahymanol, and 2 beta,20 alpha-dimethyltetrahymanol. Incorporation of [(2)H(3)]methyl-L-methionine indicated that the additional methyl groups originated from methionine, probably with S-adenosylmethionine acting as methyl donor, with retention of the three deuterium atoms. The simultaneous presence of hopane and gammacerane derivatives seems a characteristic feature of the genus Bradyrhizobium and the phylogenetically closely related Rhodopseudomonas palustris.

Cutting edge: human gamma delta T cells are activated by intermediates of the 2-C-methyl-D-erythritol 4-phosphate pathway of isoprenoid biosynthesis.

Activation of V gamma 9/V delta 2 T cells by small nonprotein Ags is frequently observed after infection with various viruses, bacteria, and eukaryotic parasites. We suggested earlier that compounds synthesized by the 2-C:-methyl-D-erythritol 4-phosphate (MEP) pathway of isopentenyl pyrophosphate synthesis are responsible for the V gamma 9/V delta 2 T cell reactivity of many pathogens. Using genetically engineered Escherichia coli knockout strains, we now demonstrate that the ability of E. coli extracts to stimulate gamma delta T cell proliferation is abrogated when genes coding for essential enzymes of the MEP pathway, dxr or gcpE, are disrupted or deleted from the bacterial genome.

Identification of gcpE as a novel gene of the 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid biosynthesis in Escherichia coli.

The 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis is essential in most eubacteria and plants and has remarkable biotechnological interest. However, only the first steps of this pathway have been determined. Using bioinformatic and genetic approaches, we have identified gcpE as a novel gene of the MEP pathway. The distribution of this gene in bacteria and plants strictly parallels that of the gene encoding 1-deoxy-D-xylulose 5-phosphate reductoisomerase, which catalyses the first committed step of the MEP pathway. Our data demonstrate that the gcpE gene is essential for the MEP pathway in Escherichia coli and indicate that this gene is required for the trunk line of the isoprenoid biosynthetic route.

Electronic origin of the structural versatility in linear trichromium complexes of dipyridylamide.

Spin unrestricted DFT calculations on Cr3(dpa)4Cl2 (dpa = dipyridylamide) suggest that the linear (Cr3)6+ metal framework could adopt either a symmetric conformation, or a strongly nonsymmetric one, depending on the nature of the spin coupling between the localized metal electrons.

Genetic evidence of branching in the isoprenoid pathway for the production of isopentenyl diphosphate and dimethylallyl diphosphate in Escherichia coli.

An alternative mevalonate-independent pathway for isoprenoid biosynthesis has been recently discovered in eubacteria (including Escherichia coli) and plant plastids, although it is not fully elucidated yet. In this work, E. coli cells were engineered to utilize exogenously provided mevalonate and used to demonstrate by a genetic approach that branching of the endogenous pathway results in separate synthesis of the isoprenoid building units isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). In addition, the IPP isomerase encoded by the idi gene was shown to be functional in vivo and to represent the only possibility for interconverting IPP and DMAPP in this bacterium.

Deuterium-labelled isotopomers of 2-C-methyl-D-erythritol as tools for the elucidation of the 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid biosynthesis.

Escherichia coli synthesizes its isoprenoids via the mevalonate-independent 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. The MC4100dxs::CAT strain, defective in deoxyxylulose-5-phosphate synthase, which is the first enzyme in this metabolic route, exclusively synthesizes its isoprenoids from exogenous 2-C-methyl-D-erythritol (ME) added to the culture medium. The fate of the hydrogen atoms in the MEP pathway was followed by the incorporation of [1,1-(2)H(2)]ME and [3,5,5,5-(2)H(4)]ME. The two C-1 hydrogen atoms of ME were found without any loss in the prenyl chain of menaquinone and/or ubiquinone on the carbon atoms derived from C-4 of isopentenyl diphosphate (IPP) and on the E-methyl group of dimethylallyl diphosphate (DMAPP), the C-5 hydrogen atoms on the methyl groups derived from IPP C-5 methyl group and the Z-methyl group of DMAPP. This showed that no changes in the oxidation state of these carbon atoms occurred in the reaction sequence between MEP and IPP. Furthermore, no deuterium scrambling was observed between the carbon atoms derived from C-4 and C-5 of IPP or DMAPP, suggesting a completely stereoselective IPP isomerase or no significant activity of this enzyme. The C-3 deuterium atom of [3,5,5,5-(2)H(4)]ME was preserved only in the DMAPP starter unit and was completely missing from all those derived from IPP. This finding, aided by the non-essential role of the IPP isomerase gene, suggests the presence in E. coli of two different routes towards IPP and DMAPP, starting from a common intermediate derived from MEP.

Bacterial triterpenoids of the hopane series as biomarkers for the chemotaxonomy of Burkholderia, Pseudomonas and Ralstonia spp.

Hopanoid fingerprints allowed to differentiate bacteria formerly connected to the genus Pseudomonas. Whereas all strains related to Pseudomonas and Ralstonia were devoid of any detectable hopanoid, these pentacyclic triterpenoids were found in the Burkholderia species and in related soil isolates, which contained as main hopanoid a bacteriohopanetetrol carbapseudopentose ether, accompanied by significant amounts of its novel Delta(6) unsaturated homologue. Unsaturated hopanoids represent an extremely rare feature in soil bacteria and the only known indication for a catabolism of this pentacyclic carbon skeleton in bacteria.

CO2 as main carbon source for isoprenoid biosynthesis via the mevalonate-independent methylerythritol 4-phosphate route in the marine diatoms Phaeodactylum tricornutum and Nitzschia ovalis.

Isoprenoid biosynthesis was investigated in the two diatoms Phaeodactylum tricornutum and Nitzschia ovalis by labeling experiments performed in mixotrophic growth conditions with sodium [1-(13)C]acetate, 13CO2, [1-(13)C]glucose, sodium [3-(13)C]pyruvate and 1-deoxy-D-[5,5-(2)H2]xylulose. A clear dichotomy was found. Acetate was the preferred carbon source for the formation of the sterols in the cytoplasm via the mevalonate pathway. Carbon dioxide was the main source for phytol biosynthesis in the chloroplasts via the mevalonate-independent methylerythritol 4-phosphate pathway. The two diatoms showed the same compartmentation for isoprenoid biosynthesis as that previously found in higher plants, the red alga Porphyridium cruentum and the Chrysophyte Ochromonas danica.

Bacterial triterpenoids of the hopane series from the methanotrophic bacteria Methylocaldum spp.: phylogenetic implications and first evidence for an unsaturated aminobacteriohopanepolyol.

The hopanoid content of the two methanotrophic bacteria Methylocaldum szegediense and Methylocaldum tepidum was investigated. 35-Aminobacteriohopane-30R,31R,32R,33S, 34S-pentol and its 3beta-methyl homologue were present in both strains. In M. tepidum, they were accompanied by 35-aminobacteriohopane-31R,32R,33S, 34S-tetrol and its 3beta-methyl homologue. The side chain structure was identical to those previously reported from two other obligate methanotrophs, Methylococcus capsulatus and Methylomonas methanica. The two Methylocaldum species shared with the Methylococcus species the presence of 3beta-methylhopanoid as well as of a hopanoid releasing adiantol upon H(5)IO(6)/NaBH(4) treatment. A rare feature was in addition found in M. szegediense. The saturated hopanoids were accompanied by an unsaturated aminobacteriohopanepentol with a Delta(11) double bond. Comparison of the hopanoid fingerprints was in accordance with the close phylogenetic relationship of Methylococcus and Methylocaldum. The major difference was the absence of sterols in Methylocaldum which were always detected in the Methylococcus species.

On the absence of the glyceraldehyde 3-phosphate/pyruvate pathway for isoprenoid biosynthesis in fungi and yeasts.

The biosynthesis of isopentenyl diphosphate, the central intermediate of isoprenoid formation, was investigated in the fungus Aschersonia aleyrodis and the yeast Rhodotorula glutinis. The incorporation of 13C-labeled glucose or acetate into their isoprenoids showed that ergosterol in both micro-organisms, ubiquinone in R. glutinis and dihydro-ubiquinone, beta-carotene and triterpenes of the hopane series in A. aleyrodis were synthesized via the mevalonate pathway. No evidence for the presence of the alternative mevalonate-independent glyceraldehyde 3-phosphate/pyruvate pathway was found.

Distribution of the mevalonate and glyceraldehyde phosphate/pyruvate pathways for isoprenoid biosynthesis in unicellular algae and the cyanobacterium Synechocystis PCC 6714.

Isopentenyl diphosphate, the universal isoprenoid precursor, can be produced by two different biosynthetic routes: either via the acetate/mevalonate (MVA) pathway, or via the more recently identified MVA-independent glyceraldehyde phosphate/pyruvate pathway. These two pathways are easily differentiated by incorporation of [1-13C]glucose and analysis of the resulting labelling patterns found in the isoprenoids. This method was successfully applied to several unicellular algae raised under heterotrophic growth conditions and allowed for the identification of the pathways that were utilized for isoprenoid biosynthesis. All isoprenoids examined (sterols, phytol, carotenoids) of the green algae Chlorella fusca and Chlamydomonas reinhardtii were synthesized via the GAP/pyruvate pathway, as in another previously investigated green alga, Scenedesmus obliquus, which was also shown in this study to synthesize ubiquinone by the same MVA-independent route. In the red alga Cyanidium caldarium and in the Chrysophyte Ochromonas danica a clear dichotomy was observed: as in higher plants, sterols were formed via the MVA route, whereas chloroplast isoprenoids (phytol in Cy. caldarium and O. danica and beta-carotene in O. danica) were synthesized via the GAP/pyruvate route. In contrast, the Euglenophyte Euglena gracilis synthesized ergosterol, as well as phytol, via the acetate/MVA route. Similar feeding experiments were performed with the cyanobacterium Synechocystis PCC 6714 using [1-13C]- and [6-13C]-glucose. The two isoprenoids examined, phytol and beta-carotene, were shown to have the typical labelling pattern derived from the GAP/pyruvate route.