Two genomes of highly polyphagous lepidopteran pests (Spodoptera frugiperda, Noctuidae) with different host-plant ranges.

Emergence of polyphagous herbivorous insects entails significant adaptation to recognize, detoxify and digest a variety of host-plants. Despite of its biological and practical importance - since insects eat 20% of crops - no exhaustive analysis of gene repertoires required for adaptations in generalist insect herbivores has previously been performed. The noctuid moth Spodoptera frugiperda ranks as one of the world's worst agricultural pests. This insect is polyphagous while the majority of other lepidopteran herbivores are specialist. It consists of two morphologically indistinguishable strains ("C" and "R") that have different host plant ranges. To describe the evolutionary mechanisms that both enable the emergence of polyphagous herbivory and lead to the shift in the host preference, we analyzed whole genome sequences from laboratory and natural populations of both strains. We observed huge expansions of genes associated with chemosensation and detoxification compared with specialist Lepidoptera. These expansions are largely due to tandem duplication, a possible adaptation mechanism enabling polyphagy. Individuals from natural C and R populations show significant genomic differentiation. We found signatures of positive selection in genes involved in chemoreception, detoxification and digestion, and copy number variation in the two latter gene families, suggesting an adaptive role for structural variation.

Topological and functional characterization of an insect gustatory receptor.

Insect gustatory receptors are predicted to have a seven-transmembrane structure and are distantly related to insect olfactory receptors, which have an inverted topology compared with G-protein coupled receptors, including mammalian olfactory receptors. In contrast, the topology of insect gustatory receptors remains unknown. Except for a few examples from Drosophila, the specificity of individual insect gustatory receptors is also unknown. In this study, the total number of identified gustatory receptors in Bombyx mori was expanded from 65 to 69. BmGr8, a silkmoth gustatory receptor from the sugar receptor subfamily, was expressed in insect cells. Membrane topology studies on BmGr8 indicate that, like insect olfactory receptors, it has an inverted topology relative to G protein-coupled receptors. An orphan GR from the bitter receptor family, BmGr53, yielded similar results. We infer, from the finding that two distantly related BmGrs have an intracellular N-terminus and an odd number of transmembrane spans, that this is likely to be a general topology for all insect gustatory receptors. We also show that BmGr8 functions independently in Sf9 cells and responds in a concentration-dependent manner to the polyalcohols myo-inositol and epi-inositol but not to a range of mono- and di-saccharides. BmGr8 is the first chemoreceptor shown to respond specifically to inositol, an important or essential nutrient for some Lepidoptera. The selectivity of BmGr8 responses is consistent with the known responses of one of the gustatory receptor neurons in the lateral styloconic sensilla of B. mori, which responds to myo-inositol and epi-inositol but not to allo-inositol.

Greatly enhanced detection of a volatile ligand at femtomolar levels using bioluminescence resonance energy transfer (BRET).

Our goal is to develop a general transduction system for G-protein coupled receptors (GPCRs). GPCRs are present in most eukaryote cells and transduce diverse extracellular signals. GPCRs comprise not only the largest class of integral membrane receptors but also the largest class of targets for therapeutic drugs. In all cases studied, binding of ligand to a GPCR leads to a sub-nanometer intramolecular rearrangement. Here, we report the creation of a novel chimaeric BRET-based biosensor by insertion of sequences encoding a bioluminescent donor and a fluorescent acceptor protein into the primary sequence of a GPCR. The BRET(2)-ODR-10 biosensor was expressed in membranes of Saccharomyces cerevisiae. Assays conducted on isolated membranes indicated an EC(50) in the femtomolar range for diacetyl. The response was ligand-specific and was abolished by a single point mutation in the receptor sequence. Novel BRET-GPCR biosensors of this type have potential application in many fields including explosive detection, quality control of food and beverage production, clinical diagnosis and drug discovery.

Bio-benchmarking of electronic nose sensors.

BACKGROUND: Electronic noses, E-Noses, are instruments designed to reproduce the performance of animal noses or antennae but generally they cannot match the discriminating power of the biological original and have, therefore, been of limited utility. The manner in which odorant space is sampled is a critical factor in the performance of all noses but so far it has been described in detail only for the fly antenna. METHODOLOGY: Here we describe how a set of metal oxide (MOx) E-Nose sensors, which is the most commonly used type, samples odorant space and compare it with what is known about fly odorant receptors (ORs). PRINCIPAL FINDINGS: Compared with a fly's odorant receptors, MOx sensors from an electronic nose are on average more narrowly tuned but much more highly correlated with each other. A set of insect ORs can therefore sample broader regions of odorant space independently and redundantly than an equivalent number of MOx sensors. The comparison also highlights some important questions about the molecular nature of fly ORs. CONCLUSIONS: The comparative approach generates practical learnings that may be taken up by solid-state physicists or engineers in designing new solid-state electronic nose sensors. It also potentially deepens our understanding of the performance of the biological system.

Molecular basis of female-specific odorant responses in Bombyx mori.

Males and females of many moth species exhibit important differences in sexual behaviours. Much research in this field has focused on the male-specific behaviour, electrophysiology and molecular biology of sex pheromone reception. Female-specific behaviours have been less well studied although, like male-specific behaviours, they could provide opportunities for intervention and management of lepidopteran pests. Previously, we identified genes encoding putative odorant receptors (ORs) from the genome of the silkworm, Bombyx mori, some of which have higher levels of steady-state transcript in the antennae of adult females compared with males. We have identified the full-length cDNA sequences of some of these ORs and described a novel OR that is part of a female-biased clade. Using expression in Sf9 cells and a calcium-imaging assay, we tested a range of compounds for their ability to activate the most highly female-biased ORs, BmOR19, BmOR30, BmOR45 and BmOR47. BmOR19 responds to linalool, while BmOR45 and BmOR47 respond to benzoic acid > 2-phenylethanol > benzaldehyde. No activating ligands were found for BmOR30. RNA in situ hybridisation experiments reveal that BmOR19 is expressed in female olfactory sensory neurons that are co-located in the same sensilla as a second ORN expressing BmOR45 and/or BmOR47. Taken together the activity and expression of these receptors is likely explanatory of the observed electrophysiology of long sensilla trichoidea of female B. mori, previously shown to each contain one terpene (BmOR19) and one benzoic acid (BmOR45, BmOR47) sensory neuron. Plant volatiles such as linalool, benzoic acid, 2-phenylethanol and benzaldehyde are oviposition cues for females of some moths. These compounds have also been found in male-produced pheromone blends extracted from the hair pencils of many noctuid species. Hair pencil structures have not previously been reported for B. mori, but we have found hair pencil-like structures in adult male B. mori that are absent in female moths. It is proposed that BmOR19, BmOR45 and BmOR47 account for some of the female-specific odorant responses in B. mori, such as oviposition and/or detection of an as yet unidentified male-produced sex pheromone.

Response to selection for rapid chill-coma recovery in Drosophila melanogaster: physiology and life-history traits.

Resistance to low temperatures can vary markedly among invertebrate species and is directly related to their distribution. Despite the ecological importance of cold resistance this trait has rarely been studied genetically, mainly because low and variable fitness of offspring from cold-stressed mothers makes it difficult to undertake selection experiments and compare cold resistance of parents and offspring. One measure of cold resistance that varies geographically in Drosophila melanogaster and that is amenable to genetic analysis is chill-coma recovery. Three replicate lines of D. melanogaster were selected every second generation, for over 30 generations, for decreased recovery time following exposure to 0 degrees C. Correlated responses were scored to characterize underlying physiological traits and to investigate interactions with other traits. Lines responded rapidly to the intermittent selection regime with realized heritabilities varying from 33% to 46%. Selected lines showed decreased recovery time after exposure to a broad range of low temperatures and also had a lower mortality following a more severe cold shock, indicating that a general mechanism underlying cold resistance had been selected. The selection response was independent of plastic changes in cold resistance because the selected lines maintained their ability to harden (i.e. a short-term exposure to cool temperature resulted in decreased recovery time in subsequent chill-coma assays). Changes in cold resistance were not associated with changes in resistance to high temperature exposure, and selected lines showed no changes in wing size, development time or viability. However, there was a decrease in longevity in the selected lines due to an earlier onset of ageing. These results indicate that chill-coma recovery can be rapidly altered by selection, as long as selection is undertaken every second generation to avoid carry-over effects, and suggest that lower thermal limits can be shifted towards increased cold resistance independently of upper thermal limits and without tradeoffs in many life-history traits.

The latitudinal cline in the In(3R)Payne inversion polymorphism has shifted in the last 20 years in Australian Drosophila melanogaster populations.

Clinal variation has been described in a number of inversions in Drosophila but these clines are often characterized by cytological techniques using small sample sizes, and associations with specific genes are rarely considered. Here we have developed a molecular assay for In(3R)Payne in Drosophila melanogaster from eastern Australia populations. It shows in repeated samples that the inversion cline is very tightly associated with latitude and is almost fixed in tropical populations while relatively rare in temperate populations. This steep cline has shifted in position in the last 20 years. The heat shock gene, hsr-omega, located centrally inside the inversion sequence, shows a different clinal pattern to In(3R)Payne. These results suggest strong ongoing selection on In(3R)Payne over the last 100 years since the colonization of Australia that is partly independent of hsr-omega.