Antenna-specific glutathione S-transferase in male silkmoth Bombyx mori.

Glutathione S-transferases (GSTs) are multifunctional enzymes that are widely distributed in different species. GSTs detoxify exogenous and endogenous substances by conjugation to reduced glutathione. We characterized BmGSTD4, an antenna-specific GST, in male silkmoths. The full-length mRNA of Bmgstd4 was cloned by RACE-PCR and contained an open reading frame of 738 bp encoding a 245 amino acid protein. The antenna specificity of BmGSTD4 was validated at the mRNA and protein levels and BmGSTD4 was shown to localize in the sensillum of male silkmoth antennae. Homology modeling and multi-sequence alignment suggested that BmGSTD4 was a typical GST belonging to the δ class and had a canonical GST fold with a conserved N-terminus, including a glutathione-binding site and a C-terminal domain harboring a hydrophobic substrate-binding site. Restricted expression of BmGSTD4 in silkmoth antennae combined with GST activity suggested that BmGSTD4 was involved in the detoxification of harmful chemicals.

Comparisons of contact chemoreception and food acceptance by larvae of polyphagous Helicoverpa armigera and oligophagous Bombyx mori.

We compared food choice and the initial response to deterrent treated diet between fifth instars of Helicoverpa armigera, a polyphagous generalist pest, and Bombyx mori, an oligophagous specialist beneficial. Bombyx mori was more behaviorally sensitive to salicin than to caffeine. The relative sensitivities were reversed for H. armigera, which was tolerant to the highest levels of salicin found in natural sources but sensitive to caffeine. A single gustatory receptor neuron (GRN) in the medial styloconic sensillum of B. mori was highly sensitive to salicin and caffeine. The styloconic sensilla of H. armigera did not respond consistently to either of the bitter compounds. Phagostimulants also were tested. Myo-inositol and sucrose were detected specifically by two GRNs located in B. mori lateral styloconic sensillum, whereas, in H. armigera, sucrose was sensed by a GRN in the lateral sensillum, and myo-inositol by a GRN in the medial sensillum. Myo-inositol responsiveness in both species occurred at or below 10(-3) mM, which is far below the naturally occurring concentration of 1 mM in plants. Larval responses to specific plant secondary compounds appear to have complex determinants that may include host range, metabolic capacity, and gustatory repertoire.

A phylogenomics approach to characterizing sensory neuron membrane proteins (SNMPs) in Lepidoptera.

Sensory neuron membrane proteins (SNMPs) play a critical role in the insect olfactory system but there is a deficit of functional studies beyond Drosophila. Here, we use a combination of available genome sequences, manual curation, genome and transcriptome data, phylogenetics, expression profiling and gene knockdown to investigate SNMP superfamily in various insect species with a focus on Lepidoptera. We curated 81 genes from 36 insect species and identified a novel lepidopteran SNMP gene family, SNMP3. Phylogenetic analysis shows that lepidopteran SNMP3, but not the previously annotated lepidopteran SNMP2, is the true homologue of the dipteran SNMP2. Digital expression, microarray and qPCR analyses show that the lepidopteran SNMP1 is specifically expressed in adult antennae. SNMP2 is widely expressed in multiple tissues while SNMP3 is specifically expressed in the larval midgut. Microarray analysis suggest SNMP3 may be involved in the silkworm immunity response to virus and bacterial infections. We functionally characterized SNMP1 in the silkworm using RNA interference (RNAi) and behavioral assays. Our results suggested that Bombyx mori SNMP1 is a functional orthologue of the Drosophila melanogaster SNMP1 and plays a critical role in pheromone detection. Split-ubiquitin yeast hybridization study shows that BmorSNMP1 has a protein-protein interaction with the pheromone receptor (BmorOR1), and the co-receptor (BmorOrco). Concluding, we propose a novel molecular model in which BmorOrco, BmorSNMP1 and BmorOR1 form a heteromer in the detection of the silkworm sex pheromone bombykol.