Background: Eogystia hippophaecolus (Hua et al.) (Lepidoptera: Cossidae) is the major threat to seabuckthorn plantations in China. Specific and highly efficient artificial sex pheromone traps was developed and used to control it. However, the molecular basis for the pheromone recognition is not known. So we established the antennal transcriptome of E. hippophaecolus and characterized the expression profiles of odorant binding proteins. These results establish and improve the basis knowledge of the olfactory receptive system, furthermore provide a theoretical basis for the development of new pest control method.
Results: We identified 29 transcripts encoding putative odorant-binding proteins (OBPs), 18 putative chemosensory proteins (CSPs), 63 odorant receptors (ORs), 13 gustatory receptors (GRs), 12 ionotropic receptors (IRs), and two sensory neuron membrane proteins (SNMPs). Based on phylogenetic analysis, we found one Orco and three pheromone receptors of E. hippophaecolus and found that EhipGR13 detects sugar, EhipGR11 and EhipGR3 detect bitter. Nine OBPs expression profile indicated that most were the highest expression in antennae, consistent with functions of OBPs in binding and transporting odors during the antennal recognition process. OBP6 was external expressed in male genital-biased in, and this locus may be responsible for pheromone binding and recognition as well as mating. OBP1 was the highest and biased expressed in the foot and may function as identification of host plant volatiles.
Conclusions: One hundred thirty-seven chemosensory proteins were identified and the accurate functions and groups of part proteins were obtained by phylogenetic analysis. The most OBPs were antenna-biased expressed, which are involved in antennal recognition. However, few OBP was detected biased expression in the foot and external genitalia, and these loci may function in pheromone recognition, mating, and the recognition of plant volatiles.
Figure 3 Neighbor-joining phylogenetic tree of chemosensory proteins (CSPs)
Figure 3 Neighbor-joining phylogenetic tree of chemosensory proteins (CSPs)
The NJ phylogenetic analysis of CSPs of E. hippophaecolus (EhipCSP, red) was performed with reference CSPs of D. melanogaster (DmelCSP, Diptera, blue) and CSPs of Lepidoptera species (black). The stability of the nodes was assessed by bootstrap analysis with 1,000 replications, and only bootstrap values ≥0.6 are shown at the corresponding nodes. The scale bar represents 0.5 substitutions per site.
Figure 4 Neighbor-joining phylogenetic tree of sensory neuron membrane proteins (SNMPs)
Figure 4 Neighbor-joining phylogenetic tree of sensory neuron membrane proteins (SNMPs)
The NJ phylogenetic analysis of SNMPs of E. hippophaecolus (EhipSNMP, red) was performed with reference SNMPs of D. ponderosae (DponSNMP, purple), I. typographus (ItypSNMP, purple), T. molitor (TmolSNMP, purple), T. castaneum (TcasSNMP, purple), D. melanogaster (DmelSNMP, Diptera, blue), B. mori (BmorSNMP, Lepidoptera, dark), H.armigera (HarmSNMP, dark),and A. mellifera (AmelSNMP, Hymenoptera, green). The stability of the nodes was assessed by bootstrap analysis with 1,000 replications, and only bootstrap values ≥0.6 are shown at the corresponding nodes. The scale bar represents 0.04 substitutions per site.
Figure4 Neighbor-joining phylogenetic tree of sensory neuron membrane protein (SNMPs).jpg
Figure 7 Neighbor-joining phylogenetic tree of gustatory receptors (GRs)
Figure 7 Neighbor-joining phylogenetic tree of gustatory receptors (GRs)
The NJ phylogenetic analysis of GRs of E. hippophaecolus (EhipGR, red) was performed with reference GRs of B.mori (BmorGR, dark), H.armigera (HarmGR, dark)[85], A. mellifera (AmelGR, Hymenoptera, green), T. castaneum (TcasGR, Coleoptera, purple) and D. melanogaster (DmelGR, Diptera, blue). The GRs group labelled with red circle refers to detect CO2. sugar and bitter. The stability of the nodes was assessed by bootstrap analysis with 1,000 replications, and only bootstrap values ≥0.6 are shown at the corresponding nodes. The scale bar represents 0.25 substitutions per site.
Figure 5 Neighbor-joining phylogenetic tree of odorant receptors (ORs)
The NJ phylogenetic analysis of ORs of E. hippophaecolus (EhipOR, red) was performed with reference ORs of D. melanogaster (DmelOR, Diptera, blue) and ORs of Lepidoptera species (black). The red circles refer to Orco and PR lineage. The stability of the nodes was assessed by bootstrap analysis with 1,000 replications, and only bootstrap values ≥0.6 are shown at the corresponding nodes. The scale bar represents 0.5 substitutions per site.
Figure5 Neighbor-joining phylogenetic tree of odorant receptors (ORs).jpg
Figure 6 Neighbor-joining phylogenetic tree of ionotropic receptors (IRs)
The NJ phylogenetic analysis of IRs of E. hippophaecolus (EhipIR, red) was performed with reference IRs of H.armigera (HarmIR, black), D. melanogaster (DmelIR, Diptera, blue) and IRs of other Lepidoptera species (black). The IRs groups labelled with red circle were reference of Van Schooten[82]. The stability of the nodes was assessed by bootstrap analysis with 1,000 replications, and only bootstrap values ≥0.6 are shown at the corresponding nodes. The scale bar represents 0.5 substitutions per site.
Figure 6 Neighbor-joining phylogenetic tree of ionotropic receptors (IRs).jpg
Figure 2 Neighbor-joining phylogenetic tree of odorant-binding proteins (OBPs)
The NJ phylogenetic analysis of OBPs of E. hippophaecolus (EhipOBP, red) was performed with reference OBPs of D. melanogaster (DmelOBP, Diptera, blue) and OBPs of Lepidoptera species (black)[79]. The red circles refer to PBP/GOBP lineage. Pale yellow sector refer to the Lepidoptera-specific lineages. The stability of the nodes was assessed by bootstrap analysis with 1,000 replications, and only bootstrap values ≥ 0.6 are shown at the corresponding nodes. The scale bar represents 05 substitutions per site.
