Functional characterization of odorant binding proteins in Pharsalia antennata provides insights into diverse binding properties and the importance of C-terminal residues
The cerambycid beetles are important components in the terrestrial ecosystem as they play a dual role in both degrading dying trees and killing healthy plants. The factors including human activity, habitat contraction, climate changes and pesticide use have been shaping the adaptation of beetles to host plants and the environment. As suggested in research on the functions of beetles' olfactory proteins, odorant binding proteins (OBPs) have been found to be involved in insecticide resistance other than chemoreception. Here, we assessed the importance of antenna/leg-enriched PantOBPs from Pharsalia antennata in the adaptation of hosts and habitats. Transcriptome analyses led to the yields of 60 OBP-coding genes in P. antennata , with the largest set of 44 Minus-C OBPs. Using RNA sequencing and PCR approaches, we obtained tissue-enriched and sex-biased PantOBPs. Binding studies revealed that 10 PantOBPs had diverse binding properties against 92 plant-derived odorants and 32 contact insecticides. Three plant volatiles of β-ionone, ethyl-(2 E ,4 Z )-deca-2,4-dienoate and syringaldehyde as well as seven insecticides including chlorpyrifos, phoxim and rotenone were strong ligands for most PantOBPs (dissociation constant, K i < 11.70 μM). Docking simulations and point-mutation experiments demonstrated the importance of C-terminal residues in the interactions of PantOBP12, OBP38 and OBP39 with good ligands, but, in some cases, they exhibited different binding mechanisms. Our results indicate that PantOBPs in P. antennata serve a dual function in chemoreception and insecticide binding, providing insights into the strong adaptation of this beetle to host plants and the environment.
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