Two Olfactory Pathways to Detect Aldehydes on Locust Mouthpart

Abstract

Sensing chemical cues is crucial for insects through their olfactory systems to adapt the environments. The receptors employed in insect olfactory system belong to the Odorant Receptor (ORs) and Ionotropic Receptor (IRs) families. In general, ORs and IRs are present in distinct olfactory sensory neurons and function independently. Here, we present evidence that in locust, the abundant host plant odor Hexanal is detected by both IR- and OR-expressing neurons. Use of the palp opening response (POR) as a simple behavioral paradigm in conjunction with RNA interference (RNAi) revealed that these two pathways are both needed for the detection of Hexanal. Two-color fluorescence in situ hybridization showed that OR2 and odorant-binding protein 1 (obp1) were co-localized in palps sensilla basiconica. Obp2a and IR8a were co-localized as well, but associated with sensilla chaetica on the palps. Furthermore, both OR2- and obp1-knockdowns showed reduced POR responses to Hexanal and E-2-Hexenal, and the same was true for Hexanal with IR8a- and obp2a-knockdowns. Detection to E-2-Hexenal was independent of IR8a-mediated gene silencing. Besides, Hexanal and E-2-Hexenal evoked dose-dependent responses in palp basiconica via extracellular recordings. Our results indicate that both OR and IR pathways are involved in the detection of one aldehyde.

Expression of odorant‐binding proteins in mouthpart palps of the desert locust Schistocerca gregaria

“…Utilizing the olfactory co‐receptor Orco as marker for OSNs, Orco‐positive cells were visualized in the palps of S. gregaria ; these putative OSNs were organized in clusters. This observation and recent findings for the closely related locust L. migratoria (Zhang et al , ; Li et al , ) suggest that the palps indeed have a functional role for odour detection.…”

“…OBPs are supposed to be involved in solubilizing and transferring the hydrophobic odorants, but may have additional functions as well (Pelosi, ; Xu et al , ; Pelosi et al , ; ). Although most of our knowledge about OBPs is based on studies concentrating on holometabolous dipteran and lepidopteran species (Vogt et al , ; Robertson et al , ; Harada et al , ; Schultze et al , ; Pelosi et al , ), progress has also recently been made in analysing OBPs of hemimetabolous locusts, notably the desert locust S. gregaria and the migratory locust L. migratoria (Jin et al , ; Xu et al , ; Zhang et al , ; Wang et al , ; ; Zhang et al , ; Jiang et al , ; ; Pregitzer et al , ; Zhang et al , ; Li et al , ).…”

“…So far, the knowledge about molecular elements relevant for chemosensation in the palps of locust is limited. Recently, some receptor types and OBPs were found to be expressed in the palps of L. migratoria (Wang et al , ; Zhang et al , ; Li et al , ). In this study, we set out to decipher the expression and sensilla specificity of OBPs on labial and maxillary palps in S. gregaria .…”

Odorant Binding Proteins of the Desert Locust Schistocerca gregaria (Orthoptera, Acrididae): Topographic Expression Patterns in the Antennae

“…This view would be analogous to the finding for Drosophila melanogaster where OBP subtypes expressed in gustatory sensilla are involved in the reception of tastants ( Jeong et al, 2013 ). This is further supported by a recent study demonstrating that knock-down of a sensilla chaetica-specific OBP subtype in Locusta migratoria caused a reduced neuronal response to chemical stimuli ( Zhang et al, 2017 ). This finding further supports the notion that OBPs are intimately involved in detecting chemical compounds via sensilla chaetica.…”

Expression and Localization of Olfactory Receptor AcerOr1 from Chinese Honey Bee, Apis cerana cerana (Hymenoptera, Apidae)

“…Insect olfactory receptors (ORs) are heteromeric, ligand-gated, seventransmembrane ion channels that consist of a highly conserved co-receptor subunit (Orco) and an odorant-specific binding subunit (OR). They are mainly expressed on the dendrites of olfactory receptor neurons (ORN) in olfactory and gustatory organs [1][2][3], and participate in the detection of volatile odors and the conversion of these chemical cues into electrical signals [4,5]. To understand the molecular basis of odor responses in insects, the identification of insect ORs is needed.…”