The Preferential Binding of a Sensory Organ Specific Odorant Binding Protein of the Alfalfa Plant Bug Adelphocoris lineolatus AlinOBP10 to Biologically Active Host Plant Volatiles

Abstract

Semiochemicals such as sex pheromones and plant volatiles are crucial components of insect mating systems and host plant localization. In the olfactory signal transduction pathway, odorant-binding proteins (OBPs) are important elements that function in the first step of the pathway by carrying hydrophobic semiochemicals across the sensillum lymph to the olfactory receptors (ORs). In this study, we examined the binding affinities of semiochemicals to AlinOBP10, a putative OBP from the alfalfa plant bug, Adelphocoris lineolatus, that we demonstrate is expressed mainly in sensory organs. We then characterized the biological activities of the high affinity semiochemicals by measuring their electrophysiological activities in antennae and behavioral responses in the plant bug. AlinOBP10 displayed weak binding affinities to two major putative pheromone components, hexyl butyrate and (E)-2-hexenyl butyrate. In contrast, AlinOBP10 exhibited higher binding affinities to six host plant volatiles, namely myrcene, β-pinene, β-ionone, 3-hexanone, (E)-2-hexenal, and 1-hexanol. The biological activities of these six putative ligands were further studied in electroantennogram recordings and Y-tube olfactometer trials. The three compounds, (E)-2-hexenal, 1-hexanol, and 3-hexanone elicited strong electrophysiological responses, but elicited distinct behaviors. While 3-hexanone was attractive to female adults, (E)-2-hexenal and 1-hexanol were significant repellents. Although a weak electrophysiological response was elicited with β-pinene, it was a strong repellent. These results demonstrate that AlinOBP10 can interact with attractants, as well as repellents, with some specificity toward plant volatiles over sex pheromones.

Functional analysis of female‐biased odorant binding protein 6 for volatile and nonvolatile host compounds in Adelphocoris lineolatus (Goeze)

“…In A. lineolatus, 14 OBP genes have been identified (Gu et al, 2011b). The antennae-enriched OBPs, including AlinOBP1, 2, 3, 5 10 and 13, all displayed preferential binding properties to host plant volatiles and/or bugproduced compounds (Gu et al, 2010(Gu et al, , 2011aSun et al, 2013Sun et al, , 2014bWang et al, 2013). In particular, AlinOBP1 and AlinOBP13 are specifically expressed in the lymph of the multiporous sensilla trichodea, the basiconica and the spoke channel peg and function in exclusively olfactory roles in response to biologically relevant odorants (Gu et al, 2011c;Sun et al, 2014b).…”

“…In A. lineolatus, olfactory systems such as the antennae sensilla have been morphologically characterized (Sun et al, 2014b). Additionally, studies involving OBP identification, tissue distribution and odour-binding repertoire in A. lineolatus have been conducted (Gu et al, 2011b,c;Sun et al, 2013Sun et al, , 2014bWang et al, 2013). However, these studies mainly focused on sex-independently expressed OBPs such as A. lineolatus OBP1 (AlinOBP1; Gu et al, 2011c), AlinOBP5 (Wang et al, 2013) and AlinOBP10 (Sun et al, 2013).…”

“…Additionally, studies involving OBP identification, tissue distribution and odour-binding repertoire in A. lineolatus have been conducted (Gu et al, 2011b,c;Sun et al, 2013Sun et al, , 2014bWang et al, 2013). However, these studies mainly focused on sex-independently expressed OBPs such as A. lineolatus OBP1 (AlinOBP1; Gu et al, 2011c), AlinOBP5 (Wang et al, 2013) and AlinOBP10 (Sun et al, 2013). As gender-biased olfactory responses in mirid bugs have been extensively reported, and female rather than the male adults are more responsive to plantproduced volatile compounds responsible for host plant alteration (Chinta et al, 1994;Blackmer et al, 2004;Williams et al, 2010;Sun et al, 2014aSun et al, , 2015, the physiological function of female antennae-biased OBPs should be studied.…”

Identification and characterization of the distinct expression profiles of candidate chemosensory membrane proteins in the antennal transcriptome of Adelphocoris lineolatus (Goeze)

“…Previously, many electrophysiological and behavioural assays uncovered that there was clear sexual dimorphism when adult A. lineolatus and other mirid bugs responded to different olfactory cues (Chinta et al, 1994;Williams et al, 2010;Sun et al, 2013Sun et al, , 2015. However, until now, the mechanism at the molecular level of this phenomenon has not been well explained.…”

“…In our previous work on olfactory sensilla characterizations (Gu et al, 2012;Sun et al, 2014a), functional explorations of odorant carrier proteins such as odorantbinding proteins (OBPs; Gu et al, 2011;Sun et al, 2013Sun et al, , 2014aWang et al, 2013) and chemosensory proteins (CSPs; Sun et al, 2015) were carried out to explore the host selection preferences of A. lineolatus. Some important OBPs and CSPs involved in the detection of host volatiles and sex pheromones were identified successfully in these studies.…”