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

Abstract

The polyphagous mirid bug Adelphocoris lineolatus relies heavily on olfactory cues to track suitable host plants. Thus, a better understanding of the molecular basis of its olfactory detection could contribute to the development of effective pest management strategies. In the present study, we report the expression profile of the odorant binding protein gene A. lineolatus odorant binding protein 6 (AlinOBP6). Quantitative real-time PCR experiments suggest that AlinOBP6 is female adult antennae-biased. Cellular immunolocalization analyses show that AlinOBP6 is highly expressed in the lymph of both multiporous sensilla basiconica and uniporous sensilla chaetica. A ligand binding analysis showed that recombinant AlinOBP6 not only bound tightly to host plant volatile compounds but also to nonvolatile compounds. Homology modelling and molecular docking analyses confirmed these unusual ligand binding profiles and revealed that the amino acid residues involved in the recognition of volatile and nonvolatile compounds are distinct. The results of our study are the first to suggest that an antenna- and female-biased OBP in an hemipteran insect is expressed in both olfactory and gustatory sensilla as a mechanism to respond to volatile and nonvolatile host compounds. These findings warrant further research into the molecular mechanisms of chemosensation for mirid bugs in responsive to host plant location.

Identification and Characterization of Odorant Binding Proteins in the Forelegs of Adelphocoris lineolatus (Goeze)

“…To date, two OBPs in A. lineolatus have been implicated in the perception of bitter substances, such as catechin and quercetin. One is the antennal contact sensilla-expressed AlinOBP6 (Sun et al, 2017b ), and the other is AlinOBP11, which is expressed highly in mouthparts (Sun et al, 2016 ) and the tarsal gustatory sensillum lymph of Sch2 (Figures 5K–N ). These results indicate that mirid bug species, at least for A. lineolatus have evolved a complex gustatory repertoire to perceive important taste substances for host plant-seeking behavior.…”

“…The molecular mechanisms of A. lineolatus olfaction, in particular OBP identification and their binding repertoires to plant volatiles have been extensively studied (Gu et al, 2011b ; Sun L. et al, 2013 ; Sun et al, 2014b ). Interestingly, we found that antennae-enriched or mouthpart-biased OBPs potentially bind to non-volatile plant secondary metabolites (Sun et al, 2016 , 2017b ). Mirid species reportedly contact the host plant surface via foreleg tarsi, and therefore, it is reasonable to hypothesize that OBPs expressed on tarsi help mirid bugs to respond to contact substances on host plant surfaces.…”

Identification and expression analysis of chemosensory genes in the tea green leafhopper, Empoasca onukii Matsuda

“…For example, 12 of 14 OBPs in A. lineolatus (Gu et al, 2011), 21 of 33 OBPs in L. lineolaris (Hull et al, 2014), five of nine OBPs in A. gossypii (Gu, Wu, et al, 2013), seven of 13 OBPs in S. avenae (Xue et al, 2016) and at least six of 10 OBPs in N. lugens (Zhou et al, 2014) were highly expressed in the antennae of insects. In the present study, 24 of 33 EonuOBPs were primarily or uniquely expressed in the antennae of E. onukii than that in the body (Figure 4) (Sun, Wang, Yang, et al, 2017). Moreover, one subclass of OBP families named pheromone binding proteins (PBPs) was highly abundant in antenna and showed high binding affinity to insect sex pheromones (Gu, Zhou, Wang, Zhang, & Guo, 2013).…”

“…So far, various investigations suggested that antenna‐enriched OBPs played crucial roles in the olfactory perception process. For instance, an antenna‐enriched OBP (AlinOBP6) can bound tightly to host plant volatile and non‐volatile compounds (host secondary metabolites), implying AlinOBP6 related to host plant detection and location (Sun, Wang, Yang, et al., ). Moreover, one subclass of OBP families named pheromone binding proteins (PBPs) was highly abundant in antenna and showed high binding affinity to insect sex pheromones (Gu, Zhou, Wang, Zhang, & Guo, ).…”

Characterization of MaltOBP1, a Minus-C Odorant-Binding Protein, From the Japanese Pine Sawyer Beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae)

“…Studies involving OBP identification (Li L. et al, 2017;Zhao et al, 2018), protein structural analysis (Northey et al, 2016;Falchetto et al, 2019), immunocytochemistry in specific olfactory sensilla Zhang et al, 2018), ligand binding properties (Sun et al, 2017(Sun et al, , 2018, and in vivo RNA interference (Yin et al, 2018;He et al, 2019) have demonstrated that insect OBPs play crucial roles in odorant discrimination, binding, and transportation. These proteins carry lipophilic odorants to the olfactory receptor cells in the sensillar lymph surrounding the sensory dendrite (Pelosi et al, 2014(Pelosi et al, , 2018.…”