IDENTIFICATION OF THE WESTERN TARNISHED PLANT BUG (Lygus hesperus) OLFACTORY CO‐RECEPTOR ORCO: EXPRESSION PROFILE AND CONFIRMATION OF ATYPICAL MEMBRANE TOPOLOGY

Abstract

Lygus hesperus (western tarnished plant bug) is an agronomically important pest species of numerous cropping systems. Similar to other insects, a critical component underlying behaviors is the perception and discrimination of olfactory cues. Consequently, the molecular basis of olfaction in this species is of interest. To begin to address this issue, we utilized homology‐based PCR as a commonly accepted abbreviation but if necessary it is polymerase chain reaction methods to identify the L. hesperus olfactory receptor co‐receptor (Orco) ortholog, a receptor that has been shown to be essential for olfaction. The L. hesperus Orco (LhOrco) shares significant sequence homology with known Orco proteins in other insects. Parallel experiments using the sympatric sister species, Lygus lineolaris (tarnished plant bug), revealed that the Lygus Orco gene was completely conserved. Surprisingly, a majority of the membrane topology prediction algorithms used in the study predicted LhOrco to have both the N and C terminus intracellular. In vitro immunofluorescent microscopy experiments designed to probe the membrane topology of transiently expressed LhOrco, however, refuted those predictions and confirmed that the protein adopts the inverted topology (intracellular N terminus and an extracellular C terminus) characteristic of Orco proteins. RT‐PCR analyses indicated that LhOrco transcripts are predominantly expressed in adult antennae and to a lesser degree in traditionally nonolfactory chemosensory tissues of the proboscis and legs. Expression is not developmentally regulated because transcripts were detected in all nymphal stages as well as eggs. Taken together, the results suggest that LhOrco likely plays a critical role in mediating L. hesperus odorant perception and discrimination.

An olfactory receptor from Apolygus lucorum (Meyer-Dur) mainly tuned to volatiles from flowering host plants

“…All 4 protein sequences were predicted to possess seven transmembrane domains and they were highly divergent, with amino acid sequence identities of 20-30% when compared with ORs from different species (Fig. 1) (Supplementary material S2), a common phenomenon observed between insect ORs within and between species (Cao et al, 2014;Hull et al, 2012;Sparks et al, 2014;Zhou et al, 2014), except for the pheromone receptors (PRs) in Lepidoptera insects and Orco (Vosshall and Hansson, 2011;Grosse-Wilde et al, 2011;Liu et al, 2012;Zhang et al, 2013b).…”

Cloning and expression profiling of odorant‐binding proteins in the tarnished plant bug, Lygus lineolaris

“…Those data have since been supplemented with recent genome and EST-based OBP projects in aphids , the lucerne plant bug (Adelphocoris lineolatus) (Gu et al, 2011a), the green plant bug (Apolygus lucorum) (Gu et al, 2011a;Hua et al, 2012), and the brown planthopper (Nilaparvata lugens Stål) (Noda et al, 2008;Xu et al, 2009;He et al, 2011). Our understanding of the molecular components comprising the Lygus olfactory system is even more incomplete with sequence and expression data currently limited to Lygus antennal protein (LAP), a 'classic' OBP preferentially expressed in adult male L. lineolaris and L. hesperus antennae (Dickens et al, 1995(Dickens et al, , 1998Vogt et al, 1999), and the recently identified Lygus OR coreceptor (Hull et al, 2012). To derive a better molecular understanding of olfaction in L. lineolaris (and Lygus spp.…”

Positive selection in extra cellular domains in the diversification of Strigamia maritima chemoreceptors

“…For GRs, the prediction of the transmembrane domains is less clear-cut because not all of the domains are as prominently hydrophobic as most transmembrane proteins such as GPCRs, channels, and transporters, and various transmembrane prediction programs regularly under-predict them and sometimes over-predict them; they consequently also often indicate the incorrect orientation in the membrane (e.g., Benton et al, 2006;Smart et al, 2008;Zhang et al, 2011;Hull et al, 2012). The orientation in the membrane is known for the conserved Odorant Receptor Co-Receptor or Orco protein and other ORs (Benton et al, 2006;Lundin et al, 2007;Smart et al, 2008;Tsitoura et al, 2010;Hull et al, 2012), which are clearly related to the GR family in the insect chemoreceptor superfamily (Robertson et al, 2003), as well as for one GR (Zhang et al, 2011). It is the opposite of the GPCR orientation, with the N-terminus internal to the cell.…”