The major antennal chemosensory protein of red imported fire ant workers

Abstract

Some chemosensory proteins (CSPs) are expressed in insect sensory appendages and are thought to be involved in chemical signaling by ants. We identified fourteen unique CSP sequences in EST libraries of the red imported fire ant, Solenopsis invicta. One member of this group (Si-CSP1) is highly expressed in worker antennae, suggesting an olfactory function. A shotgun proteomic analysis of antennal proteins confirms the high level of Si-CSP1 expression, and also shows expression of another CSP and two odorant-binding proteins (OBPs). We cloned and expressed the coding sequence for Si-CSP1. We used cyclodextrins as solubilizers to investigate ligand binding. Fire ant cuticular lipids strongly inhibit Si-CSP1 binding to the fluorescent dye N-phenyl-naphthylamine, suggesting cuticular substances are ligands for Si-CSP1. Analysis of the cuticular lipids shows that the endogenous ligands of Si-CSP1 are not cuticular hydrocarbons.

Comparative genomics of chemosensory protein genes reveals rapid evolution and positive selection in ant-specific duplicates

“…The orthologous group (CSP7 in ants) containing the proteins for binding cuticular hydrocarbons used as nestmate recognition cues in Camponotus and Linepithema does not show accelerated evolution or positive selection, and thus no signs of arms race with intruders. Interestingly, the nestmate cue binder in C. japonicus and L. humile is not orthologous with the putative nestmate cue binder of S. invicta, an observation that fits well with the hypothesis that different substances are used for nestmate recognition (González et al, 2009).…”

“…This orthologous group CSP7 has an overall dN/dS ratio similar to other orthologous groups (dN/dS ¼ 0.13) and no sites are indicated to evolve under positive selection by SLAC, and the model including positive selection does not fit the data significantly better in M1a-M2a comparison in codeml. The third possible involvement of CSP in Table 2 The ratio of nonsynonymous to synonymous changes (dN/dS) estimated for each orthologous group (CSP1-CSP7) in ants separately nestmate recognition is in S. invicta, where SinvCSP19 codes for the major protein expressed in antennae (González et al, 2009). This gene (SinvCSP19) belongs to the largest S. invicta-specific expansion including eight genes, one of which is a pseudogene.…”

“…The abbreviations used here are, respectively, Cflo, Hsal, Sinv, Lhum, Pbar, Aech and Acep. We first searched the predicted protein models of each ant species using the protein sequences of insect CSPs Gong et al, 2007;González et al, 2009;Xu et al, 2009;Vieira and Rozas, 2011) and e-value of 1.0 e-3. Adding the hits of the first search to queries, we searched the ant genome assemblies using tblastn.…”

“…Changes in this protein could thus putatively alter workers' acceptance of individuals and discrimination between friends and foes. The major protein expressed in the antennae of the red imported fire ant Solenopsis invicta is also a CSP that binds cuticular substances but not hydrocarbons (González et al, 2009). This does not rule out its possible role in nestmate recognition if recognition in the fire ants is based on other substances than hydrocarbons (González et al, 2009).…”

“…The major protein expressed in the antennae of the red imported fire ant Solenopsis invicta is also a CSP that binds cuticular substances but not hydrocarbons (González et al, 2009). This does not rule out its possible role in nestmate recognition if recognition in the fire ants is based on other substances than hydrocarbons (González et al, 2009). The Argentine ant, Linepithema humile was also shown to express CSP as a major protein in its antennae (Ishida et al, 2002).…”