Odorant and Gustatory Receptors in the Tsetse Fly Glossina morsitans morsitans

Abstract

Tsetse flies use olfactory and gustatory responses, through odorant and gustatory receptors (ORs and GRs), to interact with their environment. Glossina morsitans morsitans genome ORs and GRs were annotated using homologs of these genes in Drosophila melanogaster and an ab initio approach based on OR and GR specific motifs in G. m. morsitans gene models coupled to gene ontology (GO). Phylogenetic relationships among the ORs or GRs and the homologs were determined using Maximum Likelihood estimates. Relative expression levels among the G. m. morsitans ORs or GRs were established using RNA-seq data derived from adult female fly. Overall, 46 and 14 putative G. m. morsitans ORs and GRs respectively were recovered. These were reduced by 12 and 59 ORs and GRs respectively compared to D. melanogaster. Six of the ORs were homologous to a single D. melanogaster OR (DmOr67d) associated with mating deterrence in females. Sweet taste GRs, present in all the other Diptera, were not recovered in G. m. morsitans. The GRs associated with detection of CO2 were conserved in G. m. morsitans relative to D. melanogaster. RNA-sequence data analysis revealed expression of GmmOR15 locus represented over 90% of expression profiles for the ORs. The G. m. morsitans ORs or GRs were phylogenetically closer to those in D. melanogaster than to other insects assessed. We found the chemoreceptor repertoire in G. m. morsitans smaller than other Diptera, and we postulate that this may be related to the restricted diet of blood-meal for both sexes of tsetse flies. However, the clade of some specific receptors has been expanded, indicative of their potential importance in chemoreception in the tsetse.

Carbon dioxide receptor genes in cotton bollworm Helicoverpa armigera

“…Three orthologous CO2 GR genes were identified from four lepidopteran species including B. mori, H. armigera, D. plexippus, H. melpomene, and one Coleoptera species, T. castaneum. Diptera insect species showed different numbers of putative CO2 GRs with two CO2 GRs reported in Drosophila (DmelGR21a and DmelGR63a), three CO2 GRs identified in multiple mosquito species (A. gambiae, A. aegypti and C. quinquefasciatus) (Robertson and Kent 2009) and four CO2 GRs found in the tsetse fly (Glossina morsitans) (Obiero et al 2014).…”

“…The successfully cloned GR ORF sequences were further subcloned into PIB/V5-His vectors (Anderson et al 2009;Briscoe et al 2013;Dahanukar et al 2007;Erdelyan et al 2012;Obiero et al 2014;Robertson and Kent 2009;Terrapon et al 2014). GenBank accession numbers of these genes can be found in Table 1.…”

“…The orthologous genes of these threeCO2 receptors were also identified in other mosquito species such as Aedes aegypti (Erdelyan et al 2012) and Culex quinquefasciatus (Robertson and Kent 2009). Recently published genome and transcriptome sequences from various insect species revealed that putative CO2 gustatory receptors are conserved in many insect species including mosquitoes, moths, butterflies, beetles and flies (Anderson et al 2009;Briscoe et al 2013;Dahanukar et al 2007;Erdelyan et al 2012;Obiero et al 2014). However, CO2 GRs are absent in other species like honeybees, human louses, wasps, ants and blacklegged ticks (Robertson and Kent 2009), suggesting that these latter species may use different mechanisms for CO2 sensation.…”

“…However, CO2 GRs are absent in other species like honeybees, human louses, wasps, ants and blacklegged ticks (Robertson and Kent 2009), suggesting that these latter species may use different mechanisms for CO2 sensation. Among the insect species that have CO2 GRs, the numbers of genes present in the genome vary (Anderson et al 2009;Briscoe et al 2013;Dahanukar et al 2007;Erdelyan et al 2012;Obiero et al 2014;Robertson and Kent 2009). Beetles, moths, butterflies and mosquitoes possess three CO2 GR genes in their genomes while Drosophila only has two (Briscoe et al 2013;Robertson and Kent 2009), and a recent study on tsetse fly reported that there are four GR genes orthologous to the Drosophila CO2 receptors (Obiero et al 2014).…”

Evolution of herbivory in Drosophilidae linked to loss of behaviors, antennal responses, odorant receptors, and ancestral diet

“…Families of mammalian olfactory receptor proteins have been remodeled during transitions to flight, aquatic lifestyles, and frugivory (15)(16)(17)(18). Similarly, the evolution of diet specialization in Drosophila species correlates with chemoreceptor gene losses (19)(20)(21), and hematophagous flies have lost gustatory receptors that detect sweet compounds (22). More profound changes such as the evolution of new protein families are associated with major evolutionary transitions such as the evolution of flight in insects (23).…”