Two Gr Genes Underlie Sugar Reception in Drosophila

Abstract

We have analyzed the molecular basis of sugar reception in Drosophila. We define the response spectrum, concentration dependence, and temporal dynamics of sugar-sensing neurons. Using in situ hybridization and reporter gene expression, we identify members of the Gr5a-related taste receptor subfamily that are coexpressed in sugar neurons. Neurons expressing reporters of different Gr5a-related genes send overlapping but distinct projections to the brain and thoracic ganglia. Genetic analysis of receptor genes shows that Gr5a is required for response to one subset of sugars and Gr64a for response to a complementary subset. A Gr5a;Gr64a double mutant shows no physiological or behavioral responses to any tested sugar. The simplest interpretation of our results is that Gr5a and Gr64a are each capable of functioning independently of each other within individual sugar neurons and that they are the primary receptors used in the labellum to detect sugars.

Carbon dioxide receptor genes in cotton bollworm Helicoverpa armigera

“…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.…”

“…Two gustatory receptors (GRs), DmelGR21a and DmelGR63a, were identified through their expression in ab1C olfactory receptor neurons in the CO2-sensitive ab1 sensilla on the antennae (Dahanukar et al 2007;Jones et al 2007). …”

“…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).…”

“…Currently, most studies on insect CO2 receptors are focused on Drosophila or mosquitoes (Cayirlioglu et al 2008;Dahanukar et al 2007;Erdelyan et al 2012;Hartl et al 2011;Jones et al 2007;McMeniman et al 2014;Montell 2013;Turner and Ray 2009) and are aimed at discovering compounds for vector control that can modulate CO2 receptors in mosquitoes (Tauxe et al 2013;Turner and Ray 2009). Little attention has been paid to the CO2 receptors of agricultural pests.…”

“…For example, alternatives to heavy insecticide use, such as interfering with CO2 reception, would be helpful for controlling Helicoverpa armigera, which is one of the most destructive agricultural pests known (Sharm 2001). So far, insect CO2 receptors have only been functionally characterised in vivo using transgenic Drosophila, mutated mosquitoes or RNAi techniques (Cayirlioglu et al 2008;Dahanukar et al 2007;Erdelyan et al 2012;Hartl et al 2011;Jones et al 2007;McMeniman et al 2014;Montell 2013;Turner and Ray 2009). These approaches are not established for Lepidoptera.…”