A gustatory receptor tuned to d-fructose in antennal sensilla chaetica of Helicoverpa armigera

• Helicoverpa armigera females extend their proboscis when the distal part of the antenna is stimulated with fructose.
• In the distal part of the antenna we characterize sensilla chaetica responding to fructose.
• Among three candidate gustatory receptors identified, we show that HarmGR4 is tuned to fructose specifically.
• HarmGR4 is expressed in the gustatory sensory neuron of the contact chemosensilla on the distal part of the antenna.

Insect gustatory systems play important roles in food selection and feeding behaviors. In spite of the enormous progress in understanding gustation in Drosophila, for other insects one of the key elements in gustatory signaling, the gustatory receptor (GR), is still elusive. In this study, we report that fructose elicits behavioral and physiological responses in Helicoverpa armigera (Harm) to fructose and identify the gustatory receptor for this sugar. Using the proboscis extension reflex (PER) assays we found that females respond to fructose following stimulation of the distal part of the antenna, where we have identified contact chemosensilla tuned to fructose in tip recording experiments. We isolated three full-length cDNAs encoding candidate HarmGRs based on comparison with orthologous GR sequences in Heliothis virescens and functionally characterized the responses of HarmGR4 to 15 chemicals when this receptor was expressed in Xenopus oocytes with two-electrode voltage-clamp recording. Among the tastants tested, the oocytes dose-dependently responded only to d-fructose (EC50 = 0.045 M). By combining behavioral, electrophysiological and molecular approaches, these results provide basic knowledge for further research on the molecular mechanisms of gustatory reception.

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