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.
Keywords: Gustatory receptor; Helicoverpa armigera; Proboscis extension reflex; Xenopus laevis oocyte; d-fructose.
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