Functional validation of the carbon dioxide receptor in labial palps of Helicoverpa armigera moths. (June 2016) - Ning, Chao
Abstract: Adult moths possess an organ in their labial palps, the labial-palp pit organ, which is specialized for sensing carbon dioxide (CO2 ). They use CO2 as a cue to detect healthy plants and find food or lay eggs on them. The molecular bases of the CO2 receptor in Drosophila melanogaster and Aedes aegypti have been reported, but the molecular mechanisms of the CO2 receptor in Lepidoptera remains elusive. In this study, we first re-examined three putative Helicoverpa armigera CO2 gustatory receptor genes ( HarmGr1, HarmGr2, and HarmGr3 ), and then analyzed expression patterns of them. RT-PCR results verified they were predominantly expressed in the labial palps of H. armigera. Thus, we used in situ hybridization to localize the expression of three genes in the labial palps. We found that all three genes were co-expressed in the same cells of the labial palps. Next, we employed the Xenopus laevis oocyte expression system and the two-electrode voltage-clamp recording to study the function of the three genes. Results showed that only oocytes co-expressing HarmGr1 and HarmGr3 or co-expressing HarmGr1, HarmGr2 and HarmGr3 gave robust responses to NaHCO3 . Finally, we confirmed that the sensory cells in labial palps of both females and males show dose dependent responses to CO2 stimuli by using single sensillum recording. Our work uncovers that HarmGr1 and HarmGr3 are indispensable and sufficient for CO2 sensing in labial palps of H. armigera . Graphical abstract: Highlights: The sensory neurons in labial palps of Helicoverpa armigera strongly respond to CO2 stimuli. Three putative CO2 receptor genes, Gr1, Gr2 and Gr3 are predominantly expressed in the labial palps. In situ hybridization results show that all three genes are co-expressed in the same cells of labial palps. The Xenopus oocytes co-expressing Gr1 and Gr3 or co-expressing Gr1, Gr2 and Gr3 give robust responses to NaHCO3 . Gr1 and Gr3 are indispensable and sufficient genes for CO2 sensing in H. armigera.