Insect odorant receptors (ORs) expand by gene duplication and divergence in their sequence and function. In the hawkmoth Manduca sexta, a recent lineage-specific OR expansion forms a cluster of 5 paralogous MsexOR genes orthologous to one OR of Bombyx mori. In this study, we aim to characterise the function of this OR cluster. We hypothesized that these 5 MsexORs have a response profile similar to their orthologue OR in B. mori, which responds to esters. We heterologously expressed individual MsexORs in the antennae of the vinegar fly Drosophila melanogaster, and electrophysiologically tested olfactory responses to a set of 80 chemically diverse and ecologically relevant odours. We found that the paralogous MsexORs not only respond to esters, but also to some terpenes and aldehydes, showing a broader tuning than their B. mori orthologue. The ligands include major volatile components of hawkmoth-pollinated flowers and are known to elicit feeding behaviour in adult M. sexta. Odour response profiles of the ORs showed positive correlation primarily with Ca2+ activity of feeding-associated glomeruli in the AL. One of the ORs, MsexOR36 and the feeding-associated glomerulus 12 showed the highest correlation (Spearman r = 0.67, p<0.0001). We also found a positive correlation of MsexOR36 response with odour-evoked proboscis contact duration in wind-tunnel assays (Spearman r =0.28, p=0.012). These results indicate a possible role of these ORs, especially MsexOR36, in feeding. Therefore, we have generated a MsexOR36 knock-out line by CRISPR-Cas9 gene-editing. Using this knock-out line, we aim to understand the role of a single, feeding-associated OR in olfactory perception and behaviour in M. sexta.
This study was funded by the Max Planck Society.