Female-Biased Odorant Receptor MmedOR48 in the Parasitoid Microplitis mediator Broadly Tunes to Plant Volatiles

Abstract

Odorant receptors (ORs) play a crucial role in insect chemoreception. Here, a female-biased odorant receptor MmedOR48 in parasitoid Microplitis mediator was fully functionally characterized. The qPCR analysis suggested that the expression level of MmedOR48 increased significantly after adult emergence and was expressed much more in the antennae. Moreover, an in situ hybridization assay showed MmedOR48 was extensively located in the olfactory sensory neurons. In two-electrode voltage clamp recordings, recombinant MmedOR48 was broadly tuned to 23 kinds of volatiles, among which five plant aldehyde volatiles excited the strongest current recording values. Subsequent molecular docking analysis coupled with site-directed mutagenesis demonstrated that key amino acid residues Thr142, Gln80, Gln282, and Thr312 together formed the binding site in the active pocket for the typical aldehyde ligands. Furthermore, ligands of MmedOR48 could stimulate electrophysiological activities in female adults of the M. mediator. The main aldehyde ligand, nonanal, aroused significant behavioral preference of M. mediator in females than in males. These findings suggest that MmedOR48 may be involved in the recognition of plant volatiles in M. mediator, which provides valuable insight into understanding the olfactory mechanisms of parasitoids.