Identification and expression pattern analysis of chemosensory receptor genes in the Macrocentrus cingulum (Hymenoptera: Braconidae) antennae

Macrocentrus cingulum is an important polyembryonic endoparasitic wasp that attacks larvae of the Asian corn borer, Ostrinia furnacalis (Guenee) and the European corn borer, O. nubilalis (Hubner). Parasitoids use antennae as the main sensory organ to recognize herbivore-induced plant volatiles as host searching cues. The antennal olfaction proteins, odorant receptors (ORs) and ionotropic receptors (IRs) are involved in olfactory signal transduction pathway as a sensory neuron response. In the present study, we constructed a cDNA library from the male and female antennae for identifying the olfaction-related genes in M. cingulum. For that, we sequenced 3160 unique gene sequences and annotated them with gene ontology (GO), cluster of orthologous groups of proteins (COG), and KEGG ontology (KO). Through the homology search, we identified 9 odorant receptors (ORs), 3 ionotropic receptors (IRs) and 1 odorant binding protein (OBP) genes from the cDNA library sequences. Additionally, the expression patterns of these ORs and IRs in different tissues (antennae, heads, thoraxes, abdomens, and legs) were demonstrated by RT-PCR. The qualitative gene expression analyses showed that most of the OR genes were more highly expressed in female than male antennae; whereas IRs, unlike ORs, were more expressed in various male than females tissues. We are the first to report ORs and IRs in M. cingulum, which should help in deciphering the molecular basis of olfaction system in this wasp.