Systemic and sex-biased regulation of OBP expression under semiochemical stimuli

Constitutive expression of Odorant-Binding Proteins (OBPs) in antennae and other body parts has been examined mainly to infer their involvement in insect olfaction, while their regulation in response to semiochemical stimuli has remained poorly known. Previous studies of semiochemical response were basically done using electrophysiology, which integrates the response of the set of OBPs present in an antenna or sensillum, without revealing the regulation of OBPs or which ones might be involved. In this study we used boll weevil as a model and mined its OBPs by RNA-Seq to study their simultaneous antennal expression by qPCR under controlled semiochemical stimuli with aggregation pheromone and plant volatiles. In the absence of a semiochemical stimulus, 23 of 24 OBPs were constitutively expressed in the antenna in both sexes. Semiochemicals changed systemically the expression of OBPs in both sexes. There were different patterns of up- and down-regulation in female antennae for each semiochemical stimulus, consistent with female chemical ecology. On the other hand, the only response in males was down-regulation of some OBPs. We suggest that these systemic changes in OBP expression might be related to enhancing detection of the semiochemical stimuli and/or priming the olfactory system to detect other environmental chemicals.