Date Published: April 23, 2013
Publisher: Public Library of Science
Author(s): Mengjing Sun, Yang Liu, William B. Walker, Chengcheng Liu, Kejian Lin, Shaohua Gu, Yongjun Zhang, Jingjiang Zhou, Guirong Wang, Richard David Newcomb. http://doi.org/10.1371/journal.pone.0062098
Moths depend on olfactory cues such as sex pheromones to find and recognize mating partners. Pheromone receptors (PRs) and Pheromone binding proteins (PBPs) are thought to be associated with olfactory signal transduction of pheromonal compounds in peripheral olfactory reception. Here six candidate pheromone receptor genes in the diamondback moth, Plutella xyllostella were identified and cloned. All of the six candidate PR genes display male-biased expression, which is a typical characteristic of pheromone receptors. In the Xenopus-based functional study and in situ hybridization, PxylOR4 is defined as another pheromone receptor in addition to the previously characterized PxylOR1. In the study of interaction between PRs and PBPs, PxylPBPs could increase the sensitivity of the complex expressing oocyte cells to the ligand pheromone component while decreasing the sensitivity to pheromone analogs. We deduce that activating pheromone receptors in olfactory receptor neurons requires some role of PBPs to pheromone/PBP complex. If the chemical signal is not the pheromone component, but instead, a pheromone analog with a similar structure, the complex would have a decreased ability to activate downstream pheromone receptors.
Olfaction plays an indispensable role in mediating critical insect behaviors such as food selection, predator and noxious agent avoidance, and appropriate mating-partner choice , . Chemosensory systems, such as taste and smell, involve a complex process from the peripheral transduction of the chemical signal through olfactory neurons to electrical signal processing in central nervous system . In the field of insect olfactory research, moth pheromone communication is a valuable model system for studying the fundamental aspects of animal sensory perception at the molecular level, as the detection of female-released sex pheromone by male antennae is extremely sensitive and specific , . In moths, the mating partner selection is mostly dependent on the sensitive identification of female-released pheromones by specialized sensory neurons in trichoid sensilla on male antennae .
In the present study, we have identified six receptors from P. xylostella that could be assigned to the relatively conserved group of moth pheromone receptors in an insect OR phylogenetic tree (Figure 2). The predominant expression of these six receptors in male antennae in the gene expression profile experiments further supported the notion that they may represent receptors for pheromones (Figure 3). In addition to male-biased expression of all six receptors, PxylOR1 and PxylOR6 were faintly expressed in labial palps in male moths and PxylOR6 was also very faintly expressed in proboscises (Figure 2A). Given the fact that labial palps and proboscises are also olfactory appendages with chemosensory functions, the expression patterns of PxylOR1 and PxylOR6 genes could be understood. A previous report has also shown that moth pheromone receptor genes are expressed in secondary olfactory appendages . Interestingly for PxylOR1 and PxylOR5, very faint PCR bands were obtained with cDNA from male moth legs. Sun et.al reported that three PxylPBPs were expressed in male moth legs , and Sengul et.al also reported that an OBP gene was expressed in male fly legs . So there may also be associated olfactory function in male insect legs. Alternatively, the OBPs and/or PBPs may display biological functionality in a non-olfactory context.