A Comparison of the Olfactory Gene Repertoires of Adults and Larvae in the Noctuid Moth Spodoptera littoralis Erwan Poivet 1 , Aurore Gallot 1,2 , Nicolas Montagne ´ 3 , Nicolas Glaser 1 , Fabrice Legeai 2 , Emmanuelle Jacquin-Joly 1 * 1 INRA, UMR 1272, Physiologie de l’Insecte, Signalisation et Communication, Versailles, France, 2 IRISA, E ´ quipe GenScale, Campus Universitaire de Beaulieu, Rennes, France, 3 UPMC - Universite ´ Paris 6, UMR 1272, Physiologie de l’Insecte, Signalisation et Communication, Paris, France Abstract To better understand the olfactory mechanisms in a lepidopteran pest model species, the cotton leafworm Spodoptera littoralis, we have recently established a partial transcriptome from adult antennae. Here, we completed this transcriptome using next generation sequencing technologies, namely 454 and Illumina, on both adult antennae and larval tissues, including caterpillar antennae and maxillary palps. All sequences were assembled in 77,643 contigs. Their analysis greatly enriched the repertoire of chemosensory genes in this species, with a total of 57 candidate odorant-binding and chemosensory proteins, 47 olfactory receptors, 6 gustatory receptors and 17 ionotropic receptors. Using RT-PCR, we conducted the first exhaustive comparison of olfactory gene expression between larvae and adults in a lepidopteran species. All the 127 candidate olfactory genes were profiled for expression in male and female adult antennae and in caterpillar antennae and maxillary palps. We found that caterpillars expressed a smaller set of olfactory genes than adults, with a large overlap between these two developmental stages. Two binding proteins appeared to be larvae-specific and two others were adult-specific. Interestingly, comparison between caterpillar antennae and maxillary palps revealed numerous organ-specific transcripts, suggesting the complementary involvement of these two organs in larval chemosensory detection. Adult males and females shared the same set of olfactory transcripts, except two male-specific candidate pheromone receptors, two male-specific and two female-specific odorant-binding proteins. This study identified transcripts that may be important for sex-specific or developmental stage-specific chemosensory behaviors. Citation: Poivet E, Gallot A, Montagne ´ N, Glaser N, Legeai F, et al. (2013) A Comparison of the Olfactory Gene Repertoires of Adults and Larvae in the Noctuid Moth Spodoptera littoralis. PLoS ONE 8(4): e60263. doi:10.1371/journal.pone.0060263 Editor: Richard David Newcomb, Plant and Food Research, New Zealand Received December 6, 2012; Accepted February 24, 2013; Published April 2, 2013 Copyright: ß 2013 Poivet et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by INRA AIP Bioressources and ANR-09-BLAN-0239-01 fundings. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: emmanuelle.jacquin@versailles.inra.fr Introduction In insects, both larvae and adults use their olfactory system to detect chemical cues in their environment, searching for food, for a mate or for adequate oviposition sites. In holometabolous insects, larvae and adults represent two morphologically different mobile forms with radically different physiologies and ecologies. The larvae feed, grow and accumulate energy in order to perform metamorphosis whereas the adults usually feed on different substrates and take over reproductive responsibilities. Accordingly, both forms are sensitive to different chemical cues. Thus, it is expected that their molecular equipment required for odor detection should be different. This has been verified in only a few model species, including the Diptera Drosophila melanogaster [1] and Anopheles gambiae [2] and the Lepidoptera Bombyx mori [3], species for which complete repertoires of olfactory genes have been described thanks to their sequenced genomes. These repertoires group several large families of proteins involved in different steps of odorant detection [4]. In the peripheral organs, odorant molecules first interact with binding proteins to cross the aqueous sensillum lymph to the olfactory receptor neurons (ORNs). Among these binding proteins, odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are proposed to bind general odorant compounds like host volatiles [5,6], although the role of CSPs in chemoreception remains unclear. Pheromone- binding proteins (PBPs) consist of a subclass of OBPs and are proposed to specifically bind the sex pheromone components [7,8]. After crossing the lymph, odorant molecules interact with receptors expressed in the ORN dentritic membrane. Two families of such receptors have been described in insects, the olfactory receptors (ORs) and the ionotropic receptors (IRs) [9], that are involved in the recognition of different volatile families in D. melanogaster [10,11,12]. ORs are seven-transmembrane domain receptors with an inverted membrane topology compared to G protein-coupled receptors [13]. They are specific to insects, they are very divergent between and within species, and are proposed to function as ion channels via heterodimerization with a subunit conserved within insects [13,14,15,16], referred to as Orco [17]. Ligand spectra of large OR repertoires have been studied in detail only in D. melanogaster [18] and A. gambiae [19,20], but numerous lepidopteran ORs specialized in the detection of sex pheromones – the so-called pheromone receptors (PRs) – have also been PLOS ONE | www.plosone.org 1 April 2013 | Volume 8 | Issue 4 | e60263