Microgénomique de la sensille phéromonale d’un lépidoptère: une approche novatrice pour comprendre les mécanismes olfactifs – LepidOLF

Context: Noctuid moths represent a diverse and important group that includes the most devastating pests on the planet. As insect olfaction underlies several behaviors critical for crop aggression, including reproduction, host/crop selection, oviposition, this sensory modality appears as an attractive target to play on the capacity of insects to perceive and respond to olfactory cues. A good knowledge on the molecular mechanisms of olfactory recognition and its modulation is a pre-require to identify new targets for the development of safe control strategies. Some genes encoding proteins involved in the specificity of the process and its dynamic have been identified in insects. However, most of the functional studies do not take into account their interactions in their in situ environment and we still lack a global view of the mechanisms. Objectives: Our general objective is to get information on the protein networks that lead to the olfactory response and its modulation. The originality of our project is to consider the olfactory events as a whole, resulting from the activation/intervention of different molecular elements. To pursue this objective, we will take advantage of the pheromone reception system of a moth, the noctuid Spodoptera littoralis, on which we have accumulated a large background. Moth pheromone reception is a very sensitive and specific system and is known to be modulated by well-characterized factors. In addition, pheromone detection takes place in specific sensilla carried by the antenna - the pheromone-sensitive sensilla - that can be viewed as 'micro-noses', each functioning independently. The sensilla are classified in different functional types. The specificity of these different functional types is supposed to be trigger by a differential combination of expressed olfactory genes. In this context, the first main objective of the project is to answer this fundamental question: which proteins act in concert in a specific sensillum to ensure the specificity and the dynamic of the response' In a first step, we propose to analyse the antennal transcriptome of the noctuid moth Spodoptera littoralis. Then, the specific transcriptomes of different sensilla types will be determined and compare by an original microgenomics study. In particular, we will establish the natural context of olfactory receptors functioning. Indeed, they appear as good targets for the design of chemical inhibitors/modulators but recent studies revealed that their functionality is dependent on the presence of several partners that should be taken into account. Our second main objective is to investigate the contribution of the peripheral system to the olfactory modulation. Olfactory modulation has been so far studied focusing on the contribution of the central nervous system and on a limited number of genes. We propose to get a global view of the modulatory network by functional genomics approach. We will focus on two well characterized phenomenons in S. littoralis: the modulation of the pheromone sensitivity according to circadian rhythm and the modification of the insect behavioural response after a brief pre-exposition to the pheromone. Methodology and expected results: New sequencing methodologies (454) together with bioinformatics tools will be used to complete a previous antennal EST collection established in S. littoralis. This will lead to an almost complete repertoire of olfactory genes in this species, among them a list of olfactory receptors. This antennal gene repertoire will then be used to develop a micrroarray dedicated to the antennae. An original and innovative microgenomic approach (laser capture microdissection of specific sensilla and hybridization of their RNAs on the array) will be used to establish the molecular signature of the pheromone sensitive sensilla and to identify olfactory genes putatively involved in pheromone reception. We will also take advantage of the antennal array established to identify genes up- or down-regulated as a function of olfactory modulation (circadian rhythm and pheromone pre-exposition). This will allow us identifying natural mechanisms to play on the insect olfactory sensitivity. At term, this project should open the way to partnerships with private companies for the development of molecules targeted on olfactory receptors, but also on other specific antennal protein families that will be highlighted by our strategy.