Short Communication Discrimination of alarm pheromone (E)-b-farnesene by aphid odorant-binding proteins Huili Qiao a , Elena Tuccori a , Xiaoli He b , Angelo Gazzano c , Linda Field b , Jing-Jiang Zhou b , Paolo Pelosi a, * a Department of Agricultural Chemistry and Biotechnologies, University of Pisa via S. Michele, 4, 56124 Pisa, Italy b Department of Biological Chemistry, Rothamsted Research, Harpenden, UK c Department of Veterinary Anatomy, Biochemistry and Physiology, University of Pisa, Pisa, Italy article info Article history: Received 17 November 2008 Received in revised form 23 February 2009 Accepted 5 March 2009 Keywords: Odorant-binding protein Aphids Acyrthosiphon pisum Ligand-binding (E)-b-farnesene abstract OBPs have been recently demonstrated to be required for odour perception in insects and directly involved in odour discrimination. In aphids they might represent new interesting targets for the control of their population in agriculture. Based on sequence information available in the EST database, we have cloned four genes encoding odorant-binding proteins (OBP) in Acyrthosiphon pisum and homologous genes in other aphid species. Unlike OBPs from other orders of insects, that are greatly divergent, in aphids these proteins have been found to be highly conserved, with differences between species limited to only few amino acid substitutions. On the contrary, similarities between OBP sequences of the same species are poor with 31% or less of identical amino acids. Three selected OBPs (OBP1, OBP3 and OBP8) have been expressed in bacteria and purified. Ligand-binding experiments have shown similar behaviour of the three proteins towards several organic compounds, but also some significant selectivities. In particular, (E)-b-farnesene, the alarm pheromone and its related compound farnesol exhibited good affinity to OBP3, but did not bind the other two proteins. We suggest that OBP3 could mediate response of aphids to the alarm pheromone. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Several aphid species are major pests in agriculture, affecting many different crops. The damage associated with their presence is mainly due to the vectoring of plant virus diseases which infect many crop plants. Aphids include a great number of species of different size, colour and shape, and occupying many niches. Despite such diversity, a single alarm pheromone, (E)-b-farnesene (Pickett et al., 1992; Bowers et al., 1972), is produced and utilised by most aphids. Out of 23 species examined, 21 contain (E)-b- farnesene in their pheromonal blend, while in 16 of them this compound represents the only or the major component (Francis et al., 2005). (E)-b-farnesene is secreted in the presence of danger and induces an immediate typical behaviour of dispersal. Simi- larly, the sex pheromone of many aphids is a mixture of nepe- talactone and its related alcohols nepetalactols with each species having its own pheromonal blend (Birkett and Pickett, 2003; Dawson et al., 1996). Both types of pheromones are not suitable for use in population control. (E)-b-farnesene is not persistent in the environment, being a volatile hydrocarbon, susceptible to oxidation, owing to the presence of several double bonds in the molecule. Moreover, its chemical synthesis is complicated and expensive. However, some plants, such as the wild potato, syn- thesise (E)-b-farnesene as a product of their metabolism and thus may be naturally protected against these insects (Gibson and Pickett, 1983), and transgenic Arabidopsis thaliana carrying the genes for synthesising (E)-b-farnesene has been produced (Beale et al., 2006). This approach could be applied to crop plants with enormous economic benefits. The use of sex pheromones in the control of aphid populations is of little practical use in these mostly parthenogenetically reproducing insects. Given the great economical impact of aphids, a better under- standing of their chemical communication system is highly desir- able in order to devise strategies and produce chemical tools for their population control. According to the current view, odorants and pheromones interact with membrane-bound olfactory recep- tors (Clyne et al., 1999; Vosshall et al., 2000), triggering olfactory neurons. However, very recently, odorant-binding proteins (OBPs), soluble polypeptides highly concentrated in the sensillar lymph bathing chemosensory neurons (Vogt and Riddiford, 1981; Pelosi * Corresponding author. Tel.: þ39 050 2216626; fax: þ39 050 2216630. E-mail address: ppelosi@agr.unipi.it (P. Pelosi). Contents lists available at ScienceDirect Insect Biochemistry and Molecular Biology journal homepage: www.elsevier.com/locate/ibmb 0965-1748/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibmb.2009.03.004 Insect Biochemistry and Molecular Biology 39 (2009) 414–419