Sniffing Out Chemosensory Genes from the Mediterranean Fruit Fly, Ceratitis capitata

Ceratitis capitata. PLoS ONE 9(1): e85523. doi:10.1371/journal.pone.0085523 Sniffing Out Chemosensory Genes from the Mediterranean Fruit Fly, Ceratitis capitata Paolo Siciliano 0 Francesca Scolari 0 Ludvik M. Gomulski 0 Marco Falchetto 0 Mose` Manni 0 Paolo Gabrieli 0 Linda M. Field 0 Jing-Jiang Zhou 0 Giuliano Gasperi 0 Anna R. Malacrida 0 Zach N. Adelman, Virginia Tech, United States of America 0 1 Department of Biology and Biotechnology, University of Pavia , Pavia , Italy , 2 Department of Biological Chemistry and Crop Protection, Rothamsted Research , Harpenden , United Kingdom The Mediterranean fruit fly, Ceratitis capitata (medfly), is an extremely invasive agricultural pest due to its extremely wide host range and its ability to adapt to a broad range of climatic conditions and habitats. Chemosensory behaviour plays an important role in many crucial stages in the life of this insect, such as the detection of pheromone cues during mate pursuit and odorants during host plant localisation. Thus, the analysis of the chemosensory gene repertoire is an important step for the interpretation of the biology of this species and consequently its invasive potential. Moreover, these genes may represent ideal targets for the development of novel, effective control methods and pest population monitoring systems. Expressed sequence tag libraries from C. capitata adult heads, embryos, male accessory glands and testes were screened for sequences encoding putative odorant binding proteins (OBPs). A total of seventeen putative OBP transcripts were identified, corresponding to 13 Classic, three Minus-C and one Plus-C subfamily OBPs. The tissue distributions of the OBP transcripts were assessed by RT-PCR and a subset of five genes with predicted proteins sharing high sequence similarities and close phylogenetic affinities to Drosophila melanogaster pheromone binding protein related proteins (PBPRPs) were characterised in greater detail. Real Time quantitative PCR was used to assess the effects of maturation, mating and time of day on the transcript abundances of the putative PBPRP genes in the principal olfactory organs, the antennae, in males and females. The results of the present study have facilitated the annotation of OBP genes in the recently released medfly genome sequence and represent a significant contribution to the characterisation of the medfly chemosensory repertoire. The identification of these medfly OBPs/PBPRPs permitted evolutionary and functional comparisons with homologous sequences from other tephritids of the genera Bactrocera and Rhagoletis. - Funding: This work was partially funded by Italian Ministry of education, University and Research PRIN grant 20077RCHRW (LMG, ARM, GG), and a FAO/ IAEA(Food and Agriculture Organization of the United Nations (FAO)/International Atomic Energy Agency (IAEA)) Technical Contract No. 16966 (GG). The work was also carried out within the FAO/IAEA research CRP programme Identification of molecular and transgenic tools for sexing strategies and development of strain and sperm marking systems for fruitfly pests - Development and evaluation of improved strains of insect pests for SIT (GG). Rothamsted Research receives grant-aided support from the UK Biotechnology and Biological Sciences Research Council (BBSRC). The funders had no role in the 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. The Mediterranean fruit fly, Ceratitis capitata, is a serious agricultural pest that has expanded from its native range in East Africa to attain an almost worldwide distribution. Its biological success and invasive potential are due to its ability to readily adapt to new environments, to complete multiple generations each year utilising different host plants as they become available, and its high reproductive capacity [1]. Unlike Drosophila species that inhabit and feed on rotting and decaying organic material, the medfly has evolved an opportunistic phytophagous lifestyle [2,3]. These very different food resource exploitation strategies would be expected to be reflected in adaptive differences in the abilities of these two species to detect, and respond to, different plant volatiles and odours. Insect chemoreception is facilitated by a signal transduction cascade involving three main groups of molecules, odorantbinding proteins (OBPs) [4,5], chemosensory proteins (CSPs) [6], and the chemoreceptor superfamily formed by the olfactory (OR), gustatory (GR) and ionotropic (IR) receptor families [5]. Insect OBPs are small, globular, abundant water-soluble proteins, characterised by a domain of six a-helices, joined by either two or three disulphide bonds [7,8], that are secreted into the sensillar lymph by non-neuronal auxiliary cells. Odorant molecules that enter the pores in the sensilla are bound and solubilized by OBPs and transported through the aqueous lymph to activate the membrane bound ORs [5,9,10]. The Drosophila OBP gene family has been divided into a number of subfamilies, defined on distinctive structural and functional features and phylogenetic relationships (Classic, Minus-C, Plus-C, Dimer, PBP/GOBP, ABPI and ABPII, CRLBP, and D7 subfamilies)[1016]. In Drosophila OBPs have been shown to be implicated in the recognition of the male courtship pheromone [17,18] and hostplant selection [19]. However, not all OBPs are restricted to chemosensory tissues and may participate in other physiological functions [6,2023]. Chemoreception plays an important role in medfly courtship behaviour. The mating system is based on arboreal aggregations (leks) of sexually mature males [2427]. The males actively defend favoured positions in the lek and emit a sex pheromone from their everted rectal ampulla which is both attractive to females and able to call other males to the lek site [24,28]. When a receptive female approaches, the male vibrates his wings in a continuous manner, apparently wafting a plume of pheromone towards the female [29]. The components of the pheromone mixture emitted by the male have been identified [3034]. Medfly females use a different pheromone to mark fruit after oviposition that acts as a deterrent to further egg-laying [2]. Despite the evident importance of plant volatiles and pheromones in medfly behaviour, little is known about the chemosensory proteins involved in their detection [35,36]. Here we report the identification of a number of OBP transcripts. We used EST libraries [23,35] derived from adult heads as these include the main olfactory organs of the medfly, from the male reproductive tract as studies have shown that OBPs are expressed in such tissues in other insects [3739], and from embryos, which, being enriched for late embryonic stages, could provide sequences involved in larval perception during their development in the fruit. A subset of the identified OBPs that shared the hi (...truncated)