Abstract
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.
Highlights
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
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]
General Approach The experimental approach used in this paper included: (i) identification of putative OBP transcripts from three EST libraries constructed from embryo, male/female head, testes/male accessory glands [23,35] and their annotation in the recently released medfly genome; (ii) assessment of OBP transcript tissue-specificity and phylogenetic analyses of their predicted proteins; (iii) genetic characterisation of a subset of OBP genes that may represent PBPrelated protein (PBPRP) candidates; (iv) assessment of the relative transcript abundances of these candidate genes in the main olfactory organs of each sex; (v) analysis of the effects of maturation/mating/time of day on transcript abundances in the antennae of each sex
Summary
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. 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]. Not all OBPs are restricted to chemosensory tissues and may participate in other physiological functions [6,20,21,22,23]
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