ESTs for Pests: A genomic approach to medfly control

Genome projects of various insect species have been vigorously promoted in the last decade. Among model organisms, genome sequences have been completed in the fruitfly Drosophila melanogaster, the malaria mosquito Anopheles gambiae, the domesticated silkworm Bombyx mori, the honeybee Apis mellifera and the major arbovirus vector, Aedes aegypti. Although an important goal of any sequence project is to obtain a genomic sequence and to identify a complete set of genes, the ultimate goal is to gain an understanding of the expression of these genes, their life-stage and tissue-specificity and regulation, and to predict the biochemical function and cellular role of each gene product. An even more ambitious goal is to understand the myriad of interactions within the genome and its products as a whole. Genome information provides powerful tools for understanding biological mechanisms and functions and is essential for biology, medical sciences and agriculture. To date genome projects have not been applied to any fruitfly species of the family Tephritidae, despite their great agriculture importance as invasive pests and target species for intensive control. Exploring the genome of tephritids will make a strong impact on our knowledge of their biology, allowing exploitation in biotechnology efforts for improving methodologies in pest control. Among tephritids, the most notorious species is the Mediterranean fruitfly (medfly), Ceratitis capitata. Given that it was the first true fruitfly species to extend its species range, the medfly has been the subject of the majority of tephritid genetic studies over the last two decades and has become a model species for the study of invasion processes and for the development and refinement of control methods, particularly the Sterile Insect Technique (SIT). Despite research into the behaviour and classical and population genetics of this organism, the quantity of sequence data available is limited. We have utilized an expressed sequence tag (EST) approach to obtain detailed information on transcriptome signatures that relate to a variety of physiological systems in the medfly; this information emphasizes on reproduction, sex determination, and chemosensory perception, since the study was based on normalized cDNA libraries from embryos and adult heads. A total of 21,253 high-quality ESTs were obtained from the embryo and head libraries. Clustering analyses performed separately for each library resulted in 5201 embryo and 6684 head transcripts. Considering an estimated 19% overlap in the transcriptomes of the two libraries, they represent about 9614 unique transcripts involved in a wide range of biological processes and molecular functions. Of particular interest are the sequences that share homology with Drosophila genes involved in sex determination, olfaction, and reproductive behaviour. The sequences obtained in this study represent the first major dataset of expressed genes in a tephritid species of agricultural importance. This resource provides essential information to support the investigation of numerous questions regarding the biology of the medfly and other related species and also constitutes an invaluable tool for the annotation of complete genome sequences. Our study has revealed intriguing findings regarding the transcript regulation of sex determination genes, as well as insights into the comparative genomics of genes implicated in chemosensory reception and reproduction.