Abstract
The transformer (tra) gene appears to act as the genetic switch that promotes female development by interaction with the transformer2 (tra-2) gene in several dipteran species including the Medfly, housefly and Drosophila melanogaster. In this study, we describe the isolation, expression and function of tra and tra-2 in the economically important agricultural pest, the oriental fruit fly, Bactrocera dorsalis (Hendel). Bdtra and Bdtra-2 are similar to their homologs from other tephritid species. Bdtra demonstrated sex-specific transcripts: one transcript in females and two transcripts in males. In contrast, Bdtra-2 only had one transcript that was common to males and females, which was transcribed continuously in different adult tissues and developmental stages. Bdtra-2 and the female form of Bdtra were maternally inherited in eggs, whereas the male form of Bdtra was not detectable until embryos of 1 and 2 h after egg laying. Function analyses of Bdtra and Bdtra-2 indicated that both were indispensable for female development, as nearly 100% males were obtained with embryonic RNAi against either Bdtra or Bdtra-2. The fertility of these RNAi-generated males was subsequently tested. More than 80% of RNAi-generated males could mate and the mated females could lay eggs, but only 40-48.6% males gave rise to progeny. In XX-reversed males and intersex individuals, no clear female gonadal morphology was observed after dissection. These results shed light on the development of a genetic sexing system with male-only release for this agricultural pest.
Highlights
Sexual reproduction is an essential and universal phenomenon among animals to maintain species numbers and diversity
PCRs were performed on adult male and female cDNA using primers designed on the basis of the conserved amino acid motifs in the tra homologs of B. oleae, C. capitata and A. suspensa
Bdtra-2 has a non-sex-specific transcript which leads to the production of Tra-2 protein that is 251 amino acids in length
Summary
Sexual reproduction is an essential and universal phenomenon among animals to maintain species numbers and diversity. B. dorsalis is one of the most destructive pests throughout Southeast Asia and a number of the Pacific Islands and is considered to be one of the most important pest species in world agriculture by some entomologists [6,7]. In order to control the population of this species and other economically important agricultural pests, an effective, biologically-based control system has been developed, termed the sterile insect technique (SIT) [9]. For most SIT targets, large scale sex separation is considered highly desirable or essential for the release of only males [10,11]. A comprehensive understanding of sexual differentiation in the B. dorsalis species offers an opportunity to promote the development of novel sexing strategies and genetic control techniques to fight this pest
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