MOLECULAR CHARACTERIZATION OF THE CDNA ENCODING ECDYSONE RECEPTOR ISOFORM B1 AND ITS EXPRESSION IN THE ORIENTAL FRUIT FLY, BACTROCERA DORSALIS (DIPTERA: TEPHRITIDAE)

The 20-hydroxyecdysone (20E) plays a critical role in a series of biological processes, via the ecdysone receptor/USP heterodimeric complex in arthropod. In order to clarify the regulatory mechanism of 20E, we characterized a full-length cDNA encoding a putative ecdysone receptor isoform B1 and named it as BdEcR-B1 in the oriental fruit fly, Bactrocera dorsalis. The BdEcR-B1 gene was 3,111 bp long, with an open reading frame of 2,304 bp, which encoded 767 amino acids with a predicated molecular weight of 83.3 kDa and an isoelectric point of 6.74. Alignment analysis revealed that the deduced protein sequence had 80% identity to EcR-B1 isoforms of various dipteran species, indicating that this gene was highly conserved during the evolution of the Diptera. Phylogenetic analysis suggested that BdEcR-B1 was orthologous to the EcR-B1 proteins identified in other insect species. Quantitative real-time PCR showed that BdEcR-B1 was expressed at all tested developmental stages, and the expression of BdEcR-B1 reached a significantly higher level just prior to the larval-pupa molt stage and in 4-d old pupa than those in other stages. Moreover, the BdEcR-B1 gene much more strongly expressed in gut and Malpighian tubule than those in the trachea and fat body, which suggests that this gene may be involved in tissue-specific function during larval development.