Abstract: 【Aim】 This study aims to isolate two sex determining genes (transformer and transformer 2), analyze their genomic DNA and cDNA structures and determine their expression profiles during different developmental stages and in adult tissues of the guava fruit fly, Bactrocera correcta. The findings will provide basic knowledge for further functional study of these two sex-determinating genes and the construction of the genetic sexing strain of the guava fruit fly. 【Methods】 The full-length cDNA sequences and their intronic seqences were isolated by PCR and RACE technique. The structure prediction, sequence alignment and phylogenetic analysis of the coding products of these two sex determining genes were performed by using different bioinformatics softwares. Based on the cDNA sequences of these two genes, specific primers were designed to investigate their developmental and tissue expression profiles by semi-quantitative RT-PCR. 【Results】 Two full-length cDNA sequences of transformer and transformer 2 were isolated from B. correcta and named as Bcotra and Bcotra2, respectively. Bcotra is transcribed sex-specifically: female transtranscript is 1 673 bp in length, which encodes a polypeptide of 413 amino acids (GenBank accession number KP712876), while male transcript is 2 025 bp in length, which encodes a truncated and non-functional polypeptide with in-frame stop codons on the two addtional exons that do not exist in female transcript (GenBank accession number KP712877). No sex-specific transtript was detected in Bcotra-2. Bcotra-2 is 1 458 bp in length, which encodes a polypeptide of 251 amino acids with the classic characteristics of RNA binding proteins (GenBank accession number KM658207). Bcotra-2  harbors 8 exons and 7 introns. Sequence alignment and phylogenetic analysis of the products coded by these two sex determining genes respectively with the known Tra and Tra-2 from other Dipteran insects revealed that Bcotra-2 shows higher homology than that of Bcotra with their respective homologues. The semi-quantitative RT-PCR result showed that Bcotra and Bcotra-2 was expressed in different developmental stages and various adult tissues of B. correcta. 【Conclusion】 In this study, the genomic and cDNA stuctures of two sex determining genes were identified in B. correcta. Both Bcotra and Bcotra-2 were detected during different developmental stages and in various adult tissues. The presence of Tra/Tra-2 binding sites, intronic splicing silencer sequence and RNA binding protein binding sites suggests that the regulation of sex development in B. correcta may rely on the interation between the post-translation of Bcotra and Bcotra-2. The fragment of 963 bp female-specific intron of Bcotra can be used for the vector construction to develop genetic sexing strains.

Key words: Bactrocera correcta, sex determination, transformer, transformer 2, sex-specific splicing, expression profile