De novo Assembly and Characterization of the Testis Transcriptome and Development of EST-SSR Markers in the Cockroach Periplaneta americana

The cockroach Periplaneta americana is a notorious pest and threat to health worldwide, with a high reproductive ability. However, a limited amount of data is available on the developmental stage-specific transcriptomes of P. americana. To identify genes involved in developmental processes and to develop additional SSR markers in P. americana, we carried out de novo assembly of the P. americana transcriptome using Illumina sequencing. After removing low-quality sequences, we obtained 64,954,709 contigs, which were further assembled into 125,390 unigenes with an average length of 711 bp. Based on similarity searches against known proteins, we identified 48,300 unigenes based on a cut-off E-value of 10(-5). The assembled sequences were annotated according to gene descriptions, gene ontology and clusters of orthologous groups. A total of 14,195 potential SSRs were identified, and 41 of 63 randomly chosen primer pairs successfully amplified the predicted SSR markers, seven of which were polymorphic in size in P. americana. Furthermore, the Spag6 gene was confirmed to be testes specific, and the fru and RPSA genes were related to the development of the testis. This is the special report of a P. americana transcriptome obtained using Illumina sequencing technology, and a large number of molecular markers were developed.