De novo analysis of the Tenebrio molitor (Coleoptera: Tenebrionidae) transcriptome and identification of putative glutathione S-transferase genes

Abstract

We performed the Illumina sequencing of the yellow mealworm beetle, Tenebrio molitor L., a global stored grain pest and a model for insect physiological studies, and analyzed the transcriptome dataset. We obtained 82,001,576 clean reads that were assembled into 31,785 unigenes with a mean size of 1,022 bp. Among these unigenes, 16,025 (50.41 %) showed significant similarity (E value <10−5) to known proteins in the NCBI non-redundant database. Gene ontology, Cluster of Orthologous Groups and Kyoto Encyclopedia of Genes and Genomes analyses were used to classify functions of the unigenes. We identified 27 putative glutathione S-transferase (GST) genes, including 2 delta, 13 epsilon, 1 omega, 5 sigma, 1 theta and 1 zeta class GSTs, and 2 microsomal GSTs and 2 “unclassified” GSTs. Quantitative reverse transcription-PCR assay showed that 2 and 3 GST genes were mainly expressed in larval and pupal stages, respectively; while 10 genes were mainly expressed in the adult stage. Tissue-specific expression analysis found that, among the 27 GST genes, 8 were expressed predominately in the midgut, 13 were mainly detected in Malpighian tubules, and only one gene specifically distributed in the fat body. This work provides the first insights into the T. molitor GSTs at the molecular level: the results may assist in a functional study for the GSTs in this insect species.