Analysis of a normalised expressed sequence tag (EST) library from a key pollinator, the bumblebee Bombus terrestris

The bumblebee, Bombus terrestris (Order Hymenoptera), is of widespread importance. This species is extensively used for commercial pollination in Europe, and along with other Bombus spp. is a key member of natural pollinator assemblages. Furthermore, the species is studied in a wide variety of biological fields. The objective of this project was to create a B. terrestris EST resource that will prove to be valuable in obtaining a deeper understanding of this significant social insect.

A normalised cDNA library was constructed from the thorax and abdomen of B. terrestris workers in order to enhance the discovery of rare genes. A total of 29'428 ESTs were sequenced. Subsequent clustering resulted in 13'333 unique sequences. Of these, 58.8 percent had significant similarities to known proteins, with 54.5 percent having a "best-hit" to existing Hymenoptera sequences. Comparisons with the honeybee and other insects allowed the identification of potential candidates for gene loss, pseudogene evolution, and possible incomplete annotation in the honeybee genome. Further, given the focus of much basic research and the perceived threat of disease to natural and commercial populations, the immune system of bumblebees is a particularly relevant component. Although the library is derived from unchallenged bees, we still uncover transcription of a number of immune genes spanning the principally described insect immune pathways. Additionally, the EST library provides a resource for the discovery of genetic markers that can be used in population level studies. Indeed, initial screens identified 589 simple sequence repeats and 854 potential single nucleotide polymorphisms.

The resource that these B. terrestris ESTs represent is valuable for ongoing work. The ESTs provide direct evidence of transcriptionally active regions, but they will also facilitate further functional genomics, gene discovery and future genome annotation. These are important aspects in obtaining a greater understanding of this key pollinator species.