Transcriptome Response to Elevated Atmospheric CO Concentration in the Formosan Subterranean Termite, Shiraki (Isoptera: Rhinotermitidae)

Background: Carbon dioxide (CO) is a pervasive chemical stimulus that plays a critical role in insect life, eliciting behavioral and physiological responses across different species. High CO concentration is a major feature of termite nests, which may be used as a cue for locating their nests. Termites also survive under an elevated CO concentration. However, the mechanism by which elevated CO concentration influences gene expression in termites is poorly understood.

Methods: To gain a better understanding of the molecular basis involved in the adaptation to CO concentration, a transcriptome of Shiraki was constructed to assemble the reference genes, followed by comparative transcriptomic analyses across different CO concentration (0.04%, 0.4%, 4% and 40%) treatments.

Results: (1) Based on a high throughput sequencing platform, we obtained approximately 20 GB of clean data and revealed 189,421 unigenes, with a mean length and an N50 length of 629 bp and 974 bp, respectively. (2) The transcriptomic response of to elevated CO levels presented discontinuous changes. Comparative analysis of the transcriptomes revealed 2,936 genes regulated among 0.04%, 0.4%, 4% and 40% CO concentration treatments, 909 genes derived from termites and 2,027 from gut symbionts. Genes derived from termites appears selectively activated under 4% CO level. In 40% CO level, most of the down-regulated genes were derived from symbionts. (3) Through similarity searches to data from other species, a number of protein sequences putatively involved in chemosensory reception were identified and characterized in , including odorant receptors, gustatory receptors, ionotropic receptors, odorant binding proteins, and chemosensory proteins.

Discussion: We found that most genes associated with carbohydrate metabolism, energy metabolism, and genetic information processing were regulated under different CO concentrations. Results suggested that termites adapt to ∼4% CO level and their gut symbionts may be killed under high CO level. We anticipate that our findings provide insights into the transcriptome dynamics of CO responses in termites and form the basis to gain a better understanding of regulatory networks.