Transcriptome response to elevated atmospheric CO 2 concentration in the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae).

Background: Carbon dioxide (CO ₂ ) is a pervasive chemical stimulus that plays a critical role in insect life, eliciting behavioral and physiological responses across different species. High CO ₂ 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 ₂ concentration. However, the mechanism by which elevated CO ₂ 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 ₂ concentration, a transcriptome of Coptotermes formosanus Shiraki was constructed to assemble the reference genes, followed by comparative transcriptomic analyses across different CO ₂ 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 C. formosanus to elevated CO ₂ levels presented discontinuous changes. Comparative analysis of the transcriptomes revealed 2,936 genes regulated among 0.04%, 0.4%, 4% and 40% CO ₂ concentration treatments, 909 genes derived from termites and 2,027 from gut symbionts. Genes derived from termites appears selectively activated under 4% CO ₂ level. In 40% CO ₂ 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 C. formosanus , 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 ₂ concentrations. Results suggested that termites adapt to ∼4% CO ₂ level and their gut symbionts may be killed under high CO ₂ level. We anticipate that our findings provide insights into the transcriptome dynamics of CO ₂ responses in termites and form the basis to gain a better understanding of regulatory networks.
Competing Interests: The authors declare there are no competing interests.