Transcriptomic response of an antarctic polyextremophile to distinct sublethal abiotic stressors
While terrestrial Antarctica is most associated with snow and ice, communities residing in these environments are subject to suite of abiotic stressors, including wide temperature fluctuations, highly variable osmotic concentrations, and risk of desiccation. The midge Belgica antarctica, Antarctica's only endemic insect, is highly tolerant of a variety of environmental insults, and the mechanisms that underscore this impressive tolerance are an intense area of investigation. Distinct abiotic stressors can converge on the same cellular injuries, so shared molecular mechanisms across stressors could underscore the evolution of this species' polyextremophilic nature. Further, distinct stressors can often occur in close succession, so shared molecular responses could suggest that cross protection plays an important role in these hostile environments. To investigate the extent of shared mechanisms in response to these stressors, we quantified transcriptomic responses of the Antarctica midge Belgica antarctica following sublethal exposure to five stressors: heat, cold, desiccation, hyper- and hypoosmotic stress. Our results suggest that a few transcriptional mechanisms are shared by physiologically similar stressors, which may explain cross-protection observed in previous physiological studies. Specifically, the greatest extent of shared mechanisms was observed between distinct stressors that all result in cellular dehydration. Shared gene expression modules were consistent with both cross- tolerance (predominantly molecular chaperone mediated stress responses and cell structure maintenance) and cross-talk (for example, MAPK and JNK signalling pathways) occurring between distinct stressors. Further, for hypo- and hyperosmotic stress, both of which involve submersion in water, p53 signalling pathways was activated by both. However, contrary to our expectations, most of genes involved in these stress responses were specific to one stressor. In addition, we also quantified gene expression prior to and after a period of recovery, and similarity between dehydration-inducing stressors (i.e., freezing, desiccation, and hyperosmotic stress) was highest following recovery, with between 57.7 and 61.7% of genes shared between pairs of these stressors. Taken together our results show that transcriptional mechanisms across distinct abiotic stressors are largely specific to a single stressor, although several shared molecular processes may facilitate cross- protection between certain stressors. Together, this study provides a comprehensive resource for molecular stress responses in this polyextremophilic species and provides insights into how multiple stress tolerance may have evolved.Samples: Belgica antarctica larvae were exposed to 5 stress treatments (Freezing, Heat, Dehydration, Hyposmotic, Hyposmotic). From these, some groups were allowed to recover for 12h. Two groups of untreated larvae were maintained at 4C for 0 and 12 h. Each group (N=12) had 3 biological replicates. Each replicate had 10 larvae. Total number of sequenced samples was 36.