How to resist soil desiccation: Transcriptional changes in a Mediterranean earthworm during aestivation

Earthworms have a central role in ministering the terrestrial ecosystems and are proving to have an important role in modulating the effects climate change has on soil. Aestivation is a form of dormancy employed by the organisms living in deserts and arid environments, when confronted with prolonged periods of drought. Understanding global metabolic adjustments required for withstanding the harsh conditions of the ever more severe Iberian drought, we performed a global transcriptomic exploration of the endogeic earthworm Carpetania matritensis during aestivation. There were a total of 6352 differentially expressed transcripts in the aestivating group, with 65% being downregulated. Based on GO and KEGG enrichment analyses, downregulated genes seem to be indicative of an overall metabolic depression during aestivation. Indeed we noted a reduction of protein turnover and macromolecule metabolism coupled with suppression of genes involved in digestion. Upregulated genes, namely antioxidant genes and DNA repair genes showed clear signs of abiotic stress caused by ROS generation. Abiotic stress led to transcriptomic changes of genes involved in immune response, mostly affecting the NF-kb signaling pathway as well as changes in apoptotic genes indicating the necessity of investigating these processes in a tissue specific manner. Lastly we uncovered a possible mechanism for water retention by nitrogenous waste accumulation. This study provides the first ever transcriptomic investigation done on aestivating earthworms and as such serves as a general framework for investigation on other earthworm species and other soil invertebrates, which is becoming increasingly important with the current scenario of climate change.