Small heat shock proteins with two alpha-crystallin domains: a new set of proteins in the earthworm Eisenia fetida with differential transcriptional responses to stressors

Climate change and the growing environmental pollution are two of the main challenges that life faces today. Soil invertebrates such as earthworms are increasingly exposed to stress from climate change (e.g., rising temperatures and drought) and chemical pollution. The heat shock proteins are central to the stress response. Eisenia fetida, a widely used model for soil ecotoxicology, relies on molecular chaperones like small heat shock proteins (sHSPs) for stress tolerance. Furthermore, sHSPs generate interest for their potential as molecular indicators of soil pollution and for thermotolerance acquisition. Previously, we have described a set of genes coding for sHSPs with a single ACD. Here we report the first identification of sHSPs with multiple α-crystallin domains (ACDs) in an annelid. These genes were isolated from an E. fetida transcriptome, their domain architecture was defined, and their expression was analyzed under environmental stressors: heat shock, desiccation, and exposure to the pollutants bisphenol A (BPA) and endosulfan. Gene expression patterns were stimulus-specific. Prolonged sub-lethal heat and desiccation each induced distinct subsets of the multi-ACD sHSP genes, highlighting their tailored roles in abiotic stress. In contrast, exposure to BPA at optimal conditions did not produce a response, while endosulfan produced a minimal response. Combined exposure to endosulfan and elevated temperature triggered a significant upregulation of these chaperone genes indicating synergetic stress. This work relates the response of dimeric sHSPs to monomeric ones and provides perspective on the temporal changes of the small heat shock protein response and their contribution in earthworm adaptation in changing environments.