Thermal Stress-Induced Alterations to Oxylipin Signal Receptors in the Cnidarian-Dinoflagellate Symbiosis.

The continuous exchange of molecular signals between partners in the cnidarian-dinoflagellate symbiosis is fundamental for maintaining a healthy relationship. This homeostasis is affected by rising seawater temperatures resulting from climate change (i.e., coral bleaching), though little is known about how these molecular signals are altered. Here, we investigated the localisation and abundance of four receptors in the sea anemone Exaiptasia diaphana ('Aiptasia') exposed to thermal stress. Using immunohistochemistry, we examined Transient Receptor Potential channel A1 (TRPA1), Prostaglandin E2 receptors 2 (EP2) and 4 (EP4) and Glutamate receptor ionotropic kainate 2 (GRIK2). TRPA1, EP2 and EP4 are involved in oxylipin-mediated signalling via hydroxyoctadecadienoic acid (HODE) and prostaglandin E2 (PGE2), while GRIK2, part of the ionotropic glutamate receptor (iGluR) family, has been linked to chemosensory perception in invertebrates. All four receptors were detected in both gastrodermis and epidermis across treatments. While EP4 abundance was unaffected, EP2 increased significantly at 31°C and 34°C in both tissue layers. TRPA1 abundance increased at 34°C in both layers, and GRIK2 increased at 31°C in the gastrodermis and at 34°C in both layers. These results suggest that lipid signalling pathways are thermally modulated, potentially contributing to symbiosis dysfunction and bleaching.