Oxylipin Receptors and Their Role in Inter‐Partner Signalling in a Model Cnidarian‐Dinoflagellate Symbiosis

ABSTRACT Oxylipin signalling is central in biology, mediating processes such as cellular homeostasis, inflammation and molecular signalling. It may also facilitate inter‐partner communication in the cnidarian‐dinoflagellate symbiosis, though this aspect remains understudied. In this study, four oxylipin receptors were characterised using immunohistochemistry and immunoblotting in the sea anemone Exaiptasia diaphana (‘Aiptasia’): Prostaglandin E2 receptor 2 (EP2) and 4 (EP4), Transient Receptor Potential cation channel A1 (TRPA1) and Glutamate Receptor Ionotropic, Kainate 2 (GRIK2). Receptor abundance and localisation were compared between aposymbiotic anemones and symbiotic anemones hosting either native Breviolum minutum or non‐native Durusdinium trenchii . All receptors were localised to the putative symbiosome of freshly isolated symbionts, suggesting a role in host‐symbiont crosstalk. EP2, EP4 and TRPA1 abundance decreased in the gastrodermis of anemones hosting B . minutum , indicating potential downregulation of pathways mediated by these receptors. In contrast, GRIK2 abundance increased in anemones hosting D . trenchii in both the epidermis and gastrodermis; GRIK2 acts as a chemosensor of potential pathogens in other systems and could play a similar role here given D . trenchii 's reputation as a sub‐optimal partner for Aiptasia. This study contributes to the understanding of oxylipin signalling in the cnidarian‐dinoflagellate symbiosis and supports further exploration of host‐symbiont molecular signalling.