Oxylipin signalling in a coral-dinoflagellate symbiosis

Abstract

The symbiotic relationship of cnidarians with dinoflagellates of the family Symbiodiniaceae is based on host-symbiont recognition processes and continuous molecular exchange between partners. However, the molecular signals involved are unresolved. Oxylipin signalling plays a pivotal role in mediating various cellular processes, including inflammation and molecular signalling. Its function in the cnidarian-dinoflagellate symbiosis, including its potential role in inter-partner molecular communication, remains unclear. Here, prostaglandin EP2 receptors 2 (EP2) and 4 (EP4) were localised and quantified using immunohistochemistry in the tissues of the coral Acropora sp. aff. tenuis . Both coral larvae and polyps of juvenile colonies were examined when in symbiosis with one of their two native dinoflagellate symbionts, Cladocopium goreaui and Durusdinium trenchii , during early (3 days) and later (30 days) stages of symbiosis establishment (relative to aposymbiotic corals). EP2 and EP4 were present in both the gastrodermis and epidermis of larvae and polyps, regardless of their symbiotic state. Abundance of EP2 and EP4 was affected by symbiotic state, symbiont identity, coral life-stage, and the age of the symbiosis. Specifically, D. trenchii , but not C. goreaui , decreased host EP2 levels in larvae and polyps, and EP4 levels in coral polyps. Conversely, C. goreaui , but not D. trenchii , decreased EP4 levels in coral larvae. This research enhances our understanding of oxylipin pathway regulation in the coral-dinoflagellate symbiosis across various life-stages, and in response to different symbiont species, laying the groundwork for deeper exploration into the molecular signalling mechanisms that underlie this symbiosis and the influence of coral metamorphosis on these mechanisms.

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