Meeting Abstract
Warming oceans threaten to wipe out coral reefs around the world by jeopardizing the mutualistic relationship between corals and their intracellular algae. Under environmental stress (often high temperature) corals bleach and lose their algal symbionts. The prevailing model for bleaching suggests that the generation of destructive reactive oxygen species, triggered by a combination of light and heat stress, plays a central role. However, severe bleaching can still occur under heat stress alone in deeper, low light coral reefs, indicating that other mechanisms are involved. Inter-partner glycan-lectin signaling is a pathway in which dysfunction may lead to bleaching. Glycans are sugar molecules on the symbiont cell that are recognized by host lectins during the onset of symbiosis. In vitro manipulation of symbiont glycans results in decreased uptake of symbionts by hosts, and some host lectins are downregulated under heat stress. We hypothesize that heat-induced changes in the algal glycome will reduce symbiont uptake, and that this is caused by the host mounting an immune response against heat stressed symbionts. First, to assess if heat stress reduces symbiont uptake, aposymbiotic Aiptasia pallida, a sea anemone that is a globally adopted model system for the study of coral symbiosis, was recolonized at ambient temperature with heat stressed symbionts, Symbiodinium minutum (32°C for 3 or 7 days). Results showed decreasing uptake with longer durations of heat stress, and this was not attributable to symbiont mortality. We will also present results on tests assessing the symbiont glycome under heat stress, and tests on host immunity during symbiont uptake by measuring NF-kB expression, a proxy for immune response.
