Cnidarian-Dinoflagellate Symbioses

Our group investigates the cellular and molecular interactions underlying mutualistic symbioses between cnidarians, such as corals and anemones, and their photosynthetic dinoflagellate symbionts Symbiodinium spp. These partnerships are of fundamental importance as they form the trophic and structural foundation of coral reef ecosystems. We are interested in the establishment, maintenance and breakdown of these cooperative associations and approach the study of these phenomena at the cellular and molecular level. The Weis group has used a variety of model associations in these examinations and has in recent years focused on the Hawaiian stony coral, Fungia scutaria and a tropical sea anemone Aiptasia pallida.

Onset of Symbiosis: Processes of Recognition

Most host species must acquire symbionts anew with each generation and therefore must engage in a complex recognition process with the symbiont that involves the host innate immune system and results in the establishment of a stable specific symbiosis. We are examining onset of symbiosis both during the cnidarian host larval stage as well as during re-infection of aposymbiotic adults. These processes include initial MAMP-PRR signaling, such as host lectin-symbiont glycan interactions, phagocytosis of the symbiont by host gastrodermal cells and then a cessation of phagosomal maturation that results in symbiont persistence within host vacuoles. We are using both descriptive and hypothesis-driven approaches to investigating onset of symbiosis. Identification and characterization of host innate immunity genes including lectins, TRAFs, MASPs, members of the complement pathway and NOS are underway. We are using confocal microscopy to examine the dynamics of first infection, such as the location of symbionts, cytoskeletal dynamics of phagocytosis and localization of innate immune gene expression. We are using inhibitor and gene knockdown approaches to empirically investigate the involvement of host innate immunity signaling pathways membrane trafficking and cytoskeletal dynamics.

Symbiosis Dysfunction: Coral Bleaching

We are interested in the cellular mechanisms underlying the breakdown of coral-dinoflagellate symbioses that results in coral bleaching. Coral bleaching is a serious and growing environmental problem that is triggered by a variety of environmental triggers, most importantly elevated temperature. It is now well-documented that elevated temperature and UVR causes oxidative stress in both symbiont and host. Our group is interested in the downstream effects of this stress in the host that ultimately result in loss of symbionts from the host tissues. The picture emerging is complex and involves a variety of cellular pathways. We are investigating roles for apoptosis, autophagy and innate immunity in the detection and elimination of symbionts from stressed host tissues.