Transcriptome landscape of a thermal-tolerant coral endosymbiont reveals molecular signatures of symbiosis and dysbiosis

Abstract

Warming oceans disrupt the critical endosymbiosis between corals and their photosynthetic dinoflagellate endosymbionts of the family Symbiodiniaceae. Durusdinium trenchii is a heat-tolerant species of Symbiodiniaceae and enhances survival of its coral host, but the basis for tolerance is largely unknown. To identify the underpinnings of heat tolerance and symbiosis, we compared the in hospite and free-living transcriptomes of D. trenchii under stable temperature conditions and acute hyperthermal stress. We discovered that under stable conditions, in hospite cells exhibit lower transcriptional activity than free-living counterparts, suggesting the shutdown of genes uniquely required for a free-living lifestyle. However, under hyperthermal stress the transcriptional response was larger in hospite, indicating an exacerbated stress environment within the host cell. Significantly, we unraveled the molecular signatures of symbiont heat tolerance within the host, which is a critical step to enable the development of engineered endosymbionts as a tool for restoration of coral reefs.