Sex, Scavengers, and Chaperones: Transcriptome Secrets of Divergent Symbiodinium Thermal Tolerances.
Corals rely on photosynthesis by their endosymbiotic dinoflagellates (Symbiodinium spp.) to form the basis of tropical coral reefs. High sea surface temperatures driven by climate change can trigger the loss of Symbiodinium from corals (coral bleaching), leading to declines in coral health. Different putative species (genetically distinct types) as well as conspecific populations of Symbiodinium can confer differing levels of thermal tolerance to their coral host, but the genes that govern dinoflagellate thermal tolerance are unknown. Here we show physiological and transcriptional responses to heat stress by a thermo-sensitive (physiologically susceptible at 32 °C) type C1 Symbiodinium population and a thermo-tolerant (physiologically healthy at 32 °C) type C1 Symbiodinium population. After nine days at 32 °C, neither population exhibited physiological stress, but both displayed up-regulation of meiosis genes by ≥ 4-fold and enrichment of meiosis functional gene groups, which promote adaptation. After 13 days at 32 °C, the thermo-sensitive population suffered a significant decrease in photosynthetic efficiency and increase in reactive oxygen species (ROS) leakage from its cells, whereas the thermo-tolerant population showed no signs of physiological stress. Correspondingly, only the thermo-tolerant population demonstrated up-regulation of a range of ROS scavenging and molecular chaperone genes by ≥ 4-fold and enrichment of ROS scavenging and protein-folding functional gene groups. The physiological and transcriptional responses of the Symbiodinium populations to heat stress directly correlate with the bleaching susceptibilities of corals that harbored these same Symbiodinium populations. Thus, our study provides novel, foundational insights into the molecular basis of dinoflagellate thermal tolerance and coral bleaching.
Centre for Marine Bio-Innovation, The University of New South Wales, Sydney, NSW, Australia School of Biological Earth and Environmental Sciences, The University of New South Wales, Sydney, NSW, Australia rachylevin@gmail.com.
Rachel A
RA
Levin
Australian Institute of Marine Science, Townsville MC, QLD, Australia.
Victor H
VH
Beltran
Macquarie University, Sydney, NSW, Australia.
Ross
R
Hill
Centre for Marine Bio-Innovation, The University of New South Wales, Sydney, NSW, Australia Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore.
Staffan
S
Kjelleberg
Centre for Marine Bio-Innovation, The University of New South Wales, Sydney, NSW, Australia Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore The iThree Institute, University of Technology Sydney, Sydney, NSW, Australia.
Diane
D
McDougald
Centre for Marine Bio-Innovation, The University of New South Wales, Sydney, NSW, Australia School of Biological Earth and Environmental Sciences, The University of New South Wales, Sydney, NSW, Australia Sydney Institute of Marine Science, Mosman, NSW, Australia.
Peter D
PD
Steinberg
Australian Institute of Marine Science, Townsville MC, QLD, Australia School of BioSciences, The University of Melbourne, Parkville, VIC, Australia.
Madeleine J H
MJ
van Oppen
D000064:Acclimatization / Q000235:genetics; D000222:Adaptation, Physiological / Q000235:genetics; D000818:Animals; D037421:Anthozoa / Q000235:genetics* / Q000378:metabolism; D057231:Climate Change; D057894:Coral Reefs; D004141:Dinoflagellida / Q000235:genetics* / Q000378:metabolism; D006358:Hot Temperature; D018832:Molecular Chaperones / Q000235:genetics; D010788:Photosynthesis / Q000235:genetics; D013312:Stress, Physiological / Q000235:genetics; D013559:Symbiosis; D059467:Transcriptome
D018832:Molecular Chaperones
acclimation; bleaching; coral; dinoflagellate; symbiodinium; thermal tolerance; transcriptomics.