Symbiosis-supporting genes may trigger coral bleaching in response to heat, whereas the heat shock factor 1 (HSF1) gene is involved in protecting corals against heat stress, according to a pair of studies. Coral reefs worldwide are under increasing threat from climate change-induced heat stress, which can lead to death by bleaching, defined as the loss of symbiotic algae that reside in and exchange nutrients with corals. However, relatively little is known about the molecular and cellular processes involved in coral heat stress and bleaching. John Pringle and colleagues used a technique called RNAseq to examine heat stress-induced changes in gene expression in a coral relative, the sea anemone Aiptasia, which is symbiotic with algae similar to those found in corals. Within the first 3 hours of exposure to a high temperature (34 ºC), 524 genes showed more than a fourfold increase in expression levels in symbiotic anemones. This early heat-stress response appeared to be driven in part by two proteins--nuclear factor kappa B (NF?B) and heat shock factor 1 (HSF1)--that function as transcription factors regulating the activity of many genes. Next, the authors identified 337 genes whose expression levels were at least four times higher in symbiotic anemones compared with algae-free anemones. More than one-quarter of these putative symbiosis-supporting genes showed at least a threefold decrease in expression levels during the first 12 hours of heat exposure, many hours before bleaching occurred. According to the authors, this finding suggests that the heat-induced decrease in expression of symbiosis-supporting genes may trigger bleaching. In a related article, the authors used the genome-editing technology CRISPR/Cas9 to generate Acropora millepora coral larvae with mutations in the HSF1 gene. Little mortality was observed among mutant larvae exposed to 27 ºC, or among nonmutant larvae exposed to 34 ºC for 48 hours. By contrast, nearly two-thirds of mutant larvae died during the 48-hour period of heat exposure, indicating that HSF1 plays an important role in protecting corals against heat stress. The findings suggest that coral populations with naturally high HSF1 expression levels may be resilient to climate change. According to the authors, the studies together shed light on coral biology and may guide conservation efforts aimed at predicting, preventing, and mitigating the effects of climate change on corals.
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Article #19-20779:
"Reduced thermal tolerance in a coral carrying CRISPR-induced mutations in the gene for a heat-shock transcription factor," by Phillip A. Cleves et al.
Article #20-15737:
"Insights into coral bleaching under heat stress from analysis of gene expression in a sea anemone model system," by Phillip A. Cleves, Cory J. Krediet, Erik M. Lehnert, Masayuki Onishi, and John R. Pringle.
MEDIA CONTACT:
John Pringle
Stanford University School of Medicine, CA
e-mail: <jpringle@stanford.edu>
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