A breakthrough in understanding the molecular basis of coral heat tolerance

Reef-building corals are cnidarian animals (Anthozoa, Scleractinia) that mostly live in colonies composed of hundreds of thousands of tiny coral polyps. The polyps house dinoflagellate algal photosymbionts of the family Symbiodiniaceae inside their gastrodermal cells (Fig. 1 A ), and this mutualistic association builds the three-dimensional structure of the reefs via deposition of calcium carbonate skeletons. Scleractinian corals thus support a tremendous diversity and biomass of coral reef organisms. However, much of the biology of corals is poorly understood, partly due to a lack of advanced genetic tools for both the corals and the Symbiodiniaceae. In PNAS, Cleves et al. (1) catapult the field forward by describing an efficient protocol for applying the CRISPR technology to the coral Acropora millepora . They show that a CRISPR knockout of the gene encoding Heat Shock Transcription Factor 1 ( HSF1 ) in larvae of this coral reduces their heat shock tolerance, thus confirming a role for HSF1 in protecting corals from heat stress.Fig. 1. The scleractinian coral, Acropora millepora . ( A ) Close-up of individual polyps showing the endosymbiotic Symbiodiniaceae algae as brown pigmentation and as individual cells in the Inset . Symbiodiniaceae cells are ∼5 to 10 µm in diameter. Image credit: Katarina Damjanovic (photographer). ( B ) Bleached and unbleached adult colonies during a natural bleaching event on the Great Barrier Reef. Image credit: Ray Berkelmans (photographer). ( C ) Aposymbiotic larva. Image credit: Kate Quigley (photographer).Gaining a deeper understanding of the coral heat stress response is urgent given that climate warming, and particularly the resulting increased frequency and severity of summer heat waves, are responsible for the alarmingly rapid loss of coral reefs worldwide. Exposure to elevated temperature can result in the loss of the symbiotic algae from the coral … [↵][1]1To whom correspondence may be addressed. Email: madeleine.van{at}unimelb.edu.au. [1]: #xref-corresp-1-1