J Phycol. 2021 Oct 26. doi: 10.1111/jpy.13219. Online ahead of print.
ABSTRACT
Global warming increases the temperature of the ocean surface, disrupting dinoflagellate-coral symbiosis and resulting in a phenomenon called coral bleaching. Photosynthetic dinoflagellates of the family Symbiodiniaceae include bleaching-tolerant and bleaching-sensitive coral symbionts. Therefore, understanding the molecular mechanisms for changing symbiont diversity is potentially useful to assist recovery of coral holobionts (corals and their associated microbes, including multiple species of Symbiodiniaceae), although sexual reproduction has not been observed in the Symbiodiniaceae. Recent molecular phylogenetic analysis estimates that the Symbiodiniaceae appeared 160 million years ago and diversified into fifteen groups, five genera of which (Symbiodinium, Durusdinium, Breviolum, Fugacium, and Cladocopium) now have available draft genomes. Comparative genomic analyses have suggested that crown groups have fewer gene families than early-diverging groups, although many genes probably acquired via gene duplications and horizontal gene transfers (HGTs) have been found in each decoded genome. Because UV stress is likely a cause of coral bleaching and because the highly conserved gene cluster for mycosporine-like amino acid (MAA) biosynthesis has been found in thermal-tolerant symbiont genomes, here I briefly review genomic features of the Symbiodiniaceae and focus on possible acquisition of a biosynthetic gene cluster for MAAs, which absorb UV radiation. On the basis of highly conserved noncoding sequences, I hypothesize that HGTs have occurred among members of the Symbiodiniaceae and have contributed to diversification of Symbiodiniaceae-host relationships. Finally, I propose that bleaching tolerance may be strengthened by multiple MAAs from both symbiotic dinoflagellates and corals.
PMID:34699617 | DOI:10.1111/jpy.13219