Scientists have identified a gene that improves the heat tolerance of the algae that live symbiotically with coral species, and could potentially help the corals adapt to some warming. Symbiodinium is a unicellular alga that provides its coral host with photosynthetic products in return for nutrients and shelter. However, high sea temperatures can cause the breakdown of this symbiotic relationship and lead to the widespread expulsion of Symbiodinium from host tissues, an event known as coral beaching. If bleached corals do not recover, they starve to death, leaving only their white, calcium-carbonate exoskeleton. Now, researchers from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have identified special genes, called retrotransposons, which could help the algae adapt more rapidly to heat stress. The team conducted analyses to find out which genes were turned on or off when Symbiodinium was exposed to heat stress.
Surprisingly, most genes commonly associated with heat stress were turned off, while a small number of retrotransposons were turned on. Retrotransposons are small genetic sequences that have the ability to replicate and position themselves in new locations in their host’s genome. “The ability of retrotransposons to copy themselves and integrate these new copies into the host genome makes them genetic parasites,” said geneticist and principal investigator, Manuel Aranda. The team suggests that the activation and replication of Symbiodinium’s retrotransposons in response to heat stress could lead to a faster evolutionary response, “since producing more mutations increases the chance of generating a beneficial one that allows the symbionts to cope better with this specific stress,” Aranda said.
The researchers next plan to investigate coral genomes to find out if they too have retrotransposons that are activated in response to heat stress. “If they do, it would mean they might be able to genetically adapt faster than we thought,” said Aranda. They also plan to investigate the possibility of “hijacking” the molecular machinery of retrotransposons to engineer more resilient genomes in both Symbiodinium and their coral hosts.