Ancient jumping genes may give corals a new lease on life

Jumping genes could make an alga, and its coral host, more tolerant to warming sea temperatures.

Symbiodinium microadraticum is a unicellular alga that provides its coral host with photosynthetic products in return for nutrients and shelter.

Symbiodinium microadraticum is a unicellular alga that provides its coral host with photosynthetic products in return for nutrients and shelter.

© 2017 Jit Ern Chen

A particular gene is shown by KAUST researchers to help the heat tolerance of an alga that lives symbiotically with coral, which could potentially help Red Sea 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 KAUST have identified special genes, called retrotransposons, which could help the algae adapt more rapidly to heat stress. 

The team, led by postdoc Jit Ern Chen and Ph.D. student Guoxin Cui, conducted analyses to determine 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,” says geneticist and principal investigator Manuel Aranda. “Every integration event is basically a new mutation in the host genome. Very often these new copies disable or disrupt host genes. However, sometimes they can also change how certain genes behave. They are often bad, like most mutations, but some can produce advantageous effects.”

Aranda and his team suggest 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 explains.

The team next plans 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,” says 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.

References

  1. Chen, J. E., Cui, G., Wang, X., Liew, Y. J. & Aranda, M. Recent expansion of heat-activated retrotransposons in the coral symbiont Symbiodinium microadriaticum. The ISME Journal advance online publication, 20 October 2017.| article