Coral researchers test gene-editing

An international team has succeeded in using CRISPR to investigate the functions of crucial genes for a common reef species. Elizabeth Finkel reports.

Understanding the genetics of coral is a key priority for saving global reefs.
Understanding the genetics of coral is a key priority for saving global reefs.
Image Source RF/Justin Lewis/Getty Images

We’ve just lost about half of the Great Barrier Reef, adding to the global decline of at least 50% of the world’s reefs in the last three decades.

Now, one of the most powerful tools in the genetic toolbox has been enlisted to the cause of saving coral reefs – the DNA-editing technology known as CRISPR. It promises to fast-track the almost non-existent art of coral breeding.

A team of researchers from Stanford University and the University of Texas at Austin, both in the US, with colleagues from the Australian Institute of Marine Science (AIMS) in Townsville, Queensland, have succeeded for the first time in applying the editing tool to three genes of the coral Acropora millepora. Their findings are published in the journal Proceedings of the National Academy of Science.

The idea, for now, is not to release genetically modified coral onto the reef, but to reveal the functions of coral genes. That will help researchers select and breed natural varieties that have the best chance of surviving the challenges of climate change.

“It’s a great step forward,” says Madeleine van Oppen, a coral researcher at the University of Melbourne and AIMS, who was not involved with the study.

CRISPR has revolutionised the ability to change the DNA of everything from wheat to Asian elephants.

Compared to previous methods of altering DNA code, the technique is far more precise, faster and cheaper.

Researchers can use it to discover the function of genes by making it “delete” genes, then look at the consequences. Once researchers know the function of genes, they can also use CRISPR to edit them to the desired coding, and reap the benefits – for instance, making a wheat plant resistant to powdery mildew.

However coral, so far, has resisted being edited. Every new species requires a process of trial and error to figure out how to put the CRISPR editor to work at the earliest embryonic stages. As AIMS’s Line Bay, a co-author of the paper, explains, “the key problem is getting access to the coral embryos; most coral species broadcast their spawn and do it usually only once a year.”

To capture the coral spawn, the American team members made use of SeaSim, a state of the art aquarium at AIMS that precisely mimics the conditions of the reef. In November 2016, they harvested freshly-spawned and fertilised A. millepora eggs and injected them with CRISPR molecules primed to edit three different genes coding for green fluorescent protein (GFP), red fluorescent protein (RFP) and fibroblast growth factor 1a (FGF1a).

The first two genes give corals their pretty green or red colour and might play a role in helping coral manage stress. The FGF1a gene is thought to play a role in the metamorphosis of the rice-grain-like larvae to a flower-like polyp. However, until now, researchers have not had a tool to test their presumptions about the exact functions of the genes.

Their experiments were a success to the extent that they were for the first time able to generate coral individuals in which each of the target genes had been edited.

So far, however, they have yet to discover how the lack of these genes affected fitness.

For Bay, the power of the new tool lies predominantly in testing which genes are protective against coral stress.

She refers to two recent “good news” publications that showed that reefs off Australia’s North Western shelf, such as Scott reef, as well as those of the Great Barrier Reef, show high diversity.

This kind of diversity is the “fuel for natural selection”, says Line. Indeed, she says she has already begun attempting to breed individuals that survived the 2016 and 2017 bleaching events to see if they are more tolerant to marine heat waves.

But breeding coral individuals and testing the fitness of their offspring is where wheat breeding was decades ago. Applying CRISPR to coral should enable the equivalent of “precision agriculture”, allowing coral breeders to fast-track the production of the genetically best-endowed individuals, rather than the trial and error of traditional approaches.

And as for using CRISPR to release genetically manipulated corals onto the reef? Line says that still a long way off and may never be appropriate for the Great Barrier Reef. For one thing, she points out that there are multiple genomes at work: that of the coral polyp, the symbiotic algae and a multitude of other microbes such as bacteria and viruses.

“Getting the final combination right will present anther level of challenge,” she says. “My prediction is that [genetically edited coral] will not be ready for some time. However, it’s important to test these techniques now, while we still have some time.”

Ella finkel twic.jpg?ixlib=rails 2.1
Elizabeth Finkel is editor-in-chief of Cosmos.
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