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Genetic engineering has already established itself as an invaluable tool for studying gene functions in organisms.
Our new study, published in Proceedings of the National Academy of Sciences, now demonstrates how gene editing can be used to pinpoint genes involved in corals’ ability to withstand heat stress.
A better understanding of these genes will lay the groundwork for experts to predict the natural response of coral populations to climate change. And this could drive efforts to improve coral adaptation, through selective breeding of naturally heat-tolerant corals.
A threatened national treasure
The Great Barrier Reef is among the most majestic, unique and economically valuable ecosystems in the world. It stretches for more than 2,000 kilometers, has more than 600 types of coral, 1,600 types of fish, and is of immense cultural significance, especially to traditional owners.
But warming ocean waters caused by climate change is leading to mass bleaching and coral reef mortality, threatening the reef’s long-term survival.
Learn more: The first step to preserving the Great Barrier Reef is to understand what lives there
Many research efforts focus on how we can prevent coral reef deterioration by helping it adapt and recover from the conditions that cause it stress.
Understanding the genes and molecular pathways that protect corals from heat stress will be key to achieving these goals.
Although hypotheses exist about the roles of particular genes and pathways, rigorous testing of these has been difficult, largely due to a lack of tools to determine gene function in corals.
But in the past decade or so, CRISPR / Cas9 gene editing has emerged as a powerful tool for studying gene function in non-model organisms.
CRISPR: a technological marvel
Scientists can use CRISPR to make precise changes to the DNA of a living organism by “cutting” its DNA and changing its sequence. This can involve inactivating a specific gene, introducing a new piece of DNA, or replacing a piece.
In our 2018 research, we demonstrated that it is possible to make precise mutations in the coral genome using CRISPR technology. However, we were unable to determine the functions of our specific target genes.
For our latest research, we used an updated CRISPR method to sufficiently disrupt the thermal shock transcription factor 1, or HSF1, in coral larvae.
Based on the role of this protein-encoding gene in model organisms, including closely related sea anemones, we hypothesized that it would play an important role in corals’ heat response.
Phillip Cleves / Carnegie Institute for Science, CC BY-NC-ND
Previous research had also shown that HSF1 can affect a large number of heat response genes, acting as a kind of “master switch” to turn them on.
By turning off this master switch, we expected to see significant changes in the corals’ heat tolerance. Our prediction proved accurate.
Read more: What is CRISPR, the gene editing technology that won the Nobel Prize in Chemistry?
What we discovered by injecting coral eggs
We spawned corals at the Australian Institute of Marine Science during the annual mass spawning event in November 2018.
We then injected the CRISPR / Cas9 components into the fertilized coral eggs to target the HSF1 gene in the common and widespread staghorn coral. Acropora millepora.
Mikaela Nordborg / Australian Institute of Marine Science, Author provided
We were able to demonstrate a strong effect of HSF1 on the heat tolerance of corals. In particular, when this gene was mutated using CRISPR (and is no longer functional) corals were more vulnerable to heat stress.
Larvae with stunned copies of HSF1 died under heat stress when the water temperature was raised from 27 ℃ to 34 ℃. In contrast, the larvae with the functional gene survived well in the warmer water.
We understand what we already have
It might be tempting now to focus on using gene-editing tools to design heat-resistant coral strains to accelerate the Great Barrier Reef’s adaptation to warm waters.
However, genetic engineering should be used primarily to increase our knowledge of the fundamental biology of corals and other reef organisms, including their response to heat stress.
This will not only help us more accurately predict the natural response of coral reefs to climate change, but will also shed light on the risks and benefits of new coral management tools, such as selective breeding.
It is our hope that these genetic insights provide a solid foundation for future coral reef conservation and management efforts.
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