Some (coral) like it hot

Warming oceans are bad news for coral, but an improved CRISPR-Cas9 technique has revealed a “heat shield” gene that could be used to identify species with the best chance of adaptation.

A research team led by Philip Cleves of the Carnegie Institute for Science, US, removed a gene called Heat Shock Transcription Factor 1 (HSF1) from the Australian coral Acropora millepora. The work is reported in the journal PNAS.

HSF1-free coral had a much higher mortality rate at warmer temperatures than unmodified coral, suggesting that HSF1 plays a role in protecting coral from heat, and that coral with naturally higher concentrations of the protein could be better at adaptation.

“Understanding the genetic traits of heat tolerance of corals holds the key to understanding not only how corals will respond to climate change naturally but also balancing the benefits, opportunities and risks of novel management tools such as selective breeding and movement of corals among reefs,” says Lin Bay of the Australian Institute of Marine Science.

CRISPR-Cas9 technology works by removing a small part of the DNA, which changes the gene’s function. A specific DNA sequence is selected as a target for Cas9, which then “cuts” it out.

Putting the CRISPR-Cas9 editing apparatus into the organism is the next challenge: to replicate across an organism, it needs to be placed into its initial single cell, which for a coral is a fertilised egg, and immensely fragile.

The team used a microinjection and a powerful microscope to inject the CRISPR-Cas9 and 90% of the resulting larvae had non-functioning HSF1, a very high success rate compared to previous CRISPR techniques. 

Researchers tested how well the HSF1-free coral survived different temperatures. At 27 degrees Celsius, it had no problems, but in 34-degree water nearly two thirds died within 48 hours. In contrast, the unmodified coral survived well. 

While it’s unlikely that genetically modified coral will be introduced to the ecosystem, this provides an important gene that can be targeted to screen for heat resistant coral for breeding programs. It’s also an improved CRISPR-Cas9 method, which could speed up the pace of understanding coral genetics.

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