The disease white syndrome spreads across an Acropora coral.

Credit: ARC Centre of Excellence, Coral Reef Studies

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SYDNEY: Corals may have more genes than humans, say researchers sequencing the coral genome. The species adds to the list of seemingly simple organisms that have a surprisingly large number of genes.

The research also suggests that though corals are distant from humans in evolutionary terms, we may share some of the same immune system genes that protect us from disease.

The findings could provide the key to treating diseased and devastated coral reefs around the world – and may have implications for treating human disease too.

Genetic potential

"Based on the rate of gene discovery, we estimate that corals have as many as 20,000 or 25,000 genes, compared with the human complement of 20,000 to 23,000" said David Miller of the Australian Research Council's Centre of Excellence for Coral Reef Studies at James Cook University in Townsville, Queensland.

In collaboration with biologists at the Australian National University in Canberra, Miller's team is leading efforts to sequence the genomes of the coral species Acropora Millepora. Though the genome sequences have not been fully elucidated, the geneticists have used a sequencing method known as Expressed Sequence Tags to estimate the number of potential genes.

They reveal their findings in an upcoming issue of the journal Genome Biology.

Corals add to a growing number of seemingly-simple organisms, such as the single-celled amoeba and the pathogen trichomonas – as well as some insects and plants – which have as many, or more, genes than mammals.

So, why do corals need such a large genome? "That's really the $64,000 question," said Miller. He argued that they probably use this genetic complement "in far less sophisticated ways than do mammals."

An "emerging view" is that animals have a tendency for this number of genes, he said, "unless there's an evolutionary advantage for them to have lost some." This dispels the idea that organisms which look simple have relatively simple genomes, and that as organisms became more complex, they accumulated genes.

Reef saver

Further analysis of the coral genes exposed surprising similarity between the immune systems of coral and humans. With so little currently known about the immune system of invertebrates, the knowledge could be useful in the treatment of coral disease – a growing problem in the wake of global warming, which is detrimentally heating the oceans.

The research has already helped the group to understand more about white syndrome, a devastating coral disease. The syndrome is likely a result of uncontrolled cell death in coral, and armed with current knowledge of the human immune system, Miller's team has been able to identify candidate molecules for further study of the causes behind it.

But there could be implications for treating human disease too. "Hopefully it will go both ways," said Miller. "Because there is such a degree of similarity between human and coral innate immune systems, there is the chance to apply knowledge of human pathways to coral disease [and] the relative simplicity of coral innate immunity could help us to better understand aspects of of human disease."