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Stanford University School of Medicine

Annoying anemones shed light on coral reef biology

I stopped by John Pringle’s office last week to hear about what he’s been up to. A lot! As we mentioned here a few months ago, Pringle, PhD, a professor of genetics who spent the first decades of his career studying yeast genetics and cell biology, has switched gears and is looking for ways to help corals — while continuing a lifetime of basic research.

Corals and the incredibly species-rich ecosystems they support are disappearing fast in nearly every part of the world's oceans. Coral reefs protect coastlines, sustain rich fisheries and support some of the most species-rich habitats in the world. Yet, around the world, a third of all coral has died.

The first sign of stress is a fading, or "bleaching," of the coral that reflects the loss of photosynthetic algae that live inside the coral. In a quest to understand the molecular underpinnings of bleaching in corals, Pringle and two colleagues at Stanford helped sequence the genome of a small sea anemone that serves as a model for corals. They report their work this week in PNAS.

I asked Pringle what they'd found. But first, he wanted to tell me about his colleagues Christian Voolstra, PhD, Sebastian Baumgarten, and others at the Red Sea Research Center, in Thuwal, Saudi Arabia, where much of the experimental work and analysis took place. Pringle said the center is part of the King Abdullah University of Science and Technology, or KAUST, a six-year-old university with top researchers from around the world and a $20 billion endowment.

Although it’s easy to mistake coral for some kind of weird rock, corals are animals. But lab animals they are not. They grow slowly, in large colonies of tiny individuals, die easily and retreat inside their hard coral quarters when they aren't happy.

A better option, Pringle learned, was a sea anemone called Aiptasia. Aiptasia is a pest that drives aquarium hobbyists to distraction. It thrives in captivity, takes over aquaria, and is seemingly impossible to eradicate — in short, the perfect lab animal.

Moreover, Aiptasia shares with corals a close "symbiotic" relationship with a photosynthetic alga, called Symbiodinium, that provides 90 to 95 percent of the animals’ energy needs. It resembles the relationship we have with the microbiome bacteria in our guts. Except, in the case of Aiptasia, it's more like having a backyard vegetable garden growing under your skin and supplying strawberries and snap peas directly to your gut.

"The big problem corals are facing around the world is the breakdown of that relationship," said Pringle. One of the first signs that a coral is in trouble is that it begins to lose its color, or bleaches — a sign that the relationship between the coral and its alga is breaking down. Without their algae, the corals soon die.

To understand how the relationship fails, the team of researchers sequenced the genome of Aiptasia and began looking for patterns of gene expression in both anemone and alga when they were under stress. Ultimately, identifying the molecular signals that trigger or foretell bleaching could show that corals are stressed and give conservation biologists a chance to intervene before it's too late.

Corals and anemones are both very picky about which kinds of algae they welcome into their bodies. "Why they care which alga, I don't know," mused Pringle. So he and his colleagues were fascinated to find a set of proteins in both the anemone and two corals that include molecular elements like those used by our immune system to recognize foreign microbes. Pringle speculated that such proteins might help corals and anemones distinguish their own alga from all the other algae in the sea. The main goal at the Pringle lab, Pringle said, is to develop the genetic tools to decisively answer such basic questions.

Previously: From yeast to coral reefs: Research that extends beyond the lab and The value of exploring jellyfish eyes: Scientist-penned book supports “curiosity-driven” research

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