How coral pick the right dinoflagellates

The architecture of coral reefs is built on the symbiotic relationship between the coral and various species of single-celled algae called dinoflagellates.

The photosynthetic dinoflagellates share the sugars they synthesise with their coral hosts, which in turn provide the inorganic carbon building blocks the algae needs, along with phosphorous, nitrate, and sulfur.

It’s a delicate balance, which has scientists wondering how the coral determine which algal species are compatible and which should be rejected, and then how to ingest and maintain them in a mutually beneficial way.

Now a team of cell, genomic and developmental biologists from Carnegie Institute for Science, US, thinks it has the answer.

Focussing on the pulsing, feathery, soft coral Xenia, they used a range of genomic, bioinformatic and developmental tools to identify the type of cell required for the right relationship to begin.

They discovered that it expresses a distinct set of genes, which enable it to identify, “swallow”, and maintain an alga in a specialised compartment, as well as to prevent the alga from being attacked by its immune system as a foreign invader.

The uptake process occurs over five stages, with stage three representing mature, alga-hosting cells, and stage one being pre-symbiotic-relationship and stage five being post-alga-expulsion.

This knowledge can be applied to increase our understanding of other coral species, Yixian Zheng and colleagues say, and hopefully help mitigate the impact of climate change, which is causing many coral hosts to lose their algal tenants, leading to coral bleaching

They now plan to investigate how environmental stress affects progression through the five stages, which stage is most crucial for recovery after a bleaching event, and the genes that function at each stage.

The findings are published in the journal Nature.