Researchers at the University of Haifa, the Weizmann Institute of Science and the Center for Genome Regulation (CRG) have mapped all the different types of cells of the first calyx-shaped column coral (Stylophora pistillata), a reef-building coral native to the Indo-Pacific Ocean. The study, published Tuesday in the journal Cell, is the first to detect the presence of special immune cells in corals. These findings provide new insights into the molecular biology and evolution of corals and will contribute to current and future conservation efforts to protect coral reef ecosystems threatened by rising temperatures and ocean acidification.
The atlas shows that calyx-shaped column corals have 40 different cell types during the three main phases of their life cycle. Researchers have discovered molecular mechanisms responsible for important biological processes, such as the formation of coral skeletons, which are home to a large number of marine species. The team also discovered how corals can establish symbiotic relationships with photosynthetic algae that inhabit their cells.
The researchers were also surprised to find the presence of specialized immune cells that employ many genes commonly associated with the function of immune cells in vertebrates. Previously, innate immunity was thought to play a role in protecting the health of algal symbiotes and adapting to temperature rises and acidification, but until now, there have been no reports of specialized immune cells in corals.
According to Dr. Tali Mass, one of the study's authors and a researcher at the University of Haifa, "Coral reefs play a vital role in the ecosystem of the ocean because they provide habitat for about 25% of the animals in the ocean and construct the world's largest biological structures. Warming and rising acidity pose a threat to the future of coral reefs, and accordingly, the genetic sequencing we have completed is extremely important for the survival of coral reefs and the future of the oceans. ”
According to Arnau Sebe Pedrós, co-author of the study and leader of crG, "Our work systematically defines the molecular biology of coral cells. This cell profile will help better understand coral responses to temperature rises and ocean acidification, and may even ultimately help design interventions to improve the resilience of the reefs we still have left. This work is also a great example of how single-cell genomics techniques are revolutionizing our understanding of animal biodiversity and evolution, bridging the gap between genomes and organisms. ”
The researchers built a cell map by measuring gene expression in each cell by using a method called single-cell RNA sequencing. In the study, single-cell RNA sequencing was almost limited to species that could be grown under laboratory conditions. Because reef-building corals are difficult to grow under laboratory conditions, Israeli researchers collected corals at different stages of their life cycle in the Gulf of Eilat and then transported them to the Weizmann Institute and the CRG in Barcelona for sequencing and analysis. This study is one of the few studies to perform single-cell analysis in species sampled in the wild.
Reef-building corals are the foundation species of many coral reefs. They begin their life as swimming juveniles, which then disperse and settle into polyangular bodies. Polykeratosomes quickly build a protein-rich matrix, forming a calcium carbonate backbone, which eventually develop into a habitat adult made up of many individual polyangular bodies. Reef-building corals are the main habitat for a wide variety of marine species, which is why coral reefs are considered rainforests of the ocean.
Reef-building corals live in tropical seas by forming symbiotic relationships with photosynthetic algae that live within their cells. Algae provide cells with photosynthetic products, which in turn provide carbon to algae. This symbiotic relationship maintains the high energy requirements for coral growth and reproduction, including the production of its skeleton.
Over the past few decades, coral reefs have been decreasing around the world. The main driver of this decline is the rise in ocean temperature and acidification, which directly affects the symbiotic relationship of corals, leading to coral bleaching, i.e. corals excreting algae that live in their tissues and affecting the formation of skeletons by reducing the rate of calcification.