b'Carnegie Science|Fall 2020 15Carnegies Tingting Xiang (far left) was lead author on the study. She is now an assistant professor at the University of North Carolina, Charlotte. From second from left to right are Carnegie coauthors Sophie Clowez, Rick Kim, and Arthur Grossman. Images courtesy Carnegie Institution for ScienceHow Corals Limit Populationsof their Symbiotic AlgaeCorals depend on their symbiotic relationships with the algae that they host. New work published in Nature Communications by a team including Carnegies Tingting Xiang, Sophie Clowez, Rick Kim, and Arthur Grossman indicates how sea anemones, which are closely related to coral, control the size of their algal populations residing within their tissue. Like corals, anemones host photosynthetic algae, which can convert the Suns energy into chemical energy. An alga shares some of the sugars that it produces with its host, which in turn provides the alga with other necessary nutrients such as carbon dioxide, phosphorus, sulfur, and nitrogen. However, the molecular mechanisms underlying this relationship have remainedThis is a fluorescence image of the sea anemone Exaiptasia mysterious. pallida, which was used in this study. The red dots each represent We are eager to understand the precisefluorescence from a single symbiotic alga, Breviolum minutum. interactions between the alga and its host becauseImage courtesy Tingting Xiang, Carnegie Institution for Scienceif algal populations within the host disappearas happens during bleaching events caused by oceanmore photosynthetically produced sugars to the warming or pollutionthe corals and anemonesanemone. The anemones then use the carbon lose access to vital sustenance and may not bebackbones of these molecules to retain and recycle able to survive. On the flip side, rampantits nitrogen-containing ammonium waste.population growth of symbiotic algae couldThis arrangement both results in more robust overtax the hosts metabolism and make themanemone growth and limits the amount of nitrogen susceptible to disease. Grossman explained. Weavailable to the algae. So, the team demonstrated want to understand how corals and anemonesthat the dynamics of nutrient exchange between maintain a balance, which may enable us to assistthe algae and the anemone change as the algal threatened reef communities. population increases. The researchersincluding StanfordOur work elucidates how the association Universitys Erik Lehnert, Jan DeNofrio, and Johnbetween anemones and algae, or coral and algae, Pringle, as well as UC-Riversides Robertensures that this symbiotic relationship remains Jinkersonrevealed that limiting the supply ofstable and beneficial to both partner organisms, shared nitrogen is key to an anemones ability tosaid lead author Xiang, who is now an assistant control the size of its symbiotic algal population. professor at the University of North Carolina, The team demonstrated that as theCharlotte. With ongoing research, we hope to even SUPPORT: populations of the symbiotic alga Breviolumbetter understand the various mechanisms and The Gordon and Betty Mooreminutum Exaiptasiaspecific regulators that are crucial for integrating , hosted by the anemone Foundation supported this work.pallida the metabolisms of these two organisms, which , reached high densities, they expressed The Stanford Genome Sequencing Service Center of theelevated levels of cellular products associatedcould eventually allow for the transplantation of Stanford Center for Genomics and Personalized Medicine, whichwith nitrogen limitation. hardier algae into bleached coral and also for is supported by the NationalCrucially, as the population of algae withinmanipulating both corals and algae to have greater Institutes of Health, provided high-throughput sequencing.the host tissue increases, they deliver more andtolerance to adverse conditions.Image courtesy iStockphoto.com/para827'