MSGID: 1:317/3 6270b02e   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Discovery about coral-algal symbiosis could help coral reefs recover   
   after bleaching events    
    Algae's ability to establish symbiosis in coral without photosynthesis   
   could help fight coral bleaching    
      
     Date:   
         May 2, 2022   
     Source:   
         University of California - Riverside   
     Summary:   
         Although photosynthesis by algae is a key part of the symbiotic   
         relationship it is not required to initiate symbiosis. The discovery   
         adds to the little-understood relationship between cnidarians and   
         algae at the molecular level and offers insight into how to jump   
         start the symbiotic relationship between the two organisms after a   
         bleaching event. It could also lead to strategies that might prevent   
         warmer oceans from breaking the symbiotic relationship between   
         the two organisms and saving what remains of the world's corals.   
      
      
      
   FULL STORY   
   ==========================================================================   
   Corals are keystone species for reef and marine ecosystems but coral   
   bleaching due to climate change and ocean warming is killing them. A   
   new open access study by researchers at the University of California,   
   Riverside, aims to shed light on how to reverse the damage and save   
   corals.   
      
      
   ==========================================================================   
   Corals, together with sea anemones and jellyfish, belong to a group   
   of animals called cnidarians that receive some of their nutrients   
   through a symbiotic relationship with photosynthetic algae living inside   
   their cells. High ocean temperatures cause a breakdown in the symbiosis   
   resulting in a 'bleached' coral that has expelled the algae. If symbiosis   
   is not initiated within a few weeks, the coral will starve to death.   
      
   The new study finds that although photosynthesis by algae is a key part of   
   the symbiotic relationship it is not required to initiate symbiosis. The   
   discovery adds to the little-understood relationship between cnidarians   
   and algae at the molecular level and offers insight into how to jump   
   start the symbiotic relationship between the two organisms after a   
   bleaching event. It could also lead to strategies that might prevent   
   warmer oceans from breaking the symbiotic relationship between the two   
   organisms and saving what remains of the world's corals.   
      
   Cnidarians form a mutualistic symbiosis with photosynthetic algae from   
   the dinoflagellate family Symbiodiniaceae that live inside of their host   
   cells. The algae perform photosynthesis, fix carbon dioxide into sugars,   
   and then give that to their hosts. Some species of coral are completely   
   dependent on the food they receive from their algal symbionts and will   
   die without it.   
      
   In return the algae receive nutrients like nitrogen and phosphorus from   
   the prey that the host catches. Photosynthesis is a key part of this   
   symbiotic relationship, but it was not known if this symbiosis can form   
   without photosynthesis.   
      
   Robert Jinkerson, an assistant professor of chemical and environmental   
   engineering at UCR, and Tingting Xiang, an assistant professor of   
   biological sciences at the University of North Carolina at Charlotte,   
   led a team to make the first mutants in Symbiodiniaceae algae -- isolate   
   mutants that lacked the ability to photosynthesize -- and use these   
   mutants to investigate symbiosis with cnidarians "We were very excited   
   to be able to generate six photosynthetic mutants and then use those   
   mutants to start to probe the symbiosis between these algae and their   
   hosts," Jinkerson said.   
      
      
      
   ==========================================================================   
   The team introduced the mutant algae into seawater tanks that contained   
   sea anemones (Exaiptasia pallida) that had not yet established symbiosis   
   with any algae. After just one day the algae could already be found   
   within the sea anemone's tentacles, even without photosynthesis.   
      
   To learn if the algae could survive in sea anemone host tissue without   
   photosynthesis for longer periods of time, the researchers infected   
   some sea anemones in darkness with mutant and non-mutant algae and kept   
   them in darkness for six months. Even after six months, algal cells were   
   still observable in the sea anemone's tissues. Although able to infect   
   the host cells and maintain itself for six months, the algae did not   
   reproduce and proliferate in number.   
      
   The group also tested four other species of algae known to form symbiotic   
   relationships with the sea anemones and found that they too could initiate   
   symbiosis in the dark.   
      
   Jinkerson, Xiang, and their colleague Masayuki Hatta in Japan then   
   introduced the algae in darkness into a tank containing juvenile polyps of   
   a stony coral, Acropora tenuis. The algae infected the coral successfully   
   in the dark.   
      
   Unexpectedly, the algae were able to proliferate in the coral tissues   
   without photosynthesis, something not observed in the sea anemones.   
      
   Finally, to learn if the pattern held true for the third member of the   
   cnidarian group, the researchers added the algae to a darkened tank   
   of upside- down jellyfish (Cassiopea xamachana) polyps. Once again,   
   the algae infected the polyps, though not as successfully as in the sea   
   anemone and coral.   
      
      
      
   ==========================================================================   
   Symbiosis establishment can proceed without photosynthesis in   
   coral, jellyfish, and sea anemone hosts, but different aspects of the   
   relationship, such as proliferation of the algae without photosynthesis,   
   depends on the specific host-algae relationship.   
      
   "Our study highlights the power of forward genetic approaches to probe   
   cnidarian Symbiodiniaceae symbiosis and provides a promising platform   
   to answer key questions in symbiosis and ultimately develop strategies   
   to save corals," said Xiang.   
      
   The discovery that photosynthesis is not essential to begin symbiotic   
   relationships is a step toward finding ways to help cnidarians survive   
   climate change.   
      
   "Time is of the essence regarding the protection of the coral reefs,   
   and our hope is that these mutants will allow ourselves and others to   
   increase the overall pace towards this goal," said co-author Joseph Russo,   
   a doctoral student in Jinkerson's lab.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_California_-_Riverside. Original written by Holly   
   Ober. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Robert E. Jinkerson, Joseph A. Russo, Casandra R. Newkirk, Andrea L.   
      
         Kirk, Richard J. Chi, Mark Q. Martindale, Arthur R. Grossman,   
         Masayuki Hatta, Tingting Xiang. Cnidarian-Symbiodiniaceae symbiosis   
         establishment is independent of photosynthesis. Current Biology,   
         2022; DOI: 10.1016/ j.cub.2022.04.021   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220502170913.htm   
      
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