title: Proteomics links the redox state to calcium signaling during bleaching of the scleractinian coral Acropora microphthalma on exposure to high solar irradiance and thermal stress.
abstract: Shipboard experiments were each performed over a 2 day period to examine the proteomic response of the symbiotic coral Acropora microphthalma exposed to acute conditions of high temperature/low light or high light/low temperature stress. During these treatments, corals had noticeably bleached. The photosynthetic performance of residual algal endosymbionts was severely impaired but showed signs of recovery in both treatments by the end of the second day. Changes in the coral proteome were determined daily and, using recently available annotated genome sequences, the individual contributions of the coral host and algal endosymbionts could be extracted from these data. Quantitative changes in proteins relevant to redox state and calcium metabolism are presented. Notably, expression of common antioxidant proteins was not detected from the coral host but present in the algal endosymbiont proteome. Possible roles for elevated carbonic anhydrase in the coral host are considered: to restore intracellular pH diminished by loss of photosynthetic activity, to indirectly limit intracellular calcium influx linked with enhanced calmodulin expression to impede late-stage symbiont exocytosis, or to enhance inorganic carbon transport to improve the photosynthetic performance of algal symbionts that remain in hospite. Protein effectors of calcium-dependent exocytosis were present in both symbiotic partners. No caspase-family proteins associated with host cell apoptosis, with exception of the autophagy chaperone HSP70, were detected, suggesting that algal loss and photosynthetic dysfunction under these experimental conditions were not due to host-mediated phytosymbiont destruction. Instead, bleaching occurred by symbiont exocytosis and loss of light-harvesting pigments of algae that remain in hospite. These proteomic data are, therefore, consistent with our premise that coral endosymbionts can mediate their own retention or departure from the coral host, which may manifest as "symbiont shuffling" of Symbiodinium clades in response to environmental stress.
authors.affiliation: From the ‡King's College London Proteomics Facility, Institute of Psychiatry, London SE5 8AF, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Weston
authors.affiliation: §Centre for Marine Microbiology and Genetics, Australian Institute of Marine Science, PMB No. 3 Townsville MC, Townsville, Queensland,4810 Australia. ‖Institute of Pharmaceutical Science, Kings College, Strand, London WC2R 2LS, United Kingdom.
authors.forename: Walter C
authors.initials: WC
authors.lastname: Dunlap
authors.affiliation: §Centre for Marine Microbiology and Genetics, Australian Institute of Marine Science, PMB No. 3 Townsville MC, Townsville, Queensland,4810 Australia. ¶ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville QLD 4811 Australia.
authors.forename: Victor H
authors.initials: VH
authors.lastname: Beltran
authors.affiliation: ‡‡Section for Bioinformatics, Department of Biochemical Engineering, Faculty of Food Technology & Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia.
authors.forename: Antonio
authors.initials: A
authors.lastname: Starcevic
authors.affiliation: ‡‡Section for Bioinformatics, Department of Biochemical Engineering, Faculty of Food Technology & Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia.
authors.forename: Daslav
authors.initials: D
authors.lastname: Hranueli
authors.affiliation: From the ‡King's College London Proteomics Facility, Institute of Psychiatry, London SE5 8AF, UK.
authors.forename: Malcolm
authors.initials: M
authors.lastname: Ward
authors.affiliation: ‖Institute of Pharmaceutical Science, Kings College, Strand, London WC2R 2LS, United Kingdom, **Department of Chemistry, King's College Strand, London WC2R 2LS, United Kingdom, Franklin-Wilkins Building, Stamford Street, London SE1 9NH, UK paul.long@kcl.ac.uk.
authors.forename: Paul F
authors.initials: PF
authors.lastname: Long
mesh_terms: D020418:Algal Proteins / Q000032:analysis; D000818:Animals; D037421:Anthozoa / Q000502:physiology* / Q000528:radiation effects; D020013:Calcium Signaling; D000458:Cyanobacteria / Q000502:physiology*; D005786:Gene Expression Regulation; D010084:Oxidation-Reduction; D010788:Photosynthesis; D040901:Proteomics / Q000379:methods*; D062327:Skin Lightening Preparations; D013312:Stress, Physiological; D013472:Sunlight; D013559:Symbiosis; D013696:Temperature
chemical_list: D020418:Algal Proteins; D062327:Skin Lightening Preparations