title: Transcriptomic characterization of the enzymatic antioxidants FeSOD, MnSOD, APX and KatG in the dinoflagellate genus Symbiodinium.
abstract: BACKGROUND
  The diversity of the symbiotic dinoflagellate Symbiodinium sp., as assessed by genetic markers, is well established. To what extent this diversity is reflected on the amino acid level of functional genes such as enzymatic antioxidants that play an important role in thermal stress tolerance of the coral-Symbiodinium symbiosis is, however, unknown. Here we present a predicted structural analysis and phylogenetic characterization of the enzymatic antioxidant repertoire of the genus Symbiodinium. We also report gene expression and enzymatic activity under short-term thermal stress in Symbiodinium of the B1 genotype.
  
  
  RESULTS
  Based on eight different ITS2 types, covering six clades, multiple protein isoforms for three of the four investigated antioxidants (ascorbate peroxidase [APX], catalase peroxidase [KatG], manganese superoxide dismutase [MnSOD]) are present in the genus Symbiodinium. Amino acid sequences of both SOD metalloforms (Fe/Mn), as well as KatG, exhibited a number of prokaryotic characteristics that were also supported by the protein phylogeny. In contrast to the bacterial form, KatG in Symbiodinium is characterized by extended functionally important loops and a shortened C-terminal domain. Intercladal sequence variations were found to be much higher in both peroxidases, compared to SODs. For APX, these variable residues involve binding sites for substrates and cofactors, and might therefore differentially affect the catalytic properties of this enzyme between clades. While expression of antioxidant genes was successfully measured in Symbiodinium B1, it was not possible to assess the link between gene expression and protein activity due to high variability in expression between replicates, and little response in their enzymatic activity over the three-day experimental period.
  
  
  CONCLUSIONS
  The genus Symbiodinium has a diverse enzymatic antioxidant repertoire that has similarities to prokaryotes, potentially as a result of horizontal gene transfer or events of secondary endosymbiosis. Different degrees of sequence evolution between SODs and peroxidases might be the result of potential selective pressure on the conserved molecular function of SODs as the first line of defence. In contrast, genetic redundancy of hydrogen peroxide scavenging enzymes might permit the observed variations in peroxidase sequences. Our data and successful measurement of antioxidant gene expression in Symbiodinium will serve as basis for further studies of coral health.
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, 6140, New Zealand. thomas.krueger@epfl.ch.|Laboratory for Biological Geochemistry, ENAC, École polytechnique fédérale de Lausanne (EPFL), Lausanne, 1015, Switzerland. thomas.krueger@epfl.ch.
authors.forename: Thomas
authors.initials: T
authors.lastname: Krueger
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, 6140, New Zealand. p.fisher@uq.edu.au.|School of Civil Engineering, University of Queensland, St Lucia, QLD 4072, Australia. p.fisher@uq.edu.au.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Fisher
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, 6140, New Zealand. sbecker@cityweb.de.
authors.forename: Susanne
authors.initials: S
authors.lastname: Becker
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, 6140, New Zealand. steffipont@gmail.com.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Pontasch
authors.affiliation: School of Biological Sciences & ARC Centre of Excellence for Coral Reef Studies, University of Queensland, Brisbane, QLD, 4072, Australia. s.dove@cms.uq.edu.au.
authors.forename: Sophie
authors.initials: S
authors.lastname: Dove
authors.affiliation: Global Change Institute, University of Queensland, Brisbane, QLD 4072, Australia. oveh@uq.edu.au.
authors.forename: Ove
authors.initials: O
authors.lastname: Hoegh-Guldberg
authors.affiliation: Comparative Genomics Centre, School of Pharmacy and Molecular Sciences & ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia. bill.leggat@jcu.edu.au.
authors.forename: William
authors.initials: W
authors.lastname: Leggat
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, 6140, New Zealand. simon.davy@vuw.ac.nz.
authors.forename: Simon K
authors.initials: SK
authors.lastname: Davy
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D057894:Coral Reefs; D004141:Dinoflagellida / Q000145:classification* / Q000201:enzymology / Q000235:genetics*; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010544:Peroxidases / Q000737:chemistry / Q000235:genetics*; D010802:Phylogeny; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics*; D013559:Symbiosis; D059467:Transcriptome
chemical_list: D010544:Peroxidases; D013482:Superoxide Dismutase