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Keywords:

  • carotenoid;
  • dinoflagellates;
  • P457;
  • peridinin;
  • Symbiodinium ;
  • symbiosis

The molecular structure of the carotenoid lactoside P457, (3S,5R,6R,3′S,5′R,6′S)-13′-cis-5,6-epoxy-3′,5′-dihydroxy-3-(β-d-galactosyl-(1[RIGHTWARDS ARROW]4)-β-d-glucosyl)oxy-6′,7′-didehydro-5,6,7,8,5′,6′-hexahydro-β,β-caroten-20-al, was confirmed by spectroscopic methods using Symbiodinium sp. strain NBRC 104787 cells isolated from a sea anemone. Among various algae, cyanobacteria, land plants, and marine invertebrates, the distribution of this unique diglycosyl carotenoid was restricted to free-living peridinin-containing dinoflagellates and marine invertebrates that harbor peridinin-containing zooxanthellae. Neoxanthin appeared to be a common precursor for biosynthesis of peridinin and P457, although neoxanthin was not found in peridinin-containing dinoflagellates. Fucoxanthin-containing dinoflagellates did not possess peridinin or P457; green dinoflagellates, which contain chlorophyll a and b, did not contain peridinin, fucoxanthin, or P457; and no unicellular algae containing both peridinin and P457, other than peridinin-containing dinoflagellates, have been observed. Therefore, the biosynthetic pathways for peridinin and P457 may have been coestablished during the evolution of dinoflagellates after the host heterotrophic eukaryotic microorganism formed a symbiotic association with red alga that does not contain peridinin or P457.