SHICK, J.M.*; FERRIER-PAG�S, C.; ALLEMAND, D.; Univ. of Maine, Orono; Centre Scientifique de Monaco; Centre Scientifique de Monaco: UV-induced biosynthesis of algal mycosporine-like amino acids (MAAs) and their conversion to secondary MAAs in the zooxanthellate coral, Stylophora pistillata

UV-na�ve colonies of S. pistillata contained minimal amounts of MAAs. After increasing rapidly during acute UV irradiation, total MAA concentrations stabilized between 14 and 28 days of exposure. Four MAAs reportedly produced collectively by cultures of zooxanthellae (Symbiodinium spp.) of diverse origins were the first to increase in coral colonies, followed by six additional MAAs. Decreases in the four �algal� MAAs between days 14 and 28 were balanced by stoichiometric increases in the six secondary MAAs, suggesting a precursor-product relationship. Chemical blockade of algal MAA-biosynthesis did not prevent the conversion of previously existing algal MAAs to secondary MAAs. Discontinuing UV exposure also caused primary MAAs to decline while secondary MAAs continued to increase, likely a manifestation of different kinetics of up-regulation and turnover of the putative enzymes involved in the de novo biosynthesis of primary MAAs and those converting them to secondary MAAs. The continued accumulation of secondary MAAs after cessation of UV exposure also indicates that UV is not required catalytically but is a signal that up-regulates the conversion enzymes. Zooxanthellae cultured from S. pistillata contained only two MAAs�shinorine, and traces of mycosporine-glycine. Adding a homogenate of host tissue to zooxanthella cultures did not elicit the appearance of additional MAAs, so apparently the difference between the holobiont and the endosymbionts in their MAA complements is not caused by a �host factor� that qualitatively affects the algal biosynthesis of MAAs. Conversion of algal to secondary MAAs in the host seems likely. [Supported by National Geographic Society and Centre Scientifique de Monaco.]