Gene duplication, loss and selection in the evolution of saxitoxin biosynthesis in alveolates☆

摘要: A group of marine dinoflagellates (Alveolata, Eukaryota), consisting ∼10 species the genus Alexandrium, Gymnodinium catenatum and Pyrodinium bahamense, produce toxin saxitoxin its analogues (STX), which can accumulate in shellfish, leading to ecosystem human health impacts. The genes, sxt, putatively involved STX biosynthesis, have recently been identified, however, evolution these genes within is not clear. There are two reasons for this: uncertainty over phylogeny dinoflagellates; that sxt many Alexandrium other dinoflagellate genera known. Here, we determined STX-producing based on a concatenated eight-gene alignment. We presence, diversity sxtA, domains A1 A4 sxtG 52 strains further 43 thirteen alveolates. confirmed presence high sequence conservation domain A4, 40 (35 1 Pyrodinium, 4 Gymnodinium) 8 dinoflagellates, absence from non-producing species. found three paralogs A1, widespread distribution sxtA1 non-STX producing indicating duplication events this gene. One paralog, clade 2, may be particularly related biosynthesis. Similarly, appears generally restricted species, while amidinotransferase gene were dinoflagellates. investigated role positive (diversifying) selection following sxtG, negative clades sxtA1, suggesting they functionally constrained. Significant episodic diversifying was some 3 pressure diversification function.