Polyketides and fatty acids: Decoding the polyketide and fatty acid synthases evolution in <i>Amphidinium carterae</i> (Dinophyceae)

Amphidinium carterae is a harmful bloom-forming dinoflagellate, a key source of polyketide metabolites-such as amphidinolides, amphidinols and amphidinins-and a producer of fatty acids. The biosynthesis of these compounds is mediated by polyketide synthases (PKSs) and fatty acid synthases (FASs). This study aimed to identify PKS and FAS genes present in the transcriptome of A. carterae and to understand the biosynthesis of polyketides and fatty acids, as well as the evolution of these secondary metabolites. A total of 24 transcripts encoding single-domain KS and seven multi-domain PKS transcripts were identified, including one with three KS domains and another comprising nine modules, the largest PKS reported in dinoflagellates to date. Phylogenetic analyses revealed a distinct clade separating single-domain and multi-domain PKSs in dinoflagellates, all of which resembled a type I PKSs. The modular architecture observed in A. carterae was like other dinoflagellates, suggesting a conserved domain structure likely shaped by gene duplication events. Seven transcripts were related to FASs; each transcript encoded an individual type II FAS, with a subcellular localization in the plastid. Gene duplication events appear to be a critical factor in the evolution of dinoflagellate PKSs. Furthermore, the similarity in multi-domain PKS architecture across different dinoflagellate species indicates that polyketide biosynthesis shares a common evolutionary origin within this group.