CASTOE, T.A.; STEPHENS, T.S.*; PARKINSON, C.L.; CALESTANI, C.; University of Central Florida; University of Central Florida; University of Central Florida; University of Central Florida: Evidence for complex evolutionary origins of a sea urchin polyketide synthase gene

Polyketide synthases (PKSs) are a large family of multifunctional proteins identified mainly in bacteria, fungi and plants. A polyketide synthase gene (SpPks) was previously isolated from sea urchin embryos and proven to be required for the biosynthesis of the larval pigment echinochrome. To address the evolutionary origin of SpPks, we exhaustively surveyed for PKS homologs/ orthologs /paralogs across all available NCBI accessioned genomic data. Phylogenetic trees based on this amino acid alignment were estimated using maximum parsimony (MP) and Bayesian Markov-chain Monte Carlo (MCMC) phylogenetic methods. We conducted phylogenetic analyses on three partitions of the dataset: 1) the entire alignment, 2) the PKS domain only, and 3) the acyl-transferase (AT) domain only. Phylogenetic results support a complex evolutionary history having lead to SpPks. Two interesting patterns of evolutionary relationships are evident: 1) while sea urchin pks do appear to have orthologs in the chicken and fish, many other clades of animals with whole genome sequenced distinctly lack a pks ortholog (including ecdysozoans, and other vertebrates; 2) the most closely related sequences to the animal clade including sea urchin pks includes only bacteria, lacking orthologs in fungi and other organisms that are closer relatives to this clade. These two features associated with estimates of the phylogeny of sea urchin pks indicate that gene loss (in ancestral fungi, invertebrate and vertebrate lineages) must have occurred. Also, the close relationship between this animal clade and bacteria suggest that horizonal gene transfer between a bacterium and an inclusive ancestor of animal groups sampled (i.e, predating the ancestor of vertebrates and sea urchins) may have occurred.