Novel Insights into Evolution of Protistan Polyketide Synthases through Phylogenomic Analysis

Polyketide synthase (PKS) enzymes are large multi-domain complexes that structurally andfunctionally resemble the fatty acid synthases involved in lipid metabolism. Polyketide biosynthesisof secondary metabolites and hence functional PKS genes are widespread among bacteria, fungi andstreptophytes, but the Type I was formerly known only from bacteria and fungi. Recently Type I PKSgenes were also uncovered in the genomes of some alveolate protists. Here we show that the newlysequenced genomes of representatives of other protist groups, specifically the chlorophytesOstreococcus tauri, O. lucimarinus, and Chlamydomonas reinhardtii, and the haptophyte Emilianiahuxleyi also contain putative modular Type I PKS genes. Based on the patchy phylogeneticdistribution of this gene type among eukaryotic microorganisms, the question arises whether theyoriginate from recent lateral gene transfer from bacteria. Our phylogenetic analyses do not indicatesuch an evolutionary history. Whether Type I PKS genes originated several times independently duringeukaryotic evolution or were rather lost in many extant lineages cannot yet be answered. In any case,we show that environmental genome sequencing projects are likely to be a valuable resource whenmining for genes resembling protistan PKS I genes.

John, U., Beszteri, B., Derelle, E., Van de Peer, Y., Read, B., Moreau, H., Cembella, A. (2008) Novel Insights into Evolution of Protistan Polyketide Synthases through Phylogenomic Analysis. Protist 159(1):21-30.

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