RESEARCH ARTICLE Diversity and Evolutionary History of Iron Metabolism Genes in Diatoms

Ferroproteins arose early in Earth’s history, prior to the emergence of oxygenic photosyn-thesis and the subsequent reduction of bioavailable iron. Today, iron availability limits pri-mary productivity in about 30 % of the world’s oceans. Diatoms, responsible for nearly half of oceanic primary production, have evolved molecular strategies for coping with variable iron concentrations. Our understanding of the evolutionary breadth of these strategies has been restricted by the limited number of species for which molecular sequence data is avail-able. To uncover the diversity of strategies marine diatoms employ to meet cellular iron de-mands, we analyzed 367 newly released marine microbial eukaryotic transcriptomes, which include 47 diatom species. We focused on genes encoding proteins previously identified as having a role in iron management: iron uptake (high-affinity ferric reductase, multi-copper oxidase, and Fe(III) permease); iron storage (ferritin); iron-induced protein substitutions (fla-vodoxin/ferredoxin, and plastocyanin/cytochrome c6) and defense against reactive oxygen species (superoxide dismutases). Homologs encoding the high-affinity iron uptake system components were detected across the four diatom Classes suggesting an ancient origin fo