"Diatoms are the most successful group of eukaryotic phytoplankton in the modern ocean. Recently completed whole genome sequences have revealed a wealth of information about the evolutionary origins and metabolic adaptations that may have led to their ecological success. A major finding is that they have acquired genes both from their endosymbiotic ancestors and by horizontal gene transfer from marine bacteria. This unique melting pot of genes encodes novel and largely unexplored capacities for metabolic management. The project will address the current gap in knowledge about the physiological functions of diatom gene products and about the evolutionary mechanisms that have led to diatom success in contemporary oceans. We will exploit genome-enabled approaches to pioneer new research topics addressing:1. How has diatom evolution enabled interactions between chloroplasts and mitochondria that have provided diatoms with physiological and metabolic innovations?2. What are the relative contributions of DNA sequence variation and epigenetic processes in diatom adaptive dynamics?By combining these questions, we will uniquely be able to identify sentinel genes that have driven major physiological and metabolic innovations in diatoms, and will explore the mechanisms that have selected and molded them during diatom evolution. We will focus our studies largely on diatom responses to nutrients, in particular nitrate and iron, and will exploit the advantages of Phaeodactylum tricornutum as a model diatom species for reverse genetics. The proposed studies will revisit textbook understanding of photosynthesis and nitrogen metabolism, and will refine hypotheses about why diatoms dominate in contemporary ocean settings. By placing our studies in evolutionary and ecological contexts, in particular by examining the contribution of epigenetic processes in diatoms, our work will furthermore provide insights into how the environment selects for fitness in phytoplankton."