"The coccolithophorid Emiliania huxleyi is a globally important phytoplankton species with a major role in ocean carbon cycling and the production of the climate active gas DMS, yet almost all information on this organism comes from the diploid, not the haploid phase. We propose to characterize the inherent and dynamic properties of the haploid and diploid stages and address whether sex and programmed cell death represent alternative outcomes of stress response pathways. Our research is motivated by the recent completion of the whole genome sequence of E. huxleyi by the Joint Genome Institute, the new availability of pure haploid cultures, the new discovery by the host team that haploid cells are completely resistant to viruses infecting the diploid phase, and the recent discoveries that the many phytoplankton, including E. huxleyi, can exhibit programmed cell death in response to abiotic and biotic stress, which may affect a major fraction of phytoplankton-fixed carbon. We will take an integrated approach synthesizing genomics, transcriptomics, flow cytometry, cell biology and physiology. This research proposed research will improve understanding of the functional importance of phytoplankton life cycles and programmed cell death, improve annotation of the completed E. huxleyi genome, and be placed in an environmental context by ongoing work on the environmental abundance of haploid and diploid E. huxleyi stages. The proposed research will strengthen existing collaborations and establish new collaborations between Europe and the USA and within Europe. The applicant brings skills in flow cytometry, quantitative PCR, and genome annotation to the prospective host scientist (de Vargas) at Station Biologique de Roscoff. This project will reinforce European excellence in phytoplankton research on an organism with significant importance to climate regulation. The project will enhance European competitiveness in post-genomic research on environmentally important organisms."