"Emiliania huxleyi is a cosmopolitan phytoplankton belonging to the coccolithophores, eukaryotic phototrophs that dominate the modern oceans. Coccolithophores are considered to be among the largest producers of calcite on earth, and as such, are a major vehicle for the transport of carbon to the deep sediments. They are important producer of DMS, a gas thought to strongly influence climate regulation. E.huxleyi forms massive annual blooms in the oceans that are routinely infected and terminated by giant double-stranded DNA lytic viruses (Phycodnaviridae). Currently, very little information is available on the molecular basis for the intricate interactions between E.huxleyi and its specific viruses. We are still lacking a fundamental understanding of the life cycles of Phycodnaviridae within their hosts and of the genes involved in lytic versus chronic infections. In this project we will investigate the co-regulation of intracellular signal transduction pathways involved in host/virus during infection. We will specifically examine the role of chemical signals (infochemicals) and their potential role in mediating the interface between host and virus. The recent availability of genomic resources for the E. huxleyi host and its specific virus 86 (EhV86) provide an unprecedented opportunity to explore cellular pathways triggered during execution of viral infection and to gain insights into the origin of programmed cell death (PCD) in unicellular organisms. We will analyze natural coccolithophore blooms with our newly-discovered biomarkers as “fingerprints” to evaluate the importance of viral infection during bloom succession. This work has great potential to reveal novel insights into the molecular mechanisms of virus-host interactions, including the role of virally-induced infochemicals and their role in regulating phytoplankton cell fate. Ultimately,we hope to gain a better understanding of the chemical co-evolution of host–virus arms race in the marine environment."