ogens to reprogram a living host cell. Eukaryotic cells permanently have to cope with environmental cues and to integrate developmental signals. Cell survival or death is the possible outcome. Likely most E. huxleyi blooms are terminated by viral infection via virus-induced apoptosis, as a form of . Indeed, as Bidle et al showed the virus rather makes use of and induces PCD in E. huxleyi for its benefit and proliferation rather than the host inducing PCD to terminate virus proliferation. Recently, it has been shown that BI-1 is required for full susceptibility of barley to powdery mildew, suppressing the defense response of the host. Accordingly BI1 could therefore well be a susceptibility factor of E. huxleyi strains and involved in virus-induced cells apoptosis. LRR motifs are found in many plant and animal proteins and are usually involved in protein-protein interactions and ligand binding. Receptor-ligand 
interactions are very sensitive to point mutations of the DNA-sequence, which can lead to viral resistance/or can allow pathogens to avoid recognition. LRRs are also found in the human Interleukin-1 and Toll-like receptors, which participate in the regulation of immune responses. The identification of MAPK is consistent with recent observations of Marchant et al., which have 12411425 shown that MAPK is a determinant of virus infection even knowing that the MAPK pathway is involved in many substantial regulative processes. It has furthermore been shown, that the vaccinia virus replication requires the MAPK pathway. Animal dsDNA enveloped viruses like herpes simplex virus and vaccinia virus enter their host either via clathrinmediated MedChemExpress DMXB-A endocytosis or by fusion with the plasma membrane. Both processes involve the fusion of the virion envelope with a cell membrane, either the plasma membrane or a vesicle membrane. In general, the first step of virus infection involves attachment of virus particles to host-specific cell surface receptors Genome Variations in Emiliania huxleyi prior to entering the host cell. Once inside the host cell, viruses utilize the host machinery in order to enhance the efficiency of its 15168218 replication process. This is of particular importance for EhV86 which encodes hundreds of genes as compared to only a handful in ssRNA animal viruses. Consequently, the expression of a receptor on the outer surface of the host is a major determinant of the route of entry of the virus into the host and of the patterns of virus spread and pathogenesis in the host. Viruses have evolved to exploit these receptors to gain entry into cells. As each virus is looking for only one specific receptor that fits its attachment protein, the host receptor will, in part, determine the susceptibility of different hosts to the same virus. Previous studies have demonstrated that the lack of receptor expression restricts virus entry and that protein kinases influence virus entry and infectivity, suggesting that the LRR receptor-like protein kinase as well as MAPK and serine/ threonine protein kinase could be involved in virus susceptibility, infection or induced defence mechanisms. We have identified three leucine-rich repeat receptor-like protein kinases and MAPK among the genes present only in virus-susceptible E. huxleyi strains. These genes suggest the route of entry of the virus into the host for the virus-susceptible group and may be similar to above described animal virus infection pathways. It also shows that the lack of them due to possible point muta