Exploring the phenotypic landscape of algal resistance to lytic viral infection

Phytoplankton are unicellular photoautotrophs that form the basis of marine food webs and account for ~50% of the global net primary production. Phytoplankton can form large-scale oceanic blooms, which play key roles in global biogeochemical cycles. The seasonal blooms are often terminated by lytic viruses, yet some “seed” population can survive viral infection and serve as the next bloom inoculum. In recent years, an arsenal of resistance mechanisms and active defense systems against viruses was discovered in bacteria. However, in diverse algal lineages, resistance mechanisms against viruses are poorly understood. Here, we investigated molecular components of resistance mechanisms in the tractable host-virus model system, the bloom-forming algae Emiliania huxleyi and its large dsDNA virus, E. huxleyi virus (EhV). We generated extensive transcriptomic datasets of algal strains that exhibit a spectrum of resistance and susceptibility phenotypes to viral infection. By 3’ RNA sequencing we compared the inherent differences in gene expression between the susceptible and resistant strains, and identified potential genes related to resistance. Next, we conducted bulk 3’ RNA-seq analysis during a detailed time course of viral infection, through the stages of population demise and recovery. We are currently analyzing the cellular response of E. huxleyi to infection and aim to track the transcriptomic patterns of the newly discovered resistance-related genes. This work will shed light on algal resistance mechanisms to viral infection, how they emerge in the population and how they shape bloom succession in the ocean.