VIRUSES OF SEAWEEDS

Seaweeds is the common collective name for multicellular or macro-algae that play very important ecological roles in many aquatic communities. Major concerns have been raised about the health and sustainability of ecosystems reliant on key seaweed species in response to increasing anthropogenic influences, changing environmental conditions, and pathogen-related effects. To date, viral infection has been reported in at least 54 species of seaweeds. These data are comprised primarily of transmission electron microscopy observations of virus-like particles (VLPs) and viral sequences isolated from seaweed material (either from seaweed-associated virus particles or integrated in seaweed DNA as endogenous viral elements). Most VLPs in red seaweed are small (<80 nm) and icosahedral, and, therefore, not distinctive enough to be identified to a particular family or species. In contrast, the large (typically >150 nm) icosahedral VLPs reported in several brown and one green seaweed likely belong to the distinctive giant or megaviruses known as nucleo-cytoplasmic large DNA viruses (NCLDVs). The available evidence suggests that: (i) brown seaweeds and other stramenopile groups are infected by NCLDVs, (ii) red seaweeds are infected by dsRNA viruses related to fungal viruses, and (iii) Archaeplastida (plants, red, and green seaweed) was infected by NCLDVs in the past. The best studied seaweed virus genus is the NCLDV Phaeovirus. Currently, members of the genus Phaeovirus are known to infect seven species from four families of the order Ectocarpales and putatively infect eight species from three families of the order Laminariales, commonly known as kelp. This chapter seeks to provide an overview of the current state of seaweed virology research with a focus on the expansion in Phaeovirus diversity.