Viruses infecting higher plants are typically small RNA viruses that encode only a few genes. Although small viruses have recently been discovered that infect algae, many viruses infecting eukaryotic algae are huge dsDNA viruses with genomes ranging from 160 to 560 kb with up to 600 protein-encoding genes and are the subject of this review. These large viruses (family Phycodnaviridae), are found in aqueous environments throughout the world and play dynamic, albeit largely undocumented, roles in regulating algal communities such as the termination of massive algal blooms commonly referred to as red and brown tides.
This review focuses on one genus in the Phycodnaviridae, the chloroviruses, which are large, icosahedral, plaque-forming, dsDNA-containing viruses that replicate in certain unicellular, chlorella-like green algae. Their structure, their initial stages of infection, and many of their genes resemble bacteriophages more than viruses that infect eukaryotes – i.e. they are not your everyday plant virus.
Chloroviruses: not your everyday plant virus. Trends Plant Sci. Nov 17 2011
Viruses infecting higher plants are among the smallest viruses known and typically have four to ten protein-encoding genes. By contrast, many viruses that infect algae (classified in the virus family Phycodnaviridae) are among the largest viruses found to date and have up to 600 protein-encoding genes. This brief review focuses on one group of plaque-forming phycodnaviruses that infect unicellular chlorella-like green algae. The prototype chlorovirus PBCV-1 has more than 400 protein-encoding genes and 11 tRNA genes. About 40% of the PBCV-1 encoded proteins resemble proteins of known function including many that are completely unexpected for a virus. In many respects, chlorovirus infection resembles bacterial infection by tailed bacteriophages.