Virus Replication in Multicellular Photosynthetic Life Forms

Abstract

Photosynthesis originated from endosymbiosis of cyanobacterial‐like organisms, which ultimately became chloroplasts. It is an ancient process that has evolved to produce a variety of types of photosynthetic eukaryotic organisms that we find today, that is, terrestrial plants and aquatic algae. Similarly, viruses are considered ancient with growing evidence for the theory that viruses arose before the last universal cellular ancestor. Despite both photosynthetic and virus life forms having evolved side by side since time immemorial, plants and eukaryotic algae have very different viruses that infect them. Very little similarities are shared in both the types and nature of the infection. In fact, viruses of photosynthetic eukaryotic multicellular organisms exemplify how different algae are from plants. Key Concepts Photosynthetic organisms appeared 3.2–3.5 billion years ago. The most abundant and diverse viruses have dsDNA genomes. NCLDVs are estimated to have evolved 2–2.7 billion years ago, close to the origin of eukaryotes. The known host range of NCLDVs includes multiple eukaryotic kingdoms, which is the broadest of any dsDNA virus group, which usually infect a single kingdom. The family Phycodnaviridae (‘phyco’=algae, ‘dna’=DNA, ‘viridae’=virus family) are NCLDVs that infect algae. Most plant viruses (66.7%) have ssRNA genomes. Plant viruses use long‐distance transport as a key mechanism for transmission. This would be possible in some macroalgae which have vascular tissue (sieve tubes), such as kelps, but these sieve tubes are less extensive than the xylem and phloem of plants. The NCLDVs are a major algal virus group which may be absent in plants, which are instead predominately infected by ssRNA viruses. Eukaryotic multicellular macroalgae or seaweed are predominantly infected by dsDNA viruses.