Organization and evolution of the virosphere and the replicator space

Area of Science:

• Virology
• Evolutionary Biology
• Genomics

Background:

• Viruses are obligate intracellular symbionts that numerically dominate the biosphere and represent a major reservoir of genetic diversity.
• Viral genomes encompass all forms of RNA and DNA, suggesting ancient origins linked to primordial replicators.
• Recent advancements in metagenomics and metatranscriptomics have unveiled unprecedented viral diversity within the virosphere.

Purpose of the Study:

• To synthesize current understanding of the global virosphere's organization.
• To outline major trends and events in viral evolution.
• To present a high-level taxonomy of viruses.

Main Methods:

• Review of extensive metagenomic and metatranscriptomic data mining.
• Analysis of viral hallmark genes and shared gene families.
• Synthesis of existing literature on virus-host coevolutionary dynamics.

Main Results:

• Viruses exhibit immense diversity with multiple independent origins, lacking universal genes but sharing hallmark genes that define viral groups.
• Virus-host coevolution is characterized by reciprocal "arms races" and gene exaptation, where hosts and viruses exchange genetic material.
• The virosphere is globally organized, with significant evolutionary trends and distinct viral taxonomic groups.

Conclusions:

• Viral evolution is inseparable from host evolution, driven by continuous adaptation and genetic exchange.
• Understanding viral diversity, origins, and evolution is crucial for comprehending biosphere organization and dynamics.
• The study provides a framework for classifying and understanding the vast and complex world of viruses.