Theoretical arguments and empirical evidence consistently show that all cellular life forms can serve as hosts for multiple viruses. Viruses exhibit enormous diversity, in fact, the sequence diversity of a single virus family may exceed the diversity of the entire domain of cellular life, thus making the identification of the deep evolutionary relationships and ancestry of viral genes extremely challenging.
On July 13, 2022, the National Center for Biotechnology Information published a report titled “The logic of virus evolution”< /span>‘s article, This research explains the macroevolution of viruses with a simple functional logic, and defines the evolutionary process of viruses:
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Gene gain that yields the surprising diversity of viral genomes is governed by the simple logic of cellular proteins adapting to functions critical or beneficial for viral reproduction.
This adaptation involves the direct acquisition of a cellular function or extension, that is, a change in the function of the acquired protein, usually accompanied by the original activity. eliminate.
This logic of repurposing cellular proteins determines the macroevolutionary trajectory of viruses, including the emergence of new viruses in interactions with the arms race group.
01< strong>The arms race between viruses and host cells
The standard concept of virus evolution is that in a perennial arms race, viruses and cellular hosts locked together. In this race, the host evolves and diversifies anti-virus defense mechanisms, and the virus responds with an evolved anti-defense system that suppresses the host’s defenses.
Complementary to the arms race is the widespread gene flow between viruses and their hosts. Viruses often acquire host genes and use them to play a role in viral reproduction and virus-host interactions, whereas hosts capture viral genes and repurpose them for defense and other cellular functions.
In contrast to horizontal gene transfer between organisms, gene flow between virus and host is a key feature of virus reproduction This process occurs strictly intracellularly, bringing the replicated viral genome into close contact with the host’s genome and mRNA.
From these perspectives, the researchers studied how viruses capture host genes and how nearly 4 billion years of virus-host co-evolution shaped viral genomes.
02viral marker protein VHPs
The researchers first identified a small group of viruses through comparative analysis of the viral proteome marker proteins (VHPs). These proteins are widely distributed in different viruses. Replication-associated VHPs play a role in viral genome replication, while structural VHPs play a key role in virion including genome packaging to capsid formation.
Since the amino acid sequences of viral capsid protein CPs typically evolve much more rapidly than replication-related VHPs, researchers have established different Evolutionary relationships of virome CPs to infer their origin. It was finally found that VHPs were most likely evolved from cellular ancestors in the early stages of life evolution, after the appearance of modern types of cells.
0 >3 Virus evolution framework
In view of the huge size of viruses and their genes Diversity, the researchers eventually contained many evolutionary routes into a simple and logical conceptual framework:
The evolution of viruses is shaped by a core set of essential proteins involved in genome replication that date back to the precellular stages of evolution.
In addition to these apparently primitive proteins, the evolution of viruses can be described as the capture of genes from the hostand other mobile genetic elements whose genes play various roles in horizontal transmission between viruses and in viral reproduction.
In general, genes captured from the host follow two distinct evolutionary paths: when Proteins evolved by direct recruitment when they performed the same functions as their ancestors in viral reproduction; by dissimilation when host genes were repurposed for virus-specific functions.
However, the direct recruitment and extroversion of host genes for viral function show general convergence, and different viruses can independently acquire different characteristics. related or distantly related genes. This high rate of convergence appears to be dictated by a relatively narrow range of functions involved in viral replication and expression. The functional diversity of genes involved in virus-host interactions is much greater.
In general, the larger the viral genome, the more helper functions it encodes. Growth of the viral genome is the result of the acquisition of various helper genes that increase the fitness or operational autonomy of the virus, although their available functions are highly dependent on the host cell. To say that is largely redundant.
The logic behind this apparent functional redundancy in viruses may involve the ability to overcome host constraints on these functions in antiviral defenses span>. Furthermore, this redundant function can enhance the host’s metabolic potential to maintain active viral reproduction and ensure that proteins best suited for viral reproduction are localized through specialized subcellular targeting signals.
In summary, the evolutionary logic of viruses is determined by the key biological characteristics of the virus, that is, specialized Sexual intracellular parasitism. This way of life provides the virus with numerous opportunities to directly invade the host’s activities, and also determines the necessity of overcoming a large number of host defense systems. Instead, viral genes are captured by the host in many cases, and some protein functions that have evolved in the viral genome environment are expanded by the host, demonstrating the extensive bidirectional transfer of genes and functions between viruses and cells.
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