How giant viruses fuel the genetic evolution of organisms

Viruses are small invaders that cause a wide range of diseases, from rabies to the spotted tomato virus. COVID-19: in humans. But viruses can do more than cause disease և Not all viruses are small.

Major viruses, especially in the nuclear-cytoplasmic majority DNA: A family of viruses can integrate their genome into their host by dramatically altering the genetic makeup of that organism. This family of DNA viruses, otherwise known as “giant” viruses, has long been known in scientific circles, but the extent to which they affect eukaryotic organisms is still shrouded in mystery.

“Viruses play a major role in the evolution of life on Earth. One of the ways in which cell life evolves is through a process called endogenous process, in which they introduce new genomic material into their hosts. “When a giant virus endogenizes the host algae genome, it creates a huge amount of raw material for working with evolution,” said Frank Eylward, an assistant professor in the Department of Biological Sciences at the Tech College of Science in Virginia.

Mohammad Monir Moniruzaman, a postdoctoral researcher at Aylmard Laboratory, studies endogenous viral elements, which are fragments of raw viral DNA or whole sequences that are inserted into the genome of an infected host.

Together, Elvard և Moniruzaman recently discovered that endogenous viral elements from giant viruses are much more common in chlorophytic green algae than previously thought.

Their results will be published today (November 18, 2020) Nature:,

A huge virus in the state of Virginia

From left to right: Frank Eylvard, Mohammad Monir Moniruzaman, Alaina Weinheimer, Carolina Alejandra Martinez Gutierrez. Image by Alex Crookshanks. Loan: Virginia Tech

Chlorophytes, a group of green algae, are a powerful group of photosynthetic organisms that form the basis of the food chain of many ecosystems, producing enormous amounts of food and oxygen on the planet. Chlorophytes develop in our lakes, ponds, their dynamics with giant viruses, as well as their unique evolutionary history, were important in Alivard և Moniruzaman’s research.

Chlorophytic algae are close relatives of terrestrial plants, and the study of their interactions with giant viruses may shed some light on the roles that viruses played in the early development of plants.

“We now know that endogenous viral elements are present in chlorophytes, which makes you think that plants can also interact with these giant viruses. There is some evidence to suggest that some early plants, such as mosses and fruits, experienced these endogenous events during the evolutionary period. But we are not sure about the extent of this phenomenon in other early plants, ”said Moniruzaman, the first author of this paper.

To learn more about the prevalence of endogenous viral elements in algae, Moniruzzaman և Aylward performed bioinformatics analysis on the sequential genomes of different groups of algae.

They found that 24 of the 65 genomes analyzed had certain types of viral signatures in their genomes that resulted from the repetitive endogenization of different viruses. In one algae organism, Tetrabaena socialis, researchers found that about 10 percent of its genes are derived from a virus in the large nuclear cytoplasmic DNA family.

Although the endogenousity of viruses has been well studied, studies have generally been limited to small ones RNA viruses such as human immunodeficiency virus (HIV), retrovirus, which is responsible for the development of acquired immune deficiency syndrome (AIDS).

Ellward և Moniruzaman’s study is one of the first to focus on large eukaryotic DNA viruses, which is a major breakthrough in the field.

Electron micrograph of the giant AaV virus, which infects and kills unicellular algae, causing harmful algae to thrive. Giant viruses that belong to the same AaV group can often insert their genomes into the genomes of their hosts. Image courtesy of El Paso, University of Texas at Chuan Xiao Yuehyao Xian; Steven Wilhelm և Eric R. Ganymede, University of Tennessee, Knoxville.

“These large endogenous viral elements are much more common than previously thought. Now that we have a systematic analysis, other researchers are really starting to pay attention. This study shows that endogenous viral elements are quite common, so it may be a common mechanism of genome evolution. “I think these results will deepen our view of the role of giant viruses as mere agents of host mortality, for key players in the evolution of the host genome,” Moniruzaman said.

Now that Moniruzzaman և Aylward has confirmed that endogenization occurs in larger viruses, they wonder what conditions cause those viruses to first introduce EVEs into green algae, and why hosts show no signs of rejecting them.

“We do not know what the mechanism is or how DNA is stored, but it is possible that endogenization is a random, almost random process. “And when viral DNA is endogenous, it can change the evolutionary dynamics of the recipient, so that it can have a further impact on the development of that lineage.”

Of particular interest to Moniruzaman is the idea that there is a potentially beneficial relationship between the host and his virus.

“There may be a reason why the host stores these viral genomes. It is not that these viral genes become hostile or fail to survive in the environment. So that’s the thing. Are endogenous viral elements beneficial to the host? And how do they get in there and stay there? ” Moniruzaman asked.

Reference. 2020 On November 18, Nature:,
DOI: 10.1038 / s41586-020-2924-2:

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