How Giant Viruses Fuel the Genetic Evolution of Organisms

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Viruses are small intruders that trigger a large range of illness, from rabies to tomato identified wilt infection and, most just recently, COVID-19 in human beings. But infections can do more than generate illness — and not all infections are small.

Large infections, particularly those in the nucleo-cytoplasmic big DNA infection household, can incorporate their genome into that of their host — drastically altering the hereditary makeup of that organism. This household of DNA infections, otherwise referred to as “giant” infections, has actually been understood within clinical circles for rather a long time, however the degree to which they impact eukaryotic organisms has actually been shrouded in secret — previously.

“Viruses play a central role in the evolution of life on Earth. One way that they shape the evolution of cellular life is through a process called endogenization, where they introduce new genomic material into their hosts. When a giant virus endogenizes into the genome of a host algae, it creates an enormous amount of raw material for evolution to work with,” stated Frank Aylward, an assistant teacher in the Department of Biological Sciences in the Virginia Tech College of Science and an affiliate of the Global Change Center housed in the Fralin Life Sciences Institute.

Mohammad ‘Monir’ Moniruzzaman, a postdoctoral scientist in Aylward’s laboratory, research studies endogenous viral components, which are pieces or entire series of raw viral DNA that have actually been placed into the contaminated host’s genome.

Together, Aylward and Moniruzzaman have actually just recently found that endogenous viral components that stem from huge infections are a lot more typical in chlorophyte green algae than formerly believed.

Their findings will be released today (November 18, 2020) in Nature.

Giant Virus Virginia Tech Researchers

From delegated right: Frank Aylward, Mohammad ‘Monir’ Moniruzzaman, Alaina Weinheimer, Carolina Alejandra Martínez Gutiérrez. Image thanks to Alex Crookshanks. Credit: Virginia Tech

Chlorophytes, a group of green algae, are a crucial group of photosynthetic organisms that are at the base of the food cycle on numerous communities and produce huge quantities of food and oxygen throughout the world. Chlorophytes prosper in our lakes and ponds — and their characteristics with huge infections along with their distinct evolutionary history, were main to Aylward and Moniruzzaman’s research study.

Chlorophyte algae are close loved ones of land plants, and studying their interactions with huge infections might shed some light on the functions that the infections played throughout the early advancement of plants.

“We now know that endogenous viral elements are common across chlorophytes, which makes you think that plants might also interact with these giant viruses. There is some data that suggests that some early plants, like moss and ferns, did experience these endogenization events over the evolutionary timeline. But we are not exactly sure about the extent of this phenomenon in other early plants,” stated Moniruzzaman, the very first author on this released paper.

To discover more about the occurrence of endogenous viral components in algae, Moniruzzaman and Aylward carried out a bioinformatic analysis on the sequenced genomes of various algae groups.

They found that 24 of the 65 genomes that were evaluated had some sort of viral signatures in their genomes, which stemmed from duplicated endogenization of unique infections. In one algal organism, Tetrabaena socialis, scientists discovered that around 10 percent of its genes stem from an infection in the nucleo-cytoplasmic big DNA infection household.

Although the endogenization of infections have actually been well studied, research studies have actually primarily been restricted to little RNA infections, such as the human immunodeficiency infection (HIV), the retrovirus that is accountable for triggering gotten immunodeficiency syndrome (HELP).

Aylward and Moniruzzaman’s research study is among the very first to put a spotlight on big eukaryotic DNA infections, which marks a significant shift in the field.

Electron micrograph picture of a AaV, a huge infection that contaminates and eliminates a unicellular alga that triggers damaging algae flowers. Giant infections that come from the exact same group as AaV can often place their genomes into the genomes of their hosts. Image thanks to Chuan Xiao and Yuejiao Xian, University of Texas at El Paso; Steven W. Wilhelm and Eric R. Gann, University of Tennessee, Knoxville.

“These large endogenous viral elements are a lot more common than previously thought. Now that we have a systematic analysis, other researchers are really going to start to pay attention. This study shows that endogenous viral elements are pretty common, and so it might possibly be a common mechanism of genome evolution. I think these results will broaden our view on the role of giant viruses as mere agents of host mortality to significant players in host genome evolution,” stated Moniruzzaman.

Now that Moniruzzaman and Aylward have actually verified that endogenization is taking place in bigger infections, they question what conditions are triggering these infections to inject EVEs into green algae in the very first location — and why the hosts reveal no indications of declining them.

“We don’t know what the mechanism is or how the DNA is being maintained, but it is possible that the endogenization is a random, almost accidental process. And once the viral DNA is endogenized, it can alter the evolutionary dynamics of the host, and that it could further influence the evolution of that lineage,” stated Aylward.

The concept that there is a possibly advantageous relationship at play in between the host and its infection is of specific interest to Moniruzzaman.

“There might be a reason as to why the host is keeping these viral genomes within them. It’s not like these viral genes are causing the hosts to become unsuccessful or unable to survive in the environment. So that’s the thing: Are the endogenous viral elements beneficial to the host? And how are they getting in there and staying in there?” asked Moniruzzaman.

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



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