Criss-Crossing Viruses Give Rise to Peculiar Hybrid Variants 2 November 2020

Criss-crossing viruses give rise to peculiar hybrid variants 2 November 2020

variant.

Varsani, a virologist at the Arizona State Univeristy Biodesign Center for Fundamental and Applied Microbiomics, is deeply intrigued with these new viruses, which are starting to crop up in greater abundance and diversity in a wide range of environments.

"It is great to see the research groups that first identified cruciviruses around the same time teaming up for the sharing and mining of Cruciviruses are a hybrid form containing both RNA and metagenomic data with an aim to identify a larger DNA genomic material. Here, a single-stranded DNA diversity of cruciviruses," says Varsani, an virus (yellow) containing a Rep protein sequence, which associate professor with ASU School of Life directs the virus' replication, borrows genetic information Sciences. from an RNA virus (blue) , specifically, a coding sequence for the RNA virus's capsid protein.The result is New virus in town a chimerical virus with both DNA and RNA components--a crucivirus (seen in the right panel). Crucivirus sequences were identified by Varsani's Credit: Shireen Dooling for the Bioodesign Institute. colleague and co-author Kenneth M. Stedman and his group at Portland State University. The team detected the viruses flourishing in an extreme environment—Boiling Springs Lake (BSL) in Lassen For millions of years, viruses have participated in a Volcanic National Park, Northern California. Around far-flung, import-export business, exchanging the same time, Varsani and Mya Breitbart's fragments of themselves with both viral and non- research group identified a crucivirus in a dragonfly viral agents and acquiring new features. What sample from Florida. these tiny entities lack in outward complexity, they make up for with their astonishing abilities to swap Since their discovery in 2012, cruciviruses have out modular genomic components and ceaselessly been found in diverse environments around the reinvent themselves. world, from lakes in upstate New York and Florida, to the Antarctic and deep-sea sediments. Some 80 In new research appearing in the journal mBio, distinct cruciviruses had been identified, prior to the Arvind Varsani and his colleagues investigate a current study, which expands the number to 461. recently discovered class of viruses that have taken the characteristic versatility of the viral world The first cruciviruses were identified using a to new heights. technique known as viral metagenomics, in which viral genetic material obtained directly from the Referred to as cruciviruses, these minute forms environment is sequenced rather than being reveal a fusion of components from both RNA and cultivated or cultured from a host species or natural DNA viruses, proving that these previously distinct reservoir. genomic domains can, under proper conditions, intermingle, producing a hybrid or chimeric viral The results of these early investigations revealed

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peculiar genetic sequences, radically distinct from specialized features that give the virus its ability to anything that had been seen before. This puncture the host cell membrane and inject viral sequences clearly displayed the signature of a DNA nucleic acid into the cell's cytoplasm. virus, yet also contained a gene that appeared to be derived from an RNA virus. Analysis indicates that the capsid protein of cruciviruses is closely related to the capsid protein Using a shotgun approach to trawl through a of another virus from the family Tombusviridae —a potentially vast sequence space, viral single-stranded RNA virus known to infect plants. metagenomics enables researchers to identify all of This hybrid viral character, containing both DNA- the genomic patterns present in an environmental and RNA virus derived coding components, is what sample, then separate out distinct viral sequences, makes cruciviruses so unique. like a fisherman retrieving a variety of sea creatures from his net. Uncertain origins

The technique has revolutionized the discipline of But how did a run-of-the-mill cressdnavirus come to virology. In addition to identifying a galaxy of acquire its RNA virus capsid protein coding previously unknown viruses, metagenomics has sequence? This remains an issue of considerable offered up exciting clues about genetic diversity debate, though presumably some form of lateral and is helping to unlock some of the secrets of viral gene transfer occurred. evolution, all without the need to initially isolate viral species or cultivate viruses in the lab. Viruses can acquire genes from their immediate progenitors, the way genetic traits are passed from Form and function human parents to their offspring. Viruses, however, are far more genetically promiscuous, collecting Cruciviruses belong to a broader class of viruses new genes from the cells they infect, from other known as CRESS, (for circular Rep-encoding single-unrelated viruses and even from bacterial stranded) DNA viruses which have recently been symbionts. (The phenomenon is also common classified into the phylum Cressdnaviricota. The among bacteria, which can use horizontal gene defining characteristic of such viruses is their mode transfer to acquire antibiotic resistance.) of replication, which relies on a specific component, known as the Rep protein. The Rep protein is Through some such mechanism, a cressdnavirus important for guiding the replication method of acquired an RNA virus capsid-like gene, creating these viruses, known as rolling circle DNA the first crucivirus. It also appears that various replication. Presence of the Rep protein and rolling cruciviruses have actively exchanged functional circle replication pinpoints a virus as belonging to elements among themselves, further scrambling cressdnaviruses and helps researchers untangle their evolutionary history. the devilishly complex relationships and lineages found in the viral world. While the HOW of crucivirus DNA-RNA recombination remains mysterious, the WHY may In addition to the Rep found in cressdnaviruses, be more straightforward. Clearly, the ability to cruciviruses contain another centrally important borrow genetic traits from such distantly related feature—a capsid protein that is similar to that viral sources could provide single-stranded DNA previously found only in RNA viruses. Capsids are viruses with a considerable adaptive edge. vitally important, forming the outer shell or envelope that encloses the virus's identity—its genetic Collector's edition sequence. The capsid shelters the vital nucleic acids sequestered within from digestion by host cell In the current study, researchers explored a vast enzymes, enables virus particles to attach dataset including 461 cruciviruses and 10 capsid- themselves to host cells and allows viruses to encoding circular genetic elements identified from evade host cell defenses. Finally, capsids contain varied environments and organisms, making this

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the most expansive investigation of crucivirus virus groups may arise though prolific recombination sequences yet undertaken. events between distantly related forms.

The samples were found in environments ranging More information: Ignacio de la Higuera et al, from temperate lakes to permafrost and lurking Unveiling Crucivirus Diversity by Mining within organisms including red algae and Metagenomic Data, mBio (2020). DOI: invertebrates. The study points to the 10.1128/mBio.01410-20 stramenopiles/alveolates/Rhizaria or SAR supergroup, (a diverse assemblage of eukaryotes, including many photosynthetic organisms) as the plausible candidate hosts for these unusual viruses, Provided by Arizona State University though this has yet to be verified.

After examining the windfall of sequences, the researchers assembled similarity networks of cruciviral proteins with related viruses to try to better understand the twisting evolutionary paths that may have given rise to them, finding a rich cross-pollination of viral traits between many large families of viruses including Geminiviridae, Circoviridae, Nanoviridae, Alphasatellitidae, Genomoviridae, Bacilladnaviridae, Smacoviridae, and Redondoviridae.

Intriguing questions remain

The findings may provide new insights into the early transition from RNA as the primary hereditary molecule of life to the adoption of more complex DNA genomes that has come to dominate life in the cellular world. The existence and behavior of cruciviruses suggest that viruses may have played a crucial role in this all-important transition, acting as a kind of genomic bridge between the RNA and DNA worlds, during the earliest emergence of life, though much more work is needed to explore these possibilities.

Recombining in endless forms, viruses have become the planet's most ubiquitous biological entities, affecting every living organism and occupying every ecological niche. Increasingly, viruses are revealing themselves not only as agents of disease but as drivers of species evolution and vital actors in the molding of ecosystems.

The expanded abilities of cruciviruses to borrow genomic elements from the most far-flung regions of viral sequence space suggest that entirely new

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APA citation: Criss-crossing viruses give rise to peculiar hybrid variants (2020, November 2) retrieved 28 September 2021 from https://phys.org/news/2020-11-criss-crossing-viruses-peculiar-hybrid-variants.html

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