Viroids and Viroid-Like Agent Diversity Revealed

A team of researchers at the National Library of Medicine (NLM) and collaborating academic research centers have developed a computational pipeline to identify and better understand viroids and viroid-like closed circular RNAs (cccRNAs, which are also called circular RNAs) . This is a type of single-stranded RNA that, unlike linear RNA, forms a tight, continuous loop. The findings were published in the journal A cell.

Viroids are circular RNAs of only 250 to 400 nucleotides and are the smallest and simplest of known viruses and are believed to cause infection only plants. The different types of RNAs such as viroid and viroid are not well understood, which has led researchers to investigate more about these viruses and their potential abundance in other environments and hosts.

By searching a collection of 5,131 metatranscriptomes and 1,344 plant transcriptomes for viroid-like cccRNAs, the researchers discovered 11,378 cccRNAs spanning 4,409 species. This finding was a fivefold increase compared to previously known substances such as viroids.

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Within this diverse collection, the researchers found that this unique group of microbes is not limited to a few plants as previously thought, but is common and abundant in areas of all species and most regions, compared to the most well-known RNA viruses. In addition, other human relatives of Hepatitis Delta Virus (Hepatitis D) were discovered, which sheds light on the origin of this important human virus, as well as on different types of viruses.

“This work opens up new avenues for researchers around the world,” said Eugene V. Koonin, PhD, study co-author and senior investigator in the Computational Biology Division of NLM’s Intramural Research Program. He added: “We are currently conducting a follow-up investigation.”

Reference: Lee BD, Neri U, Roux S, et al. Mining metatranscriptomes reveals a vast world of viroid-like circular RNAs. A cell. 2023. do: 10.1016/j.cell.2022.12.039

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