An international team of scientists in which the Institute of Plant Molecular and Cellular Biology (IBMCP) – a joint center of the Higher Council for Scientific Research (CSIC) and the Polytechnic University of Valencia (UPV) – has discovered more than 20,000 new species of minimal agents including examples of novel giant infectious RNAs, RNA virus hybrids, and circular viroids.

How life originated is one of humanity’s classic questions about which very little is still known. It is accepted that billions of years ago, a world of RNA gave rise to the first self-replicating entities made up of RNA molecules with a double function: informative (equivalent to current DNA) and catalytic (in the form of ribozymes equivalent to enzymes). current protein).

Among the vestiges that have remained from that world of RNA is the ribosome (the ribozyme that decodes genetic information, key in all living beings) or the simplest known biological entities, such as RNA viruses and, above all, tiny circular RNA subviral agents, which confirm that genetic information is not only perpetuated as DNA.

To date, only a few dozen of these minimal circular RNA genomes were known, many with ribozymes, exclusively in plants (viroids and other viroidal RNAs) and animals (Hepatitis Delta), and which were historically associated with the world’s primordial agents. of RNA.

Now, drawing on genetic information collected from across the globe over the past decades, an international research team has discovered more than 20,000 new species of these tiny agents.

“Although we still do not know the potential hosts of most of them, it is confirmed that these vestiges of the precellular RNA world would be much more common than previously thought. Using molecular approaches, it has been shown that some of these tiny RNA genomes circular replicate in various species of fungi associated with plants and soil.These results suggest that we would have in fungi and other fungal-like organisms the possible evolutionary origin of plant viroids and the Delta-type agents of human hepatitis described more than 40 years,” explains Marcos De la Peña, a CSIC researcher at the IBMCP, in a statement.

As De la Peña points out, the discovery of this new world of RNA with minimal circular genomes will allow us not only to better understand what that primordial RNA world could have been like, but also to discover new forms of infectious agents that may still survive today, replicating in very hosts. simple as bacteria, archaea or protists, “being the evolutionary origin of many of the viral and viroidal agents that until now we only knew about in more evolved beings such as plants and animals”.

Together with the IBMCP, the National Research Council (Italy); Stanford University (USA); the Pasteur Institute (France) and the University of Toronto (Canada), among others.