The <scp>RNA</scp> virosphere: How big and diverse is it?

Abstract

Three years into the COVID-19 pandemic, humanity continues to be reminded of the impact of RNA viruses on the economy and society. Discovery-based surveys during these last 3 years have built upon decades of advances and have been reshaping knowledge of the RNA virosphere. For example, four parallel studies, exploring thousands of metatranscriptomes from diverse environments, have transformed our understanding of the ribovirian kingdom Orthornavirae, which harbours viruses that replicate via virus-encoded RNA-directed RNA polymerases (RdRps) (Figure 1A). Together, these four studies have augmented the known RNA virosphere by more than an order of magnitude, mapped orthornaviran RNA virus ecologies on a global scale, and perhaps uncovered a key missing link in our understanding of how early life evolved billions of years ago. However, a recent rarefaction analysis indicates that RNA virus discovery, orthornaviran or otherwise, is not even close to saturation (Figure 1B).