The surprising discovery of entities smaller than viruses raises profound questions about what life is and how it got started<\/p>\n
Theodor Diener had a problem. It was 1967, and he and a colleague had successfully isolated the infectious agent causing potato spindle tuber disease, which devastates crops. But it wasn\u2019t like anything they recognised. Although they called it a virus, it didn\u2019t behave like one.<\/p>\n
It took Diener four years to demonstrate that the mysterious entity was something even simpler than a virus: a single \u201cnaked\u201d molecule that could infect the cells of potato plants and thereby reproduce. He suggested calling it a viroid. It was the smallest replicating agent ever identified. At a stroke, Diener had expanded our understanding of life in the microscopic world.<\/p>\n
You might think that such a dramatic discovery would go, er, viral. Yet hardly anyone noticed. Apart from a few other plant pathologists, the scientific world largely forgot about viroids for half a century. So obscure were they that, in 2020, when Benjamin Lee at the National Center for Biotechnology Information in Bethesda, Maryland, was advised to try looking into viroids, he had never even heard of them.<\/p>\n