Image of a cell

Theodor O. Diener

  • National Medal of Science
  • Biological Sciences

For the discovery of viroids, the smallest known agent of infectious disease. This discovery has opened new avenues of molecular research into some of the most serious diseases afflicting plants, animals, and humans.

Around the time Theodor O. Diener was born in the early 1920s, farmers began to notice a disease was causing their potatoes to shrivel and become deformed. Unable to pin down the true cause of the disease, many plant pathologists assumed a virus was to blame. It wasn’t until 50 years after the disease first described that Diener, who was working in the Department of Agriculture, discovered the true cause — a viroid.

About an 80th the size of a typical virus, viroids behave similar to viruses in that they both hijack a cell and use it to make copies of itself. Other than having a much smaller size and being of a much simpler makeup, viroids also differ from viruses in the fact that they lack a protein coat. Before Diener discovered them, scientists did not even know viroids existed and believed an organism without protein could not replicate itself.

Since Diener’s discovery, scientists have found more than 30 species of viroids affecting various types of plants. Viroids may offer insight into the early stages of life on Earth, when many scientists believe life was solely RNA-based. In 1989, Diener proposed that the viroids may be relics of such a time, and scientists have continued to study this possibility in the years since.

By Jacob Kerr