What are Viroids?
Viroids are small RNA particles which infect plants. Viroids are remarkable for their extremely tiny size (only a few hundred nucleic acid bases, the smallest with only 220) relative to the larger viruses, which contain at least 2,000 bases. Viroids were discovered and given their name by Theodor Diener, a plant pathologist at the Agricultural Research Service in Maryland, in 1971. Viroids are a subviral agent about 80 times smaller than typical viruses. Their discovery was considered a major breakthrough in 20th century biology. Unlike viruses, viroids lack a protein coat, and don’t even encode any protein products in their structure. Traditional viruses hijack the central genetic machinery of the cell and cause it to pump out copies of the virus. Viroids instead take control of RNA polymerase II, an enzyme that synthesizes messenger RNA within the cell, and uses that to produce copies of itself. Prior to the discovery of viroids, it was thought that agents lacking protein could never