viroid

noun

1. an infectious agent of plants similar to a virus but consisting of only a short, single strand of RNA without a protein coat.

noun

1. any of various infective RNA particles, smaller than a virus and known to cause some plant diseases

n.

1. An infectious particle, smaller than a virus, that consists solely of a strand of RNA and is capable of causing disease in plants.

1. An infectious agent that consists solely of a single strand of RNA and causes disease in certain plants. Viroids lack the protein coat (known as a capsid) of viruses and are the smallest known infectious agents. Containing only about 250 to 375 base pairs, they are much smaller than the smallest genomes of viruses and have no genes for encoding proteins. After invading a host cell, viroids are thought to mimic the cell’s DNA, so that the cell’s RNA polymerase replicates them in the nucleus. Viroids are believed to cause disease by interfering with the host cell’s gene regulation. They are destructive to many important commercial plants, including potatoes, tomatoes, cucumbers, coconuts, and chrysanthemums.