Viroid

Article By:

Horst, R. K. Department of Plant Pathology, Cornell University, Ithaca, New York.

Last reviewed:August 2021

DOI:https://doi.org/10.1036/1097-8542.733200

A small, infectious, nucleic acid particle containing an independently replicating single-stranded circular RNA that can infect certain flowering plants. Viroids are the smallest known disease agents and can infect many monocot and dicot flowering plants (angiosperms) [see illustration]. The single-stranded circular ribonucleic acids (RNAs) found in viroids consist of 246–467 nucleotides, with an estimated molecular weight (the sum of the atomic weights of a molecule's constituent atoms) of as little as 1.0–1.3 × 10⁴ (in contrast, conventional plant virus genomes have molecular weights of approximately 2 × 10⁶). Conventional viruses are made up of nucleic acids encapsulated in proteins (capsids), whereas viroids are uniquely characterized by the absence of a capsid. In spite of their small size, viroid RNAs can replicate and produce characteristic disease syndromes when introduced into cells. So far, the viroids thus far identified are associated only with plants. Possibly, viroids may be found to affect other forms of life, including humans. For example, it is possible that viroid infectious agents are involved in instances where a viral etiology of disease has been assumed, but where no causal virus has been identified. See also: Nucleic acid; Nucleotide; Plant; Plant cell; Plant pathology; Plant virus; Ribonucleic acid (RNA); Virus

The content above is only an excerpt.