Viroid

Definition

A viroid is a small, circular, and infectious RNA molecule that lacks a protein coat and is capable of replicating within the cells of certain plants. Viroids are the smallest known plant pathogens and are distinct from viruses, which have a protein coat and more complex genetic material.

5 Must Know Facts For Your Next Test

1. Viroids are the smallest known plant pathogens, with genomes ranging from 246 to 467 nucleotides in length.
2. Viroids do not encode any proteins and instead rely on host cell machinery for their replication and spread.
3. Viroids can induce a variety of disease symptoms in plants, including stunting, chlorosis, and necrosis, depending on the specific viroid and host plant.
4. Viroids are primarily transmitted through mechanical means, such as contaminated tools, or by vegetative propagation of infected plant material.
5. Unlike viruses, viroids do not have a protein coat and are not encapsulated, which makes them more susceptible to environmental degradation.

Review Questions

• Explain the key differences between viroids and viruses in terms of their genetic material and structural features.
  • The primary difference between viroids and viruses is their genetic material and structural organization. Viroids are composed solely of a small, circular, and infectious RNA molecule, lacking a protein coat or any other structural components. In contrast, viruses have a more complex genetic material, typically consisting of DNA or RNA, and are encapsulated within a protein coat. This structural difference allows viruses to infect a wider range of host organisms, while viroids are limited to infecting certain plant species.
• Describe the role of host cell machinery in the replication and spread of viroids.
  • Viroids, unlike viruses, do not encode any proteins and instead rely entirely on the host cell's machinery for their replication and spread. Viroids hijack the host cell's transcription and translation processes to replicate their RNA genome and produce new viroid particles. This dependence on the host cell's resources makes viroids more vulnerable to environmental degradation and less capable of infecting a wide range of host organisms compared to viruses, which have their own protein-based mechanisms for replication and transmission.
• Analyze the potential impact of viroids on plant health and agriculture, and discuss strategies for their detection and management.
  • Viroids can have a significant impact on plant health and agricultural productivity, as they can induce a variety of disease symptoms, such as stunting, chlorosis, and necrosis, in infected plants. The economic consequences of viroid-induced plant diseases can be substantial, particularly for crops that are susceptible to specific viroid strains. To mitigate the impact of viroids, strategies for their detection and management are crucial. This includes the development of reliable diagnostic tools, the implementation of strict biosecurity measures to prevent the spread of infected plant material, and the exploration of genetic resistance or other control methods to limit the proliferation of viroids in agricultural settings.

Related terms

Virusoid:

A virusoid is a small, circular, and infectious RNA molecule that is dependent on a helper virus for its replication and transmission, unlike viroids which are self-replicating.

Prion:

A prion is an infectious agent composed primarily of a misfolded protein that can induce other, normally folded proteins of the same type to also misfold, leading to various neurodegenerative diseases.

Satellite RNA: Satellite RNAs are small, circular, and subviral RNA molecules that depend on a helper virus for their replication and transmission, similar to virusoids but distinct from self-replicating viroids.