key term - Viroid

Definition

A viroid is a small, infectious agent composed solely of a short strand of circular RNA without any protein coating. Unlike viruses, viroids do not encode proteins and rely entirely on the host's cellular machinery for replication. They primarily infect plants, leading to various diseases that can significantly impact agricultural productivity.

5 Must Know Facts For Your Next Test

1. Viroids were first discovered in 1971 by Theodor O. Diener while studying the tobacco plant and are known to be the smallest infectious agents.
2. Unlike viruses that contain both RNA or DNA and a protein coat, viroids consist only of a circular RNA molecule that can be as short as 246 nucleotides.
3. Viroids replicate within host cells by hijacking the host's RNA polymerase, which leads to the production of multiple copies of the viroid RNA.
4. They can cause a wide range of diseases in plants, often resulting in symptoms like stunting growth, yellowing leaves, and reduced yield.
5. Viroids are transmitted through mechanical means, such as grafting or contact with infected tools and plants, making them significant threats to agriculture.

Review Questions

• How do viroids differ from traditional viruses in terms of structure and replication mechanisms?
  • Viroids differ from traditional viruses primarily in their structure; they consist solely of a short circular strand of RNA without any protein coating. While viruses typically have a protein coat and can encode several proteins necessary for their life cycle, viroids do not encode proteins at all. Instead, they rely on the host's cellular machinery for replication, using the host's RNA polymerase to produce copies of their RNA.
• Discuss the impact of viroid infections on agricultural systems and how these infections can be managed.
  • Viroid infections can severely impact agricultural systems by reducing crop yields and quality due to diseases they cause in plants. Symptoms include stunted growth and poor fruit development. Management strategies include using certified disease-free planting materials, implementing strict sanitation practices to prevent mechanical transmission, and utilizing resistant plant varieties when available. Monitoring and early detection are also crucial for managing viroid-related diseases effectively.
• Evaluate the significance of viroids in the study of molecular biology and plant pathology.
  • The significance of viroids extends beyond their role as plant pathogens; they provide insights into molecular biology due to their unique structure and replication mechanisms. Studying viroids helps researchers understand RNA biology and the interactions between pathogens and host plants. Furthermore, insights gained from viroid research can lead to advancements in genetic engineering and biotechnology aimed at enhancing plant resistance to various diseases.

Related terms

RNA:

Ribonucleic acid, a molecule essential for coding, decoding, regulation, and expression of genes, serving as the genetic material in some viruses and viroids.

Pathogen: An organism, such as a viroid, virus, or bacteria, that causes disease in its host, often leading to detrimental effects on health or agriculture.

Chronic Canker Disease: A disease in plants caused by the viroid known as Apple scar skin viroid, characterized by symptoms like cankers on stems and poor fruit development.