Journal of Biology and Today's World

Disclosing the Impact of Tiny RNA Molecules in the Agriculture

Romy Iqbal^{* *}Correspondence: Romy Iqbal, Department of Molecular Biotechnology, University of Angers, Cedex Angers, France, Email:

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Description

Viroids, often overshadowed by their larger and more complex counterparts like viruses and bacteria, are remarkable and enigmatic entities in the world of microbiology. These tiny, infectious RNA molecules are devoid of a protein coat, yet they have the ability to cause diseases in plants. First discovered in the 1960s, viroids have since been the subject of extensive research, revealing their unique biology, diverse structures, and significant implications for agriculture. This overview explores the world of viroids, focusing on their history, structure, replication, pathogenicity, and the ongoing efforts to manage viroid-induced diseases.

Structure of viroids

Viroids are unique in their simplicity. They consist of a single-stranded, circular RNA molecule that is relatively short, typically ranging from 246 to 401 nucleotides. Unlike viruses, viroids lack the coding capacity for proteins, and they do not possess a lipid envelope or capsid protein. Instead, their pathogenicity arises from their RNA structure and the host's cellular machinery.

Viroids are categorized into two families based on their secondary structures:

Pospiviroidae: Members of this family have a rod-like secondary structure. They include well-known viroids like the Potato Spindle Tuber Viroid (PSTVd) and Tomato Chlorotic Dwarf Viroid (TCDVd).

Avsunviroidae: These viroids have a branched secondary structure. The Avocado Sunblotch Viroid (ASBVd) and Peach Latent Mosaic Viroid (PLMVd) are examples of viroids in this family.

Replication mechanism

Despite their minimalistic nature, viroids implement interesting reproduction mechanism. Viroids enter host plant cells through wounds or natural openings and are then processed by cellular enzymes. The key steps in viroid replication are as follows:

Rolling circle replication: Viroids replicate via a rolling circle mechanism. The viroid RNA serves as a template for RNA polymerase enzymes within the host cell. These enzymes synthesize multiple copies of the viroid RNA, forming a concatemeric RNA molecule.

Ligation: The concatemeric RNA is cleaved into individual viroid RNA molecules. These individual viroids are then ligated by host enzymes to form circular viroid RNA molecules.

Infection spread: The newly formed circular viroid molecules are ready to infect neighboring cells and propagate the infection within the host plant.

Pathogenicity

Viroids primarily cause diseases in plants. They can infect a wide range of crop species, including potatoes, tomatoes, avocadoes, citrus fruits, and many others. Viroid-induced diseases manifest through a variety of symptoms, including stunted growth, leaf distortion, chlorosis (yellowing), and necrosis (cell death). These symptoms can lead to reduced crop yields and economic losses for agriculture.

The pathogenicity of viroids arises from their interference with normal cellular processes. They disrupt the regulation of gene expression and metabolism in host plants. Viroids can also trigger the host's defense mechanisms, leading to an overproduction of Reactive Oxygen Species (ROS) and the activation of RNA silencing pathways. These  responses contribute to the disease symptoms observed in infected plants.

Conclusion

Viroids, despite their tiny size and lack of protein coat, are unique and potent agents of causing disease in the field of microbiology. Their discovery challenged existing paradigms and opened up new opportunities of research into the molecular mechanisms of infection and replication. Understanding viroid biology is crucial for agriculture, as viroids continue to threaten crop production and food security. Ongoing research efforts aim to develop effective strategies for viroid detection, prevention, and management, with the ultimate goal of mitigating their impact on plants and agriculture. As viroid research advances, it promises to provide valuable insights into the broader field of RNA-based pathogens and their interactions with host organisms.