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Viroids: Small but Mighty Infectious Agents

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Viroids are the simplest known infectious agents, consisting of circular RNA without protein-coding capacity, affecting plant health and agriculture. They replicate uniquely within host cells, influencing our understanding of RNA biology and gene regulation. Studies on viroids like PSTVd and CEVd offer insights into RNA replication and host-pathogen interactions, with significant implications for crop diseases and economic impact.

Exploring Viroids: The Simplest Infectious Agents

Viroids are the smallest infectious agents known, consisting only of a short strand of circular, single-stranded RNA without any protein-coding capacity. These pathogens are capable of infecting and causing diseases in higher plants, leading to economic losses in agriculture. The study of viroids has shed light on the molecular mechanisms of RNA replication and has raised questions about the evolution of early life forms, potentially offering a glimpse into the RNA world hypothesis, which suggests that RNA molecules were precursors to current life forms based on DNA and proteins.
Close-up view of blue-gloved hands holding a petri dish with colorful microbial colonies on agar, against a blurred lab bench with scientific equipment.

The Mechanism of Viroid Replication

Viroid replication is a unique process that takes place within the nucleus or chloroplasts of the host plant cell and involves two key stages: transcription and processing. The host's RNA polymerase II transcribes the viroid RNA into a longer intermediate, which then undergoes self-cleavage through ribozyme activity inherent to the viroid's RNA structure. The resulting linear RNA molecules are subsequently ligated to form new circular viroids. This replication mechanism is distinct from that of viruses and does not involve the production of proteins.

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00

The ______ world hypothesis posits that ______ molecules were the forerunners to modern life forms that utilize DNA and proteins.

RNA

RNA

01

Viroid replication sites in host cells

Occurs in nucleus or chloroplasts of host plant cells.

02

Role of host's RNA polymerase II in viroid replication

Transcribes viroid RNA into a longer intermediate.

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