What type of acellular agent is a naked strand of RNA that infects plants?

A naked strand of RNA that infects plants is classified as a viroid. Viroids are unique amongst infectious agents as they consist solely of a short strand of circular or linear RNA without any protein coat. This distinguishes them from viruses, which typically contain both genetic material (either RNA or DNA) and a protein capsid.

Viroids can disrupt the normal functioning of plant cells by interfering with the host's RNA, leading to various plant diseases. The mechanism by which viroids cause pathogenesis is thought to involve the hijacking of the plant's cellular machinery, affecting growth and development. This ability to cause disease using only naked RNA highlights the simplicity and specificity of viroids compared to more complex agents like viruses and bacteriophages.

In contrast, bacteriophages are viruses that specifically infect bacteria and consist of both nucleic acid and protein components. Viruses are more complex and also contain a nucleic acid core, along with a surrounding protein coat, while prions are misfolded proteins that cause neurodegenerative diseases in animals. These differences clarify why the accurate description of a plant-infecting acellular agent is a viroid.