What are viroids?

Viroids are indeed best described as single-stranded RNA molecules that do not encode proteins. They are the smallest known agents of infectious disease and are primarily known for affecting plants. Unlike viruses, viroids lack a protective protein coat and consist solely of a short, circular RNA sequence. This RNA can replicate within host cells, leading to diseases in plants without producing any proteins of their own.

Viroids exploit the host's cellular machinery for replication, and this unique mechanism contributes to their pathogenic effects. The simplicity of viroids contrasts with the more complex structures of viruses and other pathogens that typically involve protein encoding and protective layers. This simplicity is key to understanding how viroids operate, as they rely entirely on the host's cell mechanisms for propagation and do not have the genetic machinery to produce proteins independently.