Viroids and Prions

Infectious agents include bacteria, fungus, protozoans, viruses, viral vectors, and prions. Viroids and prions are tiny infectious particles with virus-like characteristics. These forms, nevertheless, diverge fundamentally from a conventional viral particle. Viruses have two primary elements: genetic material and a protein capsid. Viruses and prions both include genetic information as well as protein capsids. Viroids are contagious RNA molecules that make people sick in the plant kingdom and are tiny and transparent. Prions are microscopic proteinaceous molecules that cause disease in humans and other animals. The main distinction between prions and viroids is that prions lack nucleic acids while viroids lack protein.

Viroids

The Viroids were initially found in 1971 by a plant pathologist named Theodor Otto Diener. When working for the Agricultural Research station Service, he discovered an acellular particle that he termed viroid, which means “virus-like.” There are now 33 viroid varieties recognised. Viroids are the tiniest infectious pathogens, consisting only of a single strand of circular, single-stranded self-replicating RNA with no protein coating. 

On the other hand, Viroids are composed of nucleic acid, which will not code for almost any protein. They lack a protein covering that would safeguard the genetic data. Viroids are known to cause a variety of plant diseases. They use the phloem vascular conduits and plasmodesmata to attach to the owner’s protein and then migrate inside the cell (Plant). Chlorosis, stunting, veinal discolouration, epinasty, vein clearing, isolated necrotic patches, mottling of leaflets, and demise of the host are all indications of viroid illness. The first viroid was discovered in tuber spindles syndrome, which caused plantlets to sprout slowly and develop numerous abnormalities. The viroid’s replication method is based on the RNA polymerase II enzyme. This enzyme aids in the manufacture of mRNA molecules from DNA in the host cell. Instead, it catalyses “rolling circle” RNA synthesis utilising the viroid’s RNA as a template in the viroid. They may have catalytic activity, allowing them to self-cleave and ligate unit-size genomes from bigger replication intermediate. Avsunviroids (such as the Avocado Sun-blotch viroid) and Pospiviroids are two types of viroids (e.g., Potato spindle tuber viroid).

Prions

The name ‘prion’ was coined to characterise unknown infectious organisms that cause numerous neurodegenerative disorders in invertebrates, particularly Creutzfeldt-Jakob disease (CJD) in humans. The term comes from the phrase “protein infect particles,” which alludes to the once-controversial idea that now the infectious agent causing such diseases is made entirely of protein and lacks a nucleic acid genome. (Nucleic acids, which allow viruses and bacteria to proliferate, are found in all prior knowledge diseases.) The prion hypothesis explains why the unknown infected individual is immune to ultraviolet light, that dissolves nucleic acids, yet vulnerable to proteins disrupting chemicals.”Researchers made a huge breakthrough when they identified that now the infectious agent is mostly made up of a particular protein in a regular cellular membrane, but with a different shape, or orientation. Some researchers speculated that now the deformed protein may attach to those other molecules of the same type and cause those to change their shape as well, resulting in a chain of events that spreads the sickness and generates fresh infectious material. The genome for this protein has now been mapped, and investigations with transgenic mice have supported the prion hypothesis. The proof in favour of the idea is becoming very robust, if not infallible. 

Conclusion

The prion looks to have been the first infection caused discovered that does not rely on DNA or RNA genes for transmission. Spongiform encephalopathies are caused by an infectious structural variation of a normal cellular specific protein PrP (prion protein). Prions have been linked to severe neurological disorders in people and cattle, including kuru, and bovine spongiform encephalopathy (BSE). Persons with kuru and BSE often notice decreased motor function and strange behaviours, which are frequently preceded by death. Viroids lack a capsid or an outer envelope, and they can only increase within a host cell. Viroids aren’t proven to cause many diseases in humans, yet they’re to blame for poor harvests and millions in agricultural losses.