#viroids

Video by Scishow: Viroids: Possibly the Smallest Pathogens on Earth:

Potato spindle tuber disease wasn't a life-or-death situation, but it led to the discovery of viroids: infectious, replicating bits of RNA 

Recently I learned about viroids. A viroid is basically a short strand of circular, single-stranded RNA, about 100 times smaller than a virus.

The hop stunt viroid is a quite common hop disease in the hop garden of Washington and can lead to slow or no plant growth.

Read more: https://en.wikipedia.org/wiki/Viroid

We may have an adequate understanding of the human body in that, well, we invented aspirin and sequenced the genome, but researchers still find out new things about the humble homo sapien all of the time. Case in point? Scientists just discovered a previously unknown entity hanging out in the human gut and mouth. The researchers are calling these virus-like structures “obelisks”, due to their presumed microscopic shape. These entities replicate like viruses, but are much smaller and simpler. Due to the minuscule size, they fall into the “viroid” class, which are typically single-stranded RNAs without a protein shell. However, most viroids are infectious agents that cause disease and it doesn’t look like that’s the case with these lil obelisks, as reported by Live Science. So why are they inside of us and what do they do? That’s the big question. The discoverers at Stanford University, the University of Toronto and the Technical University of Valencia have some theories. They may influence gene activity within the human microbiome, though they also hang out in the mouth. To that end, they have been found using the common mouth-based bacterium Streptococcus sanguinis as a host. It’s been suggested that these viroids infect various bacteria in both the mouth and gut, though we don’t know why.

Viroids are infectious RNA. These are Circular RNA molecules which infect plants. Viroids are the smallest infectious pathogens known. This RNA molecule Don’t code for proteins and disrupt regulatory systems in plants. It Causes growth problems in plants. Eg Hepatitis D viroid causes Hepatitis D in humans (in combination with virus).  The human pathogen hepatitis D virus is a defective RNA virus similar to viroids .

History of Virods: Viroids, the first known representatives of a new domain of "sub-viral pathogens", were discovered, initially characterized, and named byTheodor Otto Diener, plant pathologist at the U.S Department of Agriculture's Research Center in Beltsville, Maryland, in 1971. The first viroid to be identified was Potato spindle tuber viroid (PSTVd). Some 33 species have been identified. The "RNA world fossils" hypothesis suppose that viroids were present all along the"green line" giving rise to plants, and probably before, and does not explain why they have not been found (yet) in other organisms.

VIROID DISEASES:- 1) Potato spindle tuber viroid (PSTVd)a. May be limiting to potato growersb. First viroid characterizedc. Many variants describedd. Control with detection in mother stock, clean seed 

To read more http://microamaze.blogspot.in/2015/12/viroids.html

 with love