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Question

Are there already virioids discovered or can be artificially designed, which have harmful effects for humans or insects?

Submitted by: Volker


Answer

Expert response from Allan Felsot

Professor and Extension Specialist, Washington State University

Monday, 12/06/2017 18:57

Viroids are very small pieces of circular RNA that have the potential of causing plant diseases. These entities are infectious agents that are different from viruses because they have no protein coat encircling their genetic material. Thus far, viroids are only known to be effective infectious agents in plants. Viroids have not been associated with any animal disease, and they have not been found in animal cells and tissues. 

 

Biotechnological tools are being used in plant breeding to produce cultivars that can resist the infections caused by viroid diseases. Such breeding is being pushed along by basic biochemistry studies of how these small strings of nucleic acids can cause plant disease. The prevailing hypothesis is that the RNA which constitutes a viroid may function similarly to naturally occurring small inhibitory RNAs that can regulate the process of translation of the specific messenger RNA code into proteins. RNAs characteristic of viroids seems to act in a very specific manner to cause disease. In other words, a viroid that might be infectious in papaya or coconut is not likely to infect plants in completely different families. 

 

Some laboratory successes in breeding viroid resistant plants have been published. To date, no publications have appeared wherein a viroid was synthesized. The safety of viroids in humans has not been directly tested, but because viroids are naturally occurring in plant cells, humans have been exposed to them by eating fruit that is not necessarily showing symptoms of plant disease. Thus, viroids should not be of concern for human safety because only plant cells are infected and their natural occurrence suggests humans have been eating these pieces of RNA for a long time. 

 

The following articles describe pathogenic aspects of viroids and cover their molecular biology. All of these articles should be available for free by searching on the article title name in GOOGLE Scholar. 

 

  • Daròs, J.A., Elena, S.F. and Flores, R., 2006. Viroids: an Ariadne's thread into the RNA labyrinth. EMBO reports, 7(6), pp.593-598.
  • Diener, T.O., 1974. Viroids: the smallest known agents of infectious disease. Annual Reviews in Microbiology, 28(1), pp.23-40
  • Ding, B., 2010. Viroids: Self‐replicating, mobile, and fast‐evolving noncoding regulatory RNAs. Wiley Interdisciplinary Reviews: RNA, 1(3), pp.362-375. 
  • Flores, R., Hernández, C., Alba, A.E.M.D., Daròs, J.A. and Serio, F.D., 2005. Viroids and viroid-host interactions. Annu. Rev. Phytopathol., 43, pp.117-139.
  • Navarro, B., Gisel, A., Rodio, M.E., Delgado, S., Flores, R. and Di Serio, F., 2012. Viroids: how to infect a host and cause disease without encoding proteins. Biochimie, 94(7), pp.1474-1480.
  • Wang, M.B., Bian, X.Y., Wu, L.M., Liu, L.X., Smith, N.A., Isenegger, D., Wu, R.M., Masuta, C., Vance, V.B., Watson, J.M. and Rezaian, A., 2004. On the role of RNA silencing in the pathogenicity and evolution of viroids and viral satellites. Proceedings of the National Academy of Sciences of the United States of America, 101(9), pp.3275-3280