Tomato bushy stunt virus : a resilient model system to study virus–plant interactions

SUMMARY Taxonomy: Tomato bushy stunt virus (TBSV) () is the type species of the plant‐infecting Tombusvirus genus in the family Tombusviridae . Tomato bushy stunt virus and its experimental host Nicotiana benthamiana . (A) The image on the left shows a transmission electron micrograph of the ∼33‐nm TBSV particles illustrating the typical granular appearance. The image on the right represents an atomic model of the X‐ray crystallographic structure of the T = 3 virion (). Although the particle is made of 180 identical coat protein subunits, the colouring scheme shows the quasi‐equivalent arrangement of subunits around five‐fold and three‐fold axis. The image is used with permission from http://mmtsb.scripps.edu/viper/ (). To directly quote from this site: ‘This rendering is designed to give an impression similar to that of a cryo‐electron miscroscopy reconstruction at 20 Å resolution.’ (B) Symptoms of TBSV on N. benthamiana 1 week post‐inoculation (right), compared with a healthy plant (left). The image was taken just prior to total necrotic collapse of the infected plant. image Physical properties: TBSV virions are non‐enveloped icosahedral T = 3 particles assembled from 180 coat protein subunits (42 kDa) whose arrangement causes a granular appearance on the surface structure. The particles are ∼33 nm in diameter and composed of 17% ribonucleic acid and 83% protein. Encapsidated within the virion is the TBSV genome that consists of a positive‐sense single‐stranded RNA of approximately 4.8 kb, which lacks the 5′‐cap or 3′‐poly(A) tail typical for eukaryotic mRNAs. Host range: In nature, TBSV has a fairly restricted host range, mostly encompassing a few dicotyledonous species in separate families, and affected agricultural crops comprise primarily vegetables. The experimental host range is broad, with over 120 plant species in more than 20 different families reported to be susceptible although in most plants the infection often remains localized around the site of entry. The differences between hosts with regards to requirements for cell‐to‐cell and long‐distance movement have led to the development of TBSV as an attractive model system to obtain general insights into RNA transport through plants. Symptoms: Symptoms induced by TBSV are largely dependent on the host genotype; they can vary from necrotic and chlorotic lesions, to a systemic mild or severe mosaic, or they may culminate in a lethal necrosis. The original TBSV isolates from tomato plants caused a mottle, crinkle and downward curling of leaves with the youngest leaves exhibiting tip necrosis upon systemic infection. Tomato fruit yield can be greatly reduced by virus infection. Plants may be stunted and a proliferation of lateral shoots leads to a bushy appearance of the infected tomato plants, hence the nomenclature of the pathogen. Useful sites: http://image.fs.uidaho.edu/vide/descr825.htm ; http://www.ictvdb.rothamsted.ac.uk/ICTVdB/74010001.htm (general information); http://mmtsb.scripps.edu/viper/info_page.php?vipPDB=2tbv (structural information).