Editing Plant virus (section)

=== By insects ===

[[File:Viruses-08-00303-g001.png|thumb|upright=2|Plant virus transmission strategies in insect vectors]]

Plant viruses need to be transmitted by a [[Vector (epidemiology)|vector]], most often [[insects]] such as [[leafhoppers]]. One class of viruses, the [[Rhabdoviridae]], has been proposed to actually be insect viruses that have evolved to replicate in plants. The chosen insect vector of a plant virus will often be the determining factor in that virus's host range: it can only infect plants that the insect vector feeds upon. This was shown in part when the [[old world]] [[white fly]] made it to the United States, where it transferred many plant viruses into new hosts. Depending on the way they are transmitted, plant viruses are classified as non-persistent, semi-persistent and persistent. In non-persistent transmission, viruses become attached to the distal tip of the [[insect mouthparts|stylet]] of the insect and on the next plant it feeds on, it inoculates it with the virus.<ref>{{cite journal |last1=Gray |first1=Stewart M. |last2=Banerjee |first2=Nanditta |title=Mechanisms of Arthropod Transmission of Plant and Animal Viruses |pmid=10066833 |journal=Microbiology and Molecular Biology Reviews |volume=63 |issue=1|pages=128–148 |pmc=98959 |date=March 1999|doi=10.1128/MMBR.63.1.128-148.1999}}</ref> Semi-persistent viral transmission involves the virus entering the [[foregut]] of the insect. Those viruses that manage to pass through the gut into the [[haemolymph]] and then to the [[salivary glands]] are known as persistent. There are two sub-classes of persistent viruses: propagative and circulative. Propagative viruses are able to replicate in both the plant and the insect (and may have originally been insect viruses), whereas circulative can not. Circulative viruses are protected inside aphids by the chaperone protein [[symbionin]], produced by bacterial [[symbionts]]. Many plant viruses encode within their genome [[polypeptide]]s with domains essential for transmission by insects. In non-persistent and semi-persistent viruses, these domains are in the coat protein and another protein known as the helper component. A bridging [[hypothesis]] has been proposed to explain how these proteins aid in insect-mediated viral transmission. The helper component will bind to the specific domain of the coat protein, and then the insect mouthparts – creating a bridge. In persistent propagative viruses, such as [[tomato spotted wilt virus]] (TSWV), there is often a lipid coat surrounding the proteins that is not seen in other classes of plant viruses. In the case of TSWV, 2 viral proteins are expressed in this lipid envelope. It has been proposed that the viruses bind via these proteins and are then taken into the insect [[Cell (biology)|cell]] by receptor-mediated [[endocytosis]].