Entry of virus into plant cells

A plant cell's special architecture, namely the presence of a rigid and fairly thick cell wall, presents a unique challenge for virus entry. Initial entry into the plant cell must take advantage of some break in integrity of the cell wall. Apparently, when the virus enters such a break and becomes situated in close proximity to the plant cell's plasma membrane, it can enter the cell without interaction with specific receptors.

Breaks or lesions in the plant cell's wall are most often produced by organisms that feed on the plant or by mechanical means. Above ground, invertebrates, such as aphids, leafhoppers, white flies, and thrips, are known vectors for a number of plant viruses. Nematodes, which feed on the root system of the plant, are another source of viral infection. In some cases, the virus is transferred from the invertebrate to the plant without growing in the vector. This is the case for Geminivirus transmission by white flies. Alternatively, viruses may replicate in both their invertebrate and plant hosts. This is seen with tomato spotted wilt virus (a plant bunya-virus) and its thrip vector. In either case the viruses gain entry to cytoplasm of the plant host cell after the insect has begun to feed on plant tissue.

Mechanical damage to the plant's cell wall also can be a means of entry for plant viruses. This approach is used most often in experimental settings when the leaf surface is scratched or abraded prior to inoculation with a virus suspension. This also may happen in nature as a result of agricultural applications, such as harvesting. Brome mosaic virus, transmitted by beetles, can also gain entry into the plant during cutting operations.

Once inside the plant cell cytoplasm, viruses are uncoated and gene expression begins following patterns similar to those described for animal viruses. Passage of progeny virus from the initial site of infection to new host cells takes place through cell-to-cell connections called plasmodesmata and through the plant's circulatory system, the phloem. For this reason, most

Receptor-mediated fusion of an enveloped virus with the plasma membrane

Receptor-mediated endocytotic entry of an enveloped virus

Nucleocapsid^w ■

Receptor m m

Attachment

Attachment

Cell membrane

Fusion of viral and cellular envelopes

Nucleocapsid released inside cell

Formation of an endocytotic vesicle

Receptor binding

Acidification*

Viral envelope

forms patch on

plasma membrane

V \

Release of

<2?

nucleocapsid into

cell's interior

Cell membrane

Receptor binding

Co-receptor binding

Viral membrane Glycoprotein Receptor

Co-receptor binding

Membrane fusion

Pore formation

Fig. 6.3 (a) The two basic modes of entry of an enveloped animal virus into the host cell. Membrane-associated viral glycoproteins either can interact with cellular receptors to initiate a fusion between the viral membrane and the cell plasma membrane, or can induce endocytosis. The fate of the input virus membrane differs in the two processes. (b) High-resolution schematic of the process of membrane fusion. The interaction between viral and cellular membrane-associated proteins results in the "clearance" of an area of the two lipid bilayers so that they can become closely juxtaposed leading to fusion. (c) The fusion of pseudorabies virus with the plasma membrane of an infected cultured cell is shown in this series of electron micrographs (scale bars = 150 nm). Although each electron micrograph represents a single event "frozen in time," a logical progression from the initial association between viral envelope glycoproteins and the cellular receptor on the plasma membrane through the fusion event is shown. The final micrograph contains colloidal gold particles bound to antibodies against the viral envelope glycoproteins (dense dots). With them, the envelope can be seen clearly to remain at the surface of the infected cell. (Micrographs reprinted with the kind permission of the American Society for Microbiology from Granzow H, Weiland F, Jons A, Klupp B, Karger A, Mettenleiter T. Ultrastructural analysis of the replication cycle of pseudorabies virus in cell culture: a reassessment. Journal of Virology 1997;71:2072-2082.) (d) The association of the viral capsid with the intracellular transport machinery following membrane fusion. This process leads to the virion and associated viral genome being transported to its appropriate location inside the cell to initiate the next step of the infection process - the expression of viral genes.

Pseudorabies Infection Cycle
Fig. 6.3 Continued

plant virus infections end up as systemic infections of the whole organism; thus, a single lesion and virus entry can result in virus lesions appearing throughout the plant.

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Responses

  • HAYDEN
    How do viruses gain entry into a plant?
    3 years ago
  • LLOYD
    How do virus gain entry into a plant to transmit diseases?
    3 years ago
  • SADIE
    How do virus gain entrance into the plant?
    3 years ago
  • kenzie
    How does virus gain entrance to a plant host cell?
    3 years ago
  • angelica
    How do virus enter plant cell?
    3 years ago
  • ilse
    How do viruses gain into plants?
    3 years ago
  • Furuta
    How do viruse gain entry into plants?
    2 years ago
  • Terenzio
    How does viruses gain entry into plants?
    2 years ago
  • fiona
    What ways can virus gain entrance into their host plant?
    2 years ago
  • guido
    How do plant viruses enter host cell?
    1 year ago
  • primrose
    How do plant viruses enter host cells?
    1 year ago
  • mia
    How do plant virues enter host cell?
    1 year ago
  • MARTHA AZIZ
    How do virus get entry into plant cell?
    10 months ago
  • LEROY
    How do plant viruses gain access to plant tissue?
    9 months ago
  • eoin
    How the virus enters the plant cells to breed in it.?
    4 months ago
  • bisirat berhane
    What happens when a virus enters a plant cell?
    2 months ago

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