Alfalfa mosaic virus: coat protein-dependent
initiation of infection
John F. Bol
Institute of Molecular Plant Sciences, Gorlaeus Laboratories,
Leiden University, PO Box 9502, 2300 RA Leiden, the Netherlands
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| Taxonomy: |
Alfalfa mosaic virus (AMV)
is the type species of the genus Alfamovirus and belongs to the
family Bromoviridae. In this family, the tripartite RNA genomes of
bromo-, cucumo- and probably oleaviruses are infectious as such, whereas
infection with the three genomic RNAs of alfamo- and ilarviruses requires
addition to the inoculum of a few molecules of coat protein (CP) per RNA
molecule. RNAs 1 and 2 encode the replicase proteins P1 and P2, RNA 3
encodes the movement protein and CP. CP is translated from the subgenomic
RNA 4. |
| Physical properties: |
RNAs 1 (3.65 kb), 2
(2.6 kb) and 3 (2.2 kb) are separately encapsidated into
bacilliform particles which are 19 nm wide and 35-56 nm long. In
addition, the virus preparations contain spheroidal particles each
containing two copies of RNA 4 (0.88 kb). Virus particles contain
16-17% RNA and are mainly stabilized by protein-RNA interactions. The
3'-termini of the viral RNAs contain a homologous sequence of 145
nucleotides that can adopt two alternative conformations: one represents a
high-affinity binding site for CP, the other resembles a tRNA-like
structure and is required for minus-strand promoter activity. |
| Hosts: |
AMV mostly infects herbaceous
plants, but several woody species are included in the natural host range.
The experimental and natural host ranges include over 600 species in 70
families. At least 15 aphid species are known to transmit the virus in the
stylet-borne or non-persistent manner. |
| Economic importance: |
AMV is a significant pathogen in
alfalfa and sweet clover and can spread from these forages to neighbouring
crops like pepper, tobacco or soybean. The recent introduction of the
soybean aphid (Aphis glycines) in the mid-west states of the USA
has increased the incidence of AMV in soybean. AMV occurs world-wide in
potato and is referred to as 'calico mosaic' because of its characteristic
symptoms on the foliage. However, the economic importance of AMV in potato
is limited. |
| Useful websites: |
www.socgenmicrobiol.org.uk/JGV/080/1089/0801089A.PDF
(review paper)
www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/10010001.htm
(host range and physical properties)
http://mmtsb.scripps.edu/viper/1amv.html
(structural information). |
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