Alfalfa mosaic virus
| Alfalfa mosaic virus | |
|---|---|
 |
|
| Symptoms of AMV on potato leaves | |
| Virus classification | |
| Group: | Group IV ((+)ssRNA) |
| Family: | Bromoviridae |
| Genus: | Alfamovirus |
| Species: | Alfalfa mosaic virus |
Alfalfa mosaic virus (AMV), also known as Lucerne mosaic virus or Potato calico virus, is a worldwide distributed phytopathogen that can lead to necrosis and yellow mosaics on a large variety of plant species, including commercially important crops. It is the only Alfamovirus of the Bromoviridae family. In 1931 Weimer J.L. was the first to report AMV in alfalfa (Medicago sativa). Transmission of the virus occurs mainly by some aphids (plant lice), by seeds or by pollen to the seed.
The virion has a capsid (coat protein) but no envelope. The icosahedral symmetry of the capsid is round to elongated. The range for the length of the virion particle is about 30–57 nm. AMV is a multipartite virus and is composed of 4 particles (3 bacilliform and 1 spheroidal) with a diameter of 18 nm. The genetic material of AMV consists of 3 linear single strands RNAs (RNA 1, RNA 2 and RNA 3) and a subgenomic RNA (RNA 4) which is obtained by transcription of the negative- sense strand of RNA 3. RNA 1 and 2 encode proteins needed for replication. RNA 3 is required for the synthesis of the protein responsible for cell-to-cell movement. RNA 4 encodes the capsid. Beside encapsidation and its role in movement the viral coat protein also plays a role in the initiation of RNA replication. This property is called genome activation and means that the genomic nucleic acid is not infectious without the capsid. Specific association of the coat protein with the RNA 3’- terminal sequences or with the subgenomic mRNA is required for the infection. Bacilliform particles contain separately encapsidated RNAs 1, 2 and 3. Spheroidal particles each have two copies of RNA 4. The nucleotide sequence of the complete genome has been determined and the length of the genome is 8274 nucleotides ( or 9155 including the subgenomic RNA). RNA 1, 2, 3 and 4 are respectively 3644 (3.65kb), 2593 (2.6kb), 2037 (2.2kb) and 881 (0.88kb) nucleotides long.
The AMV cycle can be split up in 5 steps:
(Most details of the replication cycle are still unknown).
AMV infects over 600 plant species in 70 families (experimental and natural hosts). Some hosts: potato (Solanum tuberosum), pea (Pisum sativum), tobacco (Nicotiana tabacum), tomato (Lycopersicon esculentum), bluebeard (Caryopteris incana), ...
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