Molecular Plant Pathology - Pathogen Profiles
Cucumber mosaic virus, a model for RNA virus evolution
Marilyn J. Roossinck
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73402,
Cucumber mosaic virus (CMV) is the type member of the Cucumovirus
genus, in the family Bromoviridae. Additional members of the genus
are Peanut stunt virus (PSV) and Tomato aspermy virus (TAV).
The RNAs 3 of all members of the genus can be exchanged and still yield a
viable virus, while the RNAs 1 and 2 can only be exchanged within a
||The virus particles are about 29 nm
in diameter, and are composed of 180 subunits (T = 3 icosahedral
symmetry). The particles sediment with an s value of approximately 98. The
virions contain 18% RNA, and are highly labile, relying on RNA-protein
interactions for their integrity. The three genomic RNAs, designated RNA 1
(3.3 kb in length), RNA 2 (3.0 kb) and RNA 3 (2.2 kb) are packaged in
individual particles; a subgenomic RNA, RNA 4 (1.0 kb), is packaged with
the genomic RNA 3, making all the particles roughly equivalent in
composition. In some strains an additional subgenomic RNA, RNA 4A is also
encapsidated at low levels. The genomic RNAs are single stranded, plus
sense RNAs with 5' cap structures, and 3' conserved regions that can be
folded into tRNA-like structures.
||CMV can harbour molecular parasites
known as satellite RNAs (satRNAs) that can dramatically alter the symptom
phenotype induced by the virus. The CMV satRNAs do not encode any proteins
but rely on the RNA for their biological activity.
||CMV infects over 1000 species of
hosts, including members of 85 plant families, making it the broadest host
range virus known. The virus is transmitted from host to host by aphid
vectors, in a nonpersistent manner.
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