Brome mosaic virus
L. C. Lane
Dept. of Plant Pathology, University of Nebraska, Lincoln, NE 68583, USA
Described by McKinney, Fellows & Johnston (1942).
- Weidelgrasmosaik-Virus (Rev. appl. Mycol. 39: 589)
- Ryegrass streak virus (Rev. appl. Mycol. 44: 152)
- Trespenmosaik-Virus (Rev. appl. Mycol. 44: 2517)
- Marmor graminis (Rev. appl. Mycol. 23: 427)
An RNA-containing virus about 26 nm in diameter. It is easily transmitted mechanically and infects
many species of Gramineae and several dicotyledonous plants. It is of particular interest for its ease
of purification, for its divided genome, and because it is readily reassembled from RNA and protein.
Causes mosaic of bromegrass (Bromus inermis
) and other wild grasses. The virus has not caused
documented economic losses.
Central USA, Eastern Europe, South Africa.
Host Range and Symptomatology
Brome mosaic virus infects species in roughly 50 genera of the Gramineae. Among dicotyledonous
plants its host range is restricted to a few genera in about six families. A complete host range has
been tabulated (Lane, 1974
- Zea mays (maize). Seedlings of most varieties show primary lesions or streaks
(Fig.1) followed by necrosis and death
- Chenopodium spp. Brome mosaic is one of the few grass viruses that produce local lesions on
Chenopodium amaranticolor, C. hybridum
(Fig.3) and C. quinoa.
- Hordeum vulgare (barley). Mild mosaic.
- Chenopodium hybridum
(Fig.3) is a local lesion host.
The isolate of
McKinney et al. (1942)
is regarded as the type strain. Clearly distinct
natural isolates have not been found, although slight differences in stability and other properties
have been noted. Natural mutants, such as electrophoretic variants, and chemically induced mutants can
be selected (Lane, 1974
Transmission by Vectors
Nematodes of the genus Xiphinema
transmitted the virus in the laboratory
(Schmidt, Fritsche & Lehmann, 1963
but vectors have not been demonstrated in the field. Attempts to
transmit the virus with aphids and mites have been unsuccessful
Broad bean mottle
cowpea chlorotic mottle
, the other two
, are transmitted by beetles
(Walters & Dodd, 1969
Walters & Surin, 1973
Transmission through Seed
All reports have been negative (Lane, 1974
Transmission by Dodder
Antisera with dilution end-points greater than 1/1000 have been prepared but antibody titres drop
sharply after reaching a maximum
Serological studies are complicated by the instability
of the virus above pH 6 and its tendency to interact ionically with the sulphate groups of agar and
agarose below this pH. Under appropriate conditions, antisera specific to intact virus particles or
to the dissociated coat protein can be prepared
(von Wechmar & van Regenmortel, 1968
Brome mosaic virus is a distant serological relative of
cowpea chlorotic mottle virus
(Scott & Slack, 1971
The ability of RNAs 1 and 2 from brome mosaic virus and RNA 3 from cowpea chlorotic
mottle virus to form a viable genetic hybrid, albeit with a much reduced growth rate and host range
also indicates a relationship. Similar physical properties and coat protein amino
acid compositions indicate a relationship between brome mosaic and
broad bean mottle
Stability in Sap
The properties of the virus in sap vary. On the average, infectivity survives 10 min at 80°C
or dilution of 104
Easily purified with or without an ultracentrifuge. A simple method is to grind barley tissue
(roughly 2 weeks after infection) with an equal weight of 0.5 M sodium acetate buffer adjusted to pH
4.5 with acetic acid and then emulsify with a small amount of chloroform. Centrifuge the suspension
for 10 min at 5000 rev/min. Filter the supernatant fluid and precipitate the virus by adding
polyethylene glycol M.Wt 6000 to 6 % (w/v). After 15 min of stirring on ice, collect the precipitate
by centrifuging 15 min at 5000 rev/min. Resuspend the pellet in distilled water to about 1/10 the
original volume and emulsify with a few ml of chloroform. Centrifuge the emulsion 10 min at 5000
rev/min and precipitate virus from the upper phase by adding polyethylene glycol to 6% (w/v) and
mixing with 1/10 volume of 5 M NaCl. After 15 min of stirring on ice, collect the precipitate by
centrifugation and resuspend in 50 mM sodium acetate, 1 mM magnesium acetate, pH 5. Virus may be
further purified by differential centrifugation (90 min at 40,000 rev/min and 5 min at 20,000
rev/min). Purified virus may be stored frozen by adding 1/20 volume of ethylene glycol as a
cryopreservative. Contaminating nucleases gradually degrade RNA within the virus. Quality of virus
preparations is best judged by analyzing the integrity of the RNA by gel electrophoresis.
Properties of Particles
The virus is stable from pH 3 to 6. Above pH 7 it swells and is degraded by contaminating
(Incardona & Kaesberg, 1964
Divalent cations (e.g. 1 mM Mg2+
) stabilize the virus above pH 6
Sedimentation coefficient (s20, w): (87.3-0.47 c) S at pH 3-6 and
(78.7-0.64 c) S at pH 7 and above
(Incardona & Kaesberg, 1964), where c is
the virus concentration in mg/ml.
M.Wt: 4.6 x 106 (Bockstahler & Kaesberg, 1962).
The isoelectric point varies considerably with ionic strength; it is pH 6.8 by isoelectric focusing
(Rice & Horst, 1972).
Partial specific volume: 0.71 cm3/g (estimated,
Bockstahler & Kaesberg, 1962).
Electrophoretic mobilities as a function of pH are given by
Bockstahler & Kaesberg (1962) and
Johnson, Wagner & Bancroft (1973).
Extinction coefficient (E(0.1%, 1cm)) at 260 nm, uncorrected for light-scattering is 5.15
(Bockstahler & Kaesberg, 1962).
A260/A280 is 1.75.
Amax/min is 1.53 (L. C. Lane, unpublished data).
The buoyant density in CsCl is roughly 1.35 g/cm3
Particles are isometric
) and roughly 26 nm in diameter with hollow centres roughly 8 nm
(Anderegg, Wright & Kaesberg, 1963
The 180 protein subunits are clustered into hexamers and pentamers
(Bancroft, Hills & Markham, 1967
The virus consists of three types of
particle differing slightly in buoyant density, all of which are required for infectivity. Heavy
particles contain RNA-1, light particles contain RNA-2 and those of intermediate density contain one
molecule each of RNA-3 and RNA-4
(Lane & Kaesberg, 1971
Particle CompositionNucleic acid:
Single-stranded RNA, about 22% of the particle weight
(Bockstahler & Kaesberg, 1962
G:A:C:U = 28:27:21:24
(Bockstahler & Kaesberg, 1965
The RNA is readily isolated by phenol
extraction and consists of four RNA species of M.Wt 1.1 x 106
(RNA-1), 1.0 x 106
(RNA-2), 0.7 x 106
(RNA-3), and 0.3 x 106
(RNA-4), occurring in roughly, but not
exactly, equimolar ratio. RNA species 1, 2 and 3 are required to infect and RNA-3 contains the coat
(Lane & Kaesberg, 1971
RNA-4 is a nucleotide sequence derived from that of RNA-3
(Shih, Lane & Kaesberg, 1972
RNA species 1 to 4 code respectively for proteins of M.Wt
1.2 x 105
, 1.1 x 105
, 0.35 x 105
and 0.2 x 105
. The last
is the coat protein, which is preferentially translated from mixtures containing RNA-4
(Shih & Kaesberg, 1973
All four RNA species can be charged at the 3' end with the amino acid tyrosine
by plant-derived amino acyl tRNA synthetases
(Hall, Shih & Kaesberg, 1972
). All four 3' termini
have similar sequences
(Bastin et al., 1976
The 3' terminal nucleotide sequence of RNA-4 (P. Kaesberg, personal communication) is:
160 C A C G C A G A C C U C U U A C A A G A
140 G U G U C U A G G U G C C U U U G A G A
120 G U U A C U C U U U G C U C U C U U C G
100 G A A G A A C C C U U A G G G G U U C G
80 U G C A U G G G C U U G C A U A G C A A
60 G U C U U A G A A U G C G U A C C G G G
40 U G U A C A G U U G A A A A A C A C U G
20 U A A A U C U C U A A A A G A G A C C A OH
The 5' terminal sequence of RNA-4
(Das Gupta et al., 1975
|7MeG||p p p||G U A
||U U A||A U A
||A U G||U C G||A C U||U C A||G G A
||A C U
||G G U|
|A A G||A U G||A C U||C G C
||G C G||C A G||C G U||C G
The 5' ends of all four RNA species are capped with 7-methyl guanosine.
The coat protein can be isolated by disrupting the virus and precipitating the RNA with
CaCl2. The protein weighs 20,300 daltons. Its amino acid composition is given by
Stubbs & Kaesberg (1964).
The N-terminal methionine in the amino acid sequence given in the previous
section is replaced by an acetyl group in the mature coat protein. The C-terminus is arginine (P.
Kaesberg, personal communication).
The virus contains no polyamines (Nickerson & Lane, 1977).
Relations with Cells and Tissues
In tobacco protoplasts, the endoplasmic reticulum around the nucleus proliferates during the
first 6 h of infection. Later, virus particles are found scattered throughout the cytoplasm. Some
virus particles associate in a helical array around the outside of membranous tubules which are
about 30 nm in diameter
(Burgess, Motoyoshi & Fleming, 1974
). In oat and barley leaves,
photosynthetic tissue (mesophyll cells) is more severely affected than other tissues, and virus is
often seen in chloroplast invaginations. Both hosts contain virus crystals at late stages in the
disease. Chloroplasts degenerate in yellowed areas of the leaves
A membrane-bound RNA polymerase, which is specific to infected tissue, may be isolated. A virus-induced
protein of M. Wt 35,000 appears to be a component of the polymerase
(Hariharasubramanian et al., 1973).
The polymerase can be dissociated from the membrane with nonionic detergents and is
stimulated by, but not dependent on, added brome mosaic virus RNA
(Kummert & Semal, 1977).
Brome mosaic virus is distinguishable from most other viruses of Gramineae by its symptoms in
maize and by its ability to infect several non-graminaceous hosts. In view of the ease of
purification (it can be purified in high yield from naturally infected bromegrass), cursory
physical characterization is advisable for purposes of identification.
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- Walters & Dodd, Phytopathology 59: 1055, 1969.
- Walters & Surin, Pl. Dis. Reptr 57: 833, 1973.
Sweet corn leaves, (left) healthy, (right) infected, 5 days after inoculation.
Sweet corn plants, (left) healthy, (right) infected, 10 days after inoculation.
Local lesions in Chenopodium hybridum.
Virus particles from a purified preparation in 1% uranyl acetate, pH 4.7. Bar represents
100 nm. Enlarged particle in inset shows detailed structure.