Department of Biochemistry and Biophysics, University of California, Davis, California 95616, USA
Type member: cowpea mosaic virus, SB isolate.
Two types of ribonucleoprotein particle and, in some isolates, a protein
particle, all c.
28 nm in diameter, all apparently with icosahedral
symmetry, sedimenting at c.
118 S, 98 S and 58 S and
34, 25 and 0% single-stranded RNA, respectively. Two RNA
species (with 3'-terminal polyadenylate sequences in most members examined), M. Wt
2.1 x 106
and 1.4 x 106
, both necessary for
infection. All three types of particle contain 60 molecules of each of two
distinct coat polypeptides, M. Wt c.
22,000 and 42,000. Thermal inactivation
point (10 min) 60-75°; survival in sap at 4-25° a few days to a few weeks;
concentration in sap 10-1000 mg/l. Host range of an individual member typically
only a few genera: usually symptoms are systemic mosaic or mottling and stunting,
occasionally systemic wilting and collapse or necrotic ring symptoms or seed
discoloration. Virus particles accumulate in the cytoplasm, sometimes in
crystalline arrays. Readily transmissible by inoculation of sap; many members
are transmitted by beetles and possibly other chewing insects, and some to
progeny through seed.
Several members have been favoured objects of study by virologists; see
Van Kammen (1972),
Brown & Hull (1973),
Jaspars (1974), and
Members of the comovirus group and families of principal hosts
||Strains and synonyms
||CMI/AAB Desc. or Ref.
|Leguminosae (subclass Rosidae):
|Bean curly dwarf mosaic virus (BCDMV)
||Meiners et al., 1977
|Bean pod mottle virus (BPMV)
||type, J-10, Desmodium Virus
||108; Lee & Walters, 1970
||Bean rugose mosaic virus (BRMV)
||type, Virus Ampollado del Frijol
||246; Gamez, 1972;
Galvez et al., 1974
|Broad bean stain virus (BBSV)
|Cowpea severe mosaic virus (CPSMV)
||Arkansas, Trinidad, Vu, Vs, El Salvador, DG
|Cowpea mosaic virus (yellow strain) (CPMV)
|Echtes Ackerbohnemosaik-Virus (EAMV)
|Virus de la mosaique de la fève (MFV)
||Devergne & Smith, 1964
|Pea green mottle virus (PGMV)
||Valenta et al., 1969
|Quail pea mosaic virus (QPMV)
||238; Moore, 1973
|Red clover mottle virus (RCMV)
|Cruciferae (subclass Dilleniidae):
|Radish mosaic virus (RaMV)
||Neo-type, HZ, KV, B, DT4, S
Plakolli & tefanac, 1976
|Cucurbitaceae (subclass Dilleniidae):
|Squash mosaic virus (SqMV)
|Solanaceae (subclass Asteridae):
|Andean potato mottle virus (APMV)
||203; Fribourg et al., 1977
Geographical Distribution etc
Individual comoviruses tend to have a restricted distribution, in some
instances probably dependent upon the distribution of vectors. As a group
they have been reported in many tropical and temperate regions, especially
where humidity is generally high. Host ranges of individual members are
narrow. However, different members have natural hosts (Table 1) among four
families representing three of the six subclasses
of dicotyledonous plants. Species of Chenopodium
) are local lesion hosts of many members.
CPMV infects protoplasts from a range of cowpea cultivars, including some
that are immune as intact plants
(Beier et al., 1977
CPMV also infects tobacco protoplasts
(Huber et al., 1977
Association with Vectors
Most members are transmitted by leaf-feeding beetles. Transmission is a
specific process dependent upon beetle species, virus strain and host
(Fulton et al., 1975
Fulton & Scott, 1977
Beetles most commonly
found to be efficient comovirus vectors are of the family Chrysomelidae
(principally the genera Cerotoma
); vector species
also occur in the families Curculionidae and Coccinellidae. Beetle vectors
can acquire virus after feeding for 1 min and can retain it for days or weeks,
or even several months if dormant
(Fulton et al., 1975
Walters et al., 1972
The mechanisms of transmission are obscure; transmission
is associated with feeding and the occurrence of virus in the haemolymph
(Fulton & Scott, 1977
There is no evidence for replication in the
vector. All the viruses in Table 1 except MFV, PGMV and APMV have beetle
vectors. It is possible that some other chewing insects are comovirus vectors
(Whitney & Gilmer, 1974
Sources of virus causing initial infections in crops include seeds and
perennial weed hosts, causing spread from the edges of the field, and perhaps
overwintering beetles. Spread from an infected plant may occur in waves
(Gibbs et al., 1968
implying possible involvement of beetles. Seed transmission
has been reported for BBSV, CPSMV, CPMV, EAMV, MFV, and SqMV. Usually the
frequency of seed transmission is less than 10% (e.g.
Cockbain et al., 1976
Haque & Persad, 1975
but may be higher for SqMV.
Partridge et al. (1974)
have postulated that seed transmission is correlated with the
capsid protein-bound carbohydrate.
Relations with Cells and Tissues
The comoviruses accumulate in highest concentrations in systemically
infected leaves that were in bud or nor yet formed when the plant became
infected. Somewhat lower concentrations are achieved in inoculated, expanded
leaves and much lower concentrations in stems and other tissues. Some
comoviruses invade developing seeds.
The two coat polypeptides, L and S, are present in equimolar amounts,
apparently assembled in a T
= 1 icosahedral structure containing 60
copies of each
(Wu & Bruening, 1971
Crowther et al., 1974
of M. Wt vary from 37,000-49,000 (L) and 18,000-26,000 (S), but average about
42,000 and 22,000, respectively. In sodium dodecyl sulphate polyacrylamide gel
electrophoresis the L proteins from several different comoviruses, and also
the S proteins, comigrate. Carbohydrate is associated with the protein of
(Partridge et al., 1974
Several members form c.
S top components that lack RNA, suggesting a major contribution
from protein-protein bonds in stabilizing the particles. Estimates of the
capsid M. Wt are 4.5 x 106
for SqMV by sedimentation and
(Mazzone et al., 1962
and 4.6 x 106
(Geelen et al., 1972
implying larger M. Wt
for the capsid proteins than the averages stated above. Members have two
single-stranded RNA molecules, found both to be essential for infection
where tested. The c.
118 S bottom component contains one
molecule of RNA-1 of M. Wt c.
2.1 x 106
; the c.
98 S middle component contains one molecule of RNA-2 of M. Wt
1.4 x 106
. The components contain c.
25% RNA, respectively. Bottom component of some comoviruses forms two
, in CsCl gradients during equilibrium
centrifugation. The lower density of BU
may reflect a higher
content of polyamines, especially spermidine
At pH c. 9 several comoviruses can be resolved into two electrophoretic
each representing all of the centrifugal forms.
The relative amount of the two forms varies with the time between inoculation
and harvesting of the infected leaves. Conversion of one electrophoretic form
to the other is associated with a reduction in the M. Wt of S polypeptide,
presumably by proteolysis in vivo. In the pH range 7.5 to 8.2 CPMV
top component was electrophoretically resolved from middle and bottom
Both RNA-1 and RNA-2, or the nucleoprotein components containing them,
are required for infectivity; greater infectivity for mixtures of middle and
bottom components than for the separated components has been observed for
BPMV, BBSV, CPSMV, CPMV, EAMV, RCMV, RaMV (reviewed by
(Salazar & Harrison, 1978
If the viruses are sufficiently closely
related, pseudo-recombinant isolates can be formed by inoculating a mixture
of bottom component from one virus and middle component from another.
Properties of the pseudo-recombinants show that RNA-2/middle component
specifies some symptoms, the structure of S polypeptide (see, e.g.,
Gopo & Frist, 1977
and whether top component will be synthesized. RNA-1/bottom
component specifies some symptoms and the kinetics of in vivo
of electrophoretic forms. Pseudo-recombinants do not form between CPSMV and
CPMV or between the other pairs of distinct viruses that have been tested.
Comovirus RNA is high in uridylate (30% or greater in most instances) and low
in cytidylate. The RNA of CPMV and BPMV, and RNA-1 of RCMV
have polyadenylate sequences; these have been shown to be 3'-terminal in CPMV
(El Manna & Bruening, 1973
The RNA species of CPMV have covalently bound
protein at the 5'-termini (S. D. Daubert, G. Bruening and R. C. Najarian,
unpublished data.) Molecular hybridization experiments suggest that RNA-1 and
RNA-2 of CPMV have few extended nucleotide sequences in common (reviewed by
Most studies on replication have been made with CPMV. Coat (and presumably
other) virus proteins are synthesized on cytoplasmic ribosomes because
physiologically active concentrations of cycloheximide, but not of chloramphenicol,
inhibit their synthesis
(Owens & Bruening, 1975
Both RNA species are
translated in vitro
into polypeptides approaching in size the theoretical
(Davies et al., 1977
presumably are cleaved to form the functional proteins.
RNA complementary to particle RNA has been detected in infected tissue; the
complementary RNA, particle antigen and probably RNA polymerase activity are
all associated with cytoplasmic structures that tend to fractionate with, but
can be resolved from, chloroplast fragments
(De Zoeten et al., 1974;
Zabel et al., 1974;
Hibi et al., 1975).
replicase has been partially purified
(Zabel et al., 1976).
accumulate in crystalline aggregates
(Langenberg & Schroeder, 1975).
Magyarosy et al. (1973)
could find no functional change in
chloroplasts from SqMV-infected tissue, the number of chloroplasts was reduced;
Langenberg & Schroeder (1975) and
De Zoeten et al. (1974) found
lipid globules in chloroplasts of CPMV-infected tissue. Other changes in the
host include a shift from carbohydrate to organic and amino acid synthesis
(Magyarosy et al., 1973)
and an increase in aspartate transcarbamylase
(Niblett et al., 1974).
CPMV and BPMV were found to be more,
and more variably, sensitive to actinomycin D than most RNA viruses
(Lockhart & Semancik, 1969).
Relationships within the Taxon
Serological relationships between members are generally distant. Where
close relationships exist the assignments of isolates as the same virus or as
different strains are difficult to make and unlikely to be clarified by further
studies of symptoms, host range or vector specificity. Among the serological
relationships shown in
those between BBSV, MFV and PGMV are closest and
they should perhaps be considered to be strains of one virus; BBSV and MFV both
invade developing seeds and cause discoloration
Devergne & Cousin, 1966
QPMV and BCDMV are reported to be closely serologically related
(Meiners et al., 1977
Assignment of RaMV isolates to either the neotype (isolates
from USA and Japan) or European type on the basis of serology, host range and
pseudo-recombinant formation has been suggested
(Plakolli & Stefanac, 1976
The distinction between CPSMV and CPMV is based upon symptoms, serology, and,
generally, a lack of top component, a higher middle to bottom component ratio,
a lower specific infectivity and a wider host range for CPSMV than for CPMV
Swaans & Van Kammen, 1973;
Beier et al., 1977).
CPMV isolates are from the Old World, whereas most CPSMV isolates are from the
(Fulton et al., 1975).
A few exceptions have been reported
McLaughlin et al., 1977).
Affinities with Other GroupsBroad bean wilt virus
is very similar to the comoviruses.
The L and S coat proteins of BBWV co-migrated with those of CPMV during
electrophoresis in polyacrylamide gels, as did the respective RNA-1 and
RNA-2. BBWV forms a top component, and evidence was obtained of a requirement
for both middle and bottom component in initiating infections. The RNA has a
high uridylate to cytidylate ratio
However, unlike the comoviruses,
BBWV reaches only moderate concentrations in infected plants, is transmitted by
aphids and has a wide host range. Comoviruses also resemble, though less closely,
the nepovirus group
Strawberry latent ringspot virus
is the most
similar to the comoviruses because, unlike other nepoviruses, it has two coat
proteins close to the sizes of the comovirus proteins. An even more distant
resemblance is seen to the animal picornaviruses (e.g. poliovirus), which exhibit
3'-terminal polyadenylate, a 5'-linked protein, more than one coat protein, and
expression of the virus genome via polyproteins.
- Agrawal, Meded. LandbHoogesch. Wageningen 64: 1, 1964.
- Agrawal & Maat, Nature, Lond. 202: 674, 1964.
- Beier, Siler, Russell & Bruening, Phytopathology 67: 917, 1977.
- Brown & Hull, J. gen. Virol. 20 Suppl.: 43, 1973.
- Bruening, in Comprehensive Virology, Vol. 11, p. 55. ed. H.Fraenkel-Conrat & R. R. Wagner, New York: Plenum, 1977.
- Campbell, Phytopathology 54: 1418, 1964.
- Cockbain, Bowen & Vorra-Urai, Ann. appl. Biol. 84: 321, 1976.
- Cronquist, The Evolution and Classification of Flowering Plants. New York: Houghton Mifflin, 1968.
- Crowther, Geelen & Mellema, Virology 57: 20, 1974.
- Davies, Aalbers, Stuik & Van Kammen, FEBS Lett. 77: 265, 1977.
- Devergne & Cousin, Annls Épiphyt. numéro hors série: 147, 1966.
- Devergne & Smith, Études de Virologie appliquée 5: 7, 1964.
- De Zoeten, Assink & Van Kammen, Virology 59: 341, 1974.
- Doel, J. gen. Virol. 26: 95, 1975.
- El Manna & Bruening, Virology 56: 198, 1973.
- Fribourg, Jones & Koenig, Phytopathology 67: 969, 1977.
- Fulton & Scott, Fitopathol. Brasileira 2: 9, 1977.
- Fulton, Scott & Gamez, in Tropical Diseases of Legumes. p. 123. ed. J. Bird & K. Maramorosch, New York: Academic Press, 1975.
- Fulton, Scott & Gamez, in Vectors of Plant Disease Agents, p. 115, ed. K. Maramorosch & K. F. Harris, New York: Academic Press, 1980.
- Galvez, Cardenas & Diaz, Proc. Am. Phytopath. Soc. 1: 122, 1974.
- Gamez, Turrialba 22: 249, 1972.
- Geelen, Van Kammen & Verduin, Virology 49: 205, 1972.
- Gibbs, Giussani-Belli & Smith, Ann. appl. Biol. 61: 99, 1968.
- Gopo & Frist, Virology 79: 259, 1977.
- Haque & Persad, in Tropical Diseases of Legumes, p. 119, ed. J.Bird & K. Maramorosch, New York: Academic Press, 1975.
- Hibi, Rezelman & Van Kammen, Virology 64: 308, 1975.
- Huber, Rezelman, Hibi & Van Kammen, J. gen. Virol. 34: 315, 1977.
- Jaspars, Adv. Virus Res. 19: 37, 1974.
- Jones & Barker, Ann. appl. Biol. 83: 231, 1976.
- Langenberg & Schroeder, J. Ultrastruct. Res. 51: 166, 1975.
- Lee & Walters, Phytopathology 60: 585, 1970.
- Lockhart & Semancik, Virology 39: 362, 1969.
- McLaughlin, Thongmeearkom, Milbrath & Goodman, Phytopathology 67: 844, 1977.
- Magyarosy, Buchanan & Schumann, Virology 55: 426, 1973.
- Mazzone, Incardona & Kaesberg, Biochim. biophys. Acta 55: 164, 1962.
- Meiners, Waterworth, Lawson & Smith, Phytopathology 67: 163, 1977.
- Moore, Pl. Dis. Reptr 57: 311, 1973.
- Niblett, Johnson & Lee, Physiol. Pl. Path. 4: 63, 1974.
- Owens & Bruening, Virology 64: 520, 1975.
- Oxelfelt, Virology 74: 73, 1976.
- Partridge, Shannon, Gumpf & Colbaugh, Nature, Lond. 247: 391, 1974.
- Plakolli & Stefanac, Phytopath. Z. 87: 114, 1976.
- Salazar & Harrison, J. gen. Virol. 39: 171, 1978.
- Shepherd, Phytopathology 53: 865, 1963.
- Swaans & Van Kammen, Neth. J. Pl. Path. 79: 257, 1973.
- Valenta & Gressnerová, Acta Virol. 10: 182, 1966.
- Valenta, Gressnerová, Marcinka & Nermut, Acta Virol. 13: 422, 1969.
- Van Kammen, A. Rev. Phytopath. 10: 125, 1972.
- Walters, Lee & Jackson, Phytopathology 62: 808, 1972.
- Whitney & Gilmer, Ann. appl. Biol. 77: 17, 1974.
- Williams, in Tropical Diseases of Legumes, p. 139, ed. J. Bird & K. Maramorosch, New York: Academic Press, 1975.
- Wu & Bruening, Virology 46: 596, 1971.
- Zabel, Weenen-Swaans & Van Kammen, J. Virol. 14: 1049, 1974.
- Zabel, Jongen-Neven & Van Kammen, J. Virol. 17: 679, 1976.
Diagram of serological relationships between comoviruses. Solid lines represent
serological relationships in which the heterologous titre was 1/64th or
more of the homologous
titre or in which an immunodiffusion pattern was judged to show a precipitin line whose
intensity for the heterologous reaction was not much less than that for the homologous
reaction. Dashed lines represent serological relationships that meet these citeria barely
(a) Agrawal & Maat, 1964;
(b) Campbell, 1964;
(c) Fribourg et al., 1977;
(d) Gamez, 1972;
(e) Gibbs et al., 1968;
(f) Jones & Barker, 1976;
(g) Meiners et al., 1977;
(h) Moore, 1973;
(i) Shepherd, 1963;
(j) D.J. Siler, H.A. Scott & G. Bruening, unpublished observations;
(k) Valenta et al., 1969;
Valenta & Gressnerová, 1966;
(l) Desc. 74.