Tomato golden mosaic virus
K. W. Buck
Department of Pure and Applied Biology, Imperial College of Science and Technology, London SW7 2BB, UK
R. H. A. Coutts
Department of Pure and Applied Biology, Imperial College of Science and Technology, London SW7 2BB, UK
- Disease first transmitted by Costa et al. (1975). Virus first purified
by Matyis et al. (1975) and characterized by Hamilton et al. (1981).
- Virus do mosaico dourado do tomateiro (Rev. Pl. Path. 55: 2599)
- A virus with geminate particles c. 25 x 13 nm containing two species
of circular single-stranded DNA. The known hosts are in the Solanaceae and the
virus is transmitted by the whitefly Bemisia tabaci. Occurs widely in
tropical areas of Brazil (Costa, 1976).
Causes a type of golden mosaic of tomato (Lycopersicon esculentum
minor economic importance (Costa, 1976
; A. S. Costa, personal communication).
Reported only from Brazil. However, similar whitefly-transmitted diseases of
tomato, which are probably caused by geminiviruses, have been reported from
Venezuela, Africa and Asia.
Host Range and Symptomatology
Known hosts are all species of Solanaceae and include Datura stramonium,
Nicotiana benthamiana, N. clevelandii, N. debneyi, N. glutinosa, N. tabacum
cvs Samsun NN, virginica,
White Burley Judys Pride and
, and Physalis
sp., which can all be infected
mechanically with high efficiency (Costa et al., 1975
et al., 1981
; K. W. Buck, R. H. A. Coutts & M. Slomka, unpublished
data). Mechanical transmission of the virus from tomato (Lycopersicon
) to tomato has been achieved with extreme difficulty, only 1.6%
of inoculated plants becoming infected. Solanum pennelli
of crosses between L. esculentum
and S. pennelli
mechanically with relative ease (Costa et al., 1975
) but potato
cv. Maris Bard) and S. nigrum
were not infected either mechanically or by grafting (K. W. Buck, R. H. A. Coutts
& E. J. F. Roberts, unpublished data). The symptoms are similar on all
susceptible species and cultivars, consisting of stunting with severe deformation
of young leaves and shoots, accompanied by a bright yellow mosaic. However,
whereas younger plants routinely give these symptoms (Costa, 1976
et al., 1981
), older plants may show a partial recovery producing
apparently healthy leaves which may later develop sporadic symptoms (K. W.
Buck & R. H. A. Coutts, unpublished data).
- Diagnostic species
- Nicotiana benthamiana. Faint chlorotic mottling on inoculated leaves
followed by curling and spiral distortion of systemically infected young leaves
and shoots, accompanied by a bright golden yellow mosaic (Fig.1) and stunting
(Hamilton et al., 1981).
- Datura stramonium. Yellow spotting on inoculated leaves followed by
a bright golden yellow mosaic on systemically infected leaves (Fig.2)
particularly around veinal areas, together with some stunting (K. W. Buck,
R. H. A. Coutts & C. J. Knight, unpublished data).
- Propagation species
- Nicotiana benthamiana. Plants with six to eight leaves are suitable for
mechanical inoculation of the expanding upper leaves with virus, viral ssDNA or
dsDNA, or cloned viral dsDNA. The most reproducible results are obtained when
plants are kept in a controlled environment (18-20°C, 75% relative humidity,
16 h photoperiod, 15,000 lx light intensity).
- Assay species
- The only assay is by recording the proportion of Nicotiana benthamiana
plants that become systemically infected. Costa (1976) reported that the
virus produced yellow local lesions on young leaves of N. glutinosa, but
this was not confirmed in other tests (K. W. Buck & R. H. A. Coutts,
Transmission by Vectors
Transmitted by the whitefly Bemisia tabaci
from tomato to tomato or
to susceptible Nicotiana
spp. (Costa, 1976
) but data on acquisition and
latent periods are lacking. However the sap-transmissible virus that causes
tomato yellow mosaic in Venezuela, which is possibly distantly related to tomato
golden mosaic virus (E. J. F. Roberts, R. H. A. Coutts & K. W. Buck,
unpublished data), can be acquired by B. tabaci
in 2 h, has a latent
period of 20 h and can be transmitted by the insects for up to 7 days after they
are removed from virus source plants. Female B. tabaci
frequently than males, and transmission was more frequent at 30-34°C than
at 20-30°C (De Uzcategui & Lastra, 1978
Transmission through Seed
The virus is moderately immunogenic. An antiserum prepared in a rabbit by one
intravenous and two intramuscular injections of 300 µg of purified virus had
a titre of 1/256 in immunodiffusion tests and gave a single precipitin line (Stein
et al., 1983
In gel double diffusion serological tests the virus was found to be moderately
closely related to another whitefly-transmitted geminivirus, African cassava
(synonym cassava latent virus) (Fig.4
) and distantly related to a
leafhopper-transmitted geminivirus, beet curly top virus
, but no relationships
were found to four other leafhopper-transmitted geminiviruses: chloris striate
, maize streak
, tobacco yellow dwarf
and wheat dwarf viruses (Stein et
). Similar results were obtained in immunosorbent electron
microscopy by Roberts et al. (1984)
who extended the list of serologically
related whitefly-transmitted geminiviruses to include bean golden mosaic
mosaic and squash leaf curl
viruses, but could not confirm a
relationship to beet
curly top virus.
In solid phase hybridization tests under high stringency conditions, tomato golden
mosaic virus DNA was found to have sequence homology with euphorbia mosaic virus
(Puerto Rican isolate kindly supplied by Dr J. Bird) (Fig.3) and several isolates
of African cassava mosaic virus (e.g. Adejare & Coutts, 1982) but not with
maize streak virus or wheat dwarf virus (K. W. Buck, R. H. A. Coutts, S. W.
MacDowell & G. Sunter, unpublished data); a probe for the larger DNA of African
cassava mosaic virus reacted with tomato golden mosaic virus DNA whereas that for
the smaller DNA of African cassava mosaic virus did not (Roberts et al.,
1984). Nucleotide sequence comparisons revealed 60% homology between the larger
DNA of tomato golden mosaic virus and the larger DNA of African cassava mosaic
virus (Kenyan type strain) and 40% homology between the smaller DNA molecules of
these two viruses; comparison of the amino acid sequences (predicted from the DNA
sequences) of the coat proteins of the same two viruses revealed 71% direct
homology and 85% conserved homology (Hamilton et al., 1984). Comparative
hydrophilicity analyses are shown in Fig.6.
Stability in Sap
The virus occurs in low concentration in diseased tissue and is not resistant
to heat or ageing in vitro.
The virus can be preserved for at least a year
in N. benthamiana
leaves after desiccation over calcium chloride, but
infectivity is lost when aqueous extracts, which initially have an end-point of
on N. benthamiana,
are stored at 4°C for 24 h (K. W.
Buck, R. H. A. Coutts & C. J. Knight, unpublished data).
Purified virus particles (5 to 10 mg/kg fresh leaf) can be obtained by the
following method (Stein et al., 1983
). Harvest systemically infected
leaves 15-20 days after inoculation and homogenize in 0.1 M
trisodium citrate, 0.75% sodium sulphite, 5 mM disodium EDTA, 1% 2-mercaptoethanol
and 0.325% L-ascorbic acid, pH 7.0, adjusted with NaOH (2 ml buffer/g tissue).
Add Triton X-100 to 2.5% by volume and stir for 16 h at 4°C before filtration
through muslin. Centrifuge the filtrate at low speed and then centrifuge the
supernatant fluid for 2 h at 40 000 rev/min in a Beckman Ti 45 rotor. Resuspend
the virus pellets in 0.01 M trisodium citrate, 1 mM disodium EDTA with 0.05%
2-mercaptoethanol, adjust to pH 7 with NaOH, then centrifuge the virus through
a cushion of 20% (w/v) sucrose in the same buffer (2 h at 40,000 rev/min in a
Beckman SW 50.1 rotor) and resuspend the pellets in the same buffer. Further
purify the virus by centrifugation in gradients of 10 to 50% (w/v) sucrose
for 16 h at 20,000 rev/min in a Beckman SW 28 rotor. The virus forms a sharp
light-scattering zone three-quarters of the way down the gradient. Final traces
of host proteins are removed by isopycnic centrifugation in self-generating
density gradients of caesium sulphate (35,000 rev/min; 24 h; starting density
1.34 g/ml) (V. E. Stein, unpublished data). The infectivity of partially
purified virus preparations (prior to the sucrose density gradient stage) is
stable for at least 2 years when stored at -20°C.
Properties of ParticlesA260
Buoyant density in caesium sulphate: 1.34 g/cm3. The particles are
unstable in caesium chloride.
Negatively-stained particles are predominantly geminate, c.
13 nm (Fig.5
). Unpaired quasi-isometric particles are probably formed by
disruption of the geminate ones. The particles are stable between pH 4.0 and
7.0, but are disrupted at pH 8.0 or above (Matyis et al., 1975
Particle CompositionNucleic acid:
Two segments of circular single-stranded DNA, termed A
and B (Hamilton et al., 1981
; Bisaro et al., 1982
). DNA A has
2588 nucleotides (23.4% G, 26.0% A, 19.8% C, 30.8% T) and has M. Wt (Na salt)
of 0.84 x 106
. DNA B has 2508 nucleotides (21.5% G, 29.0% A, 18.7%
C, 30.8% T), and has M. Wt (Na salt) of 0.82 x 106
). Particles obtained from plants infected with the native
Brazilian isolate (but not from those plants infected with cloned DNA) contain
a subgenomic DNA, of M. Wt c.
0.4 x 106
, derived from DNA B
(Hamilton et al., 1982
; K. W. Buck, R. H. A. Coutts, W. D. O. Hamilton,
S. W. MacDowell & V. E. Stein, unpublished data).
Protein: Only one species of polypeptide detected in the particles, of
M. Wt 28,500 (Hamilton et al., 1981; V. E. Stein, unpublished data).
The ssDNA from purified virus particles and the circular dsDNA of genome
length isolated from infected plants are both infective by mechanical
inoculation. Cloned linear dsDNA is also infective and DNA segments A and B
are both required for infectivity (Hamilton et al., 1981
Analysis of the nucleotide sequences of the cloned DNA molecules showed that
DNA A and DNA B have little sequence homology except for a region of about 200
bases which is almost identical in the two molecules. Within this common
region there is a 33-base sequence capable of forming a stable hairpin structure.
Analysis of open reading frames (ORFs) revealed six potential genes for proteins
comprised of more than 100 amino acids, four in DNA A and two in DNA B. Some of
the ORFs are in the DNA strands that occur in the virus particles and some are
in the complementary strands; this suggests that transcription is bidirectional
). The coat protein gene lies on DNA A and is encoded by the strand that
occurs in the virus particles (Hamilton et al., 1984
In addition to the genomic and subgenomic ssDNA species found in the virus
particles, several other virus-specific DNA species have been isolated from
infected plants (Hamilton et al., 1982). These include supercoiled closed
circular dsDNA of unit length with a superhelical density of -0.062 (Sunter
et al., 1984), open circular and linear dsDNA species of unit length,
and multimeric dsDNA species of two or more unit lengths.
Relations with Cells and Tissues
Isolated nuclei from infected cells contain all of the virus-specific
DNA forms detected in whole plant extracts and are active in virus DNA
replication and transcription (R. H. A. Coutts, unpublished data).
The virus may be distinguished from three other whitefly-borne geminiviruses,
tobacco leaf curl virus
(Osaki & Inouye, 1981
) and tomato yellow leaf curl
virus (Russo et al., 1980
) which do not cause mosaic symptoms on infected
plants and are apparently not sap-transmissible, and bean golden mosaic virus
whose host range is apparently limited to certain wild and cultivated species
of Leguminosae (Goodman & Bird, 1978
). Isolates of tomato yellow mosaic
virus from Venezuela (De Uzcategui & Lastra, 1978
) and India (Verma
et al., 1975
) could be strains of tomato golden mosaic virus although
only the former has been shown to be sap-transmissible and little comparative
information is available. The limited sequence comparisons among geminiviruses
so far done (Hamilton et al., 1984
; Roberts et al., 1984
that the degree of sequence homology of the 200-base common regions, or of
the smaller genome segment, could be useful in determining which geminiviruses
are separate viruses and which are strains of existing viruses. For viruses for
which cloned DNA components are available the ability or inability to form viable
pseudo-recombinants is a useful criterion. Viable pseudo-recombinants were not
formed when Nicotiana benthamiana
plants were inoculated with a mixture of
tomato golden mosaic virus DNA A and African cassava mosaic virus
DNA 2 or tomato
golden mosaic virus DNA B and African cassava mosaic virus DNA 1 (K. W. Buck,
R. H. A. Coutts, I. T. D. Petty & J. Stanley, unpublished data). Hence these
two viruses are distinct.
- Adejare & Coutts, Phytopath. Z. 103: 198, 1982.
- Bisaro, Hamilton, Coutts & Buck, Nucleic Acids Res. 10: 4913, 1982.
- Costa, A. Rev. Phytopath. 14: 429, 1976.
- Costa, Oliveira & Silva, 8th Ann. Congr. Soc. Bras. Fitopathol. Mossoro, Brazil (Abstr.) 1975.
- De Uzcategui & Lastra, Phytopathology 68: 985, 1978.
- Goodman & Bird, CMI/AAB Descr. Pl. Viruses 192: 4 pp., 1978.
- Hamilton, Sanders, Coutts & Buck, FEMS Microbiol. Lett. 11: 263, 1981.
- Hamilton, Bisaro & Buck, Nucleic Acids Res. 10: 4901, 1982.
- Hamilton, Bisaro, Coutts & Buck, Nucleic Acids Res. 11: 7387, 1983.
- Hamilton, Stein, Coutts & Buck, EMBO J. 3: 2197, 1984.
- Matyis, Silva, Oliveira & Costa, Summa Phytopath. 1: 267, 1975.
- Osaki & Inouye, CMI/AAB Descr. Pl. Viruses 232: 4 pp., 1981.
- Roberts, Robinson & Harrison, J. gen. Virol. 65: 1723, 1984.
- Russo, Cohen & Martelli, J. gen. Virol. 49: 209, 1980.
- Stein, Coutts & Buck, J. gen. Virol. 64: 2493, 1983.
- Sunter, Coutts & Buck, Biochem. Biophys. Res. Comm. 118: 747, 1984.
- Verma, Srivastava & Mathur, Pl. Dis. Reptr 59: 494, 1975.
Golden mosaic symptoms and leaf curling in Nicotiana benthamiana.
Golden mosaic symptoms and curling of a systemically infected Datura
Autoradiograph of blot-hybridizations of crude DNA extracts from (A)
Euphorbia prunifolia leaves infected with euphorbia mosaic virus, (B)
N. benthamiana leaves infected with tomato golden mosaic virus, to a
32P-labelled probe of a nick-translated mixture of the cloned
components of tomato golden mosaic virus DNA. Bands marked 1, 2 and 3 in (B)
represent the open circular, linear and supercoiled forms of tomato golden mosaic
virus dsDNA band 4 is the circular ssDNA that occurs in the virus particles
(Hamilton et al., 1982).
Gel immunodiffusion analysis. Wells contain: top, antiserum to tomato
golden mosaic virus; bottom left, African cassava mosaic virus (Kenyan type
strain); bottom right, tomato golden mosaic virus. Reproduced from Stein
et al. (1983) with permission.
Electron micrograph of virus negatively stained with 1% sodium
phosphotungstate, pH 5.0. Bar represents 100 nm. Courtesy of J. C. Matyis,
D. M. Silva, A. R. Oliveira and A. S. Costa.
Hydrophilicity analysis of the predicted amino acid sequences of the
coat protein genes of (above) tomato golden mosaic virus, (below) African cassava
mosaic virus (Kenyan type strain). Reproduced from Hamilton et al. (1984)
Potential coding regions in TGMV DNA A and DNA B. All ORFs starting with
an ATG triplet and coding for proteins with M. Wt > 10,000 are shown as thick
black arrows and the common 200-base region is shaded. Solid triangles indicate
the position of AATAAA sequences and open triangles TATA boxes. More than one
TATA box in the same region is indicated by a number adjacent to the open triangle.
A scale is marked around the outside of each circle at 100-base intervals. The
1-kb and 2-kb positions are numbered. Reproduced from Hamilton et al. (1984)