418
November 2007
Family: Alphaflexiviridae
Genus: Potexvirus
Species: Caladium virus X
Acronym: CalVX


Caladium virus X

E. B. Rivas
Plant Virus Laboratory, Centro de Pesquisa e Desenvolvimento de Sanidade Vegetal, Instituto Biológico, São Paulo, SP, Brazil.

Contents

Introduction
Main Diseases
Geographical Distribution
Host Range and Symptomatology
Strains
Transmission by Vectors
Transmission through Seed
Transmission by Grafting
Transmission by Dodder
Serology
Nucleic Acid Hybridization
Relationships
Stability in Sap
Purification
Properties of Particles
Particle Structure
Particle Composition
Properties of Infective Nucleic Acid
Molecular Structure
Genome Properties
Satellites
Relations with Cells and Tissues
Ecology and Control
Notes
References
Acknowledgements
Figures

Introduction

A virus with flexuous rod-shaped particles c. 460 x 14 nm, containing a single capsid protein of approximately 26 kDa. The virus was isolated from the aroid Caladium bicolor in Brazil and is readily transmitted by mechanical inoculation to a few species of dicots and monocots.

Main Diseases

Caladium virus X (CalVX) was detected in a mixed infection with Dasheen mosaic virus (DsMV) in Caladium bicolor (Araceae) (Rivas et al., 2005). The plant showing chlorotic spots and necrotic rings (Fig.1) was found in a domestic garden in São Paulo State, Brazil (Rivas et al., 2004) and has not yet been found elsewhere.

Geographical Distribution

So far known only in a single plant from southeast Brazil.

Host Range and Symptomatology

Experimentally, CalVX has been transmitted to a few species by mechanical inoculation (Rivas et al., 2005).

The virus induces local necrotic lesions in Gomphrena globosa (Amaranthaceae), Chenopodium spp. (Chenopodiaceae), Plantago sp. (Plantaginaceae), Portulaca oleracea var. sativa (Portulacaceae), and Datura stramonium (Solanaceae).

The virus infects systemically Caladium spp., Colocasia esculenta, Philodendron sp., and Nicotiana benthamiana. The symptoms in experimentally infected aroids characteristically tend to disappear. In Caladium species, CalVX can induce chlorotic spots, green rings (Fig.2), mosaic, red pinpoints and degeneracy.

Diagnostic species

Philodendron sp. displays chlorotic spots in inoculated leaves, and yellow vein-banding, chlorotic spots and rings in systemic infections (Fig.3).

G. globosa develops local necrotic spots with red halos (Fig.4).

N. benthamiana displays necrotic spots and ring spots in inoculated leaves, and necrotic streak, necrotic pinpoints and mild leaf deformation in systemic infections (Fig.5).

Propagation species

N. benthamiana, Philodendron sp., C. esculenta.

Assay species

Chenopodium spp., D. stramonium and G. globosa.

Insusceptible species

Anthurium andraeanum, Dieffenbachia sp., N. glutinosa, N. tabacum 'White Burley', Petunia hybrida.

Transmission by Vectors

Not transmitted by the aphid Myzus persicae from aroids to aroids.

Transmission through Seed

Not seed-borne in N. benthamiana.

Serology

CalVX is serologically unrelated to other potexviruses: Alternanthera mosaic virus, Bamboo mosaic virus, Cactus virus X, Cassava common mosaic virus, Clover yellow mosaic virus, Cymbidium mosaic virus, Dioscorea latent virus, Foxtail mosaic virus, Hosta virus X, Hydrangea ringspot virus, Narcissus mosaic virus, Nerine virus X, Papaya mosaic virus, Potato virus X (PVX), Tulip virus X, Viola mottle virus, White clover mosaic virus and PVX-Brazilian isolate (Rivas et al., 2005).

Relationships

The RdRp domain of CalVX shared significant identity with potexviruses, ranging from 65.8% (Cymbidium mosaic virus) to 60.3% (Cassava common mosaic virus) and from 68.0% (Strawberry mild yellow edge virus) to 58.4% (Foxtail mosaic virus) at the nucleotide and amino acid levels, respectively.

Phylogenetic analysis using the RdRp region suggests that the virus shares a common ancestor with Cymbidium mosaic virus, Potato aucuba mosaic virus, Pepino mosaic virus, White clover mosaic virus, Narcissus mosaic virus and Scallion mosaic virus lineages (Rivas et al., 2005; Fig.6).

Stability in Sap

In N. benthamiana sap, the thermal inactivation point is between 60 and 65 °C, dilution end-point is between 10-2 and 10-3, and infectivity is lost at room temperature (c. 24 °C) after 6 days (Rivas, 2002).

The virus can be maintained in dried tissues of G. globosa and N. benthamiana for 3 years if stored below -10 °C.

Purification

Homogenize infected leaves of N. benthamiana, 14-17 days after inoculation, or G. globosa, 13 days after inoculation, at the rate of 1 g in 4 ml buffer (0.01 M phosphate, pH 8.0, containing 0.5% Na2SO3). Clarify by low speed centrifugation and chloroform (1:1 v/v). Precipitate the virus by adding polyethylene glycol (M. Wt 6000) to 4% plus 0.6% NaCl. Suspend the pellet from low speed centrifugation in the same buffer and give the preparation one cycle of differential centrifugation (10 min at 6000g; 120 min at 79000g) (Rivas, 2002).

No light-scattering zones of virus particles were observed when the pellet was loaded onto 0-50% and 10-40% linear sucrose density gradients, or centrifuged in CsCl at 1.28 g/ml. In these conditions, the virus was in high concentration in the pellets (Rivas, 2002).

Properties of Particles

A260/A280: 1.32.

Particle Structure

The virus particles are flexuous filaments measuring c. 460 x 14 nm in 2% uranyl acetate.

Particle Composition

Nucleic acid: RNA, probably single-stranded, c. 9.8% of the particle weight (estimated from A260/A280).

Protein: A single polypeptide species with an apparent molecular mass of 26,000, estimated by electrophoresis in polyacrylamide/SDS gels.

Genome Properties

Only the sequence of the RNA-dependent RNA polymerase domain (GenBank accession number AY727533) has been determined but it is expected that the genome organisation will resemble that of other potexviruses.

Relations with Cells and Tissues

In epidermal cells of G. globosa leaves, complex (Fig.7) and banded (Fig.8) inclusion bodies have been observed by light microscopy. In ultra-thin sections of mesophyll cells, masses of virus-like particles in the cytoplasm, electron-dense crystalline inclusions in the nucleus (Fig.9) and cytoplasm (Fig.10) could be observed. Sometimes, the inclusions appear to be enveloped by a membrane.

Notes

CalVX was isolated from Caladium bicolor co-infected with the potyvirus Dasheen mosaic virus (DsMV). Chlorotic and necrotic spots and rings were present in leaves from naturally infected plant. CalVX was biologically purified by a single passage in G. globosa, since DsMV cannot be mechanically transmitted to this plant, and subsequently propagated in N. benthamiana. Attempts to transmit CalVX in combination with DsMV by Myzus persicae failed.

References

  1. Rivas, Ph. D. Thesis, Univ. São Paulo, 152 pp., 2002.
  2. Rivas, Duarte, Alexandre, Galleti, Harakava & Fernandes, Journal of Plant Pathology 87: 109, 2005.
  3. Rivas, Galleti, Duarte, Alexandre & Estelita, Arquivos do Instituto Biológico 71: 457, 2004.
  4. Tamura, Dudley, Nei & Kumar, Molecular Biology and Evolution 24: 1596, 2007.


Figure 1

Chlorotic spots and rings, and necrotic rings in leaf of Caladium bicolor naturally infected with Caladium virus X and Dasheen mosaic virus (Rivas et al., 2004; used by permission).

Figure 2

Systemic symptoms in C. bicolor experimentally infected by Caladium virus X.

Figure 3

Veinal chlorosis and necrosis, chlorotic spots and rings in experimentally infected Philodendron sp.

Figure 4

Local lesions in leaf of Gomphrena globosa.

Figure 5

Systemic symptoms in inoculated Nicotiana benthamiana.

Figure 6

Phylogenetic tree of the aligned RdRp nucleotide sequences of members of the genus Potexvirus to show the position of Caladium virus X. The tree was generated in MEGA4 (Tamura et al., 2007) using the Neighbor-Joining Maximum Composite Likelihood method. The values at the forks indicate the percentage of trees in which this grouping occurred after bootstrapping (10,000 replicates; shown only when >60%). AlsVX, Alstroemeria virus X; AltMV, Alternanthera mosaic virus; AV-3, Asparagus virus 3; BaMV, Bamboo mosaic virus; CalVX, Caladium virus X; ChMVX, Chenopodium mosaic virus X; ClYMV, Clover yellow mosaic virus; CsCMV, Cassava common mosaic virus; CVX, Cactus virus X; CymMV, Cymbidium mosaic virus; FoMV, Foxtail mosaic virus; HVX, Hosta virus X; HdRSV, Hydrangea ringspot virus; LVX, Lily virus X; MVX, Mint virus X; NVX, Nerine virus X; NMV, Narcissus mosaic virus; OpVX, Opuntia virus X; PAMV, Potato aucuba mosaic virus; PapMV, Papaya mosaic virus; PepMV, Pepino mosaic virus; PlAMV, Plantago asiatica mosaic virus; PVX, Potato virus X; SMYEV, Strawberry mild yellow edge virus; TVX, Tulip virus X; WClMV, White clover mosaic virus; ZyVX, Zygocactus virus X.

Figure 7

Light micrograph of infected G. globosa epidermal cell showing inclusion body (arrowhead) near the nucleus, stained with Calcomine orange and Luxol brilliant green. Bar represents 10 µm (Rivas et al., 2004; used by permission).

Figure 8

Light micrograph of infected G. globosa epidermal cell showing banded inclusion (arrowhead) immersed in granular and dense region around the nucleus, stained with Azure A. Bar represents 10 µm (Rivas et al., 2004; used by permission).

Figure 9

Electron micrograph of ultra-thin section of infected G. globosa mesophyll cell showing electron-dense crystalline inclusion in the nucleus. Bar represents 500 nm (Rivas et al., 2004; used by permission).

Figure 10

Electron micrograph of ultra-thin section of infected G. globosa mesophyll cell showing electron-dense crystalline inclusion in the cytoplasm. Bar represents 500 nm (Rivas et al., 2004; used by permission).