MSV Variation

Figures

Figure 1:

Composite relationship dendrogram derived from serological relationship data

The figure is a composite of data from Dekker et al. (1988) and Pinner et al. (1992). Viruses names are derived from these papers; MSV-N is the severe MSV-N of Mullineaux et al. (1984); MSV-S(R)S is a Setaria sp. strain from Rwanda, MSV-C(M)S is a Coix sp. strain from Mauritius; PanSV-K(P)B is a Kenyan strain; PanSV-P(N)P a Nigerian strain. Horizontal distances are drawn roughly to scale in terms of distance defined by serological differentiation indices (SDIs); vertical distances are arbitrary. Strain level relationships are boxed, as are species level relationships: thus nodes of the dendrogram within one of the two shaded boxes define either strain- or species-level relationships. Note the very close relationship between the maize-infecting MSV-N and Setaria-infecting MSV-S(R)S.

Figure 2:

Illustration of functionality of MSV restriction map database

2a: graphic representation of three maps, and list of restriction sites as stored in the program Resolve (EH Harley, Dept Chemical Pathology, Univ Cape Town Medical School). MSV-Kom = moderately severe local virus isolate; MSV-WES = MSV from wheat / Eleusine sp.; MSV-Set = MSV from Setaria sp. (Hughes et al., 1992). B, g, P, etc.: restriction enzyme sites (see Hughes et al., 1992). Sequence of restriction sites = positions on the genome as a number line linearised at the BamH1 site (=B). Note differences between the isolates.

2b: calculated percent nucleotide sequence divergences between pairs of maps for MSV-Kom(atipoort) (Hughes et al., 1992); MSV-N (see legend above); MSV-K(en) (Howell, 1984); MSV-S(A) (Lazarowitz, 1988); MSV-WES and MSV-Set(aria) (Hughes et al., 1992). This is done as one of the map analysis options in Resolve: here we chose 6-base-cutter enzymes only, and allowed 3% map error (actual ~ 2%). Note how similar the maize viruses are to one another (within 2%), and how different the grass viruses are (up to 27%; actual sequence divergence = 22%).

Figure 3:

Relationship dendrogram drawn from restriction map comparisons.

The dendrogram was constructed using a program called NJTREE from data produced as outlined for Fig. 2b (see also Hughes et al., 1992). We compared the grass viruses PanSV (from Karino, Mpumalanga), MSV-Setaria (from Natal); and the maize viruses MSV-Kom (Komatipoort), MSV-Ken, MSV-Koe, MSV-SA, and MSV-Mak(hatini Flats), with a map of MSV-Zim(babwe) sent by Rob Briddon, JIC, Norwich. Note the close clustering of viruses of maize - with no geographic bias being apparent - and the distant clustering of viruses of grasses.

Figure 4:

Relationship dendrogram drawn from sequence comparisons of PCR-generated DNA fragments from maize, wheat and grass strains of MSV

Approximately 250 base pair DNA fragments generated using PCR primers described by Rybicki and Hughes (1990) were cloned into E coli plasmids, and at least three independent clones were sequenced. The sequences were aligned and compared as described (Rybicki and Hughes, 1990), and a dendrogram constructed, rooted on a PanSV sequence (not shown). Names shown italicised were sequenced in our laboratory; other sequences were from publications (see text). MSV-VM and -Tas were from wheat (Vaalharts irrigation scheme and Elsenburg College, respectively); MSV-Dig was from a Digitaria sp., and MSV-WES was found in both an Eleusine sp. and in wheat in the Free State. MSV-Setaria came from a grass found in a sugarcane field in Natal. Horizontal distance scale is shown (% sequence divergence).

Figure 5:

Electropherograms stained with ethidium bromide of restriction endonuclease digests of DNA fragments generated by PCR using "streak virus specific" primers.

DNA preparations from infected plants were amplified using oligonucleotide primers specific for "African streak" viruses, then cut with xxxx, and electrophoresed. Note how differently virus DNA amplified from different hosts cuts with the same enzyme (19, MSV-Set ex Setaria; 20-22, PanSVs ex Panicum).

Figure 6:

Relationship dendrogram drawn from partial and complete genome sequences available for MSV-related Mastreviruses

Sequence names in italics were sequenced in our laboratory; all other MSV sequences and SSV-Mill(et) are from Briddon et al. (1994). Sequences were aligned using DNAMAN for Windows 95 (Lynnon Biosoft, Quebec, Canada), and a neighbour-joining phylogenetic tree constructed using the same software. Horizontal distances indicate sequence divergence; vertical distances are arbitrary. Note the close association of all maize-type MSVs, the separate clustering of MSV-Reu(nion) and MSV-Ma(uritius) within the larger group, and the clear separation of MSV-Set(aria) and other MSVs.

Copyright Ed Rybicki, November 1997
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