Browsing by Author "Briddon, Rob"

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    Comparative analysis of Panicum streak virus and Maize streak virus diversity, recombination patterns and phylogeography
    (BioMed Central Ltd, 2009) Varsani, Arvind; Monjane, Aderito; Donaldson, Lara; Oluwafemi, Sunday; Zinga, Innocent; Komba, Ephrem; Plakoutene, Didier; Mandakombo, Noella; Mboukoulida, Joseph; Semballa, Silla; Briddon, Rob; Markham, Peter; Lett, Jean-Michel; Lefeuvre, Pierre; Ry
    BACKGROUND: Panicum streak virus (PanSV; Family Geminiviridae; Genus Mastrevirus) is a close relative of Maize streak virus (MSV), the most serious viral threat to maize production in Africa. PanSV and MSV have the same leafhopper vector species, largely overlapping natural host ranges and similar geographical distributions across Africa and its associated Indian Ocean Islands. Unlike MSV, however, PanSV has no known economic relevance. RESULTS: Here we report on 16 new PanSV full genome sequences sampled throughout Africa and use these together with others in public databases to reveal that PanSV and MSV populations in general share very similar patterns of genetic exchange and geographically structured diversity. A potentially important difference between the species, however, is that the movement of MSV strains throughout Africa is apparently less constrained than that of PanSV strains. Interestingly the MSV-A strain which causes maize streak disease is apparently the most mobile of all the PanSV and MSV strains investigated. CONCLUSION: We therefore hypothesize that the generally increased mobility of MSV relative to other closely related species such as PanSV, may have been an important evolutionary step in the eventual emergence of MSV-A as a serious agricultural pathogen.The GenBank accession numbers for the sequences reported in this paper are GQ415386-GQ415401
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    Experimental evidence indicating that mastreviruses probably did not co-diverge with their hosts
    (BioMed Central Ltd, 2009) Harkins, Gordon; Delport, Wayne; Duffy, Siobain; Wood, Natasha; Monjane, Aderito; Owor, Betty; Donaldson, Lara; Saumtally, Salem; Triton, Guy; Briddon, Rob; Shepherd, Dionne; Rybicki, Edward; Martin, Darren; Varsani, Arvind
    BACKGROUND:Despite the demonstration that geminiviruses, like many other single stranded DNA viruses, are evolving at rates similar to those of RNA viruses, a recent study has suggested that grass-infecting species in the genus Mastrevirus may have co-diverged with their hosts over millions of years. This "co-divergence hypothesis" requires that long-term mastrevirus substitution rates be at least 100,000-fold lower than their basal mutation rates and 10,000-fold lower than their observable short-term substitution rates. The credibility of this hypothesis, therefore, hinges on the testable claim that negative selection during mastrevirus evolution is so potent that it effectively purges 99.999% of all mutations that occur. RESULTS: We have conducted long-term evolution experiments lasting between 6 and 32 years, where we have determined substitution rates of between 2 and 3 x 10-4 substitutions/site/year for the mastreviruses Maize streak virus (MSV) and Sugarcane streak Reunion virus (SSRV). We further show that mutation biases are similar for different geminivirus genera, suggesting that mutational processes that drive high basal mutation rates are conserved across the family. Rather than displaying signs of extremely severe negative selection as implied by the co-divergence hypothesis, our evolution experiments indicate that MSV and SSRV are predominantly evolving under neutral genetic drift. CONCLUSION: The absence of strong negative selection signals within our evolution experiments and the uniformly high geminivirus substitution rates that we and others have reported suggest that mastreviruses cannot have co-diverged with their hosts.