Browsing by Author "Lakay, Francisco"

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    Adaptive evolution by recombination is not associated with increased mutation rates in Maize streak virus
    (BioMed Central Ltd, 2012) Monjane, Aderito; Pande, Daniel; Lakay, Francisco; Shepherd, Dionne; van der Walt, Eric; Lefeuvre, Pierre; Lett, Jean-Michel; Varsani, Arvind; Rybicki, Edward; Martin, Darren
    BACKGROUND: Single-stranded (ss) DNA viruses in the family Geminiviridae are proving to be very useful in real-time evolution studies. The high mutation rate of geminiviruses and other ssDNA viruses is somewhat mysterious in that their DNA genomes are replicated in host nuclei by high fidelity host polymerases. Although strand specific mutation biases observed in virus species from the geminivirus genus Mastrevirus indicate that the high mutation rates in viruses in this genus may be due to mutational processes that operate specifically on ssDNA, it is currently unknown whether viruses from other genera display similar strand specific mutation biases. Also, geminivirus genomes frequently recombine with one another and an alternative cause of their high mutation rates could be that the recombination process is either directly mutagenic or produces a selective environment in which the survival of mutants is favoured. To investigate whether there is an association between recombination and increased basal mutation rates or increased degrees of selection favoring the survival of mutations, we compared the mutation dynamics of the MSV-MatA and MSV-VW field isolates of Maize streak virus (MSV; Mastrevirus), with both a laboratory constructed MSV recombinant, and MSV recombinants closely resembling MSV-MatA. To determine whether strand specific mutation biases are a general characteristic of geminivirus evolution we compared mutation spectra arising during these MSV experiments with those arising during similar experiments involving the geminivirus Tomato yellow leaf curl virus (Begomovirus genus). RESULTS: Although both the genomic distribution of mutations and the occurrence of various convergent mutations at specific genomic sites indicated that either mutation hotspots or selection for adaptive mutations might elevate observed mutation rates in MSV, we found no association between recombination and mutation rates. Importantly, when comparing the mutation spectra of MSV and TYLCV we observed similar strand specific mutation biases arising predominantly from imbalances in the complementary mutations G->T: C->A. CONCLUSIONS: While our results suggest that recombination does not strongly influence mutation rates in MSV, they indicate that high geminivirus mutation rates are at least partially attributable to increased susceptibility of all geminivirus genomes to oxidative damage while in a single stranded state.
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    The spread of Tomato yellow leaf curl virus from the Middle East to the world
    (Public Library of Science, 2010) Lefeuvre, Pierre; Martin, Darren P; Harkins, Gordon; Lemey, Philippe; Gray, Alistair J A; Meredith, Sandra; Lakay, Francisco; Monjane, Adérito; Lett, Jean-Michel; Varsani, Arvind
    Author Summary Tomato yellow leaf curl virus (TYLCV) poses a serious threat to tomato production throughout the temperate regions of the world. Our analysis, using a suite of bioinformatic tools applied to all publically available TYLCV genome sequences, suggests that the virus probably arose somewhere in the Middle East between the 1930s and 1950s and that its global spread only began in the 1980s after the emergence of two strains - TYLCV-Mld and -IL. In agreement with others, we also find that the highly invasive TYLCV-IL strain has jumped at least twice to the Americas - once from the Mediterranean basin in the early 1990s and once from Asia in the early 2000s. Although our results corroborate historical accounts of TYLCV-like symptoms in tomato crops in the Jordan Valley in the late 1920s, they indicate that the region around Iran is both the current center of TYLCV diversity and is the site where the most intensive ongoing TYLCV evolution is taking place. However, our analysis indicates that this region is epidemiologically isolated suggesting that novel TYLCV variants found there are probably not direct global threats. Moreover, we identify the Mediterranean basin as the main launch-pad of global TYLCV movements.