Forced recombination between distinct strains of Maize streak virus

Recombination between divergent virus genomes is believed to be a major mec hanism for generation of novel virus genotypes. We have examined the recomb ination process in geminiviruses by forcing recombination between two disti nct isolates of Maize streak virus (MSV), MSV-Kom and MSV-Set. Heterodimeri c agroinfectious constructs containing tandemly cloned mixtures of complete or partial MSV-Set and MSV-Kom genomes were used to simulate a circular di meric form similar to that which would be expected to occur following a sin gle intermolecular crossing-over event between MSV-Set and MSV-Kom replicat ive form DNAs at the long intergenic region (LIR)-movement protein gene (MP ) interface. We isolated, analysed and biologically characterized many of t he recombinant MSV genomes that were generated from the constructs in plant a. Apart from having the same simulated breakpoint at the LIR-MP interface, all the genomes examined had a second breakpoint that had been generated t hrough either intramolecular homologous recombination or a replicational re lease mechanism. The pathogenicities of six predominantly MSV-Kom-like reco mbinants were tested in maize. While all were capable of producing a sympto matic infection in this host, none was more virulent than MSV-Kom and only two were more virulent than MSV-Set. The two most virulent recombinants wer e leafhopper transmitted to a range of differentially MSV-resistant maize, wheat and barley genotypes and both were found to have unique biological pr operties.