Investigation of Maize streak virus pathogenicity determinants using chimaeric genomes.

Genes and intergenic regions were reciprocally exchanged between a highly pathogenic Maize streak virus (MSV) isolate (MSV-MatA) and three less pathogenic isolates (MSV-Kom, MSV-R2, and MSV-VW) to determine the contribution of individual genome constituents to MSV pathogenicity in maize. Comparison of disease symptoms produced by the 54 resulting chimaeras and parental viruses enabled identification of genome constituents that are primarily responsible for the heightened pathogenicity of MSV-MatA in maize. Whereas pathogenicity determinants were detected in all of the MSV genomic regions examined, generally only chimaeras containing the MSV-MatA long intergenic region, coat protein gene, and/or movement protein gene were more pathogenic than the milder MSV isolates from which most of their genomes were derived. The pathogenicity of chimeras was strongly influenced by the relatedness of their parental viruses and evidence was found of nucleotide sequence-dependent interactions between both coding and intergenic regions.