The distinct disease phenotypes of the common and yellow vein strains of Tomato golden mosaic virus are determined by nucleotide differences in the 3'-terminal region of the gene encoding the movement protein

In Nicotiana benthamiana, the common strain of the bipartite geminivirus To mato golden mosaic virus (csTGMV) induces extensive chlorosis whereas the y ellow vein strain (yvTGMV) produces veinal chlorosis on systemically infect ed leaves. In Datura stramonium, csTGMV produces leaf distortion and a seve re chlorotic mosaic whereas yvTGMV produces only small chlorotic lesions on systemically infected leaves. Genetic recombination and site-directed muta genesis studies using infectious clones of csTGMV and yvTGMV have identifie d a role in symptom production for the gene encoding the movement protein ( MP), The MP amino acid at position 272, either valine (csTGMV) or isoleucin e (yvTGMV), influenced symptoms in both hosts by inducing an intermediate p henotype when exchanged between the two strains. Exchange of an additional strain-specific MP amino acid at position 288, either glutamine (csTGMV) or lysine (yvTGMV), resulted in the change of symptom phenotype to that of th e other strain. In situ hybridization analysis in N. benthamiana demonstrat ed that there was no qualitative difference in the tissue distribution of t he two strains although csTGMV accumulated in higher amounts, suggesting th at the efficiency of virus movement rather than distinct differences in tis sue specificity of the strains is responsible for the symptom phenotypes.