PHENOTYPIC VARIATION IN TRANSGENIC TOBACCO EXPRESSING MUTATED GEMINIVIRUS MOVEMENT PATHOGENICITY (BC1) PROTEINS/

Tobacco plants were transformed with the movement protein (pathogenici ty) gene (BC1) from tomato mottle geminivirus (TMoV), using Agrobacter ium-mediated transformation, Different transgenic tobacco lines that e xpressed high levels of the BC1 protein had phenotypes ranging from pl ants with severe stunting and leaf mottling (resembling geminivirus sy mptoms) to plants with no visible symptoms. The sequence data for the BC1 transgene from the transgenic plants with the different phenotypes indicated an association of spontaneously mutated forms of the BC1 ge ne in the transformed tobacco with phenotype variations. One mutated t ransgene associated with an asymptomatic phenotype had a major deletio n at the C terminus of 119 amino acid residues with a recombination re sulting in the addition of 26 amino acid residues of unidentified orig in, This asymptomatic, mutated BC1 attenuated the phenotypic expressio n of the symptomatic BC1 in a tobacco line containing both copies of t he BC1 gene. Another mutated farm of the BC1 gene amplified from an as ymptomatic, multicopy transgenic tobacco plant did not induce symptoms when transiently expressed in tobacco via a virus vector, The symptom attenuation in the transgenic tobacco by the asymptomatic BC1 may inv olve trans-dominant negative interference.