ADDITION OF NUCLEOTIDES SIMILAR TO DELETED CAA REPEATS IN THE 5' NONCODING REGION OF TOMATO MOSAIC-VIRUS RNA FOLLOWING PROPAGATION

Previously we made a series of deletion mutants in the 5' non-coding r egion of tomato mosaic tobamovirus (ToMV) RNA and checked their abilit y to replicate in tobacco protoplasts. Long deletions in this region c aused the virus to lose the ability to replicate. Several mutants with deletions of about 10 nucleotides (short deletion mutants; SDM) retai ned the ability to replicate. In this study, we inoculated SDMs onto s ystemic host plants and observed their symptoms. One mutant (19/32) ca used severe mosaic symptoms on some tobacco plants (Nicotiana tabacum cv. Samsun) but no symptoms on others. Virus accumulation in 19/32-ino culated plants paralleled the severity of symptoms. Four CAA repeat se quences were deleted in 19/32. Progeny 19/32 from plants showing sever e systemic mosaic symptoms had acquired additional nucleotides in this region. We conclude that the CAA repeat sequence is related to the fi tness of the virus population to replicate in whole plants rather than to translation of ToMV replicase genes.