SYMPTOM ATTENUATION BY A NORMALLY VIRULENT SATELLITE RNA OF TURNIP CRINKLE VIRUS IS ASSOCIATED WITH THE COAT PROTEIN OPEN READING FRAME

Many satellite RNAs (sat-RNAs) can attenuate or intensify the symptoms produced by their helper virus. Sat-RNA C, associated with turnip cri nkle virus (TCV), was previously found to intensify the symptoms of TC V on all plants in which TCV produced visible symptoms. However, when the coat protein open reading frame (ORF) of TCV was precisely exchang ed with that of cardamine chlorotic fleck virus, sat-RNA C attenuated the moderate symptoms of the chimeric virus when Arabidopsis plants we re coinoculated with the chimeric virus, Symptom attenuation was corre lated with a reduction in viral RNA levels in inoculated and uninocula ted leaves, In protoplasts, the presence of sat-RNA C resulted in a re duction of similar to 70% in the chimeric viral genomic RNA at 44 hr p ostinoculation, whereas the sat-RNA was consistently amplified to high er levels by the chimeric virus than by wild-type TCV, TCV with a dele tion of the coat protein ORF also resulted in a similar increase in sa t-RNA C levels in protoplasts, indicating that the TCV coat protein, o r its ORF, downregulates the synthesis of sat-RNA C. These results sug gest that the coat protein or its ORF is a viral determinant for sympt om modulation by sat-RNA C, and symptom attenuation is at least partly due to inhibition of virus accumulation.