THE COAT PROTEIN OF TURNIP CRINKLE VIRUS IS INVOLVED IN SUBVIRAL RNA-MEDIATED SYMPTOM MODULATION AND ACCUMULATION

Some satellite (sat-) and defective interfering (DI) RNAs associated w ith plant viruses intensify or ameliorate the symptoms of the virus. W e recently demonstrated that the TCV coat protein (CP) is involved in symptom modulation by sat-RNA C. Two additional subviral RNAs have now been tested for effect of the CP on symptom modulation. DI RNA G, whi ch normally intensifies the symptoms of TCV, is able to attenuate symp toms if the TCV CP is replaced with the CP of cardamine chlorotic flec k virus. DI RNA G had no effect on the symptoms of TCV with a single b ase alteration in the CP open reading frame, unlike sat-RNA C, which w as able to ameliorate the symptoms of the mutant TCV. Using a hybrid s at-RNA constructed from sat-RNA C and TCV (which shares a similar 3'-e nd region with DI RNA G), the 3'-terminal 53 bases of sat-RNA C were f ound to be involved in symptom attenuation, which was directly correla ted with the lack of detectable viral genomic RNA in whole plants. Sat -RNA D had no effect on the symptoms of mutant or wild-type TCV. The a ccumulation of TCV subviral RNAs in plants and protoplasts was also fo und to be strongly influenced by the presence or absence of the wild-t ype TCV CP. (C) 1997 Academic Press.