Satellite RNA-mediated resistance to turnip crinkle virus in Arabidopsis involves a reduction in virus movement

Satellite RNAs (sat-RNAs) are parasites of viruses that can mediate resistance to the helper virus. We previously showed that a sat-RNA (sat-RNA C) of turnip crinkle virus (TCV), which normally intensifies symptoms of TCV, is able to attenuate symptoms when TCV contains the coat protein (CP) of cardamine chlorotic fleck virus (TCV-CPCCFV). We have now determined that sat-RNA C also attenuates symptoms of TCV containing an alteration in the initiating AUG of the CP open reading frame (TCV-CPm). TCV-CPm, which is able to move systemically in both the TCV-susceptible ecotype Columbia (Col-0) and the TCV-resistant ecotype Dijon (Di-0), produced a reduced level of CP and no detectable virions in infected plants. Sat-RNA C reduced the accumulation of TCV-CPm by < 25% in protoplasts while reducing the level of TCV-CPm by 90 to 100% in uninoculated leaves of Col-0 and Di-0. Our results suggest that in the presence of a reduced level of a possibly altered CP, sat-RNA C reduces virus long-distance movement in a manner that is independent of the salicylic acid-dependent defense pathway.