A defective interfering RNA molecule in cymbidium ringspot virus infections

A small RNA (DI RNA), approx. 400 bp in length, was found in plants inoculated with cymbidium ringspot tombusvirus (CyRSV). DI RNA contained sequences derived from at least three regions of the CyRSV genome and was encapsidated in CyRSV protein. DI RNA was formed in plants inoculated with purified genome-size RNA and a double-stranded form was detected in dsRNA extracted from infected tissue. Symptoms of CyRSV infection in Nicotiana clevelandii were less severe when DI RNA was present in the inocula used suggesting that DI RNA interferes with symptom expression.