Satellite RNA and its use for Transformation - Satellite RNAs are species of RNA associated with specific strains of some plant RNA viruses, although it is not necessary for their replication. Replication of this satellite RNA depends on the virus, so that it gets packaged with it to cause infection elsewhere.
Therefore, satellite RNA depends on virus for its replication and transmission, even though it is unrelated to viral genome. Presence of sat RNA leads to reduction in severity of disease symptoms, and therefore has been used for developing resistance against specific viruses.
U sing the above principle, transgenic tobacco plants have been produced which carried a DNA fragment, which when transcribed gives a species of satellite RNA which can reduce the severity of disease. Following two such attempts were made:

These transgenic plants are protected against the deleterious effect of subsequent TobRV infection. The advantage of using satellite RNA strategy over coat protein is that satellite RNA is not constitutively expressed like coat protein, but is ex. pressed only after virus infection.