Interference with brome mosaic virus replication in transgenic rice

Rice protoplasts were transformed with four separate constructs derived from the genome of brome mosaic virus (BMV) and regenerated into callus and plant lines. Constructs used for transformation were designed to yield (i) an artificial, defective, interfering RNA derived from RNA-2, (ii) a sense tRNA-like structure corresponding to the 3' end of RNA-2, (iii) an antisense sequence corresponding to the intercistronic region of BMV RNA-3, and (iv) RNA encoding the viral capsid protein. Protoplasts obtained from transgenic plants or callus lines showed up to 95% reduction in accumulation of progeny viral RNAs when inoculated with virion RNA. The addition of up to 20-fold the normal level of inoculum was required to overcome the induced resistance. The observed interference appeared to be mediated through viral RNAs rather than protein products, but was not proportional to detectable levels of messenger expression, suggesting the induction of a host defense mechanism.