Artificial microRNAs for plant virus resistance.

RNA silencing is a natural plant defense system against foreign genetic elements including viruses. This natural antiviral mechanism has been adopted to develop virus-resistant plants by the expression of long stretches of viral sequences in perfectly paired double-stranded or stem-loop forms which, in turn, are processed into virus-specific small interfering RNAs (vsiRNAs) by the host's RNA silencing machinery. Recently, another set of RNA silencing-related small RNAs, microRNAs (miRNAs), have been exploited to engineer virus resistance in plants. Expression of modified miRNA precursors results in the production of artificial miRNAs (amiRNAs) targeting viral RNA sequences. The amiRNA-mediated virus resistance is efficient and superior to the long viral RNA-based antiviral approaches in that properly selected amiRNA sequences would have little chance to target the host plant genes or to complement or recombine with other invading viruses.