Abstract
RNA silencing is a sequence-specific RNA degradation system that is important in the defense of plants against viral infection and transposition of transposable elements. The RNA silencing in transgenic plants can systemically spread from locally silenced tissues throughout the plant. Although the signals for this systemic spreading of RNA silencing have not been identified, the small RNAs with 21-25 nucleotides should be involved. Here, we report the systemic RNA silencing of the tobacco endoplasmic reticulum ω-3 fatty acid desaturase gene (NtFAD3). In the silenced stock, hpRNAs against the NtFAD3 gene are transcribed. When a scion overexpressing the NtFAD3 gene are grafted onto this silenced stocks, the systemic RNA silencing occurred. The siRNAs against the NtFAD3 gene were generated mainly in the 3' downstream region of the NtFAD3 transgene in the systemically silenced scions.
