Systemic silencing signal(s).
Grafting experiments have revealed that transgenic plants that undergo co-suppression of homologous transgenes and endogenous genes or PTGS of exogenous transgenes produce a sequence-specific systemic silencing signal that is able to propagate from cell to cell and at long distance. Similarly, infection of transgenic plants by viruses that carry (part of) a transgene sequence results in global silencing (VIGS) of the integrated transgenes although viral infection is localized. Systemic PTGS and VIGS strongly resemble recovery from virus infection in non-transgenic plants, leading to protection against secondary infection in newly emerging leaves and PTGS of transiently expressed homologous transgenes. The sequence-specific PTGS signal is probably a transgene product (for example, aberrant RNA) or a secondary product (for example, RNA molecules produced by an RNA-dependent RNA polymerase with transgene RNA as a matrix) that mimics the type of viral RNA that is targeted for degradation by cellular defence. Whether some particular cases of transgene TGS could also rely on the production of such a mobile molecule is discussed.
Fagard
M
M
Laboratoire de Biologie Cellulaire, INRA, Versailles, France.
Vaucheret
H
H
D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology*; D020868:Gene Silencing / Q000502:physiology*; D012323:RNA Processing, Post-Transcriptional; D015398:Signal Transduction