Systemic acquired silencing: transgene-specific post-transcriptional silencing is transmitted by grafting from silenced stocks to non-silenced scions

Abstract

Using grafting procedures, we investigated the transmission of co‐suppression of nitrate reductase and nitrite reductase host genes and transgenes and of post‐transcriptional silencing of a uidA transgene encoding glucuronidase in tobacco. We demonstrate that silencing is transmitted with 100% efficiency from silenced stocks to non‐silenced scions expressing the corresponding transgene. Transmission is unidirectional from stock to scion, transgene specific, locus independent and requires the presence of a transcriptionally active transgene in the target scion. The transmission of co‐suppression occurs when silenced stocks and non‐silenced target scions are physically separated by up to 30 cm of stem of a non‐target wild‐type plant. Taken together, these results suggest that a non‐metabolic, transgene‐specific, diffusable messenger mediates the propagation of de novo post‐transcriptional silencing through the plant.