- A signal of RNA silencing is moving out of the main vein of a leaf causing silencing of a green fluorescent protein transgene. The red chlorophyll fluorescence shows through in the silenced regions of the leaf.
Localised induction of RNA silencing may lead to silencing in adjacent cells or even in distant parts of the plant. We infer that the mobile signal is likely an RNA molecule because its effects are highly sequence specific. We are currently using transgene systems to identify the nature of the silencing signal through the characterisation of RNA in phloem tissue and through the analysis of mutants to identify genes required for the spread of silencing. Having characterised the signal we shall assess whether endogenous RNA silencing molecules are also mobile and part of a previously uncharacterised signalling system.