RNA silencing in GM crops:
introducing a technology and assessing the risks

A report for the Department for Environment, Food and Rural Affairs (DEFRA)

Dr Frank Schwach

Prof David C. Baulcombe

The Sainbusry Laboratory, Norwich Research Park, Norwich NR4 7UH

Table of contents

1. Executive summary
2. Introduction
3. Summary of the literature on RNA-directed post-transcriptional gene silencing
   1. The phenomenon
   2. The basic mechanism
   3. Variations on the basic mechanism
   4. Natural roles
4. Summary of the current literature on RNA-directed DNA methylation and transcriptional gene silencing
5. Applications of RNA silencing in GM organisms
   1. Why use RNA silencing?
   2. Many roads to silencing
   3. Applications of RNA silencing in the literature
6. Assessment of risks associated with RNA silencing in GM crops
   1. Silencing of non-target genes (off-target effects)
   2. Silencing of target genes in non-target tissues
   3. Stability of gene silencing
   4. Escape of viruses from silencing-based resistance
   5. Saturation of the silencing machinery
   6. Horizontal transfer of silencing
   7. Risks associated with non-intentional RNA silencing
   Literature
   Glossary
   Images (illustrated pathways)
   Survey