Review Article: The Silence of Genes in Transgenic Plants

TLDR

In genetically modified plants, transgenes can be silenced—sometimes causing co‑suppression of homologous endogenous genes predominantly post‑transcriptionally—while factors such as DNA methylation, copy number, and aberrant RNA production influence this process, and silencing can also confer virus resistance, though causal links remain unclear. The review seeks to dissect the mechanisms of sequence‑homology‑dependent gene silencing in transgenic plants. The authors discuss observations and attempt to relate them to elucidate the underlying mechanisms of gene silencing.

Abstract

In genetically modified plants, the introduced transgenes are sometimes not expressed. They can be silenced. Transgenes can also cause the silencing of endogenous plant genes if they are sufficiently homologous, a phenomenon known as co-suppression. Silencing occurs transcriptionally and post-transcriptionally but silencing of endogenous genes seems predominantly post-transcriptional. If viral transgenes are introduced and silenced, the post-transcriptional process also prevents homologous RNA viruses from accumulating; this is a means of generating virus-resistant plants. A major goal of current research is to dissect the mechanism(s) of these sequence-homology-dependent gene silencing phenomena. Various factors seem to play a role, including DNA methylation, transgene copy number and the repetitiveness of the transgene insert, transgene expression level, possible production of aberrant RNAs, and ectopic DNA–DNA interactions. The causal relationship between these factors and the link between transcriptional and post-transcriptional silencing is not always clear. In this review we discuss various observations associated with gene silencing and attempt to relate them.