The silencing of (trans)gens – A mechanism of virus resistance in plants

Abstract

Gene silencing and RNA-mediated virus resistance are two remarkable and potentially useful phenomena that occur in higher plants. However, in light of recent research it seems likely that the posttranscriptional type of gene silencing and RNA-mediated virus resistance are actually manifestations of the same phenomenon. The occurrence of both post-transcriptional gene silencing (PTGS) and RNA-mediated virus resistance require sequence homology between a transgene and an endogenous gene or a transgene and an infecting virus, respectively. Furthermore, both processes are characterized by high transcription rates of homologous, silenced (trans)genes but low steady-state levels of their transcripts (in case of virusinfected plants, low steady-state transcript levels of the silenced transgene and homologous viral RNA which eventually leads to virus resistance). Therefore, PTGS is a potential tool for creating virus-resistant transgenic plants that express a sequence homologous to the invading virus. It is very unlikely, though, that PTGS in plants has evolved solely for the purpose of transgene suppression so it is perhaps not surprising that some natural virus defense systems have been found to resemble gene silencing. In addition, although plants may combat virus infections by gene silencing, there is recent evidence that some plant viruses can fight back by suppressing the plant’s ability to carry out the silencing process. The advantages and disadvantages of the commercial use of PTGS for creating virus-resistant plants (RNA-mediated virus resistance) is also discussed.