Post-transcriptional gene silencing: Basic concepts and applications

ABSTRACT

Post-transcriptional gene silencing (PTGS)-mediated gene silencing exploits the cellular mechanism whereintranscripts having sequence similarity to the double-stranded RNA (dsRNA) molecules present in the cell will besubjected to degradation. PTGS is closely related to natural processes such as RNA-mediated virus resistance andcross-protection in plants. Gene silencing and the cellular machinery for affecting this phenomenon might haveevolved as a natural protective measure against viral infection in plants. In PTGS, small interfering RNA (siRNA)molecules of 21–23 nucleotides length act as homology guides for triggering the systemic degradation of transcriptshomologous to the siRNA molecules. PTGS phenomenon, first discovered in transgenic petunia plants harbouringchalcone synthase gene and termed co-suppression, has been subsequently exploited to target specific gene transcripts for degradation leading to manifestation of desirable traits in crop plants. Targeted gene silencing has beenachieved either through the introduction of DNA constructs encoding dsRNA or antisense RNA or by deploying cosuppression constructs producing siRNAs against the transcript of interest. Understanding the mechanism of genesilencing has led to the development of several alternative strategies for inducing gene silencing in a precise andcontrolled way. This has paved the way for using PTGS as one ofthe chief functional genomicstools in plants and hashelped in unraveling the mechanism of many cellular processes and identifying the focal points in pathways, besides,opening new vistas in genetic engineering of plants for human benefits. PTGS has shown great potential in silencingthe deleterious genes efficiently so that value-added plant products could be obtained. Thus, PTGS has ushered in anew era in the genetic manipulation of plants for both applied and basic studies. In this review, we have outlined thebasics of RNAi-mediated gene silencing and summarized the work carried out at our institute using this approach, ascase studies. In particular, adopting RNAi-mediated gene silencing (a) as a method to restore fertility in transgenicmale sterile lines developed based on orfH522 gene from sunflower PET1-CMS source, (b) as a tool to suppress theproduction of toxic proteins, ricin and RCA, in castor, and (c) as an approach to induce bud necrosis virus resistancein sunflower has been discussed. Examples from other plant systems also have been mentioned to exemplify theconcept and utility of gene silencing in crop plants.