RNA silencing manifested as visibly altered phenotypes in plants

Eukaryotes have a mechanism of RNA-guided regulation of gene expression in which double-stranded RNA inhibits the expression of genes with complementary nucleotide sequences. This mechanism plays a crucial role in many processes including development, stability of the genome, and responses against invading genetic materials. These RNA-guided pathways that control gene expression, collectively termed RNA silencing, are thought to have evolved as a form of innate immunity against viruses. RNA silencing provides a mechanism for downregulating gene expression and a tool that is suitable for analyzing gene function and engineering novel traits in organisms. The phenomenon of RNA silencing was discovered in transgenic petunia plants that had altered patterns of flower color as a consequence of overexpression of the chalcone synthase-A gene responsible for an essential enzyme to biosynthesize anthocyanins. After the visual discovery of RNA silencing in petunia, visible phenotypes have played an important role in monitoring the silenced state of a gene in various RNA silencing systems. In particular, a photobleached phenotype in leaf tissues is useful in optimizing a virus-induced gene silencing system. Loss of pigmentation in plant tissues has also led to the detection of naturally occurring RNA-silencing phenomena. Visual changes conferred by endogenous reporter genes provide highly informative assessments of RNA silencing that can be applied to a wide spectrum of plant biotechnology.