Small RNA Silencing Pathways
RNA silencing pathways use small RNA guides to destroy a complementary mRNA, inhibit its translation, or reduce its rate of transcription. RNA silencing was first discovered by plant scientists in 1990 during an attempt to engineer transgenic petunias overexpressing enzymes that limit flower pigment production [1,2]. Remarkably, the introduction of transgenes expressing either of the flower pigmentation pathway enzymes chalcone synthase or dihydroflavonol-4-reductase failed to produce more intensely pigmented flowers. Instead, the transgenes repressed-that is, “silenced”— expression of both the endogenous and transgenic copies, causing partial or complete loss of flower pigmentation. The phenomenon was therefore dubbed “cosuppression” to reflect the coordinate silencing of the transgene and the endogenous gene.