Application of RNA Interference in Plants (Report‪)‬

Introduction RNA silencing is a novel gene regulatory mechanism that limits the transcript level by either suppressing transcription (TGS) or by activating a sequence- Specific RNA degradation process [PTGS/RNA interference (RNAi)] (Agrawal et al., 2003). During the 1990s, a number of gene silencing phenomena that occur at the post-transcriptional level were discovered in plants, fungi, animals and ciliates (Baulcombe, 2000; Matzke et al. 200l). The silencing effect was first observed in plants in 1990, when the Jorgensen laboratory introduced exogenous transgenes into petunias in an attempt to up-regulate the activity of a gene for chalcone synthase, an enzyme involved in the production of specific pigments (Agrawa et al., 2003; Napoli et al., 1990). Unexpectedly, flower pigmentation did not deepen, but rather showed variegation with complete loss of color in some cases. This indicated that not only were the introduced trangenes themselves inactive, but that the added DNA sequences also affected expression of the endogenous loci (Hannon, 2002). This phenomenon was referred to as "co-suppression" (Napoli et al., 1990; Campbell, 2005). A similar phenomenon in the fungus Neurospora crassa was named quelling (Romano et al., 1992; Cogoni et al., 1996; Fire et al, 1998) identified a related mechanism, RNA interference (RNAi) in animals. The natural function of RNAi is referring to the mechanism involved in cellular defense against viruses, genomic containment of retrotransposons, and post-transcriptional regulation of gene expression. RNAi can specifically silence individual genes, creating knockout phenotypes, either in transformants that can produce the required hairpin RNAs, or upon infection with recombinant RNA viruses that carry the target gene (VIGS, viral-induced gene silencing) (Tenea, 2009). RNAi is a multistep process involving the generation of small interfering RNAs (siRNAs) in vivo through the action of the RNase III endonuclease 'Dicer'. The resulting 21- to 23-nt siRNAs mediate degradation of their complementary RNA (Zou et al., 2005; Shi, 2003). Here, the mechanism of RNAi was reviewed and then some of its applications in plants discussed (Table 1).