**6.1 RNA interference**

RNA interference is a promising gene regulatory approach in which the molecules of RNA inhibit gene expression or translation process by neutralizing target mRNA molecules. It is also known as post- translational gene silencing (PTGS), quelling. It permits down regulation of gene expression more precisely without affecting the function of other genes. RNAi has been widely utilized nowadays in enhancing nutritional value of quality, increasing shelf life or perishables, imparting insect-pest, virus and pathogen resistance and abiotic stress tolerance. The fruits and vegetables are highly susceptible to postharvest losses which deteriorate their quality and economic value.

The storage life of such produces can be enhanced by RNA interference approach. Transgenic tomatoes containing ACC oxidase dsRNA showed delayed ripening and increased shelf life due to suppression of genes for ethylene synthesis. RNAialso is involved in the enhancing of nutritional quality of food products. In tomato, SINCED1 gene which is important for ABA biosynthesis is suppressed by RNAi and those fruit showed enhanced accumulation of lycopene and beta-carotene [42]. RNAi technology is widely used in Brassica napus to increase the carotenoid content by downregulating the lycopene epsilon cyclase gene (ℇ-CYC) and possess increased content of β-carotene, violaxanthin and lutein [43]. Jiang et *al.,* 2013 [44] reported that RNAi can be successfully utilized in soybean to increase isoflavone content by silencing flavanone 3-hydroxylase (F3H) gene and the flavone synthase II (GmFNSII) gene, thus regulating flavone and isoflavone production in hairy roots. RNA interference is also applied to produce virus resistant plants. Transgenic tomato produces dsRNA which showed resistance to potato spindle tuber viroid [45]. Transgenic tobacco which expresses the coat protein (CP) gene from Tobacco mosaic virus showed resistance against the same and this technology is used for other crops also like potato against Potato virus Y [46], *Prunus domestica* resistant to *Plum pox virus.* The RNAi has been successfully implemented in common bean to induce resistance against Gemini virus *Bean golden mosaic virus* [47]. Ethylene is a major fruit ripening hormone in postharvest physiology. One of the major factor which is used to extend shelf life of harvested produce is delay in ripening process by downregulation of ethylene action. This can be achieved through antisense RNA technology. In this process, the protein coding region of a gene is inverted in reference to its promoter and thus antisense gene is constructed. The mRNA formed has similar sequence as of antisense gene of natural DNA. Endogenous and antisense RNA present on the same nucleus, their transcription results into antisense and sense RNA transcript. They are complementary to each other and forms RNA molecules having double stranded nature. The duplex thus formed inactivated mRNA and inhibits protein synthesis. Antisense RNA technology suppresses ACC oxidase and ACC synthase genes and plants possessing such techniques are resistant to over ripening and postharvest losses (**Figure 10**).
