can RNAi occur naturally in an organism or it has to be induced from outside?

Question

i mean does it happen just if we introduce dsRNA into the organism..and which organism can undergo this RNAi?

Answer 1

It seems to be a natural process that does occur in cells.

Answer 2

The effects of RNA interference can be both systemic and heritable in plants and C. elegans, although not in Drosophila or mammals. In plants, RNAi is thought to propagate by the transfer of siRNAs between cells through plasmodesmata. The first evidence that dsRNA could lead to gene silencing came from work in the nematode Caenorhabditis elegans.

RNA interference is a vital part of the immune response to viruses and other foreign genetic material, especially in plants where it may also prevent self-propagation by transposons. This phenomenon has since been recognized as a feature of the plant innate immune system, and allows the entire plant to respond to a virus after an initial localized encounter. Although animals generally express fewer variants of the dicer enzyme than plants, RNAi in some animals has also been shown to produce an antiviral response. In both juvenile and adult Drosophila, RNA interference is important in antiviral innate immunity and is active against pathogens such as Drosophila X virus. A similar role in immunity may operate in C. elegans, as argonaute proteins are upregulated in response to viruses and worms that overexpress components of the RNAi pathway are resistant to viral infection