Summary Double-stranded RNAs (dsRNAs) are abundantly present in cells, playing multiple regulatory functions. dsRNAs of viral origin activate innate immune responses. Since RNA editing and modifications affect the structure and recognition of RNAs, their alteration can result in the accumulation of aberrant endogenous dsRNAs inducing a deleterious innate immune response. Here, we present a complete protocol for the measurement of dsRNAs in a live mouse tissue using dsRNA immunoprecipitation and sequencing (dsRIP-Seq). This protocol focuses on tissue isolation, dsRNA immunoprecipitation and downstream computational analysis. For complete details on the use and execution of this protocol, please refer to Gao et al. (2020) .

Monocot DICER-LIKE3 (DCL3) and DCL5 produce distinct 24-nt small interfering RNAs (siRNAs), heterochromatic siRNAs (hc-siRNAs) and phased secondary siRNAs (phasiRNAs), respectively. The former small RNAs are linked to silencing of transposable elements and heterochromatic repeats, and the latter to reproductive processes. It is assumed that these DCLs evolved from an ancient ‘eudicot-type’ DCL3 ancestor, which may have produced both types of siRNAs. However, how functional differentiation was achieved after gene duplication remains elusive. Here, we find that monocot DCL3 and DCL5 exhibit biochemically distinct preferences for 5′ phosphates and 3′ overhangs, consistent with the structural properties of their in vivo double-stranded RNA substrates. Importantly, these distinct substrate specificities are determined by the PAZ domains of DCL3 and DCL5, which have accumulated mutations during the course of evolution. These data explain the mechanism by which these DCLs cleave their cognate substrates from a fixed end, ensuring the production of functional siRNAs. Our study also indicates how plants have diversified and optimized RNA silencing mechanisms during evolution.