Lariats-derived siRNA by PTGS pathway mediate endogenous gene silencing and translational repression

Typically, lariat RNAs undergo rapid elimination through DBR1-mediated debranching. There exists much stable lariats in Arabidopsis, indicating that a relatively high level of lariat RNAs would escape from the degradation by DBR1 under the physiological condition in plants.

However, the mechanism underlying the biogenesis and function of those stable lariat RNAs remains elusive. Surprisingly, apart from a significant increase of lariat RNAs in a weak viable dbr1 mutant (dbr1-2), large amounts of double-stranded 21,22-nt sRNAs accumulated in the intronic regions where producing lariat RNAs, indicating that lariat RNAs may be further processed into sRNAs. Moreover, the increased 21,22-nt siRNAs in dbr1 mutant were demonstrated to be produced from lariat RNAs with the assistance of the RNA-dependent RNA polymerase 6 (RDR6) and Dicer-like proteins, implying the connection between lariat RNAs and the endogenous small RNA silencing pathway in plants.