Secondary Small Interfering RNA-Based Silencing Tools in Plants: An Update

[EN] In plants, RNA silencing regulates key biological processes such as development, response to stress, genome integrity, and antiviral resistance. RNA silencing functions through diverse classes of small RNAs (sRNAs) that associate with ARGONAUTE (AGO) proteins to repress highly sequence-complementary target transcripts (Baulcombe, 2004). interfering RNAs (siRNAs) are a class of sRNAs arising from double-stranded RNA (dsRNA) precursors. Secondary siRNAs are those siRNAs whose dsRNA precursor synthesis is triggered by an upstream sRNA-guided transcript cleavage event followed by RNA-dependent RNA polymerase (RDR) activity (for a recent review see de Felippes, 2019). Many secondary siRNAs are produced in 21-nucleotide (nt) register with the sRNA-guided cleavage site by successive Dicer-Like (DCL) processing and are therefore called phased secondary siRNAs (phasiRNAs). In contrast, only a subset of secondary siRNAs act in trans to repress one or more targets distinct from their locus of origin. These siRNAs are called trans-acting siRNAs (tasiRNAs), most of which are also phased (Axtell, 2013).