Cell type-specific ablation of siRNAs by Arabidopsis RTL1 reveals a role of phloem companion cells in systemic post-transcriptional gene silencing

Dissecting these roles requires tools that selectively eliminate small RNAs in defined cell types. Virus-encoded proteins such as P19 have been widely used to neutralize small RNAs owing to their sequestration capacities.

However, their restricted binding spectrum to 21-22-nt small RNAs and lack of discrimination between miRNAs and siRNAs limit their utility. Here we show that constitutive expression of RNASE THREE-LIKE1 (RTL1) in Arabidopsis thaliana, previously shown to degrade siRNA precursors but not miRNA precursors, also degrades siRNA duplexes, irrespective of their size, sequence, or sub-cellular localization. Grafting experiments combined with small RNA sequencing revealed that shoot-derived siRNAs accumulate in dcl2 dcl3 dcl4 mutant roots, but are eliminated upon ectopic RTL1 expression, demonstrating that RTL1 efficiently degrades mobile siRNAs in vivo.