Study : Highly efficacious antiviral protection of plants by siRNAs identified in vitro


Highly efficacious antiviral protection of plants by siRNAs identified in vitro
In response to a viral infection, the plant’s RNA silencing machinery processes viral RNAs into a huge number of small interfering RNAs (siRNAs). However, very few of these siRNAs actually interfere with viral replication. A reliable approach to define the characteristics underlying the activity of these immunologically effective siRNAs (esiRNAs) has not been available so far. We developed a novel screening approach that enables a rapid functional identification of antiviral esiRNAs. The approach is essentially based on the use of a cytoplasmic extract from Nicotiana tabacum BY-2 protoplasts (BY-2 lysate, BYL), that shows Dicer-like (DCL) activity and facilitates the assembly of active RNA-induced silencing complexes (RISC) with an in vitro-translated Argonaute (AGO) protein of choice. We exposed double-stranded (ds) RNA of Tomato bushy stunt virus (TBSV) to the BYL to generate viral siRNAs (DCL assay). Total RNA was isolated from the reactions and DCL-generated TBSV siRNAs were identified by NGS. In another approach, AGO1/RISC- or AGO2/RISC-associated siRNAs were isolated using FLAG-AGO immunoprecipitation (AGO-IP) and analyzed by NGS. Subsequently, the antiviral activity of siRNAs with high affinity to AGO proteins was characterized in vitro and in vivo. Overall design: siRNA sequence data was obtained from three different DCL assays, two AGO1-IPs and three AGO2-IPs


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