The poly(A) tail blocks RDR6 from converting self mRNAs into substrates for gene silencing

Area of Science:

• Plant molecular biology
• RNA biology
• Gene silencing mechanisms

Background:

• Post-transcriptional gene silencing (PTGS) is crucial for regulating gene expression in plants.
• The precise mechanisms by which PTGS distinguishes aberrant RNAs from functional messenger RNAs (mRNAs) are not fully understood.
• RNA-DEPENDENT RNA POLYMERASE6 (RDR6) plays a key role in initiating PTGS by synthesizing double-stranded RNAs from aberrant RNA templates.

Purpose of the Study:

• To elucidate the substrate selection mechanism of RDR6 in plant PTGS.
• To determine how RDR6 differentiates between aberrant and canonical mRNAs.
• To identify the role of polyadenylation status in RDR6-mediated RNA silencing.

Main Methods:

• Investigating the template preference of RDR6 in vitro.
• Analyzing the impact of polyadenylation on RNA template selection by RDR6.
• Utilizing biochemical assays to study the initiation step of complementary strand synthesis by RDR6.

Main Results:

• RDR6 directly selects aberrant poly(A)-less mRNAs over canonical polyadenylated mRNAs.
• This selection occurs at the initiation step of complementary strand synthesis.
• The poly(A) tail of canonical mRNAs acts as a signal for exclusion from RDR6-mediated silencing.

Conclusions:

• RDR6 possesses an intrinsic ability to discriminate against polyadenylated mRNAs.
• This substrate specificity is a critical innate safeguard preventing PTGS from targeting functional cellular RNAs.
• The findings provide a molecular basis for the specificity of PTGS in plants.