TSL-phosphorylated SGS3 shifts RDR6 from terminal nucleotidyltransferase to polymerase activity to promote RNAi and immunity.

Stoichiometric phosphorylation of SGS3 by Arabidopsis Tousled (TSL) at Ser65 and Ser68 shifts RDR6 from terminal nucleotidyltransferase to polymerase activity, promoting RNAi and immunity.

• Why it matters: Dual RDR6 activities—polymerase-driven dsRNA synthesis and terminal tailing that degrades templates—need regulation, but the control mechanism was unknown.
• What they did: The study identified TSL phosphorylation of SGS3 at Ser65/Ser68 and used SGS3 phosphomimics versus hypo-phosphorylated SGS3 to compare siRNA body formation, RNA-binding affinity, and RDR6 activity.
• The result: Phosphomimics formed liquid-like siRNA bodies with lower RNA binding, enhancing RDR6 polymerase activity for dsRNA production processed by Dicer-like 2/4, while hypo-phosphorylated SGS3 formed larger solid-like aggregates that promoted terminal nucleotidyltransferase activity; viral infection drove SGS3 hypo-phosphorylation and aggregation, suppressing viral siRNA production and host defense.

AI summary of the abstract · may contain errors · not medical advice · read the paper.