ARGONAUTE10 promotes the degradation of miR165/6 through the SDN1 and SDN2 exonucleases in Arabidopsis [AGO10OE]

The degradation of small RNAs in plants and animals is associated with small RNA 3’ truncation and 3’ uridylation and thus relies on exonucleases and nucleotidyl transferases. Argonaute proteins associate with small RNAs in vivo and are essential for not only the activities but also the stability of small RNAs. Arabidopsis ARGONAUTE10 (AGO10) maintains stem cell homeostasis in meristems by sequestration of miR165/6, a conserved miRNA acting through AGO1. Here, we report that AGO10 reduces miR165/6 accumulation by enhancing its degradation. This is contrary to the stabilizing effect of all known argonaute proteins on their associated small RNAs. We show that SMALL RNA DEGRADING NUCLEASES (SDNs) are responsible for miRNA 3’ truncation in general and AGO10 promotes the degradation of miR165/6 by SDNs. Our work identifies the exonucleases responsible for miRNA 3’ truncation in vivo and uncovers a mechanism of specificity determination in miRNA turnover. This work, together with previous studies on AGO10, demonstrates that spatially regulated miRNA degradation underlies stem cell maintenance in plants. Overall design: Total and AGO1-RISC small RNAs were isolated from AGO10 overexpression lines (Four AGO1-IP samples and five total RNA samples, nine total samples)