Actions of plant Argonautes: predictable or unpredictable?

Highlights • miRNAs are likely loaded into AGO1 in the nucleus. • RICEs degrade the uridylated AGO-cleaved 5′ mRNA fragments to maintain RISC. • Nuclear AGO1 can regulate transcription and DNA repair. • AGO3 functions like the clade of AGO4/6/9 in the RdDM pathway. • AGO10 not only sequesters miRNAs but also promotes their degradation by SDN1. Argonaute (AGO) proteins are the key effector of RNA-induced silencing complex (RISC). Land plants typically encode numerous AGO proteins, and they can be typically divided into two major functional groups based on the species of their housed small RNAs (sRNAs). One group of AGOs, guided by 24-nucleotide (nt) sRNAs, canonically function in nuclei to implement transcriptional gene silencing (TGS), whereas the other group of AGOs, guided by 21-nt sRNAs, act in the cytoplasm to fulfill posttranscriptional gene silencing (PTGS). Many new discoveries have been recently made on functions and mechanisms of AGO proteins in plants, and some of the findings change our views on the conventional classification and roles of AGO proteins. In this review, we summarize our current knowledge of AGO proteins in plants. [ABSTRACT FROM AUTHOR]