Fig. 8
From: Widespread occurrence of microRNA-mediated target cleavage on membrane-bound polysomes
A proposed model of miRNA-mediated target cleavage for RNA degradation or reproductive phasiRNA biosynthesis in plants. miRNA-AGO1 complexes act on target transcripts at different locations in the cytoplasm with various outcomes: (a) miRNAs guide AGO1 proteins to independently cleave target transcripts for degradation on MBPs and FPs, and in the cytosol; (b) miRNAs such as miR2118 or miR2275 can guide AGO1 proteins to cleave reproductive 21PHAS or 24PHAS precursors on MBPs, then the phasiRNA-generating cleavage fragments dissociate from MBPs and undergo phasiRNA production through previously identified players such as SGS3, RDR6, HEN1, DCL4, and DCL5. The 21-nt phasiRNAs are loaded into AGO proteins such as rice MEL1 and can cleave target transcripts on MBPs and FPs, and in the cytosol; the 24-nt phasiRNAs are shown to be polysome-depleted in this study but their functions remain unknown. 21PHAS: 21-nt phasiRNA-generating locus; 24PHAS: 24-nt phasiRNA-generating locus; AGO: ARGONAUTE; DCL: DICER-LIKE; FP: free polysome; HEN1: HUA ENHANCER 1; MBP: membrane-bound polysome; MEL1: MEIOSIS ARRESTED AT LEPTOTENE 1; RDR6: RNA-directed RNA polymerase 6; SGS3: Suppressor of Gene Silencing 3