Endoplasmic reticulum as a hub organizing the activities of microRNAs and a subset of endogenous siRNAs in Arabidopsis [ncRNA-Seq]

The endoplasmic reticulum (ER) was implicated as the site of microRNA (miRNA)-mediated translation repression in plants. Here, we examined the ER- and rough ER-associated small RNAome, transcriptome and translatome. We found that almost all cellular transcripts were present on membrane-bound polysomes (MBPs), and miRNAs were enriched in membranes and on MBPs. miRNAs were recruited to membranes by their effector protein AGO1, whereas AGO1 associated with membranes and, partly ribosomes, in an RNA-independent manner. Most strikingly, 22 ntmiRNA isoformsand a set of 22 ntsiRNAs, were enriched in the membrane fraction and onMBPs, where they trigger phasedsecondary siRNAproduction from target transcripts. Loss of membrane association of the 22 nt small RNAs resulted in the loss of phasing in secondary siRNA production.These findings point to the ER as a hub that hosts and organizes endogenous small RNAs in plants. Examine the sRNA preference and changes of 12 samples with various biological replicates of different cell fractions in WT, ago1-27 and ago1-36 seedlings