Genome-scale, single-cell-type resolution of microRNA activities within a whole plant organ.

Loaded into ARGONAUTE(AGO) proteins, eukaryotic micro(mi)RNAs regulate gene expression via cleavage, translational repression, and/or accelerated decay of sequence-complementary target transcripts. Despite their importance in development, cell identity maintenance and stress responses, how individual miRNAs contribute to spatial gene regulation within the complex cell mosaics formed in tissues/organs has remained inaccessible in any organism to date. We have developed a non-invasive methodology to examine, at single-cell-type resolution, the AGO-loading and activity patterns of entire miRNA cohorts in intact organs, applied here to the Arabidopsis root tip. A dual miRNAome-targetome analytical interface allowing intuitive data integration/visualization was developed as the basis for in-depth investigations via single-cell-type experimentation. These uncovered an array of so far speculative or hitherto unknown types of spatial miRNA-mediated gene regulation schemes, including via widespread cell-to-cell movement between contiguous layers of distinct identities. This study provides the proof of principle that minimally invasive, genome-scale analysis of miRNA activities within and between single-cell types of whole organs is achievable.