MicroRNAs (miRNAs) are short noncoding RNAs that mediate the repression of target transcripts in plants and animals. Although miRNAs are required throughout plant development, relatively little is known regarding their embryonic functions. To systematically characterize embryonic miRNAs in Arabidopsis (Arabidopsis thaliana), we developed or applied high-throughput sequencing-based methods to profile hundreds of miRNAs and associated targets throughout embryogenesis. We discovered dozens of miRNAs that dynamically cleave and repress target transcripts, including 30 that encode transcription factors. Transcriptome analyses indicated that these miRNA:target interactions have profound effects on embryonic gene expression programs. Moreover, we demonstrated that the miRNA-mediated repression of six transcription factors are individually required for proper division patterns of various embryonic cell lineages. These data indicate that the miRNA-directed repression of multiple transcription factors is critically important for the establishment of the plant body plan, and they provide a foundation to further investigate how miRNAs contribute to these initial cellular differentiation events.
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