MicroRNA Maturation and MicroRNA Target Gene Expression Regulation Are Severely Disrupted in Soybean dicer-like1 Double Mutants

Small nonprotein-coding microRNAs (miRNAs) are present in most eukaryotes and are central effectors of RNA silencing-mediated mechanisms for gene expression regulation. In plants, DICER-LIKE1 (DCL1) is the founding member of a highly conserved family of RNase III-like endonucleases that function as core machinery proteins to process hairpin-like precursor transcripts into mature miRNAs, small regulatory RNAs, 21–22 nucleotides in length. Zinc finger nucleases (ZFNs) were used to generate single and double-mutants of putative soybean DCL1 homologs, DCL1a and DCL1b, to confirm their functional role(s) in the soybean miRNA pathway. Neither DCL1 single mutant, dcl1a or dcl1b plants, exhibited a pronounced morphological or molecular phenotype. However, the dcl1a/dcl1b double mutant expressed a strong morphological phenotype, characterized by reduced seed size and aborted seedling development, in addition to defective miRNA precursor transcript processing efficiency and deregulated miRNA target gene expression. Together, these findings indicate that the two soybean DCL1 paralogs, DCL1a and DCL1b, largely play functionally redundant roles in the miRNA pathway and are essential for normal plant development.