Hyponastic Leaves 1 protects pri-miRNAs from nuclear exosome attack

Significance MicroRNAs (miRNAs) are indispensable regulators of gene expression. Hyponastic Leaves 1 (HYL1) is a core component of the microprocessor that processes primary miRNAs (pri-miRNAs) into mature miRNAs. Here we report a noncanonical function of HYL1 in protecting pri-miRNAs from unwanted nuclear exosome activities during processing. Our observations also suggest that HYL1 may contribute differently to the Dicer-like 1 (DCL1)-mediated maturation of loop-to-base– and base-to-loop–processed pri-miRNAs. This study thus integrates the RNA surveillance system to the miRNA biogenesis pathway and sheds light on the multifaced roles of HYL1 in miRNA biogenesis.