Hyponastic Leaves 1 interacts with RNA Pol II to ensure proper transcription of microRNA genes.

HYL1 (DRB1) is a double-stranded RNA binding protein involved in miRNA processing in plants. It is a core component of the Microprocessor complex and enhances the efficiency and precision of miRNA processing by the DCL1 protein. In this work, we report a novel function of the HYL1 protein in the transcription of MIR genes. HYL1 colocalizes with RNA Polymerase II and affects its distribution along MIR genes. Moreover, proteomic experiments revealed that the HYL1 protein interacts with many transcription factors. Finally, we show that the action of HYL1 is not limited to MIR genes and impacts the expression of many other genes, a majority of which are involved in the plastid organization. These discoveries indicate HYL1 as an additional player in gene regulation at the transcriptional level, independent of its role in miRNA biogenesis.