HYL1

HYL1 is a gene that encodes a plant-specific double-stranded RNA-binding protein essential for microRNA (miRNA) biogenesis, most prominently studied in the model plant Arabidopsis thaliana. The HYL1 protein contains two double-stranded RNA-binding domains and localizes to the nucleus, where it participates in the pri-miRNA processing machinery alongside DCL1 (Dicer-like 1) and SERRATE (SE). In this complex, HYL1 assists in recognizing and accurately processing primary miRNA transcripts into precursor and mature miRNAs that guide post-transcriptional gene silencing.

Genetic and biochemical studies show that loss of HYL1 leads to reduced levels of mature miRNAs and accumulation of pri-miRNAs, producing developmental defects such as altered leaf morphology and serration, as well as broader misregulation of gene expression. These phenotypes reflect the central role of HYL1 in ensuring the fidelity and efficiency of miRNA processing, and its impact on downstream regulatory networks.

Regulation of HYL1 activity involves reversible phosphorylation. The C-terminal phosphatase CPL1 dephosphorylates HYL1 to promote miRNA biogenesis, whereas kinases such as MPK3 can phosphorylate HYL1 and modulate its function, stability, and localization. This dynamic regulation integrates environmental and developmental cues with the miRNA pathway, adjusting gene silencing accordingly.

Conservation and significance: HYL1 is conserved across land plants and is considered a core component of the canonical plant miRNA processing pathway. Its interaction with DCL1 and SE within nuclear processing bodies highlights a coordinated mechanism for miRNA maturation, making HYL1 a key factor in plant development and adaptation.