Dynamic regulation of HYL1 provides new insights into its multifaceted role in Arabidopsis

MicroRNAs (miRNAs) are 21 to 24 nucleotide non-coding RNAs that regulate gene expression. Biogenesis of miRNAs is fine-tuned by specialized microprocessor complex, the regulation of which is being continuously understood. Recruitment of HYL1 to the microprocessor complex is crucial for accurate primary-miRNA (pri-miRNA) processing and accumulation of mature miRNA in Arabidopsis thaliana. HYL1 is a double-stranded RNA binding protein also termed as DRB1, has two double-stranded RNA binding domain at N- terminal and a highly disordered C- terminal region. Also, the biological activity of HYL1 is dynamically regulated through transition from hyperphosphorylation to hypophosphorylation state. HYL1 is known to be phosphorylated by a MAP kinase MPK3 and SnRK2. However, the precise role of its phosphorylation are still unknown. Recently, the stability of HYL1 protein has been shown to be regulated by an unknown protease X. However, the identity of the protease and its molecular mechanisms are poorly understood. Here, we describe, three functionally important facets of HYL1, which provide a better picture of its association with molecular processes. First, we identified a conserved MPK3 phosphorylation site on HYL1 and its possible role in the miRNA biogenesis. Secondly, the C-terminal region of HYL1 displays tendencies to bind dsDNA. Lastly, the role of C- terminal region of HYL1 in the regulation of its protein stability and the regulation of miRNA biogenesis is documented. We show the unexplored role of C- terminal and hypothesize the novel functions of HYL1 in addition to miRNA biogenesis. We anticipate that the data presented in this study, will open a new dimension of understanding the role of double stranded RNA binding proteins in diverse biological processes of plants and animal.