Plant-specific BLISTER modulates miRNA biogenesis by regulating <i>MIR</i> transcription, HYL1 phosphorylation, and nuclear transport in <i>Arabidopsis</i>

MicroRNAs (miRNAs), processed from primary transcripts by the microprocessor complex (MC), serve as crucial post-transcriptional regulators in eukaryotes. The stability and nuclear localization of HYL1, a core MC component, are essential for maintaining complex activity. In this study, we demonstrate that the plant-specific protein BLISTER (BLI) plays a key role in miRNA biogenesis by regulating MIR transcription, HYL1 phosphorylation, and HYL1 transport in Arabidopsis. The bli mutant exhibits increased accumulation of specific miRNAs accompanied by enhanced HYL1-containing D-body formation. Biochemical evidence indicates that BLI negatively regulates MIR transcription. Moreover, BLI promotes HYL1 dephosphorylation, which facilitates its degradation. Furthermore, BLI interacts with KETCH1 to orchestrate HYL1 nuclear import. These findings establish a novel regulatory paradigm where a plant-specific protein integrates transcriptional control and post-translational modification to coordinate miRNA production, advancing our understanding of plant gene regulation mechanisms.