Abstract
The regulation of microRNA (miRNA) biogenesis is crucial for maintaining plant homeostasis under biotic and abiotic stress. The crosstalk between the RNA polymerase II (Pol-II) complex and the miRNA processing machinery has emerged as a central hub modulating transcription and cotranscriptional processing of primary miRNA transcripts (pri-miRNAs). However, it remains unclear how miRNA-specific transcriptional regulators recognize MIRNA loci. Here, we show that the Arabidopsis (Arabidopsis thaliana) HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE15 (HOS15)-HISTONE DEACETYLASE9 (HDA9) complex is a conditional suppressor of miRNA biogenesis, particularly in response to abscisic acid (ABA). When treated with ABA, hos15/hda9 mutants show enhanced transcription of pri-miRNAs that is accompanied by increased processing, leading to overaccumulation of a set of mature miRNAs. Moreover, upon recognition of the nascent pri-miRNAs, the ABA-induced recruitment of the HOS15-HDA9 complex to MIRNA loci is guided by HYPONASTIC LEAVES 1 (HYL1). The HYL1-dependent recruitment of the HOS15-HDA9 complex to MIRNA loci suppresses expression of MIRNAs and processing of pri-miRNA. Most importantly, our findings indicate that nascent pri-miRNAs serve as scaffolds for recruiting transcriptional regulators, specifically to MIRNA loci. This indicates that RNA molecules can act as regulators of their own expression by causing a negative feedback loop that turns off their transcription, providing a self-buffering system.