The HOS15-HDA9 complex associates with HYL1 to modulate miRNA expression in response to ABA signalling

MicroRNAs (miRNAs) play a crucial role in plant cell homeostasis, particularly in response to environmental biotic and abiotic stresses. The transcription of miRNAs is mediated by RNA Polymerase II which generates the primary miRNA transcripts (pri-miRNAs). HYPONASTIC LEAVES 1 (HYL1) is a miRNA biogenesis protein indirectly associated with chromatin through the interaction with the nascent pri-miRNA. HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15) facilitates the recruitment of histone deacetylases to the promoter of the target genes together with its chromatin-acting partner HISTONE DEACETYLASE 9 (HDA9). Previous works suggest an interaction between the chromatin-remodelling machinery and pri-mRNA processing at transcriptional level. However, the interaction between the HOS15-HDA9 complex together with HYL1 and their functional relevance in ABA signalling remained unclear. In this work, Park et al., show that the ABA-induced recruitment of HOS15-HDA9 complex to the miRNA loci and the following silencing of MIRNA loci depended on the recognition of nascent pri-miRNAs by HYL1. As the authors observe, these findings “indicate that nascent pri-miRNAs serve as scaffolds for recruiting transcriptional regulators, specifically to MIRNA loci.” Understanding theses mechanism is crucial for elucidating the intersection between hormone pathways and epigenetic regulation that fine-tune gene expression in plants. (Summary by Eva Maria Gomez Alvarez @eva_ga96) Plant Cell 10.1093/plcell/koad132