HYL1-dependent recruitment of HOS15 to MIRNA loci regulates micro RNA transcription in plants

GIUDICATTI, AXEL J.; MANAVELLA, PABLO A

Santa Fe-Virtual

Congreso; XXXIII Argentinian meeting of Plant Physiology; 2021

Sociedad Argentina de Fisiología Vegetal

Post-transcriptional gene silencing mediated by microRNAs (miRNAs) modulates numerous developmental and stress response pathways. In a previous work, we used a Luciferase-based forward genetic screening to identify genes required for miRNA biogenesis and activity. Among the isolated mutants with impaired miRNA activity, we identified a new allele of the gene encoding HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15). HOS15 was previously described as a partner of HDAC and E3-Ubiquitin ligase complexes and was typically associated with cold, drought and ABA responses by controlling gene expression.Here, we characterize HOS15 in the context of the miRNA pathway. Using Y2H and microscopy assays we found that HOS15 directly interacts with HYL1 but not with other proteins of the pathway. Also, we found that an over-accumulation of HOS15 lead to HYL1 degradation. Interestingly, we found that HOS15 associate with MIRNA loci to regulate some miRNAs transcription. But most importantly, HOS15 recruitment to miRNA encoding genes is lost in HYL1 mutants or plants expressing a HYL1 phosphorylated mimic. Moreover, HYL1 dimerization is also required for this recruitment. This suggests that HOS15 specificity for miRNA genes is caused by its interaction with HYL1, which is likely to recognize such loci by the hairpin structures of nascent pri-miRNAs. In turn, such recruitment of HOS15 will modulate pri-miRNA transcription creating a regulatory feedback loop. However, such regulation appears to happens only in a subset of miRNAs, as indicated by small RNA-seq analysis of HOS15 mutants. We propose a dual role of HOS15 in miRNA biogenesis. First, HOS15 can promote the transcription of miRNA genes based on the HYL1 recruitment to MIRNA locus. In a second facet, HOS15 can modulate HYL1 protein levels through degradation to indirectly affect miRNA processing.