Function Of Nuclear Argonaute 1 In Response To Various Stimuli In Arabidopsis

Argonaute(AGO)proteins are highly conserved among eukaryotes.AGO proteins bind small RNAs(sRNAs)to form RNA-induced silencing complex(RISC),which regulates gene expression at transcriptional(TGS)or post-transcriptional level(PTGS).AGO1 in Arabidopsis thaliana predominantly binds microRNAs(miRNAs)and represses target gene expression post-transcriptionally through mRNA cleavage or translational repression in the cytoplasm.We and others have previously shown that AGO1 is also present in the nucleus.However,the function of nuclear AGO1 remains largely unknown.In this study,chromatin immunoprecipitation coupled with deep sequencing(ChIP-seq)was used to identify AGO1 binding sites at the genome-wide level.ChlP-seq results revealed that AGO1 was predominantly associated with genes.These genes were highly enriched for genes responding to various stimuli,suggesting that AGO1 may play an important role in responses to stimuli.I thus investigated whether AGO1 binding to chromatin is responsive to different stimuli including plant hormones,biotic and abiotic stresses.Strikingly,these stimuli specifically triggered AGO1 binding to the chromatin of stimulus-responsive gene loci.To gain more insights into the function of nuclear AGO1 in one particular signaling pathway,I focused on JA response.The induction of AGO1 binding to JA-responsive genes was not observed in the null mutant for the JA receptor COI1 under MeJA treatment,suggesting that the induction of AGO1 binding to its target genes was not an off-target effect.Moreover,MeJA induced sRNA production from JA-responsive AGO1 target genes and sRNA production was abolished in the coil-1 mutant,hinting that sRNAs could be required for MeJA-induced AGO1 binding.A significantly larger fraction of genes associated with MeJA-induced peaks had increased expression compared to other genes.This global induction was partially abolished in agol-36,supporting that AGOl contributes to the induction of gene expression by MeJA.Finally,I found that the ago 1-36 mutation significantly alleviated MeJA-induced root growth inhibition.These results demonstrate the importance of AGO1 in the JA signaling pathway and,together with our other findings,hint that AGO1 may play a general role in many stimuli-related signaling pathways.Mass-spectrometric analysis of nuclear AGO1 co-purifying proteins showed that AGO1 interacted with the mediator complex.The interaction between AGO1 and MED25,a subunit of mediator complex was confirmed by co-immunoprecipitation(Co-IP)and such interaction was enhanced under MeJA treatment.I propose that AGO1 may regulate JA mediated signaling pathway by forming a complex with MED25.In summary,this study profiles AGO1-DNA interacting sites genome-widely in Arabidopsis and reveals a novel role of AGO1 in promoting gene transcription in response to plant hormones and stresses.