Auxin Response Factor 3 Specifies Stem Cells In Apical Meristem Via Mediating An Auxin-responsive Histone Acetylation In Arabidopsis

Stem cells in the apical meristem of plants provides tissues and organs in the post-embryonic development.The shoot meristem generates new tissues and organs to form the aerial part,while root meristem gives rise to root system.WUSCHEL(WUS)is specifically expressed in the organizing center and maintains stem cells by encoding a homeodomain transcription factor.WUSCHEL-RELATED HOMEOBOX5(WOX5),which also belongs to homeodomain family,is expressed in the quiescent center and responsible for specifying root stem cells.Auxin plays important regulatory roles in various developmental processes.Auxin Response Factors are transcription factors mediating auxin-induced gene transcription.Arabidopsis ARF family comprises 23 members,and can be divided into transcriptional activators and repressors.ARF3 has been shown to be a repressor,and regulates the development of flower,leaves or lateral roots,as well as promotes shoot regeneration.Here,we show that in arf3 mutants,root meristem size was reduced and root elongation was suppressed.Using yeast-two hybridization system,we identified an unknown function protein which interacted with ARF3,and named it as ARF3 interacting protein1(AIP1).arf3 aip1 double mutant exhibited enhanced phenotypes compared with that of arf3 single mutant.The expression signals of ARF3 overlapped with those of AIP1 in the root tip.The results indicate that ARF3 and AIP1 act synergistically in regulating root development.Further Ch IP-q PCR and EMSA analyses showed that ARF3 directly repressed the transcription of WOX5 by binding the promoter region of WOX5.By a yeast two-hybrid screening,SAP18 was identified,which is a member of histone deacetylase complex,as an interacting protein of ARF3.SAP18 associated with the promoter of WOX5,suggesting that ARF3 recruits histone deacetylase complex through interacting with AIP1,and regulates transcription of WOX5 via mediating histone acylation.Moreover,we found that ARF3 and SAP18 function on WUS in shoot meristem.Further,exogenous auxin treatment resulted in the increase of histone acetylation levels within WOX5 promoter.Our findings demonstrate that auxin affects the interaction between ARF3 and AIP1,as well as that between ARF3 and SAP18,and thus regulates the transcription of WOX5 and WUS by mediating histone acylation.In addition,different repressor ARFs interacted with AIP1 and SAP18,suggesting that mediating histone acylation might be a common manner of repressor ARFs for transcriptional regulation.Our results provided new information for understanding the mechanism of stem cell specification regulated by repressor ARFs.