Physiological And Molecular Evidences For Regulation Of Pi And Fe Homeostasis By Histone Acetyltransferases GCN5 In Arabidopsis

Epigenetics is typically defined as the study of heritable changes in gene expression that is not due to changes in DNA sequence,including DNA methylation,histone covalent modification and non-coding RNA-mediated gene silencing.Phosphorus is an essential macronutrient for plant metabolic processes,including energy metabolism,the synthesis of nucleic acids and membranes,photosynthesis,respiration,nitrogen fixation and enzyme regulation.Iron is an essential trace nutrition element of plants,its availability affects root morphogenesis,photosynthesis,nitrogen fixation,respiration and determinations of flower color and fertility.Iron deficiency impairs fundamental processes and causes reduction of chlorophyll,thus crop productivity and quality.However,the epigenetic regulation mechanisms of Pi and Fe homeostasis remain largely unknown.Through screening a set of HAT-or HDAC-related mutants,we identified histone acetyltransferase GCN5 as an important regulator of Pi and Fe homeostasis in Arabidopsis.Main results are as follows:1.We showed that gcn5 mutant exhibited lower tolerance to Pi limitation.From the Illumina high-throughput RNAseq and ChIP assay data,we identified six genes-At4 WRKY6y SBT3.5?GLR1.2?RIPK and PCKI-as candidates responsible for GCN5-mediated regulation of phosphate homeostasis.It was well clarified that the long non-coding RNA At4 inhibits the cleavage of PH02 transcript by miR399 in a target mimicry manner,but the regulation of At4 remains elusive.Here,we showed that GCN5 directly bond to the promoter of At4 and the enrichment was correlated with the course of low Pi treatment.The decreased H3K9/14ac levels at At4 core promoter region and At4 expression in gcn5 mutant lead to the impaired ability for phosphate relocation from shoot to root.However,constitutive expression of At4 in gcn5 mutant could partially recover these defects.In contrast,histone deacetylase HDA19 negatively controlled At4 expression.We put new insights into an epigenetic regulation of phosphate homeostasis in Arabidopsis.2.We reported GCN5 contributed to iron translocation from root to shoot in Arabidopsis.Iron retention was observed in root but the shoot exhibited an iron malnutrition phenotypes.Illumina high-throughput RNAseq and ChIP assay identified five GCN5-regulated candidate genes for iron homeostasis,including FRD3?EXO70H2?MLP329?BOR1 and CRK25.FRD3 facilitates Fe chelation to citrate and subsequent transport of Fe-citrate from the root to the shoot.Like gcn5,the frd3 mutant also displayed iron retention in root.Notably,GCN5-mediated H3K9/14ac acetylations of FRD3 regulated FRD3 expression.Iron retention was partly resolved by overexpressing FRD3 in gcn5 or exogenous citrate.Moreover,chlorophyll content and pollen viability were enhanced by overexpressing FRD3 in gcn5 or application of EDDHA-Fe.Our results provided novel insights into the epigenetic regulation of iron homeostasis in Arabidopsis.