A Study Of Epigenetic Regulation Of Aleurone Layer Programmed Cell Death During Maize Seed Germination

The aleurone layer is a model system which specifically responds to plant hormone gibberellin GA and abscisic acid ABA regulating gene expression and programmed cell death.Seed germination is a systematic response involving the bi-directional interaction between the embryo and the endosperm.During seed germination,the embryo secreting signal to the endosperm to induce degradation of the seed stock and weaken the endosperm function while the endosperm can sense the ambient signal,produce and secretion signals to regulate the growth of the embryo,and the hydrolase synthesized in the aleurone layer is secreted into the starchy endosperm for the degradation of the nutrients stored therein.The aleurone layer synthesizes the hydrolase and then enters the programmed cell death(PCD).PCD is the basic course of life which plays an important role in the animal and plant development,differentiation,intuitive and immune system.Recent studies have shown that ROS is an important signal for gene activation and plays an important role in plant growth and development,coping with biological and abiotic environmental stimuli and PCD.In the field of epigenetics,the regulatory factors based on the change of gene expression level caused by non-gene sequence change have become a new research hotspot.The post-translational modification of histones is not only closely related to the remodeling and functional status of chromosomes,but also plays an important role in determining cell fate and cell growth.Gene expression regulation is affected by multiple factors:histone acetylation can activate the transcription process of a particular gene.Histone lysine acetylation is highly dynamic and is co-administered by two family enzymes:histone acetyltransferase(HATs)and histone deacetylase(HDACs).Despite this,the process of cell death of chromatin modification research is still very few.The study of chromatin modification in gene expression and the process of programmed cell death during maize germination can not only reveal the functional diversity of chromatin modification or chromatin modification enzymes,but also deepen the understanding of the molecular regulation network of seed germination and programmed cell death.In this paper,we mainly studied the molecular regulation network of gene expression and programmed cell death during the process of seed germination in maize,observed the regulation of reactive oxygen species,tried to reveal the function of chromatin modification and chromatin during different programmed cell death.The relationship between modification and active oxygen regulation.This paper includes the following research:1.Histone acetylation is involved in the expression of gibberellin-regulated sodCp gene in maize aleurone layerThe cereal aleurone layer plays an important role in seed germination,and reactive oxygen species(ROS)in aleurone layers act as crucial signal molecules in this progression.Recent studies have revealed that epigenetic modification is involved in plant development and seed germination.However,little is known about a possible relationship between histone modification and ROS signaling pathway in cereal aleurone layers during seed germination.Here,we found that the expression of both HATs and HDACs were increased gradually during seed germination accompanied with an increase in global acetylation levels of histones H3 and H4 in maize aleurone layers.GA promotes seed germination,ABA inhibits seed germination.The acetylation was found to be promoted by GA and suppressed by ABA.However,when the HDACs inhibitor trichostatin A(TSA)was used,the increased H3K9ac and H4K5ac level correlated with an inhibition of the germination.These results indicated that the overall histone acetylation in the aleurone layers is not required for germination.H2O2 plays an important role in seed germination and regulates the production of a-amylase in aleurone layer.The activities of superoxide dismutase(SOD)catalyzed by H2O2 during maize seed germination were up-regulated in GA-treated seeds,however,catalase(CAT)and peroxidase(POD)were maintained a relatively low level.The changes in these enzymes explain the accumulation of H2O2 during the germination of maize seeds.During the process of seed germination,the content of H2O2 in GA-treated aleurone layers and the activity of α-amylase increased.In contrast,the activity of a-amylase the seeds treated with ABA and TSA were remained low level during the germination process.Similarly these two hormones GA and ABA exerted opposed effects on the expression of ROS related gene sodCp.Furthermore,chromatin immunoprecipitation experiments showed that the promoter region of the sodCp gene was hyperacetylated during germination,and this acetylation was promoted by GA and inhibited by both ABA and TSA.These results suggested that GA-mediated expression of the sodCp gene in aleurone layers is associated with histone hyperacetylation on the promoter and coding region of this gene,consequently leading to an accumulation of H2O2 which regulated production of a-amylase during seed germination.2.HDACs is required for GA-induced programmed cell death in maize aleurone layersRecent discoveries have shown that epigenetic regulation is an integral part of phytohormone-mediated processes.The phytohormoneGA triggers a series of events in cereal aleurone cells that lead to PCD,but the signaling cascade mediating GA-induced PCD in cereal aleurone layers remains largely unknown.Here,we showed that HDACsactivity gradually increased relative toHATsactivity,leading to a global decrease in histone H3 and H4 acetylation levels during GA-induced PCD of maize embryoless aleurone layers.HDACs inhibition prevented GA-induced PCD in embryoless aleurone cells,whereas HATs inhibition resulted in PCD even in the absence of GA.Our results show that HDACs play an important role in GA-induced programmed cell death of maize aleurone layers.H2O2 plays an important role in the process of phylogenetic cell death.Different antioxidant enzymes in plants are sensors and regulators which respond to H2O2 signal transduction.H2O2 concentrations increased in GA-or HATs-inhibitor-treated aleurone cells due to reduced levels of ROS scavengers.H2O2-treated aleurone cells showed no changes in the activity or expression of HATs and HDACs.We show that it is possible to predict whether epigenetic modification enzymes serve as a regulator of the GA-triggered PCD signaling pathway in maize aleurone layers.Taken together,these findings reveal that HDACs activity is required for GA-induced PCD in maize aleurone layers and regulates PCD via the ROS-mediated signal transduction pathway.