Unveiling the mechanism of broad-spectrum blast resistance in rice: The collaborative role of transcription factor OsGRAS30 and histone deacetylase OsHDAC1.

Rice blast, caused by Magnaporthe oryzae, significantly impacts grain yield, necessitating the identification of broad-spectrum resistance genes and their functional mechanisms for disease-resistant crop breeding. Here, we report that rice with knockdown OsHDAC1 gene expression displays enhanced broad-spectrum blast resistance without effects on plant height and tiller numbers compared to wild-type rice, while rice overexpressing OsHDAC1 is more susceptible to M. oryzae. We identify a novel blast resistance transcription factor, OsGRAS30, which genetically acts upstream of OsHDAC1 and interacts with OsHDAC1 to suppress its enzymatic activity. This inhibition increases the histone H3K27ac level, thereby boosting broad-spectrum blast resistance. Integrating genome-wide mapping of OsHDAC1 and H3K27ac targets with RNA sequencing analysis unveils how OsHDAC1 mediates the expression of OsSSI2, OsF3H, OsRLR1 and OsRGA5 to regulate blast resistance. Our findings reveal that the OsGRAS30-OsHDAC1 module is critical to rice blast control. Therefore, targeting either OsHDAC1 or OsGRAS30 offers a promising approach for enhancing crop blast resistance.

DNA methylation and lipid metabolism are involved in GA-induced maize aleurone layers PCD as revealed by transcriptome analysis.

BACKGROUND: The aleurone layer is a part of many plant seeds, and during seed germination, aleurone cells undergo PCD, which is promoted by GA from the embryo. However, the numerous components of the GA signaling pathway that mediate PCD of the aleurone layers remain to be identified. Few genes and transcriptomes have been studied thus far in aleurone layers to improve our understanding of how PCD occurs and how the regulatory mechanism functions during PCD. Our previous studies have shown that histone deacetylases (HDACs) are required in GA-induced PCD of aleurone layer. To further explore the molecular mechanisms by which epigenetic modifications regulate aleurone PCD, we performed a global comparative transcriptome analysis of embryoless aleurones treated with GA or histone acetylase (HAT) inhibitors. RESULTS: In this study, a total of 7,919 differentially expressed genes (DEGs) were analyzed, 2,554 DEGs of which were found to be common under two treatments. These identified DEGs were involved in various biological processes, including DNA methylation, lipid metabolism and ROS signaling. Further investigations revealed that inhibition of DNA methyltransferases prevented aleurone PCD, suggesting that active DNA methylation plays a role in regulating aleurone PCD. GA or HAT inhibitor induced lipoxygenase gene expression, leading to lipid degradation, but this process was not affected by DNA methylation. However, DNA methylation inhibitor could regulate ROS-related gene expression and inhibit GA-induced production of hydrogen peroxide (H2O2). CONCLUSION: Overall, linking of lipoxygenase, DNA methylation, and H2O2 may indicate that GA-induced higher HDAC activity in aleurones causes breakdown of lipids via regulating lipoxygenase gene expression, and increased DNA methylation positively mediates H2O2 production; thus, DNA methylation and lipid metabolism pathways may represent an important and complex signaling network in maize aleurone PCD.

The histone deacetylase 1/GSK3/SHAGGY-like kinase 2/BRASSINAZOLE-RESISTANT 1 module controls lateral root formation in rice.

Lateral roots (LRs) are a main component of the root system of rice (Oryza sativa) that increases root surface area, enabling efficient absorption of water and nutrients. However, the molecular mechanism regulating LR formation in rice remains largely unknown. Here, we report that histone deacetylase 1 (OsHDAC1) positively regulates LR formation in rice. Rice OsHDAC1 RNAi plants produced fewer LRs than wild-type plants, whereas plants overexpressing OsHDAC1 exhibited increased LR proliferation by promoting LR primordia formation. Brassinosteroid treatment increased the LR number, as did mutation of GSK3/SHAGGY-like kinase 2 (OsGSK2), whereas overexpression of OsGSK2 decreased the LR number. Importantly, OsHDAC1 could directly interact with and deacetylate OsGSK2, inhibiting its activity. OsGSK2 deacetylation attenuated the interaction between OsGSK2 and BRASSINAZOLE-RESISTANT 1 (OsBZR1), leading to accumulation of OsBZR1. The overexpression of OsBZR1 increased LR formation by regulating Auxin/IAA signaling genes. Taken together, the results indicate that OsHDAC1 regulates LR formation in rice by deactivating OsGSK2, thereby preventing degradation of OsBZR1, a positive regulator of LR primordia formation. Our findings suggest that OsHDAC1 is a breeding target in rice that can improve resource capture.

Histone acetylation of 45S rDNA correlates with disrupted nucleolar organization during heat stress response in Zea mays L.

The role of the nucleolus in plant response to heat stress remains largely obscure. Our current efforts focused on exploring the underlying mechanism by which nucleolar disorganization is regulated in heat stressed-maize lines. Here, two maize lines, a heat-sensitive line, ZD958, and a heat-tolerant line, ZDH, were submitted to heat stress for investigating their association with the nucleolar disruption. Immunofluorescence staining showed that nucleolar disruption increased with prolonged treatment time. After heat treatment, a significant change in nucleolus organization was observed in the ZD958 line, but the ZDH line showed mild alteration. Moreover, actinomycin D (ActD)-induced nucleolus fission led to inhibition of maize growth under the normal condition. The ZD958 line exhibited a significant increase in the level of H3K9ac and H4K5ac of the 45S rDNA accompanied by a higher transcription of the 5'-external transcribed spacer (ETS) region, while the line ZDH showed a slight increase in histone acetylation levels and the transcriptional initiation at this site after heat treatment. To our knowledge, this is the first report providing a comparative insight between heat stress, rDNA histone modifications, and nucleolus disintegration in a heat-tolerant ZDH compared with a heat-sensitive line ZD958. Our investigation might assist maize breeders in obtaining heat-tolerant lines by targeting nucleoli using epigenetics.

Characteristic and evolution of HAT and HDAC genes in Gramineae genomes and their expression analysis under diverse stress in Oryza sativa.

MAIN CONCLUSION: Comprehensive characterization of Gramineae HATs and HDACs reveals their conservation and variation. The recent WGD/SD gene pairs in the CBP and RPD/HDA1 gene family may confer specific adaptive evolutionary changes. Expression of OsHAT and OsHDAC genes provides a new vision in different aspects of development and response to diverse stress. The histone acetylase (HAT) and histone deacetylase (HDAC) have been proven to be tightly linked to play a crucial role in plant growth, development and response to abiotic stress by regulating histone acetylation levels. However, the evolutionary dynamics and functional differentiation of HATs and HDACs in Gramineae remain largely unclear. In the present study, we identified 37 HAT genes and 110 HDAC genes in seven Gramineae genomes by a detailed analysis. Phylogenetic trees of these HAT and HDAC proteins were constructed to illustrate evolutionary relationship in Gramineae. Gene structure, protein property and protein motif composition illustrated the conservation and variation of HATs and HDACs in Gramineae. Gene duplication analysis suggested that recent whole genome duplication (WGD)/segmental duplication (SD) events contributed to the diversification of the CBP and RPD3/HDA1 gene family in Gramineae. Furthermore, promoter cis-element prediction indicated that OsHATs and OsHDACs were likely functional proteins and involved in various signaling pathways. Expression analysis by RNA-seq data showed that all OsHAT and OsHDAC genes were expressed in different tissues or development stages, revealing that they were ubiquitously expressed. In addition, we found that their expression patterns were altered in response to cold, drought, salt, light, abscisic acid (ABA), and indole-3-acetic acid (IAA) treatments. These findings provide the basis for further identification of candidate OsHAT and OsHDAC genes that may be utilized in regulating growth and development and improving crop tolerance to abiotic stress.

Dynamic changes in histone modification are associated with upregulation of Hsf and rRNA genes during heat stress in maize seedlings.

Histone modification plays a significant role in plant responses to abiotic stress. However, there are little scientific studies available on the involvement of dynamic changes in histone modification in the heat stress response in maize. The present investigation was aimed to analyze the epigenetic mechanisms involved in regulating the physiological and biochemical alterations in maize seedlings under heat stress. Our results and observations indicated an increase in electrolyte leakage and hydrolytic activity of the plasma membrane H+-ATPase as well as the high pigment content and reactive oxygen species (ROS) content under high temperature. Furthermore, decondensation of ribosomal DNA (rDNA) chromatin and a simultaneous increase in rRNA gene expression were observed during heat stress, accompanied by a genome-wide increase in the levels of histone H3K4me2 and H3K9ac. Additionally, chromatin immunoprecipitation (ChIP) analysis revealed that alterations in H3K4me2 and H3K9ac levels occurred in promoter regions, which were found to be associated with the upregulation of heat stress factor (Hsf) and rRNA genes. In conclusion, short-term heat stress induces dynamic histone alterations which are associated with Hsf and rRNA gene transcription, accompanied by perturbations of cell membranes and an increase in ROS during acclimation in maize seedlings.

5-Azacytidine specifically inhibits the NIH-3T3 PCD process induced by TNF-alpha and cycloheximide via affecting BCL-XL.

DNA methylation plays a crucial role in lots of biological processes and cancer. 5-azacytidine (5-AC), a DNA methylation inhibitor, has been used as a potential chemotherapeutic agent for cancer. In this study, we used 5-AC treatment to investigate whether DNA methylation was involved in regulation of programmed cell death (PCD) in mouse embryo fibroblast NIH-3T3 cells which could undergo PCD after treatment with TNF-α and cycloheximide (CHX). The results showed that the genomic DNA of NIH-3T3 cells was hypermethylated during PCD induced by TNF-α and CHX, and 5-AC might prevent this PCD process. However, treatment with the other three DNA methylation inhibitors, 5-aza-deoxycytidine, 6-thioguanine and RG108, did not interfere with the NIH-3T3 cell PCD process. Additionally, knockdown of DNMT1 did not affect the apoptosis process. The present results and observations indicated that 5-AC specifically inhibited the NIH-3T3 apoptosis process via a genomic DNA methylation-independent pathway. During the TNF-α and CHX-inducing apoptosis process, the PCD related BCL-2 family proteins were significantly down-regulated. Furthermore, after the small interference RNA-mediated knockdown of BCL-XL, one of the BCL-2 family proteins, 5-AC did not inhibit the apoptosis process, suggesting that 5-AC inhibited the PCD process induced by TNF-α and CHX by affecting the anti-apoptotic protein BCL-XL.

Histone acetylation is involved in GA-mediated 45S rDNA decondensation in maize aleurone layers.

KEY MESSAGE: The aleurone layer is crucial to seed germination. Using dissected aleurone layers, we found that GA increased histone acetylation accompanied by rDNA decondensation in aleurone layers during maize seed germination. Aleurone layers play an important role in cereal seed germination. In this study, we reported that rDNA chromatin was decondensed, accompanied with increased rDNA expression and genomic global hyperacetylation in gibberellin (GA)-treated maize-dissected aleurone layers. The activity analysis of histone acetyltransferase (HAT) and deacetylase (HDAC) showed that GA increased the level of histone acetylation by promoting the ratio of HAT/HDAC activity in aleurone layers. HDAC inhibitors TSA and CUDC-101 elevated the histone acetylation in aleurone layers accompanied by 45S rDNA decondensation. The further chromatin immunoprecipitation experiments showed that GA treatment promoted the level of histone acetylation in the promoter region of the rRNA and HAT/HDAC genes in aleurone layers. Taken together, these data indicated that histone acetylation mediates GA-regulated 45S rDNA chromatin decondensation in aleurone layers during maize seed germination.

Histone Deacetylase Is Required for GA-Induced Programmed Cell Death in Maize Aleurone Layers.

Recent discoveries have shown that epigenetic regulation is an integral part of phytohormone-mediated processes. The phytohormone gibberellin (GA) triggers a series of events in cereal aleurone cells that lead to programmed cell death (PCD), but the signaling cascade mediating GA-induced PCD in cereal aleurone layers remains largely unknown. Here, we showed that histone deacetylase (HDAC) activity gradually increased relative to histone acetyltransferase (HAT) activity, leading to a global decrease in histone H3 and H4 acetylation levels during PCD of maize (Zea mays) embryoless aleurone layers after 3 d of treatment with GA. HDAC inhibition prevented GA-induced PCD in embryoless aleurone cells, whereas HAT inhibition resulted in PCD even in the absence of GA. Hydrogen peroxide concentrations increased in GA- or HAT inhibitor-treated aleurone cells due to reduced levels of reactive oxygen species scavengers. Hydrogen peroxide-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 HDAC activity is required for GA-induced PCD in maize aleurone layers and regulates PCD via the reactive oxygen species-mediated signal transduction pathway.

Histone acetylation and reactive oxygen species are involved in the preprophase arrest induced by sodium butyrate in maize roots.

Histone acetylation plays a critical role in controlling chromatin structure, and reactive oxygen species (ROS) are involved in cell cycle progression. To study the relationship between histone acetylation and cell cycle progression in plants, sodium butyrate (NaB), a histone deacetylase (HDAC) inhibitor that can cause a significant increase in histone acetylation in both mammal and plant genomes, was applied to treat maize seedlings. The results showed that NaB had significant inhibition effects on different root zones at the tissue level and caused cell cycle arrest at preprophase in the root meristem zones. This effect was accompanied by a dramatic increase in the total level of acetylated lysine 9 on histone H3 (H3K9ac) and acetylated lysine 5 on histone H4 (H4K5ac). The exposure of maize roots in NaB led to a continuous rise of intracellular ROS concentration, accompanied by a higher electrolyte leakage ratio and malondialdehyde (MDA) relative value. The NaB-treated group displayed negative results in both TdT-mediated dUTP nick end labelling (TUNEL) and γ-H2AX immunostaining assays. The expression of topoisomerase genes was reduced after treatment with NaB. These results suggested that NaB increased the levels of H3K9ac and H4K5ac and could cause preprophase arrest accompanied with ROS formation leading to the inhibition of DNA topoisomerase.

Overexpression of Ribosomal RNA in the Development of Human Cervical Cancer Is Associated with rDNA Promoter Hypomethylation.

The ribosomal RNA (rRNA) gene encodes rRNA for protein synthesis. Aberrant expression of the rRNA gene has been generally observed in tumor cells and levels of its promoter methylation as an epigenetic regulator affect rRNA gene transcription. The possible relationship between expression and promoter methylation of rDNA has not been examined in human clinical cervical cancer. Here we investigate rRNA gene expression by quantitative real time PCR, and promoter methylation levels by HpaII/MspI digestion and sodium bisulfite sequencing in the development of human cervical cancer. We find that indeed rRNA levels are elevated in most of cervical intraepithelial neoplasia (CIN) specimens as compared with non-cancer tissues. The rDNA promoter region in cervical intraepithelial neoplasia (CIN) tissues reveals significant hypomethylation at cytosines in the context of CpG dinucleotides, accompanied with rDNA chromatin decondensation. Furthermore treatment of HeLa cells with the methylation inhibitor drug 5-aza-2'-deoxycytidine (DAC) demonstrates the negative correlation between the expression of 45S rDNA and the methylation level in the rDNA promoter region. These data suggest that a decrease in rDNA promoter methylation levels can result in an increase of rRNA synthesis in the development of human cervical cancer.

Zinc oxide nanoparticles-induced epigenetic change and G2/M arrest are associated with apoptosis in human epidermal keratinocytes.

As an engineered nanomaterial, zinc oxide nanoparticles (ZnO NPs) are used frequently in biological applications and can make contact with human skin. Here, we systematically investigated the effects of ZnO NPs on non-tumorigenic human epidermal keratinocytes, which were used as a test model for this in vitro study, at the epigenetic and molecular levels. Our results showed that ZnO NPs induced cell cycle arrest at the G2/M checkpoint before the viability of human epidermal keratinocytes was reduced, which was associated with the chromatin changes at the epigenetic level, including increased methylation of histone H3K9 and decreased acetylation of histone H4K5 accompanied by chromatin condensation at 24 hours. The mRNA expression of the methyltransferase genes G9a and GLP was also increased upon treatment with ZnO NPs, and the acetyltransferase genes GCN5, P300, and CBP were downregulated. Reactive oxygen species were found to be more abundant after treatment with ZnO NPs for 6 hours, and DNA damage was observed at 24 hours. Transmission electron microscopy and flow cytometry confirmed that ZnO NPs were absorbed into the cell when they were added to the medium. Apoptotic human epidermal keratinocytes were detected, and the expression of the proapoptotic genes Bax, Noxa, and Puma increased significantly, while the expression of the antiapoptotic gene Bcl-xl decreased 24 hours after exposure to ZnO NPs. These findings suggest that the ZnO NPs induced cell cycle arrest at G2/M, which was associated with epigenetic changes and accompanied by p53-Bax mitochondrial pathway-mediated apoptosis.

Single-wall and multi-wall carbon nanotubes promote rice root growth by eliciting the similar molecular pathways and epigenetic regulation.

Organisms are constantly exposed to environmental stimuli and have evolved mechanisms of protection and adaptation. Various effects of nanoparticles (NPs) on crops have been described and some results confirm that NPs could enhance plant growth at the physiological and genetic levels. This study comparatively analysed the effect of carbon nanotubes (CNTs) on rice growth. The results showed that single-wall CNTs were located in the intercellular space while multi-wall CNTs penetrated cell walls in roots. CNTs could promote rice root growth through the regulation of expression of the root growth related genes and elevated global histone acetylation in rice root meristem zones. These responses were returned to normal levels after CNTs were removed from medium. CNTs caused the similar histone acetylation and methylation statuses across the local promoter region of the Cullin-RING ligases 1 (CRL1) gene and increased micrococcal nuclease accessibility of this region, which enhanced this gene expression. The authors results suggested that CNTs could cause plant responses at the cellular, genetic, and epigenetic levels and these responses were independent on interaction modes between root cells and CNTs.

Histone Modification Is Involved in Okadaic Acid (OA) Induced DNA Damage Response and G2-M Transition Arrest in Maize.

Histone modifications are involved in regulation of chromatin structure. To investigate the relationship between chromatin modification and cell cycle regulation during plant cell proliferation, Okadaic acid (OA), a specific inhibitor of serine/threonine protein phosphatase, was applied in this study. The results showed that OA caused the cell cycle arrest at preprophase, leading to seedling growth inhibition. Western blotting assay revealed that the spatial distribution of phosphorylation of Ser10 histone H3 tails (H3S10ph) signals was altered under OA treatment. Reactive oxygen species (ROS) was found to be at higher levels and TdT-mediated dUTP nick end labeling (TUNEL) assay displayed DNA breaks happened at the chromatin after treatment with OA, companied with an increase in the acetylation of histone H4 at lysine 5 (H4K5ac) level. From these observations, we speculated that the alteration of the spatial distribution of H3S10ph and the level of H4K5ac was involved in the procedure that OA induced DNA breaks and G2-M arrested by the accumulation of ROS, and that the histone H3S10ph and H4K5ac might facilitate DNA repair by their association with the chromatin decondensation.

Cell cycle arrest induced by inhibitors of epigenetic modifications in maize (Zea mays) seedling leaves: characterization of the process and possible mechanisms involved.

Epigenetic modifications play crucial roles in the regulation of chromatin architecture and are involved in cell cycle progression, including mitosis and meiosis. To explore the relationship between epigenetic modifications and the cell cycle, we treated maize (Zea mays) seedlings with six different epigenetic modification-related inhibitors and identified the postsynthetic phase (G2 ) arrest via flow cytometry analysis. Total H4K5ac levels were significantly increased and the distribution of H3S10ph signalling was obviously changed in mitosis under various treatments. Further statistics of the cells in different periods of mitosis confirmed that the cell cycle was arrested at preprophase. Concentrations of hydrogen peroxide were relatively higher in the treated plants and the antioxidant thiourea could negate the influence of the inhibitors. Moreover, all of the treated plants displayed negative results in the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) and γ-H2AX immunostaining assays after exposure for 3 d. Additionally, the expression level of topoisomerase genes in the treated plants was relatively lower than that in the untreated plants. These results suggest that these inhibitors of epigenetic modifications could cause preprophase arrest via reactive oxygen species formation inhibiting the expression of DNA topoisomerase genes, accompanied by changes in the H4K5ac and H3S10ph histone modifications.

Histone Acetylation is Involved in Gibberellin-Regulated sodCp Gene Expression in Maize Aleurone Layers.

The 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 the ROS signaling pathway in cereal aleurone layers during seed germination. Here, we found that the expression of both histone acetyltransferases (HATs) and histone deacetylases (HDACs) was increased gradually during seed germination, accompanied by an increase in global acetylation levels of histones H3 and H4 in maize aleurone layers. The acetylation was found to be promoted by GA(3) and suppressed by ABA. However, when the HDAC 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. Similarly these two hormones, GA(3) and ABA, exerted opposed effects on the expression of the 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(3) and inhibited by both ABA and TSA. These results suggested that GA(3)-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 H(2)O(2) which regulated production of α-amylase during seed germination.

Epigenetic Changes are Associated with Programmed Cell Death Induced by Heat Stress in Seedling Leaves of Zea mays.

Histone modification plays a crucial role in regulation of chromatin architecture and function, responding to adverse external stimuli. However, little is known about a possible relationship between epigenetic modification and programmed cell death (PCD) in response to environmental stress. Here, we found that heat stress induced PCD in maize seedling leaves which was characterized by chromatin DNA laddering and DNA strand breaks detected by a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) test. The activities of the reactive oxygen species (ROS)-related enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were progressively increased over time in the heat-treated seedlings. However, the concentration of H2O2 remained at relatively lower levels, while the concentration of superoxide anion ([Formula: see text]) was increased, accompanied by the occurrence of higher ion leakage rates after heat treatment. The total acetylation levels of histones H3K9, H4K5 and H3 were significantly increased, whereas the di-methylation level of histone H3K4 was unchanged and the di-methylation level of histone H3K9 was decreased in the seedling leaves exposed to heat stress compared with the control seedlings, accompanied by increased nucleolus size indicative of chromatin decondensation. Furthermore, treatment of seedlings with trichostatin A (TSA), which always results in genomic histone hyperacetylation, caused an increase in the [Formula: see text] level within the cells. The results suggested that heat stress persistently induced [Formula: see text], leading to PCD in association with histone modification changes in the maize leaves.

Transcriptional regulation of cell cycle genes in response to abiotic stresses correlates with dynamic changes in histone modifications in maize.

The histone modification level has been shown to be related with gene activation and repression in stress-responsive process, but there is little information on the relationship between histone modification and cell cycle gene expression responsive to environmental cues. In this study, the function of histone modifications in mediating the transcriptional regulation of cell cycle genes under various types of stress was investigated in maize (Zea mays L.). Abiotic stresses all inhibit the growth of maize seedlings, and induce total acetylation level increase compared with the control group in maize roots. The positive and negative regulation of the expression of some cell cycle genes leads to perturbation of cell cycle progression in response to abiotic stresses. Chromatin immunoprecipitation analysis reveals that dynamic histone acetylation change in the promoter region of cell cycle genes is involved in the control of gene expression in response to external stress and different cell cycle genes have their own characteristic patterns for histone acetylation. The data also showed that the combinations of hyperacetylation and hypoacetylation states of specific lysine sites on the H3 and H4 tails on the promoter regions of cell cycle genes regulate specific cell cycle gene expression under abiotic stress conditions, thus resulting in prolonged cell cycle duration and an inhibitory effect on growth and development in maize seedlings.

Histone acetylation associated up-regulation of the cell wall related genes is involved in salt stress induced maize root swelling.

BACKGROUND: Salt stress usually causes crop growth inhibition and yield decrease. Epigenetic regulation is involved in plant responses to environmental stimuli. The epigenetic regulation of the cell wall related genes associated with the salt-induced cellular response is still little known. This study aimed to analyze cell morphological alterations in maize roots as a consequence of excess salinity in relation to the transcriptional and epigenetic regulation of the cell wall related protein genes. RESULTS: In this study, maize seedling roots got shorter and displayed swelling after exposure to 200 mM NaCl for 48 h and 96 h. Cytological observation showed that the growth inhibition of maize roots was due to the reduction in meristematic zone cell division activity and elongation zone cell production. The enlargement of the stele tissue and cortex cells contributed to root swelling in the elongation zone. The cell wall is thought to be the major control point for cell enlargement. Cell wall related proteins include xyloglucan endotransglucosylase (XET), expansins (EXP), and the plasma membrane proton pump (MHA). RT-PCR results displayed an up-regulation of cell wall related ZmEXPA1, ZmEXPA3, ZmEXPA5, ZmEXPB1, ZmEXPB2 and ZmXET1 genes and the down-regulation of cell wall related ZmEXPB4 and ZmMHA genes as the duration of exposure was increased. Histone acetylation is regulated by HATs, which are often correlated with gene activation. The expression of histone acetyltransferase genes ZmHATB and ZmGCN5 was increased after 200 mM NaCl treatment, accompanied by an increase in the global acetylation levels of histones H3K9 and H4K5. ChIP experiment showed that the up-regulation of the ZmEXPB2 and ZmXET1 genes was associated with the elevated H3K9 acetylation levels on the promoter regions and coding regions of these two genes. CONCLUSIONS: These data suggested that the up-regulation of some cell wall related genes mediated cell enlargement to possibly mitigate the salinity-induced ionic toxicity, and different genes had specific function in response to salt stress. Histone modification as a mediator may contribute to rapid regulation of cell wall related gene expression, which reduces the damage of excess salinity to plants.

Promoter-associated histone acetylation is involved in the osmotic stress-induced transcriptional regulation of the maize ZmDREB2A gene.

Epigenetic modifications play a key role in the transcriptional regulation of stress-induced gene expression in plants. In this study, we showed that the overall acetylation levels of histone H3 lysine 9 (H3K9) and H4 lysine 5 (H4K5) in the genome were increased in maize seedlings after mannitol treatment (to mimic osmotic stress). Mannitol treatment significantly induced the upregulation of the maize osmotic stress responsive gene Zea mays dehydration-responsive element binding protein 2A (ZmDREB2A), whereas abscisic acid (ABA) did not result in the induction of this gene. The application of exogenous ABA under osmotic stress conditions strongly repressed the induction of the ZmDREB2A gene. Chromatin immunoprecipitation and chromatin accessibility by real-time PCR experiments revealed that the promoter region of the ZmDREB2A gene was quickly hyperacetylated and decondensed after the mannitol treatment, suggesting that the promoter region is poised for histone acetylation to allow for fast induction of the ZmDREB2A gene. However, under osmotic stress conditions, the ABA treatment decreased the acetylation status and chromatin accessibility to micrococcal nuclease. These results suggest that osmotic stress activates the transcription of the ZmDREB2A gene by increasing the levels of acetylated histones H3K9 and H4K5 associated with the ZmDREB2A promoter region.