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. 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. 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.

/pdf/histone-acetylation-associated-up-regulation-of-the-cell-5fa9b71gcj.pdf

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

Post-translational modifications of histone proteins play a crucial role in responding to environmental stresses Histone deacetylases (HDACs) catalyze the removal of an acetyl group from histones and are generally believed to be a transcriptional repressor In this paper, we report that cold treatment highly induces the up-regulation of HDACs, leading to global deacetylation of histones H3 and H4 Treatment of maize with the HDAC inhibitor trichostatin A (TSA) under cold stress conditions strongly inhibits induction of the maize cold-responsive genes ZmDREB1 and ZmCOR413 However, up-regulation of the ZmICE1 gene in response to cold stress is less affected The expression of drought and salt induced genes, ZmDBF1 and rab17, is almost unaffected by TSA treatment Thus, these observations show that HDACs may selectively activate transcription The time course of TSA effects on the expression of ZmDREB1 and ZmCOR413 genes indicates that HDACs appear to directly activate the ZmDREB1 gene, which in turn modulates ZmCOR413 expression After cold treatment, histone hyperacetylation and DNA demethylation occurs in the ICE1 binding region, accompanied by an increase in accessibility to micrococcal nuclease (MNase) The two regions adjacent to the ICE1 binding site remain hypoacetylated and methylated However, during cold acclimation, TSA treatment increases the acetylation status and accessibility of MNase and decreases DNA methylation at these two regions However, TSA treatment does not affect histone hyperacetylation and DNA methylation levels at the ICE1 binding regions of the ZmDREB1 gene Altogether, our findings indicate that HDACs positively regulate the expression of the cold-induced ZmDREB1 gene through histone modification and chromatin conformational changes and that this activation is both gene and site selective

https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0022132&type=printable

Trichostatin A selectively suppresses the cold-induced transcription of the ZmDREB1 gene in maize.

Under stress, isolated microspores are reprogrammed in vitro towards embryogenesis, producing doubled haploid plants that are useful biotechnological tools in plant breeding as a source of new genetic variability, fixed in homozygous plants in only one generation. Stress-induced cell death and low rates of cell reprogramming are major factors that reduce yield. Knowledge gained in recent years has revealed that initiation and progression of microspore embryogenesis involve a complex network of factors, whose roles are not yet well understood. Here, I review recent findings on the determinant factors underlying stress-induced microspore embryogenesis, focusing on the role of autophagy, cell death, auxin, chromatin modifications, and the cell wall. Autophagy and cell death proteases are crucial players in the response to stress, while cell reprogramming and acquisition of totipotency are regulated by hormonal and epigenetic mechanisms. Auxin biosynthesis, transport, and action are required for microspore embryogenesis. Initial stages involve DNA hypomethylation, H3K9 demethylation, and H3/H4 acetylation. Cell wall remodelling, with pectin de-methylesterification and arabinogalactan protein expression, is necessary for embryo development. Recent reports show that treatments with small modulators of autophagy, proteases, and epigenetic marks reduce cell death and enhance embryogenesis initiation in several crops, opening up new possibilities for improving in vitro embryo production in breeding programmes.

/pdf/microspore-embryogenesis-targeting-the-determinant-factors-3in2lo4qsw.pdf

Microspore embryogenesis: targeting the determinant factors of stress-induced cell reprogramming for crop improvement.

Knobs are cytologically observable major interstitial heterochromatin present on maize nuclei, which consist of highly tandem-repetitive elements that are always silenced. Here we investigated the genome-wide change of H3K9ac, an active chromatin mark, during cold stress using chromatin immunoprecipitation sequencing (ChIP-Seq) and identified differential cold-induced H3K9ac enrichment at repetitive sequences in maize. More detailed analysis of two knob-associated tandem-repetitive sequences, 180-bp and TR-1, demonstrated that cold activated their transcription and this cold-induced transcriptional activation of repetitive sequences is selective, transient, and associated with an increase in H3K9ac and a reduction in DNA methylation and H3K9me2. Furthermore, knob sequence expression is accompanied by localized chromatin remodelling and silencing is recovered upon prolonged treatment. In addition, no evidence of copy number change and rearrangement of these repetitive elements are found in plants subjected to cold stress. These results suggest that cold-mediated unsilencing of heterochromatic tandem-repeated sequences, accompanied with epigenetic regulation, might play an important role in the adaptation of plants to cold stimuli.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2012.02541.x

Cold stress selectively unsilences tandem repeats in heterochromatin associated with accumulation of H3K9ac.

Microspores are reprogrammed by stress in vitro towards embryogenesis This process is an important tool in breeding to obtain double-haploid plants DNA methylation is a major epigenetic modification that changes in differentiation and proliferation We have shown changes in global DNA methylation during microspore reprogramming 5-Azacytidine (AzaC) cannot be methylated and leads to DNA hypomethylation AzaC is a useful demethylating agent to study DNA dynamics, with a potential application in microspore embryogenesis This work analyzes the effects of short and long AzaC treatments on microspore embryogenesis initiation and progression in two species, the dicot Brassica napus and the monocot Hordeum vulgare This involved the quantitative analyses of proembryo and embryo production, the quantification of DNA methylation, 5mdC immunofluorescence and confocal microscopy, and the analysis of chromatin organization (condensation/ decondensation) by light and electron microscopy Four days of AzaC treatments (25 µM) increased embryo induction, response associated with a decrease of DNA methylation, modified 5mdC and heterochromatin patterns compared to untreated embryos By contrast, longer AzaC treatments diminished embryo production Similar effects were found in both species, indicating that DNA demethylation promotes microspore reprogramming, totipotency acquisition and embryogenesis initiation, while embryo differentiation requires de novo DNA methylation and is prevented by AzaC This suggests a role for DNA methylation in the repression of microspore reprogramming and possibly totipotency acquisition Results provide new insights into the role of epigenetic modifications in microspore embryogenesis and suggest a potential benefit of inhibitors, such as AzaC, to improve the process efficiency in biotechnology and breeding programs

/pdf/5-azacytidine-promotes-microspore-embryogenesis-initiation-v1ffgf32c0.pdf

5-azacytidine promotes microspore embryogenesis initiation by decreasing global DNA methylation, but prevents subsequent embryo development in rapeseed and barley

Modifications of DNA and histones in various combinations are correlated with many cellular processes. In this study, we investigated the possible relationship between histone H4 tetraacetylation, DNA methylation and histone H3 dimethylation at lysine 9 during mitosis in maize root meristems. Treatment with trichostatin A, which inhibits histone deacetylases, resulted in increased histone H4 acetylation accompanied by the decondensation of interphase chromatin and a decrease in both global H3K9 dimethylation and DNA methylation during mitosis in maize root tip cells. These observations suggest that histone acetylation may affect DNA and histone methylation during mitosis. Treatment with 5-azacytidine, a cytosine analog that reduces DNA methylation, caused chromatin decondensation and mediated an increase in H4 acetylation, in addition to reduced DNA methylation and H3K9 dimethylation during interphase and mitosis. These results suggest that decreased DNA methylation causes a reduction in H3K9 dimethylation and an increase in H4 acetylation. The interchangeable effects of 5-azacytidine and trichostatin A on H4 acetylation, DNA methylation and H3K9 dimethylation indicate a mutually reinforcing action between histone acetylation, DNA methylation and histone methylation with respect to chromatin modification. Treatment with trichostatin A and 5-azacytidine treatment caused a decrease in the mitotic index, suggesting that H4 deacetylation and DNA and H3K9 methylation may contain the necessary information for triggering mitosis in maize root tips.

/pdf/trichostatin-a-and-5-azacytidine-both-cause-an-increase-in-2wb22650wi.pdf

Trichostatin A and 5-azacytidine both cause an increase in global histone H4 acetylation and a decrease in global DNA and H3K9 methylation during mitosis in maize

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Trichostatin A and 5-azacytidine both cause an increase in global histone H4 acetylation and a decrease in global DNA and H3K9 methylation during mitosis in maize