BackgroundSalt 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.ResultsIn 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.ConclusionsThese 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.

Our previous study demonstrated that 45S ribosomal DNA (45S rDNA) clusters were chromosome fragile sites expressed spontaneously in Lolium . In this study, fragile phenotypes of 45S rDNA were observed under aphidicolin (APH) incubation in several plant species. Further actinomycin D (ActD) treatment showed that transcriptional stress might interfere with chromatin packaging, resulting in 45S rDNA fragile expression. These data identified 45S rDNA sites as replication-dependent as well as transcription-dependent fragile sites in plants. In the presence of ActD, a dramatic switch to an open chromatin conformation and accumulated incomplete 5′ end of the external transcribed spacer (5′ETS) transcripts were observed, accompanied by decreased DNA methylation, decreased levels of histone H3, and increased histone acetylation and levels of H3K4me2, suggesting that these epigenetic alterations are associated with failure of 45S rDNA condensation. Furthermore, the finding that γ-H2AX was accumulated at 45S rDNA sites following ActD treatment suggested that the DNA damage signaling pathway was associated with the appearance of 45S rDNA fragile phenotypes. Our data provide a link between 45S rDNA transcription and chromatin-packaging defects and open the door for further identifying the molecular mechanism involved.

Two complete chloroplast genome sequences of Asteropyrum, as well as those of 25 other species from Ranunculaceae, were assembled using both Illumina and Sanger sequencing methods to address the structural variation of the cp genome and the controversial systematic position of the genus. Synteny and plastome structure were compared across the family. The cp genomes of the only two subspecies of Asteropyrum were found to be differentiated with marked sequence variation and different inverted repeat-single copy (IR-SC) borders. The plastomes of both subspecies contains 112 genes. However, the IR region of subspecies peltatum carries 27 genes, whereas that of subspecies cavaleriei has only 25 genes. Gene inversions, transpositions, and IR expansion-contraction were very commonly detected in Ranunculaceae. The plastome of Asteropyrum has the longest IR regions in the family, but has no gene inversions or transpositions. Non-coding regions of the cp genome were not ideal markers for inferring the generic relationships of the family, but they may be applied to interpret species relationship within the genus. Plastid phylogenomic analysis using complete cp genome with Bayesian method and partitioned modeling obtained a fully resolved phylogenetic framework for Ranunculaceae. Asteropyrum was detected to be sister to Caltha, and diverged early from subfamily Ranunculoideae.

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 coldmediated unsilencing of heterochromatic tandem-repeated sequences, accompanied with epigenetic regulation, might play an important role in the adaptation of plants to cold stimuli.

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.