Interference of the Histone Deacetylase Inhibits Pollen Germination and Pollen Tube Growth in Picea wilsonii Mast

Assessment of alternative freezing methods for preservation at -80°C of radiata pine embryogenic cultures: A six-year study

Somatic embryogenesis is an essential component of breeding programs for Pinus radiata aimed at implementing multi-varietal forestry. Coupled with this technique, the long-term cryopreservation of embryogenic cultures is necessary to maintain the viability of the cell lines, but this entails high maintenance costs. In this research we evaluated the application of a protocol for long-term storage at -80°C in an ultra-low freezer to preserve several radiata pine embryogenic cell lines. Also, we studied the influence of several parameters to optimize the protocol, such as the effect of dimethyl sulfoxide cryoprotectant solution, the effectiveness of alternative freezing methods, the use of post thawing treatments and the addition of sodium butyrate at maturation stage. We found that the use of dimethyl sulfoxide cryoprotectant enhanced somatic embryo production; slow cooling was the only viable method for preserving embryogenic cell lines at -80°C and the use of sodium butyrate was not highly effective to improve maturation and germination stages. Moreover, we have regenerated embryogenic cell lines up to their conversion into plants after six years of storage. In line with these findings, the protocol to storage in an ultra-low freezer represents an economical alternative to preserve somatic embryogenic cultures of Pinus radiata.

A histone deacetylase inhibitor enhances rice immunity by derepressing the expression of defense-related genes

Histone deacetylase (HDAC) inhibitors (HDACis) have been widely used in plants to investigate the role of histone acetylation, particularly the function of HDACs, in the regulation of development and stress response. However, how histone acetylation is involved in rice (Oryza sativa L.) disease resistance has hardly been studied. In this paper, four HDACis including Sodium butyrate (NaBT), Suberoylanilide Hydroxamic Acid (SAHA), LBH-589 and Trichostatin A (TSA) were used to treat rice seedlings at different concentrations before inoculation of Magnaporthe oryzae. We found that only 10mM NaBT treatment can significantly enhanced rice blast resistance. However, treatment of the four HDACis all increased global histone acetylation but at different sites, suggesting that the inhibition selectivity of these HDACis is different. Notably, the global H3K9ac level was dramatically elevated after both NaBT and LBH589 treatment although LBH589 could not enhance rice blast resistance. This indicates that the HDACs they inhibit target different genes. In accordance with the phenotype, transcriptomic analysis showed that many defense-related genes were up-regulated by NaBT treatment. Up-regulation of the four genes bsr-d1, PR10B, OsNAC4, OsKS4 were confirmed by RT-qPCR. ChIP-qPCR results revealed that H3K9ac level on these genes was increased after NaBT treatment, suggesting that these defense-related genes were repressed by HDACs. In addition, by promoter motif analysis of the genes that induced by both NaBT treatment and rice blast infection, we found that the motifs bound by ERF and AHL transcription factors (TFs) were the most abundant, which demonstrates that ERF and AHL proteins may act as the candidate TFs that recruit HDACs to defense-related genes to repress their expression when plants are not infected by rice blast.

Circulating cell-free mtDNA release is associated with the activation of cGAS-STING pathway and inflammation in mitochondrial diseases

BACKGROUND

There is increasing evidence for the role of inflammation in the pathogenesis of mitochondrial diseases (MDs). However, the mechanisms underlying mutation-induced inflammation in MD remain elusive. Our previous study suggested that mitophagy is impaired in the skeletal muscle of those with MD, likely causing mitochondrial DNA (mtDNA) release and thereby triggering inflammation. We here aimed to decipher the role of the cGAS-STING pathway in inflammatory process in MDs.

METHODS

We investigated the levels of circulating cell-free mtDNA (ccf-mtDNA) in the serum of 104 patients with MDs. Immunofluorescence was performed in skeletal muscles in MDs and control. Biochemical analysis of muscle biopsies was conducted with western blot to detect cGAS, STING, TBK1, IRF3 and phosphorylated IRF3 (p-IRF3). RT-qPCR was performed to detect the downstream genes of type I interferon in skeletal muscles. Furthermore, a protein microarray was used to examine the cytokine levels in the serum of patients with MDs.

RESULTS

We found that ccf-mtDNA levels were significantly increased in those with MDs compared to the controls. Consistently, the immunofluorescent results showed that cytosolic dsDNA levels were increased in the muscle samples of MD patients. Biochemical analysis of muscle biopsies showed that cGAS, IRF3, and TBK1 protein levels were significantly increased in those with MDs, indicating that there was activation of the cGAS-STING pathway. RT-qPCR showed that downstream genes of type I interferon were upregulated in muscle samples of MDs. Protein microarray results showed that a total of six cytokines associated with the cGAS-STING pathway were significantly increased in MD patients (fold change > 1.2, p value < 0.05).

CONCLUSIONS

These findings suggest that increases in ccf-mtDNA levels is associated with the activation of the cGAS-STING pathway, thereby triggering inflammation in MDs.

Pollen Germination and Pollen Tube Growth in Gymnosperms

Pollen germination and pollen tube growth are common to all seed plants, but these processes first developed in gymnosperms and still serve for their successful sexual reproduction. The main body of data on the reproductive physiology, however, was obtained on flowering plants, and one should be careful to extrapolate the discovered patterns to gymnosperms. In recent years, physiological studies of coniferous pollen have been increasing, and both the features of this group and the similarities with flowering plants have already been identified. The main part of the review is devoted to physiological studies carried out on conifer pollen. The main properties and diversity of pollen grains and pollination strategies in gymnosperms are described.

Histone Deacetylase Inhibitors Increase the Embryogenic Potential and Alter the Expression of Embryogenesis-Related and HDAC-Encoding Genes in Grapevine (Vitis vinifera L., cv. Mencía)

The low induction rates of somatic embryogenesis are one of the main limitations in its routine application in the grapevine (Vitis vinifera L.). The use of an induction medium containing histone deacetylase inhibitors (trichostatin A and, mainly, sodium butyrate) resulted in an improvement of the embryogenic responses in grapevine (cv. Mencía) cotyledonary and recently germinated somatic embryos. The relative expression of several grapevine genes related to embryogenic competence or encoding histone deacetylase enzymes was studied in cotyledonary somatic embryos that were cultured in the presence of 0.5 mM sodium butyrate. The results showed a significant overexpression of the BBM and VvSERK2 genes after 24 h of culture, whereas the VvWOX2 gene was underexpressed less in treated versus untreated explants. The results suggest that the inhibitor may trigger a molecular response related to an increase in embryogenic competence and changes in the expression of associated genes. The treatment with sodium butyrate also produced significant variations in the expression of several histone deacetylase enzyme-encoding genes. These results may enhance the possibility of obtaining somatic embryos, reducing the seasonal constraints associated with the use of floral explants in grapevines.

Trichostatin A Affects Developmental Reprogramming of Bread Wheat Microspores towards an Embryogenic Route

Microspores can be developmentally reprogrammed by the application of different stress treatments to initiate an embryogenic pathway leading to the production of doubled haploid (DH) plants. Epigenetic modifications are involved in cell reprogramming and totipotency in response to stress. To increase microspore embryogenesis (ME) efficiency in bread wheat, the effect of the histone deacetylase inhibitor trichostatin A (TSA) has been examined in two cultivars of wheat with different microspore embryogenesis response. Diverse strategies were assayed using 0-0.4 µM TSA as a single induction treatment and after or simultaneously with cold or mannitol stresses. The highest efficiency was achieved when 0.4 µM TSA was applied to anthers for 5 days simultaneously with a 0.7 M mannitol treatment, producing a four times greater number of green DH plants than mannitol. Ultrastructural studies by transmission electron microscopy indicated that mannitol with TSA and mannitol treatments induced similar morphological changes in early stages of microspore reprogramming, although TSA increased the number of microspores with 'star-like' morphology and symmetric divisions. The effect of TSA on the transcript level of four ME marker genes indicated that the early signaling pathways in ME, involving the TaTDP1 and TAA1b genes, may be mediated by changes in acetylation patterns of histones and/or other proteins.

Putrescine modifies the pollen tube growth of tea (Camellia sinensis) by affecting actin organization and cell wall structure

The aim of the current study was to examine the effect of different exogenous putrescine concentrations (200, 400, 600, and 800 μM) on the tea pollen performance. It was shown that putrescine has a dose-dependent effect on pollen performance. Results exhibited that pollen germination and tube elongation were induced by 200 and 400 μM putrescine treatment, especially, 400 μM putrescine-enhanced pollen performance. However, pollen performance was inhibited by higher concentrations of putrescine. Putrescine concentrations above 400 μM changed the actin filament distribution in pollen tubes by affecting the distribution of sucrose synthase enzyme. Alterations of the distribution on sucrose synthase enzyme also caused the alterations in the dispersion of cellulose and callose in the cell wall, and morphological alterations such as balloon-shaped and snake-shaped pollen tube tip accompanied them. Moreover, putrescine concentrations above 400 μM caused a decrease of ROS level in apex and led to chromatin condensation of the generative nucleus. In conclusion, exogenous putrescine application can be used as a pollen performance enhancer at low concentrations while the high concentrations cause adverse effects reducing fertilization success.

Bipolar pollen germination in blue spruce (Picea pungens)

Direct growth of a pollen tube is an effective mechanism of sperm delivery characteristic for the majority of seed plants. In most cases, only one tube grows from one grain to perform the delivery function; meanwhile in Picea the appearance of two tubes from a single pollen grain is quite common during in vitro germination. Here, we describe the phenomenon of bipolar germination and test two hypotheses on its nature and possible role in gametophyte functioning. The hypothesis on "trophic" function of multiple tubes provoked by poor nutrition discussed in literature was not confirmed by in vitro growth tests; bipolar germination strongly decreased with lowering sucrose availability. The highest proportion of bipolar germination occurred in optimal conditions. We then assumed that bipolar germination occurs because turgor pressure is a non-directional force and effective systems of cell wall mechanical regulation are lacking. In hypertonic medium, bipolar germination was sufficiently lower than in isotonic medium, which was consistent with prediction of the «mechanical» hypothesis. Scanning electron microscopy and fluorescence microscopy analysis of pollen morphology and cell wall dynamics during both types of germination showed that the appearance of a single tube or bipolar germination depends on the extension of exine rupture. Cell wall softening by short-term ·OH treatment sufficiently decreased the percent of bipolar germination without affecting total germination efficiency. We concluded that mechanical properties of the cell wall and turgor pressure could shift the balance towards one of the germination patterns.

Involvement of histone acetylation and deacetylation in regulating auxin responses and associated phenotypic changes in plants

The most recent outcomes about the transcription factors and transcription complexes mediated auxin signaling pathway by the histone acetylation and deacetylation. The phytohormone auxin, is required to regulate its accumulation spatiotemporally and responses to orchestrate various developmental levels in plants. Histone acetylation and deacetylation modulate auxin biosynthesis, its distribution and accumulation. In the absence of auxin, histone deacetylase represses the expression of auxin-responsive genes. Various transcription factors and transcription complexes facilitate the proper regulation of auxin signaling pathway genes. The primary and lateral root development, promotion of flowering and initiation of seed germination are all regulated by auxin-mediated histone acetylation and deacetylation. These findings conclude the auxin mode of action, which is mediated by histone acetylation and deacetylation, and associated phenotypic responses in plants, along with the underlying mechanism of these modifications.

Trichostatin A and 5-Aza-2'-Deoxycytidine influence the expression of cold-induced genes in Arabidopsis

The expression of cold-induced genes is critical for plants to survive under freezing stress. However, the underlying mechanisms for the decision of when, where, and which genes to express are unclear when a plant meets a sudden temperature drop. Previous studies have demonstrated epigenetics to play a central role in the regulation of gene expression in plant responses to environmental stress. DNA methylation and histone deacetylation are the two most important epigenetic modifications. This study was conducted to investigate the effects of inhibiting DNA methylation and histone deacetylation on gene expression, and to explore the potential role of epigenetics in plant responses to cold stress. The results revealed that histone deacetylase inhibitors (trichostatin A) and DNA methylation inhibitors (5-Aza-2'-deoxycytosine) treatment enhanced cold tolerance. DNA microarray analysis and the gene ontology method revealed 76 cold-induced differently expressed genes in Arabidopsis thaliana seedlings that were treated to 0°C for 24 h following Trichostatin A and 5-Aza-2'-Deoxycytidine. Furthermore, analyses of metabolic pathways and transcription factors of 3305 differentially expressed genes were performed. Each four metabolic pathways were significantly affected (p < 0.01) by Trichostatin A and 5-Aza-2'-Deoxycytidine. Finally, 10 genes were randomly selected and verified via qPCR analysis. Our study indicated that Trichostatin A and 5-Aza-2'-Deoxycytidine can improve the plant cold resistance and influence the expression of the cold-induced gene in A. thaliana. This result will advance our understanding of plant freezing responses and may provide a helpful strategy for cold tolerance improvement in crops.

Transcriptomic analysis links gene expression to unilateral pollen-pistil reproductive barriers

BACKGROUND

Unilateral incompatibility (UI) is an asymmetric reproductive barrier that unidirectionally prevents gene flow between species and/or populations. UI is characterized by a compatible interaction between partners in one direction, but in the reciprocal cross fertilization fails, generally due to pollen tube rejection by the pistil. Although UI has long been observed in crosses between different species, the underlying molecular mechanisms are only beginning to be characterized. The wild tomato relative Solanum habrochaites provides a unique study system to investigate the molecular basis of this reproductive barrier, as populations within the species exhibit both interspecific and interpopulation UI. Here we utilized a transcriptomic approach to identify genes in both pollen and pistil tissues that may be key players in UI.

RESULTS

We confirmed UI at the pollen-pistil level between a self-incompatible population and a self-compatible population of S. habrochaites. A comparison of gene expression between pollinated styles exhibiting the incompatibility response and unpollinated controls revealed only a small number of differentially expressed transcripts. Many more differences in transcript profiles were identified between UI-competent versus UI-compromised reproductive tissues. A number of intriguing candidate genes were highly differentially expressed, including a putative pollen arabinogalactan protein, a stylar Kunitz family protease inhibitor, and a stylar peptide hormone Rapid ALkalinization Factor. Our data also provide transcriptomic evidence that fundamental processes including reactive oxygen species (ROS) signaling are likely key in UI pollen-pistil interactions between both populations and species.

CONCLUSIONS

Gene expression analysis of reproductive tissues allowed us to better understand the molecular basis of interpopulation incompatibility at the level of pollen-pistil interactions. Our transcriptomic analysis highlighted specific genes, including those in ROS signaling pathways that warrant further study in investigations of UI. To our knowledge, this is the first report to identify candidate genes involved in unilateral barriers between populations within a species.

Rapid and Inexpensive Method of Loading Fluorescent Dye into Pollen Tubes and Root Hairs

The most direct technique for studying calcium, which is an essential element for pollen tube growth, is Ca²⁺ imaging. Because membranes are relatively impermeable, the loading of fluorescent Ca²⁺ probes into plant cells is a challenging task. Thus, we have developed a new method of loading fluo-4 acetoxymethyl ester into cells that uses a cell lysis solution to improve the introduction of this fluorescent dye into pollen tubes. Using this method, the loading times were reduced to 15 min. Furthermore, loading did not have to be performed at low (4°C) temperatures and was successful at room temperature, and pluronic F-127 was not required, which would theoretically allow for the loading of an unlimited number of cells. Moreover, the method can also be used to fluorescently stain root hairs.