Histone deacetylases HDA6 and HDA9 coordinately regulate valve cell elongation through affecting auxin signaling in Arabidopsis

The Rhododendron Chrysanthum Pall.s' Acetylation Modification of Rubisco Enzymes Controls Carbon Cycling to Withstand UV-B Stress

Lysine acetylation of proteins plays a critical regulatory function in plants. A few advances have been made in the study of plant acetylproteome. However, until now, there have been few data on Rhododendron chrysanthum Pall. (R. chrysanthum). We analyzed the molecular mechanisms of photosynthesis and stress resistance in R. chrysanthum under UV-B stress. We measured chlorophyll fluorescence parameters of R. chrysanthum under UV-B stress and performed a multi-omics analysis. Based on the determination of chlorophyll fluorescence parameters, R. chrysanthum Y(NO) (Quantum yield of non-photochemical quenching) increased under UV-B stress, indicating that the plant was damaged and photosynthesis decreased. In the analysis of acetylated proteomics data, acetylated proteins were found to be involved in a variety of biological processes. Notably, acetylated proteins were significantly enriched in the pathways of photosynthesis and carbon fixation, suggesting that lysine acetylation modifications have an important role in these activities. Our findings suggest that R. chrysanthum has decreased photosynthesis and impaired photosystems under UV-B stress, but NPQ shows that plants are resistant to UV-B. Acetylation proteomics revealed that up- or down-regulation of acetylation modification levels alters protein expression. Acetylation modification of key enzymes of the Calvin cycle (Rubisco, GAPDH) regulates protein expression, making Rubisco and GAPDH proteins expressed as significantly different proteins, which in turn affects the carbon fixation capacity of R. chrysanthum. Thus, Rubisco and GAPDH are significantly differentially expressed after acetylation modification, which affects the carbon fixation capacity and thus makes the plant resistant to UV-B stress. Lysine acetylation modification affects biological processes by regulating the expression of key enzymes in photosynthesis and carbon fixation, making plants resistant to UV-B stress.

Protein post-translational modifications in auxin signaling

Protein post-translational modifications (PTMs), such as ubiquitination, phosphorylation, and small ubiquitin-like modifier (SUMO)ylation, are crucial for regulating protein stability, activity, subcellular localization, and binding with cofactors. Such modifications remarkably increase the variety and complexity of proteomes, which are essential for regulating numerous cellular and physiological processes. The regulation of auxin signaling is finely tuned in time and space to guide various plant growth and development. Accumulating evidence indicates that PTMs play critical roles in auxin signaling regulations. Thus, a thorough and systematic review of the functions of PTMs in auxin signal transduction will improve our profound comprehension of the regulation mechanism of auxin signaling and auxin-mediated various processes. This review discusses the progress of protein ubiquitination, phosphorylation, histone acetylation and methylation, SUMOylation, and S-nitrosylation in the regulation of auxin signaling.

Histone deacetylase MdHDA6 is an antagonist in regulation of transcription factor MdTCP15 to promote cold tolerance in apple

Understanding the molecular regulation of plant cold response is the basis for cold resistance germplasm improvement. Here, we revealed that the apple histone deacetylase MdHDA6 can perform histone deacetylation on cold-negative regulator genes and repress their expression, leading to the positive regulation of cold tolerance in apples. Moreover, MdHDA6 directly interacts with the transcription factor MdTCP15. Phenotypic analysis of MdTCP15 transgenic apple lines and wild types reveals that MdTCP15 negatively regulates cold tolerance in apples. Furthermore, we found that MdHDA6 can facilitate histone deacetylation of MdTCP15 and repress the expression of MdTCP15, which positively contributes to cold tolerance in apples. Additionally, the transcription factor MdTCP15 can directly bind to the promoter of the cold-negative regulator gene MdABI1 and activate its expression, and it can also directly bind to the promoter of the cold-positive regulator gene MdCOR47 and repress its expression. However, the co-expression of MdHDA6 and MdTCP15 can inhibit MdTCP15-induced activation of MdABI1 and repression of MdCOR47, suggesting that MdHDA6 suppresses the transcriptional regulation of MdTCP15 on its downstream genes. Our results demonstrate that histone deacetylase MdHDA6 plays an antagonistic role in the regulation of MdTCP15-induced transcriptional activation or repression to positively regulate cold tolerance in apples, revealing a new regulatory mechanism of plant cold response.

Multi-Omic Analysis Reveals the Molecular Mechanism of UV-B Stress Resistance in Acetylated RcMYB44 in Rhododendron chrysanthum

Ultraviolet-B (UV-B) radiation is a significant environmental factor influencing the growth and development of plants. MYBs play an essential role in the processes of plant responses to abiotic stresses. In the last few years, the development of transcriptome and acetylated proteome technologies have resulted in further and more reliable data for understanding the UV-B response mechanism in plants. In this research, the transcriptome and acetylated proteome were used to analyze Rhododendron chrysanthum Pall. (R. chrysanthum) leaves under UV-B stress. In total, 2348 differentially expressed genes (DEGs) and 685 differentially expressed acetylated proteins (DAPs) were found. The transcriptome analysis revealed 232 MYB TFs; we analyzed the transcriptome together with the acetylated proteome, and screened 4 MYB TFs. Among them, only RcMYB44 had a complete MYB structural domain. To investigate the role of RcMYB44 under UV-B stress, a homology tree was constructed between RcMYB44 and Arabidopsis MYBs, and it was determined that RcMYB44 shares the same function with ATMYB44. We further constructed the hormone signaling pathway involved in RcMYB44, revealing the molecular mechanism of resistance to UV-B stress in R. chrysanthum. Finally, by comparing the transcriptome and the proteome, it was found that the expression levels of proteins and genes were inconsistent, which is related to post-translational modifications of proteins. In conclusion, RcMYB44 of R. chrysanthum is involved in mediating the growth hormone, salicylic acid, jasmonic acid, and abscisic acid signaling pathways to resist UV-B stress.

Transcriptomic analysis reveals the key role of histone deacetylation via mediating different phytohormone signalings in fiber initiation of cotton

Background

Histone deacetylation is one of the most important epigenetic modifications and plays diverse roles in plant development. However, the detailed functions and mechanisms of histone deacetylation in fiber development of cotton are still unclear. HDAC inhibitors (HDACi) have been commonly used to study the molecular mechanism underlying histone deacetylation or to facilitate disease therapy in humans through hindering the histone deacetylase catalytic activity. Trichostatin A (TSA)—the most widely used HDACi has been extensively employed to determine the role of histone deacetylation on different developmental stages of plants.

Results

Through in vitro culture of ovules, we observed that exogenous application of TSA was able to inhibit the fiber initiation development. Subsequently, we performed a transcriptomic analysis to reveal the underlying mechanisms. The data showed that TSA treatment resulted in 4209 differentially expressed genes, which were mostly enriched in plant hormone signal transduction, phenylpropanoid biosynthesis, photosynthesis, and carbon metabolism pathways. The phytohormone signal transduction pathways harbor the most differentially expressed genes. Deeper studies showed that some genes promoting auxin, Gibberellic Acid (GA) signaling were down-regulated, while some genes facilitating Abscisic Acid (ABA) and inhibiting Jasmonic Acid (JA) signaling were up-regulated after the TSA treatments. Further analysis of plant hormone contents proved that TSA significantly promoted the accumulation of ABA, JA and GA₃.

Conclusions

Collectively, histone deacetylation can regulate some key genes involved in different phytohormone pathways, and consequently promoting the auxin, GA, and JA signaling, whereas repressing the ABA synthesis and signaling to improve the fiber cell initiation. Moreover, the genes associated with energy metabolism, phenylpropanoid, and glutathione metabolism were also regulated by histone deacetylation. The above results provided novel clues to illuminate the underlying mechanisms of epigenetic modifications as well as related different phytohormones in fiber cell differentiation, which is also very valuable for the molecular breeding of higher quality cotton.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00840-4.

Identification of the Karyopherin Superfamily in Maize and Its Functional Cues in Plant Development

Appropriate nucleo-cytoplasmic partitioning of proteins is a vital regulatory mechanism in phytohormone signaling and plant development. However, how this is achieved remains incompletely understood. The Karyopherin (KAP) superfamily is critical for separating the biological processes in the nucleus from those in the cytoplasm. The KAP superfamily is divided into Importin α (IMPα) and Importin β (IMPβ) families and includes the core components in mediating nucleocytoplasmic transport. Recent reports suggest the KAPs play crucial regulatory roles in Arabidopsis development and stress response by regulating the nucleo-cytoplasmic transport of members in hormone signaling. However, the KAP members and their associated molecular mechanisms are still poorly understood in maize. Therefore, we first identified seven IMPα and twenty-seven IMPβ genes in the maize genome and described their evolution traits and the recognition rules for substrates with nuclear localization signals (NLSs) or nuclear export signals (NESs) in plants. Next, we searched for the protein interaction partners of the ZmKAPs and selected the ones with Arabidopsis orthologs functioning in auxin biosynthesis, transport, and signaling to predict their potential function. Finally, we found that several ZmKAPs share similar expression patterns with their interacting proteins, implying their function in root development. Overall, this article focuses on the Karyopherin superfamily in maize and starts with this entry point by systematically comprehending the KAP-mediated nucleo-cytoplasmic transport process in plants, and then predicts the function of the ZmKAPs during maize development, with a perspective on a closely associated regulatory mechanism between the nucleo-cytoplasmic transport and the phytohormone network.

Jasmonates and Histone deacetylase 6 activate Arabidopsis genome-wide histone acetylation and methylation during the early acute stress response

BACKGROUND

Jasmonates (JAs) mediate trade-off between responses to both biotic and abiotic stress and growth in plants. The Arabidopsis thaliana HISTONE DEACETYLASE 6 is part of the CORONATINE INSENSITIVE1 receptor complex, co-repressing the HDA6/COI1-dependent acetic acid-JA pathway that confers plant drought tolerance. The decrease in HDA6 binding to target DNA mirrors histone H4 acetylation (H4Ac) changes during JA-mediated drought response, and mutations in HDA6 also cause depletion in the constitutive repressive marker H3 lysine 27 trimethylation (H3K27me3). However, the genome-wide effect of HDA6 on H4Ac and much of the impact of JAs on histone modifications and chromatin remodelling remain elusive.

RESULTS

We performed high-throughput ChIP-Seq on the HDA6 mutant, axe1-5, and wild-type plants with or without methyl jasmonate (MeJA) treatment to assess changes in active H4ac and repressive H3K27me3 histone markers. Transcriptional regulation was investigated in parallel by microarray analysis in the same conditions. MeJA- and HDA6-dependent histone modifications on genes for specialized metabolism; linolenic acid and phenylpropanoid pathways; and abiotic and biotic stress responses were identified. H4ac and H3K27me3 enrichment also differentially affects JAs and HDA6-mediated genome integrity and gene regulatory networks, substantiating the role of HDA6 interacting with specific families of transposable elements in planta and highlighting further specificity of action as well as novel targets of HDA6 in the context of JA signalling for abiotic and biotic stress responses.

CONCLUSIONS

The findings demonstrate functional overlap for MeJA and HDA6 in tuning plant developmental plasticity and response to stress at the histone modification level. MeJA and HDA6, nonetheless, maintain distinct activities on histone modifications to modulate genetic variability and to allow adaptation to environmental challenges.

Characterization of histone deacetylases and their roles in response to abiotic and PAMPs stresses in Sorghum bicolor

BACKGROUND

Histone deacetylases (HDACs) play an important role in the regulation of gene expression, which is indispensable in plant growth, development, and responses to environmental stresses. In Arabidopsis and rice, the molecular functions of HDACs have been well-described. However, systematic analysis of the HDAC gene family and gene expression in response to biotic and abiotic stresses has not been reported for sorghum.

RESULTS

We conducted a systematic analysis of the sorghum HDAC gene family and identified 19 SbHDACs mainly distributed on eight chromosomes. Phylogenetic tree analysis of SbHDACs showed that the gene family was divided into three subfamilies: RPD3/HDA1, SIR2, and HD2. Tissue-specific expression results showed that SbHDACs displayed different expression patterns in different tissues, indicating that these genes may perform different functions in growth and development. The expression pattern of SbHDACs under different stresses (high and low temperature, drought, osmotic and salt) and pathogen-associated molecular model (PAMPs) elf18, chitin, and flg22) indicated that SbHDAC genes may participate in adversity responses and biological stress defenses. Overexpression of SbHDA1, SbHDA3, SbHDT2 and SbSRT2 in Escherichia coli promoted the growth of recombinant cells under abiotic stress. Interestingly, we also showed that the sorghum acetylation level was enhanced when plants were under cold, heat, drought, osmotic and salt stresses. The findings will help us to understand the HDAC gene family in sorghum, and illuminate the molecular mechanism of the responses to abiotic and biotic stresses.

CONCLUSION

We have identified and classified 19 HDAC genes in sorghum. Our data provides insights into the evolution of the HDAC gene family and further support the hypothesis that these genes are important for the plant responses to abiotic and biotic stresses.

Poplar acetylome profiling reveals lysine acetylation dynamics in seasonal bud dormancy release

For perennials in boreal and temperate ecosystems, bud dormancy is crucial for survival in harsh winter. Dormancy is released by prolonged exposure to low temperatures and is followed by reactive growth in the spring. Lysine acetylation (Kac) is one of the major post-translational modifications (PTMs) that are involved in plant response to environmental signals. However, little information is available on the effects of Kac modification on bud dormancy release. Here, we report the dynamics of lysine acetylome in hybrid poplar (Populus tremula × Populus alba) dormant buds. A total of 7,594 acetyl-sites from 3,281 acetyl-proteins were identified, representing a large dataset of lysine acetylome in plants. Of them, 229 proteins were differentially acetylated during bud dormancy release and were mainly involved in the primary metabolic pathways. Site-directed mutagenesis enzymatic assays showed that Kac strongly modified the activities of two key enzymes of primary metabolism, pyruvate dehydrogenase (PDH) and isocitrate dehydrogenase (IDH). We thus propose that Kac of enzymes could be an important strategy for reconfiguration of metabolic processes during bud dormancy release. In all, our results reveal the importance of Kac in bud dormancy release and provide a new perspective to understand the molecular mechanisms of seasonal growth of trees.

Histone acetylation dynamics regulating plant development and stress responses

Crop productivity is directly dependent on the growth and development of plants and their adaptation during different environmental stresses. Histone acetylation is an epigenetic modification that regulates numerous genes essential for various biological processes, including development and stress responses. Here, we have mainly discussed the impact of histone acetylation dynamics on vegetative growth, flower development, fruit ripening, biotic and abiotic stress responses. Besides, we have also emphasized the information gaps which are obligatory to be examined for understanding the complete role of histone acetylation dynamics in plants. A comprehensive knowledge about the histone acetylation dynamics will ultimately help to improve stress resistance and reduce yield losses in different crops due to climate changes.

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

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.

The transcriptional repressors VAL1 and VAL2 recruit PRC2 for genome-wide Polycomb silencing in Arabidopsis

The Polycomb repressive complex 2 (PRC2) catalyzes histone H3 Lys27 trimethylation (H3K27me3) to repress gene transcription in multicellular eukaryotes. Despite its importance in gene silencing and cellular differentiation, how PRC2 is recruited to target loci is still not fully understood. Here, we report genome-wide evidence for the recruitment of PRC2 by the transcriptional repressors VIVIPAROUS1/ABI3-LIKE1 (VAL1) and VAL2 in Arabidopsis thaliana. We show that the val1 val2 double mutant possesses somatic embryonic phenotypes and a transcriptome strikingly similar to those of the swn clf double mutant, which lacks the PRC2 catalytic subunits SWINGER (SWN) and CURLY LEAF (CLF). We further show that VAL1 and VAL2 physically interact with SWN and CLF in vivo. Genome-wide binding profiling demonstrated that they colocalize with SWN and CLF at PRC2 target loci. Loss of VAL1/2 significantly reduces SWN and CLF enrichment at PRC2 target loci and leads to a genome-wide redistribution of H3K27me3 that strongly affects transcription. Finally, we provide evidence that the VAL1/VAL2-RY regulatory system is largely independent of previously identified modules for Polycomb silencing in plants. Together, our work demonstrates an extensive genome-wide interaction between VAL1/2 and PRC2 and provides mechanistic insights into the establishment of Polycomb silencing in plants.

The diverse and unanticipated roles of histone deacetylase 9 in coordinating plant development and environmental acclimation

Plants tightly control gene transcription to adapt to environmental conditions and steer growth and development. Different types of epigenetic modifications are instrumental in these processes. In recent years, an important role for the chromatin-modifying RPD3/HDA1 class I HDAC HISTONE DEACETYLASE 9 (HDA9) emerged in the regulation of a multitude of plant traits and responses. HDACs are widely considered transcriptional repressors and are typically part of multiprotein complexes containing co-repressors, DNA, and histone-binding proteins. By catalyzing the removal of acetyl groups from lysine residues of histone protein tails, HDA9 negatively controls gene expression in many cases, in concert with interacting proteins such as POWERDRESS (PWR), HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15), WRKY53, ELONGATED HYPOCOTYL 5 (HY5), ABA INSENSITIVE 4 (ABI4), and EARLY FLOWERING 3 (ELF3). However, HDA9 activity has also been directly linked to transcriptional activation. In addition, following the recent breakthrough discovery of mutual negative feedback regulation between HDA9 and its interacting WRKY-domain transcription factor WRKY53, swift progress in gaining understanding of the biology of HDA9 is expected. In this review, we summarize knowledge on this intriguing versatile-and long under-rated-protein and propose novel leads to further unravel HDA9-governed molecular networks underlying plant development and environmental biology.

Genome-wide identification of the HDAC family proteins and functional characterization of CsHD2C, a HD2-type histone deacetylase gene in tea plant (Camellia sinensis L. O. Kuntze)

The histone deacetylases (HDACs) are involved in growth, development and stress responses in many plants. However, the functions of HDACs in tea plant (Camellia sinensis L. O. Kuntze) and other woody plants remain unclear. Here, 18 CsHDAC genes were identified by genome-wide analysis in tea plant. The phylogenetic analysis demonstrated that the CsHDAC proteins were divided into three subfamilies, namely, the RPD3/HDA1 subfamily (8 members), the SIR2 subfamily (4 members) and the plant specific HD2 subfamily (6 members). The expression patterns showed that most members of CsHDACs family were regulated by different abiotic stress. High correlation was found between the expression of the CsHDACs and the accumulation of theanine, catechin, EGCG and other metabolites in tea plant. Most of the CsHDAC proteins were negative regulators. We further studied a specific gene CsHD2C (NCBI-ID: KY364373) in tea plant, which is the homolog of AtHD2C, encoded a protein of 306 aa. CsHD2C was highly expressed in leaves, young buds and stems. The transcription of CsHD2C was inhibited by ABA, NaCl and low temperature. It was found localized in the nucleus when fused with a YFP reporter gene. Overexpression of CsHD2C can rescue the phenotype related to different abiotic stresses in the mutant of AtHD2C in Arabidopsis. The stress-responsive genes RD29A, RD29B, ABI1 and ABI2 were also investigated to understand the regulating role of CsHD2C under abiotic stresses. We also found that CsHD2C could renew the change of acetylation level for histone H4 and the RNAP-II occupancy accumulation in the promoter of abiotic stress responses gene in the hd2c Arabidopsis mutant. Together, our results suggested that CsHD2C may act as a positive regulator in abiotic stress responses in tea plant.

Linking signaling pathways to histone acetylation dynamics in plants

As sessile organisms, plants face versatile environmental challenges and require proper responses at multiple levels for survival. Epigenetic modification of DNA and histones is a conserved gene-regulatory mechanism and plays critical roles in diverse aspects of biological processes, ranging from genome defense and imprinting to development and physiology. In recent years, emerging studies have revealed the interplay between signaling transduction pathways, epigenetic modifications, and chromatin cascades. Specifically, histone acetylation and deacetylation dictate plant responses to environmental cues by modulating chromatin dynamics to regulate downstream gene expression as signaling outputs. In this review, we summarize current understandings of the link between plant signaling pathways and epigenetic modifications with a focus on histone acetylation and deacetylation.

Homeostasis of histone acetylation is critical for auxin signaling and root morphogenesis

The auxin signaling and root morphogenesis are harmoniously controlled by two counteracted teams including (1) auxin/indole-3-acetic acid (AUX/IAA)-histone deacetylase (HDA) and (2) auxin response factor (ARF)-histone acetyltransferase (HAT). The involvement of histone acetylation in the regulation of transcription was firstly reported a few decades ago. In planta, auxin is the first hormone group that was discovered and it is also the most studied phytohormone. Current studies have elucidated the functions of histone acetylation in the modulation of auxin signaling as well as in the regulation of root morphogenesis under both normal and stress conditions. Based on the recent outcomes, this review is to provide a hierarchical view about the functions of histone acetylation in auxin signaling and root morphogenesis. In this report, we suggest that the auxin signaling must be controlled harmoniously by two counteracted teams including (1) auxin/indole-3-acetic acid (AUX/IAA)-histone deacetylase (HDA) and (2) auxin response factor (ARF)-histone acetyltransferase (HAT). Moreover, the balance in auxin signaling is very critical to contribute to normal root morphogenesis.

Tobacco SABP2-interacting protein SIP428 is a SIR2 type deacetylase

Salicylic acid is widely studied for its role in biotic stress signaling in plants. Several SA-binding proteins, including SABP2 (salicylic acid-binding protein 2) has been identified and characterized for their role in plant disease resistance. SABP2 is a 29 kDA tobacco protein that binds to salicylic acid with high affinity. It is a methylesterase enzyme that catalyzes the conversion of methyl salicylate into salicylic acid required for inducing a robust systemic acquired resistance (SAR) in plants. Methyl salicylic acid is one of the several mobile SAR signals identified in plants. SABP2-interacting protein 428 (SIP428) was identified in a yeast two-hybrid screen using tobacco SABP2 as a bait. In silico analysis shows that SIP428 possesses the SIR2 (silent information regulatory 2)-like conserved motifs. SIR2 enzymes are orthologs of sirtuin proteins that catalyze the NAD+-dependent deacetylation of Nε lysine-acetylated proteins. The recombinant SIP428 expressed in E. coli exhibits SIR2-like deacetylase activity. SIP428 shows homology to Arabidopsis AtSRT2 (67% identity), which is implicated in SA-mediated basal defenses. Immunoblot analysis using anti-acetylated lysine antibodies showed that the recombinant SIP428 is lysine acetylated. The expression of SIP428 transcripts was moderately downregulated upon infection by TMV. In the presence of SIP428, the esterase activity of SABP2 increased modestly. The interaction of SIP428 with SABP2, it's regulation upon pathogen infection, and similarity with AtSRT2 suggests that SIP428 is likely to play a role in stress signaling in plants.

The delayed senescence of postharvest buds in salt ions was related to antioxidant activity, HDA9 and CCX1 in broccoli (Brassica oleracea L. var. Italic Planch.)

Epigenetic regulation and salt ions play essential roles in senescence control, but the underlying regulatory mechanism of senescence has not been thoroughly revealed in broccoli postharvest buds. Here, we found 200 mmol·L^-1 NaCl, 400 mmol·L^-1 KCl, 40 mmol·L^-1 CaCl₂ and 0.5 μmol·L^-1 Trichostatin-A (TSA, a histone deacetylase inhibitor) delayed the bud senescence. They resulted in significantly inhibiting the malondialdehyde (MDA) content, and dramatically promoting the contents of superoxide dismutase (SOD), peroxidase (POD) and Chlorophyll. Furthermore, the expression of PHEOPHYTINASE (PPH) and NONYELLOWING (NYE1), but not SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), were remarkably repressed by salt ions and TSA. Interestingly, HISTONE DEACETYLASE 9 (HDA9) and CATION/Ca²⁺ EXCHANGER 1 (CCX1) were down-regulated by NaCl, CaCl₂ and TSA. Further assays demonstrated that HDA9 could not interact with CCX1 promoter. It suggested that CCX1 along with HDA9 were involved in inhibiting the senescence of broccoli buds, and regulated aging by indirect interaction.

Overexpression of ThSAP30BP from Tamarix hispida improves salt tolerance

Histone deacetylases (HDACs) play an important regulatory role in plant response to biotic and abiotic stresses. They improve plant stress resistance by increasing the degree of histone acetylation associated with stress-responsive genes. SAP30BP, a human transcriptional regulatory protein, can increase histone deacetylase activity by regulating the deacetylation levels of lysines 9 and 14 in histone H3. In this study, a ThSAP30BP gene was cloned and characterized from Tamarix hispida (a kind of woody halophyte). The expression patterns of ThSAP30BP under different abiotic stresses and hormone treatments were detected by qRT-PCR. The results showed that ThSAP30BP was significantly upregulated at most time points under various stress treatments, suggesting that ThSAP30BP may be related to the abiotic stress response of T. hispida. To further analyze the salt stress resistance function of the ThSAP30BP gene, the plant overexpression vector pROKII-ThSAP30BP was instantaneously constructed and transformed into T. hispida. Meanwhile, the empty vector pROKII was also transformed as a control. The activities of SOD and POD, the contents of H₂O₂ and MDA, the relative conductance and the staining of NBT, DAB and Evans blue were analyzed and compared under salt stress. The results showed that the overexpression of ThSAP30BP in T. hispida reduced the accumulation of ROS in plants and the cell death rate under salt stress. These results suggested that ThSAP30BP may play an important physiological role in salt tolerance of T. hispida.

Functions and mechanisms of plant histone deacetylases

Lysine acetylation, one of the major types of post-translational modifications, plays critical roles in regulating gene expression and protein function. Histone deacetylases (HDACs) are responsible for removing acetyl groups from lysines of both histone and non-histone proteins. While tremendous progress has been made in understanding the function and mechanism of HDACs in animals in the past two decades, nearly half of the HDAC studies in plants were reported within the past five years. In this review, we summarize the major findings on plant HDACs, with a focus on the model plant Arabidopsis thaliana, and highlight the components, regulatory mechanisms, and biological functions of HDAC complexes.

HISTONE DEACETYLASE 9 stimulates auxin-dependent thermomorphogenesis in Arabidopsis thaliana by mediating H2A.Z depletion

Many plant species respond to unfavorable high ambient temperatures by adjusting their vegetative body plan to facilitate cooling. This process is known as thermomorphogenesis and is induced by the phytohormone auxin. Here, we demonstrate that the chromatin-modifying enzyme HISTONE DEACETYLASE 9 (HDA9) mediates thermomorphogenesis but does not interfere with hypocotyl elongation during shade avoidance. HDA9 is stabilized in response to high temperature and mediates histone deacetylation at the YUCCA8 locus, a rate-limiting enzyme in auxin biosynthesis, at warm temperatures. We show that HDA9 permits net eviction of the H2A.Z histone variant from nucleosomes associated with YUCCA8, allowing binding and transcriptional activation by PHYTOCHROME INTERACTING FACTOR 4, followed by auxin accumulation and thermomorphogenesis.