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Mediating induced abscisic acid (ABA) biosynthesis is important for enhancing plant stress tolerance. Here, we found that rice (Oryza sativa L.) osa–miR2105 (miR2105) and the Stress/ABA-activated protein kinase (OsSAPK10) coordinately regulate the rice basic region-leucine zipper transcription factor (bZIP TF; OsbZIP86) at the posttranscriptional and posttranslational levels to control drought-induced ABA biosynthesis via modulation of rice 9-cis-epoxycarotenoid dioxygenase (OsNCED3) expression. OsbZIP86 expression is regulated by miR2105-directed cleavage of the OsbZIP86 mRNA. OsbZIP86 encodes a nuclear TF that binds to the promoter of the ABA biosynthetic gene OsNCED3. OsSAPK10 can phosphorylate and activate OsbZIP86 to enhance the expression of OsNCED3. Under normal growth conditions, altered expression of miR2105 and OsbZIP86 displayed no substantial effect on rice growth. However, under drought conditions, miR2105 knockdown or OsbZIP86 overexpression transgenic rice plants showed higher ABA content, enhanced tolerance to drought, lower rates of water loss, and more stomatal closure of seedlings, compared with wild-type rice Zhonghua 11; in contrast, miR2105 overexpression, OsbZIP86 downregulation, and OsbZIP86 knockout plants displayed opposite phenotypes. Collectively, our results show that the “miR2105-(OsSAPK10)-OsbZIP86-OsNCED3” module regulates the drought-induced ABA biosynthesis without penalty on rice growth under normal conditions, suggesting candidates for improving drought tolerance in rice.

BRAHMA (BRM) is the ATPase of the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodelling complex, which is indispensable for transcriptional inhibition and activation, associated with vegetative and reproductive development in Arabidopsis thaliana. Here, we show that BRM directly binds to the chromatin of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), which integrates multiple flowering signals to regulate floral transition, leading to flowering. In addition, genetic and molecular analysis showed that BRM interacts with GNC (GATA, NITRATE-INDUCIBLE, CARBON METABOLISM INVOLVED), a GATA transcription factor that represses flowering by directly repressing SOC1 expression. Furthermore, BRM is recruited by GNC to directly bind to the chromatin of SOC1. The transcript level of SOC1 is elevated in brm-3, gnc, and brm-3/gnc mutants, which is associated with increased histone H3 lysine 4 tri-methylation (H3K4Me3) but decreased DNA methylation. Taken together, our results indicate that BRM associates with GNC to regulate SOC1 expression and flowering time.

Plant trichomes are large single cells that are organized in a regular pattern and play multiple biological functions. In Arabidopsis, trichome development is mainly governed by the core trichome initiation regulators, including the R2R3 type MYB transcript factor GLABRA 1 (GL1), bHLH transcript factors GLABRA 3/ENHANCER OF GLABRA 3 (GL3/EGL3), and the WD-40 repeat protein TRANSPARENT TESTA GLABRA 1 (TTG1), as well as the downstream trichome regulator GLABRA 2 (GL2). GL1, GL3/EGL3, and TTG1 can form a trimeric activation complex to activate GL2, which is required for the trichome initiation and maintenance during cell differentiation. Arabidopsis JMJ29 is a JmjC domain-containing histone demethylase belonging to the JHDM2/KDM3 group. Members of the JHDM2/KDM3 group histone demethylases are mainly responsible for the H3K9me1/2 demethylation. In the present study, we found that the trichome density on leaves and inflorescence stems is significantly decreased in jmj29 mutants. The expression of the core trichome regulators GL1, GL2, and GL3 is decreased in jmj29 mutants as well. Furthermore, JMJ29 can directly target GL3 and remove H3K9me2 on the GL3 locus. Collectively, we found that Arabidopsis JMJ29 is involved in trichome development by directly regulating GL3 expression. These results provide further insights into the molecular mechanism of epigenetic regulation in Arabidopsis trichome development.

Although the interplay of covalent histone acetylation/deacetylation and ATP-dependent chromatin remodelling is crucial for the regulation of chromatin structure and gene expression in eukaryotes, the underlying molecular mechanism in plants remains largely unclear. Here we show a direct interaction between Arabidopsis SWI3B, an essential subunit of the SWI/SNF chromatin-remodelling complex, and the RPD3/HDA1-type histone deacetylase HDA6 both in vitro and in vivo. Furthermore, SWI3B and HDA6 co-repress the transcription of a subset of transposons. Both SWI3B and HDA6 maintain transposon silencing by decreasing histone H3 lysine 9 acetylation, but increasing histone H3 lysine 9 di-methylation, DNA methylation and nucleosome occupancy. Our findings reveal that SWI3B and HDA6 may act in the same co-repressor complex to maintain transposon silencing in Arabidopsis.

The changes in histone acetylation mediated by histone deacetylases (HDAC) play a crucial role in plant development and response to environmental changes. Mammalian HDACs are regulated by post-translational modifications (PTM), such as phosphorylation, acetylation, ubiquitination and small ubiquitin-like modifier (SUMO) modification (SUMOylation), which affect enzymatic activity and transcriptional repression. Whether PTMs of plant HDACs alter their functions are largely unknown. In this study, we demonstrated that the Arabidopsis SUMO E3 ligase SAP AND MIZ1 DOMAIN-CONTAINING LIGASE1 (SIZ1) interacts with HISTONE DEACETYLASE 6 (HDA6) both in vitro and in vivo. Biochemical analyses indicated that HDA6 is not modified by SUMO1. Overexpression of HDA6 in siz1-3 background results in a decreased level of histone H3 acetylation, indicating that the activity of HDA6 is increased in siz1-3 plants. Chromatin immunoprecipitation (ChIP) assays showed that SIZ1 represses HDA6 binding to its target genes FLOWERING LOCUS C (FLC) and MADS AFFECTING FLOWERING 4 (MAF4), resulting in the upregulation of FLC and MAF4 by increasing the level of histone H3 acetylation. Together, these findings indicate that the Arabidopsis SUMO E3 ligase SIZ1 interacts with HDA6 and negatively regulates HDA6 function.

MULTICOPY SUPRESSOR OF IRA1 (MSI1) is a conserved subunit of the Polycomb Repressive Complex 2 (PRC2), which mediates gene silencing by H3 lysine 27 tri-methylation (H3K27Me3). Here, we demonstrated that MSI1 interacts with the RPD3-like histone deacetylase HDA6 both in vitro and in vivo. MSI1 and HDA6 are involved in flowering and repress the expression of FLC, MAF4, and MAF5 by removing histone H3 lysine 9 (H3K9) acetylation but adding H3K27Me3. Chromatin immunoprecipitation analysis showed that HDA6 and MSI1 interdependently bind to the chromatin of FLC, MAF4, and MAF5. Furthermore, H3K9 deacetylation mediated by HDA6 is dependent on MSI1, while H3K27Me3 mediated by PRC2 containing MSI1 is also dependent on HDA6. Taken together, these data indicate that MSI1 and HDA6 act interdependently to repress the expression of FLC, MAF4, and MAF5 through histone modifications. Our findings reveal that the HDA6-MSI1 module mediates the interaction between histone H3 de-acetylation and H3K27Me3 to repress gene expression involved in flowering time control.

Induced abscisic acid (ABA) biosynthesis plays an important role in plant tolerance to abiotic stresses, including drought, cold and salinity. However, regulation pathway of the ABA biosynthesis in response to stresses is unclear. Here, we identified a rice miRNA, osa-miR2105 (miR2105), which plays a crucial role in ABA biosynthesis under drought stress. Analysis of expression, transgenic rice and cleavage site showed that OsbZIP86 is a target gene of miR2105. Subcellular localization and luciferase activity assays showed that OsbZIP86 is a nuclear transcription factor. In vivo and in vitro analyses showed that OsbZIP86 directly binds to the promoter of OsNCED3, and interacts with OsSAPK10, resulting in enhanced-expression of OsNCED3. Transgenic rice plants with knock-down of miR2105 or overexpression of OsbZIP86 showed higher ABA content, more tolerance to drought, a lower rate of water loss, more stomatal closure than wild type rice ZH11 under drought stress. These rice plants showed no penalty with respect to agronomic traits under normal conditions. By contrast, transgenic rice plants with miR2105 overexpression, OsbZIP86 downregulation, or OsbZIP86 knockout displayed less tolerance to drought stress and other phenotypes. Collectively, our results show that a regulatory network of ‘miR2105-OsSAPK10/OsbZIP86-OsNCED3’ control ABA biosynthesis in response to drought stress.One-sentence summary‘miR2105-OsbZIP86-OsNCED3’ module plays crucial role in mediating ABA biosynthesis to contribute to drought tolerance with no penalty with respect to agronomic traits under normal conditions.

Arabidopsis thaliana CONSTANS (CO) is an essential transcription factor that promotes flowering by activating the expression of the floral integrator FLOWERING LOCUS T (FT). A number of histone modification enzymes involved in the regulation of flowering have been identified, but the involvement of epigenetic mechanisms in the regulation of the core flowering regulator CO remains unclear. Previous studies have indicated that the transcription factors, FLOWERING BHLH1 (FBH1), FBH2, FBH3, and FBH4, function redundantly to activate the expression of CO. In this study, we found that the KDM3 group H3K9 demethylase JMJ28 interacts with the FBH transcription factors to activate CO by removing the repressive mark H3K9me2. The occupancy of JMJ28 on the CO locus is decreased in the fbh quadruple mutant, suggesting that the binding of JMJ28 is dependent on FBHs. Furthermore, genome-wide occupancy profile analyses indicate that the binding of JMJ28 to the genome overlaps with that of FBH3, indicating a functional association of JMJ28 and FBH3. Together, these results indicate that Arabidopsis JMJ28 functions as a CO activator by interacting with the FBH transcription factors to remove H3K9me2 from the CO locus.

Histone deacetylases (HDACs) play important roles in regulating gene expression. In yeast and animals, HDACs act as components of multiprotein complexes that modulate transcription during various biological processes. However, little is known about the interacting proteins of plant HDACs. To identify the plant HDAC complexes and interacting proteins, we developed an optimized workflow using immunopurification coupled to mass spectrometry-based proteomics in Arabidopsis thaliana. We found that the histone deacetylase HDA6 can interact with the histone methyltransferases SUVH4, SUVH5, and SUVH6 (SUVH4/5/6). Domain analysis revealed that the C-terminal regions of HDA6 and SUVH5 are important for their interaction. Furthermore, HDA6 interacts with SUVH4/5/6 and coregulates a subset of transposons through histone H3K9 methylation and H3 deacetylation. In addition, two phosphorylated serine residues, S427 and S429, were unambiguously identified in the C-terminal region of HDA6. Phosphomimetics (amino acid substitutions that mimic a phosphorylated protein) of HDA6 resulted in increased enzymatic activity, whereas the mutation of S427 to alanine in HDA6 abolished its interaction with SUVH5 and SUVH6, suggesting that the phosphorylation of HDA6 is important for its activity and function.

As the subunits of the SWI/SNF (mating-type switching (SWI) and sucrose nonfermenting (SNF)) chromatin-remodeling complexes (CRCs), Swi3-like proteins are crucial to chromatin remodeling in yeast and human. Growing evidence indicate that AtSWI3s are also essential for development and response to hormones in Arabidopsis. Nevertheless, the biological functions of Swi3-like proteins in tomato (Solanum lycopersicum) have not been investigated. Here we identified four Swi3-like proteins from tomato, namely SlSWI3A, SlSWI3B, SlSWI3C, and SlSWI3D. Subcellular localization analysis revealed that all SlSWI3s are localized in the nucleus. The expression patterns showed that all SlSWI3s are ubiquitously expressed in all tissues and organs, and SlSWI3A and SlSWI3B can be induced by cold treatment. In addition, we found that SlSWI3B can form homodimers with itself and heterodimers with SlSWI3A and SlSWI3C. SlSWI3B can also interact with SlRIN and SlCHR8, two proteins involved in tomato reproductive development. Overexpression of SlSWI3C increased the leaf size in transgenic Arabidopsis with increased expression of GROWTH REGULATING FACTORs, such as GRF3, GRF5, and GRF6. Taken together, our results indicate that SlSWI3s may play important roles in tomato growth and development.

As the subunits of the SWI/SNF (mating-type switching (SWI) and sucrose nonfermenting (SNF)) chromatin-remodeling complexes (CRCs), Swi3-like proteins are crucial to chromatin remodeling in yeast and human. Growing evidence indicate that AtSWI3s are also essential for development and response to hormones in Arabidopsis. Nevertheless, the biological functions of Swi3-like proteins in tomato (Solanum lycopersicum) have not been investigated. Here we identified four Swi3-like proteins from tomato, namely SlSWI3A, SlSWI3B, SlSWI3C, and SlSWI3D. Subcellular localization analysis revealed that all SlSWI3s are localized in the nucleus. The expression patterns showed that all SlSWI3s are ubiquitously expressed in all tissues and organs, and SlSWI3A and SlSWI3B can be induced by cold treatment. In addition, we found that SlSWI3B can form homodimers with itself and heterodimers with SlSWI3A and SlSWI3C. SlSWI3B can also interact with SlRIN and SlCHR8, two proteins involved in tomato reproductive development. Overexpression of SlSWI3C increased the leaf size in transgenic Arabidopsis with increased expression of GROWTH REGULATING FACTORs, such as GRF3, GRF5, and GRF6. Taken together, our results indicate that SlSWI3s may play important roles in tomato growth and development.

Eukaryotic genes are packed into a dynamic but stable nucleoprotein structure called chromatin. Chromatin-remodeling and modifying complexes generate a dynamic chromatin environment that ensures appropriate DNA processing and metabolism in various processes such as gene expression, as well as DNA replication, repair, and recombination. The INO80 and SWR1 chromatin remodeling complexes (INO80-c and SWR1-c) are ATP-dependent complexes that modulate the incorporation of the histone variant H2A.Z into nucleosomes, which is a critical step in eukaryotic gene regulation. Although SWR1-c has been identified in plants, plant INO80-c has not been successfully isolated and characterized. In this review, we will focus on the functions of the SWR1-c and putative INO80-c (SWR1/INO80-c) multi-subunits and multifunctional complexes in Arabidopsis thaliana. We will describe the subunit compositions of the SWR1/INO80-c and the recent findings from the standpoint of each subunit and discuss their involvement in regulating development and environmental responses in Arabidopsis.

SWI/SNF-type chromatin remodelers, such as BRAHMA (BRM), and H3K27 demethylases both have active roles in regulating gene expression at the chromatin level1–5, but how they are recruited to specific genomic sites remains largely unknown. Here we show that RELATIVE OF EARLY FLOWERING 6 (REF6), a plant-unique H3K27 demethylase6, targets genomic loci containing a CTCTGYTY motif via its zinc-finger (ZnF) domains and facilitates the recruitment of BRM. Genome-wide analyses showed that REF6 colocalizes with BRM at many genomic sites with the CTCTGYTY motif. Loss of REF6 results in decreased BRM occupancy at BRM–REF6 co-targets. Furthermore, REF6 directly binds to the CTCTGYTY motif in vitro, and deletion of the motif from a target gene renders it inaccessible to REF6 in vivo. Finally, we show that, when its ZnF domains are deleted, REF6 loses its genomic targeting ability. Thus, our work identifies a new genomic targeting mechanism for an H3K27 demethylase and demonstrates its key role in recruiting the BRM chromatin remodeler.

The circadian clock is an endogenous timekeeping network that integrates environmental signals with internal cues to coordinate diverse physiological processes. The circadian function depends on the precise regulation of rhythmic gene expression at the core of the oscillators. In addition to the well-characterized transcriptional feedback regulation of several clock components, additional regulatory mechanisms, such as alternative splicing, regulation of protein stability, and chromatin modifications are beginning to emerge. In this review, we discuss recent findings in the regulation of the circadian clock function in Arabidopsis thaliana. The involvement of chromatin modifications in the regulation of the core circadian clock genes is also discussed.

Summary The acetylation level of histones on lysine residues regulated by histone acetyltransferases and histone deacetylases plays an important but under-studied role in the control of gene expression in plants. With the aim of characterizing the Arabidopsis RPD3/HDA1 family histone deacetylase HDA5, we present evidence showing that HDA5 displays deacetylase activity. Mutants defective in the expression of HDA5 displayed a late-flowering phenotype. Expression of the flowering repressor genes FLC and MAF1 was up-regulated in hda5 mutants. Furthermore, the gene activation markers, histone H3 acetylation and H3K4 trimethylation on FLC and MAF1 chromatin were increased in hda5-1 mutants. Chromatin immunoprecipitation analysis showed that HDA5 binds to the chromatin of FLC and MAF1. Bimolecular fluorescence complementation assays and co-immunoprecipitation assays showed that HDA5 interacts with FVE, FLD and HDA6, indicating that these proteins are present in a protein complex involved in the regulation of flowering time. Comparing gene expression profiles of hda5 and hda6 mutants by RNA-seq revealed that HDA5 and HDA6 co-regulate gene expression in multiple development processes and pathways.

BRAHMA (BRM), a SWI/SNF chromatin remodeling ATPase, is essential for the transcriptional reprogramming associated with development and cell differentiation in Arabidopsis thaliana. In this study, we show that loss-of-function mutations in BRM led to defective maintenance of the root stem cell niche, decreased meristematic activity, and stunted root growth. Mutations of BRM affected auxin distribution by reducing local expression of several PIN-FORMED (PIN) genes in the stem cells and impaired the expression of the stem cell transcription factor genes PLETHORA (PLT1) and PLT2. Chromatin immunoprecipitation assays showed that BRM could directly target to the chromatin of PIN1, PIN2, PIN3, PIN4, and PIN7. In addition, genetic interaction assays indicate that PLTs acted downstream of BRM, and overexpression of PLT2 partially rescued the stem cell niche defect of brm mutants. Taken together, these results support the idea that BRM acts in the PLT pathway to maintain the root stem cell niche by altering the expression of PINs.

In eukaryotic cells, histone acetylation and deacetylation play an important role in the regulation of gene expression. Histone acetylation levels are modulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs). Recent studies indicate that HDACs play essential roles in the regulation of gene expression in plant response to environmental stress. In this review, we discussed the recent advance regarding the plant HDACs and their functions in the regulation of abiotic stress responses. The role of HDACs in autophagy was also discussed.

Chromatin remodeling is essential for gene expression regulation in plant development and response to stresses. Brahma (BRM) is a conserved ATPase in the SWI/SNF chromatin remodeling complex and is involved in various biological processes in plant cells, but the regulation mechanism on BRM protein remains unclear. Here, we report that BRM interacts with AtMMS21, a SUMO ligase in Arabidopsis (Arabidopsis thaliana). The interaction was confirmed in different approaches in vivo and in vitro. The mutants of BRM and AtMMS21 displayed a similar defect in root development. In the mms21-1 mutant, the protein level of BRM-GFP was significantly lower than that in wild type, but the RNA level of BRM did not change. Biochemical evidence indicated that BRM was modified by SUMO3, and the reaction was enhanced by AtMMS21. Furthermore, overexpression of wild-type AtMMS21 but not the mutated AtMMS21 without SUMO ligase activity was able to recover the stability of BRM in mms21-1. Overexpression of BRM in mms21-1 partially rescued the developmental defect of roots. Taken together, these results supported that AtMMS21 regulates the protein stability of BRM in root development.

As sessile organisms, plants encounter various environmental stimuli including abiotic stresses during their lifecycle. To survive under adverse conditions, plants have evolved intricate mechanisms to perceive external signals and respond accordingly. Responses to various stresses largely depend on the plant capacity to modulate the transcriptome rapidly and specifically. A number of studies have shown that the molecular mechanisms driving the responses of plants to environmental stresses often depend on nucleosome histone post-translational modifications including histone acetylation, methylation, ubiquitination, and phosphorylation. The combined effects of these modifications play an essential role in the regulation of stress responsive gene expression. In this review, we highlight our current understanding of the epigenetic mechanisms of histone modifications and their roles in plant abiotic stress response.

PHYTOCHROME INTERACTING FACTOR3 (PIF3) is a key basic helix-loop-helix transcription factor of Arabidopsis thaliana that negatively regulates light responses, repressing chlorophyll biosynthesis, photosynthesis, and photomorphogenesis in the dark. However, the mechanism for the PIF3-mediated transcription regulation remains largely unknown. In this study, we found that the REDUCED POTASSIUM DEPENDENCY3/HISTONE DEACETYLASE1-type histone deacetylase HDA15 directly interacted with PIF3 in vivo and in vitro. Genome-wide transcriptome analysis revealed that HDA15 acts mainly as a transcriptional repressor and negatively regulates chlorophyll biosynthesis and photosynthesis gene expression in etiolated seedlings. HDA15 and PIF3 cotarget to the genes involved in chlorophyll biosynthesis and photosynthesis in the dark and repress gene expression by decreasing the acetylation levels and RNA Polymerase II–associated transcription. The binding of HDA15 to the target genes depends on the presence of PIF3. In addition, PIF3 and HDA15 are dissociated from the target genes upon exposure to red light. Taken together, our results indicate that PIF3 associates with HDA15 to repress chlorophyll biosynthetic and photosynthetic genes in etiolated seedlings.

The seed maturation genes are specifically and highly expressed during late embryogenesis. In this work, yeast two-hybrid, bimolecular fluorescence complementation, and coimmunoprecipitation assays revealed that HISTONE DEACETYLASE19 (HDA19) interacted with the HIGH-LEVEL EXPRESSION OF SUGAR-INDUCIBLE GENE2-LIKE1 (HSL1), and the zinc-finger CW [conserved Cys (C) and Trp (W) residues] domain of HSL1 was responsible for the interaction. Furthermore, we found that mutations in HDA19 resulted in the ectopic expression of seed maturation genes in seedlings, which was associated with increased levels of gene activation marks, such as Histone H3 acetylation (H3ac), Histone H4 acetylation (H4ac), and Histone H3 Lys 4 tri-methylation (H3K4me3), but decreased levels of the gene repression mark Histone H3 Lys 27 tri-methylation (H3K27me3) in the promoter and/or coding regions. In addition, elevated transcription of certain seed maturation genes was also found in the hsl1 mutant seedlings, which was also accompanied by the enrichment of gene activation marks but decreased levels of the gene repression mark. Chromatin immunoprecipitation assays showed that HDA19 could directly bind to the chromatin of the seed maturation genes. These results suggest that HDA19 and HSL1 may act together to repress seed maturation gene expression during germination. Further genetic analyses revealed that the homozygous hsl1 hda19 double mutants are embryonic lethal, suggesting that HDA19 and HSL1 may play a vital role during embryogenesis.

The ABC1 protein family (ABC1P), a new family of putative kinases, widely existed in procaryote and eucaryote. A comprehensive genome-wide analysis was carried out in this study to find all ABC1Ps in rice (Oryza sativa subsp. japonica). We identified 15 ABC1P genes in rice. All the ABC1Ps contained an ABC1 domain of about 120 conserved amino acid residues and conserved kinase motifs-VAIK (VAVK, VAMK) and DFG (DEG). The phylogenetic analysis showed that all the ABC1Ps were grouped into three subgroups, and formed a total of 12 sister pairs. Conserved motifs analysed by MEME program indicated that almost all ABC1Ps contains motifs 1, 3, 7, 8 and 9. Predictably, the ABC1Ps were localized in mitochondria or chloroplasts, which implied that the ABC1Ps might be involved in energy metabolism in plants. RT-PCR assays demonstrated that all 15 ABC1P genes were active, and some of them were affected by abiotic stresses (NaCl, high temperature, methyl viologen, abscisic acid and cadmium).

HD2 proteins are plant specific histone deacetylases. Four HD2 proteins, HD2A, HD2B, HD2C, and HD2D, have been identified in Arabidopsis. It was found that the expression of HD2A, HD2B, HD2C, and HD2D was repressed by ABA and NaCl. To investigate the function of HD2 proteins further, two HD2C T-DNA insertion lines of Arabidopsis, hd2c-1 and hd2c-3 were identified. Compared with wild-type plants, hd2c-1 and hd2c-3 plants displayed increased sensitivity to ABA and NaCl during germination and decreased tolerance to salt stress. These observations support a role of HD2C in the ABA and salt-stress response in Arabidopsis. Moreover, it was demonstrated that HD2C interacted physically with a RPD3-type histone deacetylase, HDA6, and bound to histone H3. The expression of ABA-responsive genes, ABI1 and ABI2, was increased in hda6, hd2c, and hda6/hd2c-1 double mutant plants, which was associated with increased histone H3K9K14 acetylation and decreased histone H3K9 dimethylation. Taken together, our results suggested that HD2C functionally associates with HDA6 and regulates gene expression through histone modifications.

Chromatin-remodeling complexes affect gene expression by using the energy of ATP hydrolysis to locally disrupt or alter the association of histones with DNA. SWIRM (Swi3p, Rsc8p, and Moira) domain is an alpha-helical domain of about 85 residues in chromosomal proteins. SWIRM domain-containing proteins make up large multisubunit complexes by interacting with other chromatin modification factors and may have an important function in plants. However, little is known about SWIRM domain-containing proteins in plants. In this study, 67 SWIRM domain-containing proteins from 6 plant species were identified and analyzed. Plant SWIRM domain proteins can be divided into three distinct types: Swi-type, LSD1-type, and Ada2-type. Generally, the SWIRM domain forms a helix-turn-helix motif commonly found in DNA-binding proteins. The genes encoding SWIRM domain proteins inOryza sativaare widely expressed, especially in pistils. In addition,OsCHB701andOsHDMA701were downregulated by cold stress, whereasOsHDMA701andOsHDMA702were significantly induced by heat stress. These observations indicate that SWIRM domain proteins may play an essential role in plant development and plant responses to environmental stress.

hMMS21 is a SUMO E3 ligase required for the prevention of DNA damage-induced apoptosis, and acts by facilitating DNA repair in human cells. The Arabidopsis genome contains a putative MMS21 homologue capable of interacting with the SUMO E2 conjugating enzyme AtSCE1a, as indicated by a yeast two-hybrid screen and bimolecular fluorescence complementation experiments. In vitro and in vivo data demonstrated that AtMMS21 was a SUMO E3 ligase. We identified the Arabidopsis AtMMS21 null T-DNA insertion mutant mms21-1, which had a short-root phenotype, and affected cell proliferation in the apical root meristem, as indicated by impaired expression of the cell division marker CYCB1:GUS in mms21-1 roots. The mms21-1 roots had reduced responses to exogenous cytokinins, and decreased expression of the cytokinin-induced genes ARR3, ARR4, ARR5 and ARR7, compared with the wild type. Thus, our findings suggest that the AtMMS21 gene is involved in root development via cell-cycle regulation and cytokinin signalling.

BREVIPEDICELLUS (BP or KNAT1), a class-I KNOTTED1-like homeobox (KNOX) transcription factor in Arabidopsis thaliana, contributes to shaping the normal inflorescence architecture through negatively regulating other two class-I KNOX genes, KNAT2 and KNAT6. However, the molecular mechanism of BP-mediated transcription regulation remains unclear. In this study, we showed that BP directly interacts with the SWI2/SNF2 chromatin remodeling ATPase BRAHMA (BRM) both in vitro and in vivo. Loss-of-function BRM mutants displayed inflorescence architecture defects, with clustered inflorescences, horizontally orientated pedicels, and short pedicels and internodes, a phenotype similar to the bp mutants. Furthermore, the transcript levels of KNAT2 and KNAT6 were elevated in brm-3, bp-9 and brm-3 bp-9 double mutants. Increased histone H3 lysine 4 tri-methylation (H3K4me3) levels were detected in brm-3, bp-9 and brm-3 bp-9 double mutants. Moreover, BRM and BP co-target to KNAT2 and KNAT6 genes, and BP is required for the binding of BRM to KNAT2 and KNAT6. Taken together, our results indicate that BP interacts with the chromatin remodeling factor BRM to regulate the expression of KNAT2 and KNAT6 in control of inflorescence architecture., Author Summary BP is a class-I KNOX transcription factor that controls normal inflorescence architecture development by repressing the expression of two KNOX genes, KNAT2 and KNAT6. In this study, we showed that Arabidopsis BP directly interacts with the SWI2/SNF2 chromatin remodeling ATPase BRM. brm and bp mutants displayed similar inflorescence architecture defects, with clustered inflorescences, horizontally orientated pedicels, and short pedicels and internodes. Furthermore, BP and BRM co-target to KNAT2 and KNAT6 genes and repress their expression. This work reveals a new regulatory mechanism that BP associates with BRM in control of inflorescence architecture development.

Seed dormancy controls germination and plays a critical role in regulating the beginning of the life cycle of plants. Seed dormancy is established and maintained during seed maturation and is gradually broken during dry storage (after-ripening). The plant hormone abscisic acid (ABA) and DELAY OF GERMINATION1 (DOG1) protein are essential regulators of seed dormancy. Recent studies revealed that chromatin modifications are also involved in the transcription regulation of seed dormancy. Here, we showed that two Arabidopsis histone demethylases, LYSINESPECIFIC DEMETHYLASE LIKE 1 and 2 (LDL1 and LDL2) act redundantly in repressing of seed dormancy. LDL1 and LDL2 are highly expressed in the early silique developing stage. The ldl1 ldl2 double mutant displays increased seed dormancy, whereas overexpression of LDL1 or LDL2 in Arabidopsis causes reduced dormancy. Furthermore, we showed that LDL1 and LDL2 repress the expression of seed dormancy-related genes, including DOG1, ABA2 and ABI3 during seed dormancy establishment. Furthermore, genetic analysis revealed that the repression of seed dormancy by LDL1 and LDL2 requires DOG1, ABA2, and ABI3. Taken together, our findings revealed that LDL1 and LDL2 play an essential role in seed dormancy.

The chromatin remodeler BRAHMA (BRM) is a Trithorax Group (TrxG) protein that antagonizes the functions of Polycomb Group (PcG) proteins in fly and mammals. Recent studies also implicate such a role for Arabidopsis (Arabidopsis thaliana) BRM but the molecular mechanisms underlying the antagonism are unclear. To understand the interplay between BRM and PcG during plant development, we performed a genome-wide analysis of trimethylated histone H3 lysine 27 (H3K27me3) in brm mutant seedlings by chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq). Increased H3K27me3 deposition at several hundred genes was observed in brm mutants and this increase was partially supressed by removal of the H3K27 methyltransferase CURLY LEAF (CLF) or SWINGER (SWN). ChIP experiments demonstrated that BRM directly binds to a subset of the genes and prevents the inappropriate association and/or activity of PcG proteins at these loci. Together, these results indicate a crucial role of BRM in restricting the inappropriate activity of PcG during plant development. The key flowering repressor gene SHORT VEGETATIVE PHASE (SVP) is such a BRM target. In brm mutants, elevated PcG occupancy at SVP accompanies a dramatic increase in H3K27me3 levels at this locus and a concomitant reduction of SVP expression. Further, our gain- and loss-of-function genetic evidence establishes that BRM controls flowering time by directly activating SVP expression. This work reveals a genome-wide functional interplay between BRM and PcG and provides new insights into the impacts of these proteins in plant growth and development., Author Summary In flowering plants, the proper transition from vegetative growth to flowering is critical for their reproductive success and must be controlled precisely. Multiple genes have been shown to regulate the floral transition in response to environmental and endogenous cues. Among them is SHORT VEGETATIVE PHASE (SVP), a key flowering repressor gene in Arabidopsis. SVP is highly expressed during the vegetative phase to promote growth, but the mechanism by which the high expression level of SVP is maintained remains unknown. Here, we report a genome-wide study to examine the functional interplay between the BRM chromatin remodeler and the PcG proteins that catalyze trimethylation of lysine 27 on histone H3 (H3K27me3), a histone mark normally associated with transcriptionally repressed genes. We identify BRM as a direct upstream activator of SVP. BRM acts to keep the levels of H3K27me3 low at the SVP locus by inhibiting the binding and activities of the PcG proteins. Thus, our work identifies a previously unknown mechanism in regulation of flowering time and demonstrates the power of genome-wide approaches in dissecting regulatory networks controlling plant development.

Reversible histone acetylation and deacetylation at the N-terminus of histone tails play crucial roles in regulation of eukaryotic gene activity. Acetylation of core histones usually induces an ‘open’ chromatin structure and is associated with gene activation, whereas deacetylation of histone is often correlated with ‘closed’ chromatin and gene repression. Histone deacetylation is catalyzed by histone deacetylases (HDACs). A growing number of studies have demonstrated the importance of histone deacetylation/acetylation on genome stability, transcriptional regulation, and development in plants. Furthermore, HDACs were shown to interact with various chromatin remolding factors and transcription factors involved in transcriptional repression in multiple developmental processes. In this review, we summarized recent findings on the transcriptional repression mediated by HDACs in plants.

HD2 proteins were previously identified as plant specific histone deacetylases (HDACs). The molecular mechanism of the function of HD2 proteins is still unclear. Using Bimolecular fluorescence complementation assay, we demonstrated that Arabidopsis HD2 proteins, HD2A, HD2C and HD2D, can interact with RPD3-type HDACs, HDA6 and HDA19, suggesting that that these proteins may act in the same protein complex. Our study indicates that HD2 proteins may functionally associate with RPD3-type HDACs to regulate gene expression in plants.