The Arabidopsis PRCl-like ring-finger proteins are necessary for repression of embryonic traits during vegetative growth

Polycomb 组基因在维护起关键作用 transcriptionally 为在动物和植物的合适的房间区别的基因的 silenced 状态。当时 polycomb 的部件压抑的 complex2 (PRC2 ) evolutionarily 被保存，他们的功能广泛地在植物被学习， PRC1 在动物和植物之间更加不同，并且它在植物的功能是不好迄今为止描述了。以前的研究作为动物 PRC1 子单元 RING1 的相当或相同事物识别了 Arabidopsis AtRING1a 和 AtRING1b。这里，我们证明 Atring1a Atring1b 双异种在植物的生长期间展出胚胎的特点的 derepression。因此，几关键规章的基因在 embryogenesis 包含了，干细胞活动宫外地在异种被表示。而且，我们证明变异的显型和规章的基因的增加的表示被 PRC2 变异的 clf 提高。最后，我们显示出那动物 PRC1 子单元戒指手指蛋白质 BMI1， AtBMI1a， AtBMI1b 和 AtBMI1c 的三个相当或相同事物，罐头与 AtRING1a 或 AtRING1b 绑，并且另外， AtBMI1c 能与 LHP1 绑。Atbmi1a Atbmi1b 双异种显示出类似于 Atring1a Atring1b 双异种的胚胎的特点的 derepression。有趣地， AtBMI1a， AtBMI1b 和 AtBMI1c 的表示层次在 Atring1a Atring1b 异种被提高，那些在 Atbmi1a Atbmi1b 异种 AtBMI1c， AtRING1a 和 AtRING1b 被提高，建议自我规章的反馈机制。一起拿，我们的结果为合适的体的生长在胚胎的特点和规章的基因的稳定的压抑照亮象 PRC1 一样戒指手指部件的关键功能。

Chromatin Remodeling in Stem Cell Maintenance in Arabidopsis thaliana

Pluripotent stem cells are able to both self-renew and generate undifferentiated cells for the formation of new tissues and organs. In higher plants, stem cells found in the shoot apical meristem （SAM） and the root apical meristem （RAM） are origins of organogenesis occurring post-embryonically. It is important to understand how the regulation of stem cell fate is coordinated to enable the meristem to constantly generate different types of lateral organs. Much knowledge has accumulated on specific transcription factors controlling SAM and RAM activity. Here, we review recent evidences for a role of chromatin remodeling in the maintenance of stable expression states of transcription factor genes and the control of stem cell activity in Arabidopsis.

A Truncated Arabidopsis NUCLEOSOME ASSEMBLY PROTEIN 1, AtNAP1;3T, Alters Plant Growth Responses to Abscisic Acid and Salt in the Atnap 1;3-2 Mutant

Chromatin remodeling is thought to have crucial roles in plant adaptive response to environmental stimulus. Here, we report that, in Arabidopsis, the evolutionarily conserved histone chaperone, NUCLEOSOME ASSEMBLY PROTEIN 1 （NAP1）, is involved in plant response to abscisic acid （ABA）, a phytohormone important in stress adaptation. We show that simultaneous loss-of-function of AtNAP1;1, AtNAP1;20 and AtNAP1;3 （the triple mutant m123-1） caused a slight hypersensitive response to ABA in seedling growth. Strikingly, the other triple mutant m123-2 containing a different mutant allele of AtNAP1;3, the Atnap 1;3-2 allele, showed a hyposensitive response to ABA and a decreased tolerance to salt stress. This ABA- hyposensitive and salt response phenotype specifically associated with the Atnapl;3-2 mutant allele. We show that this mutant allele produced a truncated protein, AtNAP1;3T, which lacks 34 amino acids at the C-terminus compared to the wild-type protein AtNAP1;3. We further show that the heterozygous plants containing the Atnapl;3-2 mutant allele as well as transgenic plants overexpressing AtNAP1;3Texhibit ABA-hyposensitive phenotype. It thus indicates that AtNAP1;3T functions as a dominant negative factor in ABA response. The expression of some ABA-responsive genes, including genes encoding protein kinases and transcription regulators, was found perturbed in the mutant and in theAtNAP1;3Ttransgenic plants. Taken together, our study uncovered AtNAP1 proteins as positive regulators and AtNAP1;3Tas a negative regulator in ABA signaling pathways, providing a novel link of chromatin remodeling to hormonal and stress responses.

Transcription factors AS1 and AS2 interact with LHP1 to repress KNOX genes in Arabidopsis

Polycomb group proteins are important repressors of numerous genes in higher eukaryotes. However, the mechanism by which Polycomb group proteins are recruited to specific genes is poorly understood. In Arabidopsis, LIKE HETEROCHROMATIN PROTEIN 1 （LHP1）, also known as TERMINAL FLOWER 2, was originally proposed as a subunit of polycomb repressive complex 1 （PRC1） that could bind the tri-methylated lysine 27 of histone H3 （H3K27me3） established by the PRC2. In this work, we show that LHP1 mainly functions with PRC2 to establish H3K27me3, but not with PRC1 to catalyze monoubiquitination at lysine 119 of histone H2A. Our results show that complexes of the transcription factors ASYMMETRIC LEAVES 1 （AS1） and AS2 could help to establish the H3K27me3 modification at the chromatin regions of Class-I KNOTTED＇t-like homeobox （KNOX） genes BREVIPEDICELLU5 and KNAT2 via direct interactions with LHP1. Additionally, our transcriptome analysis indicated that there are probably more common target genes of AS1 and LHP1 besides Class-I KNOX genes during leaf development in Arabidopsis.

A LIM Domain Protein from Tobacco Involved in Actin-Bundling and Histone Gene Transcription

The two LIM domain-containing proteins from plants （LIMs） typically exhibit a dual cytoplasmic-nuclear dis-tribution, suggesting that, in addition to their previously described roles in actin cytoskeleton organization, they partici-pate in nuclear processes. Using a south-western blot-based screen aimed at identifying factors that bind to plant histone gene promoters, we isolated a positive clone containing the tobacco LIM protein WLIM2 （NtWLIM2） cDNA. Using both green fluorescent protein （GFP） fusion-and immunology-based strategies, we provide clear evidence that NtWLIM2 local-izes to the actin cytoskeleton, the nucleus, and the nucleolus. Interestingly, the disruption of the actin cytoskeleton by latrunculin B significantly increases NtWLIM2 nuclear fraction, pinpointing a possible novel cytoskeletal-nuclear crosstalk. Biochemical and electron microscopy experiments reveal the ability of NtWLIM2 to directly bind to actin filaments and to crosslink the latter into thick actin bundles. Electrophoretic mobility shift assays show that NtWLIM2 specifically binds to the conserved octameric cis-elements （Oct） of the Arabidopsis histone H4A748 gene promoter and that this binding largely relies on both LIM domains. Importantly, reporter-based experiments conducted in Arabidopsis and tobacco proto-plasts confirm the ability of NtWLIM2 to bind to and activate the H4A748 gene promoter in live cells. Expression studies indicate the constitutive presence of NtWLIM2 mRNA and NtWLIM2 protein during tobacco BY-2 cell proliferation and cell cycle progression, suggesting a role of NtWLIM2 in the activation of basal histone gene expression. Interestingly, both live cell and in vitro data support NtWLIM2 di/oligomerization. We propose that NtWLIM2 functions as an actin-stabilizing protein, which, upon cytoskeleton remodeling, shuttles to the nucleus in order to modify gene expression.

A Non-canonical Transferred DNA Insertion at the BRI1 Locus in Arabidopsis thaliana

Agrobacterium-mediated transformation is widely used in transgenic plant engineering and has been proven to be a powerful tool for insertional mutagenesis of the plant gsnome. The transferred DNA （T-DNA） from Agrobacterium is integrated into the plant genome through illegitimate recombination between the T-DNA and the plant DNA. Contrasting to the canonical insertion, here we report on a locus showing a complex mutation associated with T-DNA insertion at the BRI1 gene in Arabidopsis thaliana. We obtained a mutant line, named salads for its phenotype of dwarf stature and proliferating rosette. Molecular characterization of this mutant revealed that in addition to T-DNA a non-T-DNA-Iocalized transposon from bacteria was inserted in the Arabidopsis genome and that a region of more than 11.5 kb of the Arabidopsis genome was deleted at the insertion site. The deleted region contains the braesinosteroid receptor gene BRI1 and the transcription factor gene WRKY13. Our finding reveals non-canonical T-DNA insertion, implicating horizontal gene transfer and cautioning the use of T-DNA as mutagen in transgenic research.

Chromatin-remodeling factor OsINO80 is involved in regulation of gibberellin biosynthesis and is crucial for rice plant growth and development

The phytohormone gibberellin（GA） plays essential roles in plant growth and development. Here,we report that OsINO80, a conserved ATP-dependent chromatin-remodeling factor in rice（Oryza sativa）, functions in both GA biosynthesis and diverse biological processes. OsINO80-knockdown mutants, derived from either T-DNA insertion or RNA interference, display typical GA-deficient phenotypes, including dwarfism, reduced cell length, late flowering, retarded seed germination and impaired reproductive development. Consistently, transcriptome analyses reveal that OsINO80 knockdown results in downregulation by more than two-fold of over 1,000 genes, including the GA biosynthesis genes CPS_1 and GA_3ox_2, and the dwarf phenotype of OsINO80-knockdown mutants can be rescued by the application of exogenous GA3. Chromatin immunoprecipitation（Ch IP） experiments show that OsINO80 directly binds to the chromatin of CPS1 and GA_3ox_2 loci. Biochemical assays establish that OsINO80 specially interacts with histone variant H_2A.Z and the H_2A.Z enrichments at CPS_1 and GA_3ox_2 are decreased in OsINO80-knockdown mutants. Thus, our study identified a rice chromatin-remodeling factor,OsINO80, and demonstrated that OsINO80 is involved in regulation of the GA biosynthesis pathway and plays critical functions for many aspects of rice plant growth and development.

The Polycomb Complex PRC1:Composition and Function in Plants

Polycomb group（PcG） proteins are crucial epigenetic regulators conferring transcriptional memory to cell lineages.They assemble into multi-protein complexes,e.g.,Polycomb Repressive Complex 1 and 2（PRC1,PRC2）,which are thought to act in a sequential manner to stably maintain gene repression.PRC2 induces histone H3 lysine 27（H3K27） trimethylation（H3K27me3）,which is subsequently read by PRCl that further catalyzes H2A monoubiquitination（H2Aub1）,creating a transcriptional silent chromatin conformation.PRC2 components are conserved in plants and have been extensively characterized in Arabidopsis.In contrast,PRCl composition and function are more diverged between animals and plants.Only more recently,PRC1 existence in plants has been documented.Here we review the aspects of plant specific and conserved PRC1 and highlight critical roles of PRC1 components in seed embryonic trait determinacy,shoot stem cell fate determinacy,and flower development in Arabidopsis.

H3K36 Methylation Is Involved in Promoting Rice Flowering

Dear Editor, Histone H3 lysine 36 （H3K36） methylation is a conserved epigenetic mark in all eukaryotes （Berr et al., 2011; Wagner and Carpenter, 2012）. Reverse genetic analysis in Arabidopsis had uncovered a crucial role of H3K36 di- and tri-methylation （H3K36me2 and H3K36me3） in flowering-time regulation （reviewed in Berr et al., 2011）.

SDG714 Regulates Specific Gene Expression and Consequently Affects Plant Growth via H3K9 Dimethylation

Histone lysine methylation is known to be involved in the epigenetic regulation of gene expression in all eukaryotes including plants. Here we show that the rice SDG714 is primarily responsible for dimethylation but not trimethylaUon on histone H3K9 in vivo. Overexpression of YFP-SDG714 in Arabidopsis significantly inhibits plant growth and this inhibition is associated with an enhanced level of H3K9 dimethylation. Our microarray results show that many genes essential for the plant growth and development were downregulated in transgenic Arabidopsis plants overexpressing YFP-SDG714. By chromatin immunoprecipitation analysis, we show that YFP-SDG714 is targeted to specific chromatin regions and dimethylate the H3Kg, which is linked with heterochromatinization and the downregulation of genes. Most interestingly, when YFP-SDG714 production is stopped, the inhibited plants can partially restore their growth, suggesting that the perturbation of gene expression caused by YFP-SDG714 is revertible. Taken together, our results point to an important role of SDG714 in H3K9 dimethylation, suppression of gene expression and plant growth, and provide a potential method to regulate gene expression and plant development by an on-off switch of SDG714 expression.