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Cis and trans determinants of epigenetic silencing by Polycomb repressive complex 2 in Arabidopsis. Xiao J,et al Nat Genet 2017 Oct Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA. Jun Xiao, Run Jin（并列一作）, Xiang Yu, Max Shen, John D Wagner, Armaan Pai, Claire Song, Michael Zhuang, Samantha Klasfeld & Doris Wagner（通讯作者） 摘要： Polycomb蛋白复合物的基因沉默的破坏导致植物中的同源异型变化或发育相的器官特征变化。这里我们定义了称为Polycomb反应元件（PREs）的短基因组片段，其将拟南芥中沉默调控的发育基因的Polycomb抑制复合物2（PRC2）置换。我们鉴定了与这些PRE结合的转录因子家族，与PRC2在染色质上共定位，与PRC2物理相互作用并引发PRC2，并且是PRC2介导的体内基因沉默所必需的。 PRE中丰富的两个顺序序列基序是识别的转录因子的同源结合位点，对于PRE活性是必需的和足够的。因此，拟南芥中PRC2的招募很大程度上依赖于反式作用因子与顺式定位的DNA序列基序的结合。 a) A schematic of the construct used to test the ability of candidate PREs or negative control DNA fragments (NC) to recruit PRC2 and H3K27me3. The thick black line indicates the region tested by chromatin immunoprecipitation (ChIP) followed by qPCR. (b) Left, occupancy of the PRC2 component FIE on the tested fragments. Right, H3K27me3 accumulation relative to H3 on the tested fragments. Bars show mean ± s.e.m. of three independent ChIP experiments (red dots). **P < 0.01; NS, not significant (P > 0.05) relative to NC_1; one-tailed unpaired t-test. The LEC2 PRE (ref. 12) served as a positive control (PC_LEC2). See also Supplementary Figure 2a,b. (c) A schematic of the construct used to test the ability of PREs to silence active reporters. Candidate PREs and control fragments were placed between two constitutive promoters, pF3H-35S mini and pMAS, with pF3H-35S mini driving expression of GFP and the β-glucuronidase gene GUS, and pMAS driving expression of the herbicide-resistance gene BAR. (d) Visual scores of GFP intensity (on a scale of 1 to 5, where 1 indicates no reporter expression and 5 indicates full reporter expression) in 15 independent transformants in the wild type (WT; Left) or a prc2 mutant (clf-28 swn-7; Right). Shown are violin plots of GFP intensities of presumptive PREs and negative controls; red or green indicates range; white circle, median; white line, mean; vertical black line, lower to higher quartile. Black horizontal bars mark the median GFP fluorescence of the PRE populations in the wild-type background. *P < 0.05; **P < 0.01; NS, not significant (P > 0.16) relative to NC_1; one-tailed Mann–Whitney U-test. Similar results were obtained for silencing of β-glucuronidase activity and herbicide resistance (Supplementary Fig. 2c–e). Abstract: Disruption of gene silencing by Polycomb protein complexes leads to homeotic transformations and altered developmental-phase identity in plants. Here we define short genomic fragments, known as Polycomb response elements (PREs), that direct Polycomb repressive complex 2 (PRC2) placement at developmental genes regulated by silencing in Arabidopsis thaliana. We identify transcription factor families that bind to these PREs, colocalize with PRC2 on chromatin, physically interact with and recruit PRC2, and are required for PRC2-mediated gene silencing in vivo. Two of the cis sequence motifs enriched in the PREs are cognate binding sites for the identified transcription factors and are necessary and sufficient for PRE activity. Thus PRC2 recruitment in Arabidopsis relies in large part on binding of trans-acting factors to cis-localized DNA sequence motifs. 欢迎点击「PaperRss」↑关注我们！ 2Nat Commun : 植物色素相互作用因子PIF直接抑制miR156的表达增强拟南芥避光综合征（综述）Phytochrome-interacting factors directly suppress MIR156 expression to enhance shade-avoidance syndrome in Arabidopsis. Xie Y,et al Nat Commun 2017 Aug 24 这一研究成果公布在Nature Communications杂志上，文章的通讯作者是中国农业科学院生物技术研究所的王海洋研究员，第一作者为谢钰容副研究员和刘扬博士。 摘要： 植物已经发展出一系列策略，统称为避光综合征，以避免遮盖树荫并与其邻居竞争光。然而，成人植物建筑适应性变化对树荫影响的信号机制尚不清楚。在这里，我们显示在拟南芥中，与野生型相比，几种PHYTOCHROME相互作用因子（PIFS）过表达物都在正常的高红 - 红光比条件下都显示组成型避光综合征，但对模拟阴影较不敏感，而MIR156过表达显示相反的表型。模拟的阴影诱导PIF蛋白的快速积累，减少多个MIR156基因的表达，以及SQUAMOSA-PROMOTER BINDING蛋白样（SPL）家族基因的伴随升高的表达。此外，体内和体外测定表明PIF直接与多个MIR156基因的启动子结合并抑制其表达。我们的研究结果在植物色素-PIF和miR156-SPL调控模块之间建立了直接的功能联系，介导了避光综合征。植物采用发展策略来避免与邻居的光照阴影和竞争。这里，谢等人显示以光依赖性方式调节的植物色素相关因子直接抑制MIR156基因并促进SPL基因的表达以增强避光反应。 光敏色素是植物体内感受红光和远红光的主要光受体，具有抑制避荫反应的功能。然而，光敏色素如何调控下游基因表达从而调节避荫反应的分子机理尚不清楚。 在这篇文章中，研究人员发现拟南芥在遮荫条件下光敏色素的功能受到抑制，导致其互作因子（phytochrome-interacting factors, PIFs）蛋白快速积累，并且这些PIF蛋白能与MIR156基因家族多个成员启动子直接结合并抑制这些MIR156基因的表达，引起其靶基因SPL家族成员表达升高，后者进一步调控了植物株高、分枝数目、叶柄长度、叶片数目、叶片面积、开花时间等一系列重要农艺性状的改变。 这项研究首次阐明了光敏色素phyB-PIFs和miR156-SPLs调控模块之间的互作联系，完善了避荫反应的调控机理，为耐荫、耐密植作物新品种的培育奠定了理论基础。 Spotlight：以往都是miRNA调控下游基因表达，这次居然基因也逆袭了一把，表明miRNA156也存在上游mRNA表达因子对其调控！ Abstract：Plants have evolved a repertoire of strategies collectively termed the shade-avoidance syndrome to avoid shade from canopy and compete for light with their neighbors. However, the signaling mechanism governing the adaptive changes of adult plant architecture to shade is not well understood. Here, we show that in Arabidopsis, compared with the wild type, several PHYTOCHROME-INTERACTING FACTORS (PIFS) overexpressors all display constitutive shade-avoidance syndrome under normal high red to far-red light ratio conditions but are less sensitive to the simulated shade, whereas the MIR156 overexpressors exhibit an opposite phenotype. The simulated shade induces rapid accumulation of PIF proteins, reduced expression of multiple MIR156 genes, and concomitant elevated expression of the SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) family genes. Moreover, in vivo and in vitro assays indicate that PIFs bind to the promoters of several MIR156 genes directly and repress their expression. Our results establish a direct functional link between the phytochrome-PIFs and miR156-SPL regulatory modules in mediating shade-avoidance syndrome.Plants employ developmental strategies to avoid shade and compete with neighbors for light. Here, Xie et al. show that phytochrome-interacting factors, which are regulated in a light-dependent manner, directly repress MIR156 genes and promote the expression of SPL genes to enhance shade-avoidance responses. 欢迎点击「PaperRss」↑关注我们！ 3J Pineal Res：Plant mitochondria synthesize melatonin and enhance the tolerance of plants to drought stress.（植物能合成褪黑素，并且帮助植物提高抗旱能力）摘要： 在动物中报道了线粒体中褪黑激素的合成。然而，没有关于植物线粒体也产生褪黑激素的报道。在这里，我们显示植物线粒体是褪黑素合成的主要部位。在体外研究中，孤立的苹果线粒体具有产生褪黑激素的能力。亚细胞定位分析表明苹果SNAT同种型MzSNAT5位于拟南芥原生质体和苹果愈伤组织细胞的线粒体中。动力学分析表明，重组MzSNAT5蛋白在35℃下的Km和Vmax分别为55μmol/ L和0.909pmol / min / mg蛋白，表现出高的催化5-羟色胺对N-乙酰维生素的酶活性。该通路在5至75℃的宽范围的温度范围内起作用。在体内研究中，MzSNAT5是干旱诱导型的。异位表达MzSNAT5的转基因拟南芥提高了褪黑激素水平，从而提高了耐旱性。分子机制研究表明，异位表达的MzSNAT5允许植物线粒体增加褪黑素合成。褪黑激素作为一种有效的自由基清除剂，可以减少在植物中干旱胁迫下产生的活性氧升高引起的氧化应激。我们的研究结果提供了证明，工程褪黑激素富集植物表现出增强的氧化耐受性。 Spotlight: 没想到植物线粒体是褪黑素合成的主要部位，而且能抗旱 Abstract： Synthesis of melatonin in mitochondria was reported in animals. However, there is no report on whether plant mitochondria also produce melatonin. Herein, we show that plant mitochondria are a major site for melatonin synthesis. In an in vitro study, isolated apple mitochondria had the capacity to generate melatonin. Subcellular localization analysis documented that an apple SNAT isoform, MzSNAT5, was localized in the mitochondria of both Arabidopsis protoplasts and apple callus cells. The kinetic analysis revealed that the recombinant MzSNAT5 protein exhibited high enzymatic activity to catalyze serotonin to N-acetylserotonin with the Km and Vmax of 55 μmol/L and 0.909 pmol/min/mg protein at 35°C, respectively; this pathway functioned over a wide range of temperatures from 5 to 75°C. In an in vivo study, MzSNAT5 was drought inducible. The transgenic Arabidopsis ectopically expressing MzSNAT5 elevated the melatonin level and, hence, enhanced drought tolerance. The mechanistic study indicated that the ectopically expressing MzSNAT5 allows plant mitochondria to increase melatonin synthesis. As a potent free radical scavenger, melatonin reduces the oxidative stress caused by the elevated reactive oxygen species which are generated under drought stress in plants. Our findings provide evidence that engineered melatonin-enriched plants exhibit enhanced oxidative tolerance. 名词解释：褪黑激素(Melatonin) 主要是由哺乳动物和人类的松果体产生的一种胺类激素。人的松果体是附着于第三脑室后壁的、豆粒状大小的组织。也有报导哺乳动物的视网膜和副泪腺也能产生少量的褪黑激素；某些变温动物的眼睛、脑部和皮肤(如青蛙)以及某些藻类也能合成褪黑激素。 959年，科学家Lerner首次在松果体中分离出一种激素，由于这种激素能够使一种产生黑色素(melanin)的细胞发亮，故取其字首Mela；同时由于它从5-羟色胺(serotonin)衍生而来，故取其后缀tonin，因此，这种松果体激素取名为Melatonin(褪黑激素)。机体内酶促反应和非酶促反应时可能产生自由基,自由基与衰老有着密切的联系.正常机体内自由基的产生与消除处于动态平衡,一旦这种平衡被打破,自由基便会引起生物大分子如脂质、蛋白质、核酸的损伤,导致细胞结构的破坏和机体的衰老.褪黑激素通过清除自由基,抗氧化和抑制脂质的过氧化反应保护细胞结构、防止DNA损伤、降低体内过氧化物的含量. SNAT5，钠离子依赖的中性氨基酸转运蛋白5(Sodium-dependent neutral amino acid transporter5,SNAT5，目前报答较少，常见的SNAT2，钠离子依赖性的中性氨基酸转运载体2(SNAT2) 是近年发现的氨基酸转运感受体的典型代表,是体内主要的氮转运载体。 欢迎点击「PaperRss」↑关注我们！ |
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