植物干细胞调控的分子机制

植物干细胞位于茎尖分生组织区和根尖分生组织区,是植物胚后发育中新的器官产生的源泉.近几年,在干细胞及其周围组织区发现了一些与干细胞稳态维持有关的基因,这些基因产物与外源性信号（如生长素）一起组成复杂的调控网络控制植物的生长和发育.表观遗传修饰作为控制基因表达的一种方式也对植物干细胞有重要的影响.该文介绍近几年植物干细胞分化调控的最新进展.     

WOX蛋白家族调控干细胞发育分子机制的研究进展

WOX蛋白家族是植物特有的一类转录因子家族, 是植物胚胎建成、干细胞维持和器官发生等发育过程中的重要调控因子。越来越多的研究表明, 作为干细胞维持的关键因子之一, WOX蛋白家族通过相似或特异的调控网络参与植物初生分生组织(茎尖和根尖分生组织)和次生分生组织(维管分生组织)等各级干细胞的维持和分化。该文综述了近年来WOX蛋白家族调控干细胞发育分子机制的研究进展, 并对其在单、双子叶植物中功能的保守性进行了比较和分析。     

植物干细胞功能的分子调控研究进展

植物干细胞是植物体内具有自我更新和多向分化潜能的细胞群体,主要位于植物体茎尖分生组织、根尖分生组织和维管形成层中.它们既可以通过细胞分裂维持自身细胞群体的大小,也可以分化成为各种不同的组织器官.维持干细胞的分裂与分化之间的平衡,是植物通过纵向伸长生长和径向增粗生长不断积累生物量的基础,这一过程受基因、microRNAs(miRNAs)及植物激素等因子共同调控.本文概述了近年来植物干细胞调控植物生长发育的研究进展,并对今后的研究方向进行了展望.     

植物根尖生长素信号研究进展

生长素信号调控植物生长发育的各个方面。该文综述了生长素信号在植物根尖的研究进展概况,从生长素在根尖的运输与分布、生长素信号对根尖细胞命运的影响及静止中心细胞的生长素信号研究三个方面进行了阐述,并对未来该领域的研究方向进行了展望。     

C类花器官特征基因AGAMOUS(AG)调控植物花分生组织维持与终止研究进展

花分生组织的维持与终止在植物花器官发生和世代交替起着至关重要的作用。成功的花分生组织决定能够确保植物正常的生殖发育和生命周期进程。诸多研究表明AGAMOUS(AG)基因作为花器官分化和开花决定的主效调节因子,能够协调花发育过程中多种细胞命运决定。然而,关于AG参与调控植物世代交替及花分生组织维持与终止的分子调控机制尚不清晰。综述了近年来AG基因参与调控植物花分生组织维持与终止的研究进展及现状,以期为深入研究植物花器官分化过程中干细胞的维持和终止,以及干细胞活动与其他发育过程之间的分子调控过程提供参考。     

头孢霉素对拟南芥主根生长发育的影响

以拟南芥野生型和相关转基因株系为材料,设置0、50、100、200和400μg/mL头孢霉素处理,考察头孢霉素对主根伸长生长、根尖分生组织活性、生长素分布运输以及干细胞活性的影响,探究头孢霉素对拟南芥主根生长发育的毒性作用机制。结果显示:(1)头孢霉素能以浓度依赖的方式抑制拟南芥主根的生长,并抑制分生组织长度和CYCB1;1基因的表达,说明它能抑制根尖分生组织活性。(2)头孢霉素能降低根尖生长素报告基因DR5∷GUS、DR5∷GFP和生长素极性运输蛋白PIN1、PIN2、PIN3、PIN7和AUX1的表达,说明它能抑制根尖生长素的分布和极性运输。(3)头孢霉素能下调根尖静止中心标记系WOX5∷GFP、QC25和QC46的表达,以及SHR和SCR蛋白的表达,说明它能抑制根尖干细胞活性。研究表明,头孢霉素能通过抑制根尖分生组织活性、生长素的分布和极性运输以及干细胞活性,从而调节拟南芥主根的生长发育。     

植物根尖干细胞的表观遗传调控

干细胞是一类具有特化为不同细胞类型能力的多能性细胞,他为多细胞生物的器官发生、损伤修复和再生源源不断提供新细胞。干细胞的特化和维持需要复杂的基因调控网络来有序调控。此外,表观遗传调控在包括干细胞命运决定在内的许多生物学过程中发挥极其重要的作用。本文归纳了近年来对植物,主要是模式植物拟南芥（Arabidopsis thaliana（L.）Heynh.）根尖干细胞表观遗传调控方面的研究进展,重点论述了表观调控因子与控制干细胞的关键转录因子之间如何互作、调控植物根尖干细胞的自我更新和分化,并对今后研究的突破方向进行了展望。     

植物根尖干细胞的表观遗传调控

干细胞是一类具有特化为不同细胞类型能力的多能性细胞,他为多细胞生物的器官发生、损伤修复和再生源源不断提供新细胞。干细胞的特化和维持需要复杂的基因调控网络来有序调控。此外,表观遗传调控在包括干细胞命运决定在内的许多生物学过程中发挥极其重要的作用。本文归纳了近年来对植物,主要是模式植物拟南芥(Arabidopsis thaliana (L.) Heynh.)根尖干细胞表观遗传调控方面的研究进展,重点论述了表观调控因子与控制干细胞的关键转录因子之间如何互作、调控植物根尖干细胞的自我更新和分化,并对今后研究的突破方向进行了展望。     

生长素调控植物根尖干细胞维持研究取得重要进展

和动物不同,高等植物只能固着生长的特点决定了其能够根据复杂的环境条件不断地调整器官的发生和发育进程。植物生长发育的这种可塑性是由于在茎尖和根尖生长点分生组织中央有一个具有持续分裂能力和分化功能的干细胞组织结构。这些干细胞伴随着植物的一生,它们的分化不仅产生了所有的地上和地下器官,而且会根据内外环境信号来决定器官的发生、生殖生长、成熟和衰老等生物学过程。因此植物干细胞是生长发育的源泉和信号调控中心。     

多肽-受体激酶信号维持顶端分生组织稳态的分子机制

植物在一生的发育过程中不断进行着新器官的产生和既有器官的伸长,例如,叶、侧枝、花等器官的产生和根、茎的伸长,这一切都取决于其分生组织中干细胞的活动及由此产生的细胞命运决定.植物顶端分生组织的维持有着精细的调控网络,复杂的胞间信号转导保证了细胞分裂与分化之间的平衡.过去二十多年的研究表明,多肽和受体激酶在维持植物顶端分生组织的过程中起着至关重要的调控作用.本文整理了有关多肽和受体激酶维持顶端分生组织稳态的最新研究进展,梳理了这些已知调控元件之间的关系,并提出了可能存在的工作模式以及未来完善这些信号网络的研究方向.     

Apical meristems: the plant's fountain of youth

During postembryonic development, all organs of a plant are ultimately derived from a few pluripotent stem cells found in specialized structures called apical meristems. Here we discuss our current knowledge about the regulation of plant stem cells and their environments with main emphasis on the shoot apical meristem of Arabidopsis thaliana. Recent studies suggest that stem cells are localized in specialized niches where signals from surrounding cells maintain their undifferentiated state. In the shoot meristem, initiation of stem cells during embryogenesis, regulation of stem-cell homeostasis and termination of stem-cell maintenance during flower development appear to primarily involve regulation of the stem-cell niche.     

Stem cells: The root of all cells

The plant basic body plan is laid down during embryogenesis. All post-embryonic development has its origin in the stem cells located in niches in the heart of the shoot and root meristems. Creating the root niche requires auxin dependent patterning cues that provide positional information in combination with parallel inputs to specify and maintain the root stem cell niche from embryogenesis onwards. Once established, the architecture of the root niche differs from that in the shoot but recent findings reveal a conserved module for stem cell control. Important for stem cell maintenance is the balance between cell division and differentiation. Dealing with the environment is the biggest challenge for plants and that includes complete regeneration of stem cell systems upon damage. Here we will address these issues as we follow the formation, function and maintenance of the root stem cell niche during development.     

The dynamic plant stem cell niches

Stem cells exist in specific locations called niches, where extracellular signals maintain stem cell division and prevent differentiation. In plants, the best characterised niches are within the shoot and root meristems. Networks of regulatory genes and intercellular signals maintain meristem structure in spite of constant cell displacement by division. Recent works have improved our understanding of how these networks function at the cellular and molecular levels, particularly in the control of the stem cell population in the shoot meristem. The meristem regulatory genes have been found to function partly through localised control of widely used signals such as cytokinin and auxin. The retinoblastoma protein has also emerged as a key regulator of cell differentiation in the meristems.     

Coordination of apical and basal embryo development revealed by tissue-specific GNOM functions

Flowering-plant embryogenesis generates the basic body organization, including the apical and basal stem cell niches, i.e. shoot and root meristems, the major tissue layers and the cotyledon(s). gnom mutant embryos fail to initiate the root meristem at the early-globular stage and the cotyledon primordia at the late globular/transition stage. Tissue-specific GNOM expression in the gnom mutant embryo revealed that both apical and basal embryo organization depend on GNOM provascular expression and a functioning apical-basal auxin flux: GNOM provascular expression in gnom mutant background resulted in non-cell-autonomous reconstitution of apical and basal tissues which could be linked to changes in auxin responses in those tissues, stressing the importance of apical-basal auxin flow for overall embryo organization. Although reconstitution of apical-basal auxin flux in gnom results in the formation of single cotyledons (monocots), only additional GNOM epidermal expression is able to induce wild-type apical patterning. We conclude that provascular expression of GNOM is vital for both apical and basal tissue organization, and that epidermal GNOM expression is required for radial-to-bilateral symmetry transition of the embryo. We propose GNOM-dependent auxin sinks as a means to generate auxin gradients across tissues.     

生长素在植物胚胎早期发育中的作用

有性生殖是有花植物的一个重要特征, 胚胎则是实现有性生殖和世代交替的重要载体。植物胚胎从双受精开始, 经历了合子极性建立、顶基轴形成、细胞层分化和器官形成等过程, 这些过程都受到生长素的调控。近年来的研究表明, 生长素在生物合成、极性运输和信号转导3个层面上调控胚胎的发育过程。该文以双子叶植物拟南芥(Arabidopsis thaliana)为例, 综述了生长素对胚胎早期发育过程, 包括合子极性和顶基轴建立、表皮原特化和对称模式转变、胚根原特化和根尖分生组织形成及茎尖分生组织形成等发育的调控机制。     

Regulation of Shoot and Root Development through Mutual Signaling

Plants adjust their development in relation to the availability of nutrient sources. This necessitates signaling between root and shoot. Aside from the well-known systemic signaling processes mediated by auxin, cytokinin, and sugars, new pathways involving carotenoid-derived hormones have recently been identified. The auxin-responsive MAX pathway controls shoot branching through the biosynthesis of strigolactone in the roots. The BYPASS1 gene affects the production of an as-yet unknown carotenoid-derived substance in roots that promotes shoot development. Novel local and systemic mechanisms that control adaptive root development in response to nitrogen and phosphorus starvation were recently discovered. Notably, the ability of the NITRATE TRANSPORTER 1.1 to transport auxin drew for the first time a functional link between auxin, root development, and nitrate availability in soil. The study of plant response to phosphorus starvation allowed the identification of a systemic mobile miRNA. Deciphering and integrating these signaling pathways at the whole-plant level provide a new perspective for understanding how plants regulate their development in response to environmental cues.     

Stem Cell Signalling Networks in Plants

The essential nature of meristematic tissues is addressed with reference to conceptual frameworks that have been developed to explain the behaviour of animal stem cells. Comparisons are made between different types of plant meristems with the objective of highlighting common themes that might illuminate underlying mechanisms. A more in depth comparison of the root and shoot apical meristems is made which suggests a common mechanism for maintaining stem cells. The relevance of organogenesis to stem cell maintenance is discussed, along with the nature of underlying mechanisms which help ensure that stem cell production is balanced with the depletion of cells through differentiation. Mechanisms that integrate stem cell behaviour in the whole plant are considered, with a focus on the roles of auxin and cytokinin. The review concludes with a brief discussion of epigenetic mechanisms that act to stabilise and maintain stem cell populations.