The Shape of Plants: exploring developmental transitions

植物已经进化出感觉和反应机制，以优化在不同和不利的环境条件下的生长和发育。植物体上被称为分生组织的微小区域维持干细胞处于静止状态，并产生产生组织和器官的细胞。细胞从分生组织中被转移，但最终停止分裂并进行大量生长。这种从分裂到分化的转变发生的时间和地点决定了植物器官的最终大小和形状，并受到当时环境条件的强烈影响，并受到干旱和盐度等胁迫的影响。这项研究计划的总体目标是确定和理解植物决定和协调从增殖到分化的发育过渡的机制。它还建立在三十多年来对动态亚细胞细丝（称为微管（MT））的性质和功能的研究基础上。MT在所有真核生物中是进行染色体分离、细胞内运输、定向生长和运动所必需的。该研究分为三个子项目，每个子项目都侧重于发育转变（在MT功能的背景下）。我们将首先确定两种类型的MT相关蛋白，MOR 1和方舟，如何协同工作，以协调MT组装和拆卸。我们将确定这些蛋白质如何控制MT动力学，因为细胞从一个发育阶段过渡到另一个阶段，而且还响应于盐胁迫，这涉及瞬时MT分解。第二个目标将阐明如何MT相关蛋白CLASP和生长激素油菜素类固醇控制从增殖到分化的过渡。我们最近发现CLASP通过促进其受体的再循环来维持油菜素类固醇信号传导，但油菜素类固醇信号传导也下调CLASP。为了进一步探索这种负反馈回路，我们已经改造了CLASP基因不再对油菜素类固醇有反应的植物。这些“解偶联”的植物将是鉴定CLASP在调节增殖-分化转变点中发挥的特定功能的有力工具。最后，我们将探讨膜锚定纤维素结合蛋白COBRA如何在细胞扩增过程中维持单向生长。COBRA在快速扩张过程中高度表达，并且是生产纤维素所必需的，纤维素是植物细胞壁的主要张力承载组分。我们最近证实了COBRA存在于细胞壁中，但也发现它与合成纤维素的酶复合物有关，这些酶复合物沿着MT分布在细胞内。我们将使用生物化学和转录测定来检验我们的假设，即COBRA在与纤维素相互作用后发生裂解，并且其随后与纤维素合成酶复合物的结合调节纤维素的产生。

Plants have evolved sensory and response mechanisms to optimize growth and development under diverse and adverse environmental conditions. Tiny regions of the plant body called meristems maintain stem cells in a quiescent state, and produce the cells that give rise to tissues and organs. Cells are displaced from the meristem, but eventually stop dividing and undergo massive growth. When and where this transition from division to differentiation occurs determines the ultimate size and shape of plant organs, and is strongly influenced by prevailing environmental conditions, and modified by stresses such as drought and salinity.******The overarching goal of this research proposal is to identify and understand the mechanisms by which plants determine and coordinate the developmental transition from proliferation to differentiation. It also builds on more than three decades of research on the properties and functions of dynamic sub-cellular filaments called microtubules (MTs). MTs are essential in all eukaryotic organisms for carrying out chromosome separation, intracellular transport, directional growth and motility. The research is divided into three subprograms, each of which focusses on developmental transitions (in the context of MT function).******We will first determine how two types of MT-associated proteins, MOR1 and ARK, work in concert to coordinate MT assembly and disassembly. We will determine how these proteins control MT dynamics as cells transition from one stage of development to another, but also in response to salt stress, which involves transient MT disassembly.******The second objective will elucidate how the MT-associated protein CLASP and the growth hormone brassinosteroid control the transition from proliferation to differentiation. We recently discovered that CLASP sustains brassinosteroid signalling by fostering the recycling of its receptors but that brassinosteroid signalling also down-regulates CLASP. To explore this negative feedback loop further, we have engineered plants in which the CLASP gene is no longer responsive to brassinosteroids. These 'uncoupled' plants will be powerful tools for identifying the specific function CLASP plays in modulating the proliferation-differentiation transition point.******Finally, we will explore how the membrane-anchored cellulose-binding protein COBRA sustains unidirectional growth during cell expansion. COBRA is highly expressed during rapid expansion and is required for the production of cellulose, which is the major tension-bearing component of plant cell walls. We recently confirmed COBRA's presence in the cell wall, but also discovered that it associates with the enzyme complexes that synthesize cellulose, which are distributed along MTs inside the cell. We will use biochemical and transcriptional assays to test our hypothesis that COBRA undergoes cleavage after interacting with cellulose, and that its subsequent association with the cellulose synthase complex modulates cellulose production.********