Subcellular Dynamics, Cell Morphogenesis, and Organ Formation in Plants

植物的亚细胞动力学、细胞形态发生和器官形成

• 批准号: RGPIN-2015-05938
• 负责人: Ambrose, Chris
• 金额: $ 2.55万
• 依托单位: University of Saskatchewan
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=708124
• 关键词: Subcellular; Dynamics; Cell; Morphogenesis; Organ

Plants grow and respond to their surroundings through coordinated patterns of cell division and cell expansion. For example, in a root, cell division is restricted to the tip, forming an apical meristem that produces layers of cells. Behind the tip is the elongation zone, where cells cease dividing and begin expanding lengthwise to form the mature root. Since plant cells are surrounded and supported by cell walls, all cell division and expansion depends on cell wall structure and composition. Strands of cellulose called cellulose microfibrils (CMFs) form a meshwork that determines the direction of cell expansion. For example, in the root elongation zone, CMFs line up in parallel hoops that restrict lateral cell expansion and favor elongation. In contrast, dividing meristematic cells have mixed CMF orientations that prevent elongation. CMF orientation is controlled by the orientation of microtubules (MTs), which form a network of cables that line the cell membrane. MTs guide the linear movement of cellulose-synthesizing enzymes in the membrane that extrude CMFs into the adjacent cell wall. As with CMFs, MTs switch from mixed to organized patterns upon entry into cell expansion. A key area of my research program focuses on how MT and CMF patterns are controlled to determine whether a cell re-enters division or makes the switch to expansion. Being small and boxy, meristem cells have sharp edges that MTs must cross in order to generate mixed MT patterns. I have identified three proteins (CLASP, GCP2 and GCP3) that accumulate at these sharp cell edges to enable MTs to cross over. These MTs then span across multiple sides of the cell, which contributes to the mixed MT patterns that prevent cell expansion. Another specialized set of MTs called Endoplasmic MTs (EMTs) also contributes to mixed MT patterns. EMTs emanate from the cell center and attach at their tips to the cell membrane. I found that CLASP is located at the EMT-membrane attachment point, where it helps EMTs make the sharp turn to enter and line the membrane. Three objectives of my research program are: (1) to identify additional cell edge proteins and determine how they influence CMT patterns; (2) to identify additional EMT-cortex attachment proteins and determine how they influence EMT-cortex attachment and CMT patterns; and (3) to understand how complex cell expansion patterns such as lobing and branching develop, we will analyze leaf mesophyll cells as they change shape over time. To achieve these goals, I have developed Arabidopsis thaliana plants expressing fluorescent protein tags to visualize MTs, CMFs, cell edges, EMT-membrane anchors and other subcellular structures in living roots and leaves. My students and I will use fluorescence microscopy to track these elements in three-dimensions over time. The discoveries made by my research program will advance our knowledge of how plants grow and respond to their environments.

植物通过细胞分裂和细胞扩张的协调模式生长并响应周围环境。例如，在根中，细胞分裂仅限于尖端，形成产生细胞层的顶端分生组织。尖端后面是伸长区，细胞停止分裂并开始纵向扩展以形成成熟的根。由于植物细胞被细胞壁包围和支撑，所有细胞分裂和扩张都取决于细胞壁的结构和组成。称为纤维素微纤维 (CMF) 的纤维素链形成决定细胞扩张方向的网状结构。例如，在根伸长区域，CMF 排列成平行的环，限制横向细胞扩张并有利于伸长。相反，分裂的分生细胞具有混合的 CMF 方向，从而阻止伸长。 CMF 方向由微管 (MT) 的方向控制，微管形成排列在细胞膜上的电缆网络。 MT 引导膜中纤维素合成酶的线性运动，将 CMF 挤出到相邻的细胞壁中。与 CMF 一样，MT 在进入细胞扩增时从混合模式转变为有组织模式。 我的研究项目的一个关键领域集中于如何控制 MT 和 CMF 模式来确定细胞是否重新进入分裂或切换到扩张。分生组织细胞小而四四方方，具有尖锐的边缘，MT 必须穿过这些边缘才能生成混合的 MT 模式。我已经鉴定出三种蛋白质（CLASP、GCP2 和 GCP3），它们在这些尖锐的细胞边缘积聚，使 MT 能够跨越。然后，这些 MT 跨越细胞的多个侧面，这有助于形成混合 MT 模式，从而防止细胞扩张。另一组专门的 MT 称为内质 MT (EMT)，也有助于形成混合 MT 模式。 EMT 从细胞中心发出，并在其尖端附着在细胞膜上。我发现 CLASP 位于 EMT 膜附着点，它可以帮助 EMT 急转弯进入并排列膜。我的研究计划的三个目标是：（1）识别其他细胞边缘蛋白并确定它们如何影响 CMT 模式； (2) 识别其他 EMT 皮质附着蛋白并确定它们如何影响 EMT 皮质附着和 CMT 模式； （3）为了了解复杂的细胞扩张模式（例如分叶和分枝）是如何发展的，我们将分析叶子叶肉细胞随着时间的推移而改变形状。 为了实现这些目标，我开发了表达荧光蛋白标签的拟南芥植物，以可视化活体根和叶中的 MT、CMF、细胞边缘、EMT 膜锚和其他亚细胞结构。我和我的学生将使用荧光显微镜随着时间的推移在三维空间中跟踪这些元素。我的研究项目的发现将增进我们对植物如何生长和对环境的反应的了解。