Subcellular Dynamics, Cell Morphogenesis, and Organ Formation in Plants

植物通过协调的细胞分裂和细胞扩增模式生长并对周围环境做出反应。例如，在根中，细胞分裂仅限于顶端，形成顶端分生组织，产生细胞层。尖端后面是伸长区，在这里细胞停止分裂并开始纵向扩张形成成熟的根。由于植物细胞被细胞壁包围和支撑，所有细胞的分裂和扩增都取决于细胞壁的结构和组成。被称为纤维素微原纤维（CMFs）的纤维素链形成了一个网状结构，决定了细胞扩张的方向。例如，在根伸长区，CMFs排列成平行的圆环，限制了细胞的横向扩张，有利于伸长。相反，分裂的分生组织细胞有混合的CMF取向，阻止伸长。CMF的方向是由微管（MTs）的方向控制的，微管在细胞膜上形成了一个电缆网络。MTs引导膜中纤维素合成酶的线性运动，将CMFs挤出相邻的细胞壁。与CMFs一样，mt在进入细胞扩增时从混合模式切换到有组织模式。***我的研究项目的一个关键领域集中在如何控制MT和CMF模式，以确定细胞是否重新进入分裂或切换到扩展。分生组织细胞小而四四方方，有锋利的边缘，MT必须穿过这些边缘才能产生混合的MT模式。我已经确定了三种蛋白质（CLASP， GCP2和GCP3），它们聚集在这些尖锐的细胞边缘，使mt能够交叉。然后，这些MT跨越细胞的多个侧面，这有助于防止细胞扩增的混合MT模式。另一组特殊的MT称为内质MT （EMTs）也有助于混合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，在那里它可以帮助emt进行急转弯进入并排列膜。我的研究计划有三个目标：(1)鉴定额外的细胞边缘蛋白并确定它们如何影响CMT模式；(2)鉴定额外的emt -皮层附着蛋白，并确定它们如何影响emt -皮层附着和CMT模式；(3)为了理解复杂的细胞扩张模式，如分叶和分支是如何发展的，我们将分析叶肉细胞随着时间的推移形状的变化。***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，以可视化活根和叶中的MTs， CMFs，细胞边缘，emt膜锚点和其他亚细胞结构。我和我的学生将使用荧光显微镜在三维空间中追踪这些元素。我的研究项目所取得的发现将促进我们对植物如何生长和对环境作出反应的认识。********

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.********