Assembly of a polar domain - the role of electrostatic interactions at the plasma membrane during the initiation of tip growth in Arabidopsis roots

细胞极性是几乎所有活细胞的统一特征。其特征在于细胞功能的局部化特化，这些功能提供生长或运动的方向性等。在质膜，对称性破缺，因此，功能极化，发生微观和中尺度域，可以是持久的或短暂的。如何实现局部膜专业化是几十年来一直在争论。由于大多数细胞几乎从不去极化，因此研究极性的起始和极性域的形成是具有挑战性的。植物根的特征是一种细胞类型，称为毛细胞或毛细胞，从伸长过渡到尖端生长，因此需要在质膜上建立一个新的极轴和一个极性域。在这个极性结构域的蛋白质组装是如何协调的，以及哪些信号或受体触发了毛发形成的启动，目前还没有很好的了解。我们利用这一过程的高度可预测性来研究特定蛋白质和脂质向新兴根毛起始域的募集。我们的第一个目标是分析蛋白质的逐步组装，并确定特定的蛋白质-蛋白质相互作用沿着头发发育的时间轴。我们的第二个目标是通过研究成簇的磷脂酰肌醇4，5-二磷酸（PIP 2）（质膜上一类带负电荷的磷脂）的作用，揭示膜蛋白募集的机制。PIP 2聚集可以通过静电相互作用驱动蛋白质募集，而静电相互作用可以通过细胞膜电位或胞质离子浓度的变化快速调节。我们的第三个目标是揭示一种新的受体样激酶在毛发生长起始中的功能。它的特定基因表达，其早期出现在根毛起始域和增加的头发形成的功能获得性突变体指向参与这个RLK在触发或协调形成一个新的根毛。两者合计，通过解剖的动态相互作用网络组装过程中的极性毛发起始域，通过研究动态蛋白质招募的机制，并通过调查这一过程的潜在协调员，我们的目标是提供新的见解中尺度域的建立在质膜和极性生长的启动。

Cell polarity is a unifying feature of virtually all living cells. It is characterized by localized specialization of cellular functions that provide, among others, directionality for growth or motility. At the plasma membrane, symmetry breaking and, hence, functional polarization, occurs microscale- and mesoscale domains that can be persistent or short-lived. How local membrane specialization is achieved is under debate for decades. Since most cells are hardly ever unpolarized it is challenging to investigate the initiation of polarity and the formation of polar domains.Plant roots feature a cell type, called hair cells or trichoblasts, that transition from elongation to tip growth and, thus, need to establish a new polar axis and a polar domain at the plasma membrane. How the protein assembly at this polar domain is coordinated and which signals or receptors trigger the initiation of hair formation is not well understood. We take advantage of the high predictability of this process to study the recruitment of specific proteins and lipids to the emerging root hair initiation domain. Our first goal is to analyze the step-wise assembly of proteins and determine specific protein-protein interactions along the time axis of hair development. Our second goal is to unveil mechanisms of the membrane protein recruitment by investigating the role of clustered phosphatidylinositide 4,5-bisphosphate (PIP2), a class of negatively charged phospholipids at the plasma membrane. PIP2 clustering can drive protein recruitment via electrostatic interactions, which can be modulated rapidly by the cell through changes in membrane potential or cytosolic ion concentration.Our third goal is to unveil the function of a novel receptor-like kinase in the initiation of hair emergence. Its specific gene-expression, its early appearance at the root hair initiation domain and an increased hair formation in gain-of-function mutants point toward an involvement of this RLK in triggering or coordinating the formation a new root hair. Taken together, by dissecting the dynamic interaction networks during the assembly of the polar hair initiation domain, by studying a mechanism for dynamic protein recruitment and by investigating a potential coordinator of this process we aim to provide new insights in the establishment of mesoscale domains at the plasma membrane and the initiation of polar growth.