Elucidating the role of a GTPase-regulating protein family during tip growth initiation and regulation in roots

真核生物中细胞形状的多样性取决于细胞确定极性生长轴和调节细胞扩增速率的能力。形式和功能的相互依赖在使用定向生长来探索和侵入其环境并穿透致密底物的细胞中尤为明显。为了产生一个新的生长尖端，细胞集中资源，在质膜的一个受限点上最大限度地发挥机械力。这种极化生长是真核生物的共同特征，可以在真菌菌丝、神经元轴突、植物花粉管和根毛中观察到。虽然已经确定了各种细胞类型和生物体中极化生长的许多成分和调节因子，但仍有一些基本问题有待回答，例如如何定义极性结构域的位置，生长机制如何组装，或者如何启动，调节和最终完成尖端生长。为了阐明植物细胞形态发生的机制，我们研究了根表皮的一种细胞类型毛胚细胞的根毛的形成，毛胚细胞的尖端生长结构。根毛帮助植物从土壤中提取水分和矿物质养分，锚定根，并与根际微生物相互作用。在本项目中，我们将重点研究生长调节蛋白家族RopGEFs及其在细胞极化和尖端生长调节中的作用。ropgef负责激活分子开关，即所谓的rop - gtpase，它整合细胞内和细胞外信号来调节生长机制。我们最近发现，ropgef与质膜的极性结合是在根毛发育的不同阶段特定的时间：一些成员参与标记出生长的位置，而其他成员在生长开始后具有调节功能。在这里，我们的目的是阐明这种时间极性关联和活性的机制，以及不同ropgef所发挥的不同功能。本研究的发现有望引导我们更好地理解细胞形态发生和植物细胞中尖端生长结构的出现。

The diversity of cellular shapes among eukaryotes depends on the ability of cells to define polar growth axes and regulate the rate of cell expansion. The interdependence of form and function is particularly evident in cells that use directed growth to explore and invade their environment and to penetrate dense substrates. To initiate a new growing tip, cells concentrate their resources and maximize mechanical forces at a confined spot at the plasma membrane. Such polarized growth is a common feature among eukaryotes and can be observed, for instance, in fungal hyphae, neuronal axons, and plant pollen tubes and root hairs. While numerous components and regulators of polarized growth in various cell types and organisms have been identified, fundamental questions remain to be answered, such as how the position of a polar domain is defined, how the growth machinery is assembled, or how tip growth is initiated, regulated and ultimately completed.In order to elucidate the mechanisms of cell morphogenesis in plants, we investigate the formation of root hairs, tip-growing structures of trichoblast cells, a cell type of the root epidermis. Root hairs help plants to extract water and mineral nutrients from soil, to anchor the root and to interact with microbes in the rhizosphere.In this project, we are focussing on the protein family of growth-regulating RopGEFs and their functions during cell polarization and tip growth regulation. RopGEFs are responsible to activate molecular switches, so-called ROP-GTPases, that integrate intra- and extracellular signals to modulate the growth machinery. We recently found that the polar association of RopGEFs with the plasma membrane is specifically timed accross different stages of root hair development: some members are involved in marking the site of outgrowth, while others have a regulatory function after growth has begun. Here we aim to elucidate the mechanisms that underlie this timed polar association and activity, as well as the different functions that are exerted by different RopGEFs. The findings of this study are expected to lead us to a better understanding of cell morphogenesis and the the emergence of tip-growing structures in plant cells.