Ligand-receptor-like kinase signalling in Arabidopsis root development

粮食安全是一个重大的全球性问题，作物科学家乔纳森·林奇（Jonathan Lynch）提出，“第二次绿色革命”应该是一个优先事项。这应该侧重于根结构，因为根分枝对养分和水分吸收效率有重要影响。然而，在主要谷类作物中，根系构型并不是植物育种家所选择的性状。此外，在多细胞生物中，细胞间通讯在模式、生长和与环境的相互作用中起着至关重要的作用。例如，严格控制形成性细胞分裂——主要是不对称（干细胞）分裂——以产生组织和器官并防止过度增殖，对植物的胚胎后生长和发育至关重要。这种对形成性细胞分裂的控制不仅在植物中至关重要，而且在动物中也能防止不规则分裂或癌症。我们最近发现了一种蛋白，膜相关受体样激酶ACR4，它在模式植物拟南芥（Arabidopsis thaliana）的根结构控制中起着至关重要的作用，是形成细胞分裂的关键调节剂。ACR4最初在玉米中被描述为其在其他过程中的作用，并为详细分析受体样激酶信号通路在根结构和位置信息的登记和传递中的作用提供了一个明显的起点。本研究计划旨在进一步表征这种配体/受体信号机制，该机制可以整合移动信号分子来控制器官发生过程中的形成性细胞分裂，从而为研究生长发育过程中的短距离细胞-细胞通信提供一个极好的工具。首先，我们将确定那些影响细胞身份的转录变化，这些变化发生在配体驱动的信号来自邻近细胞的主根和侧根下游。这些数据将为我们其他实验提供大量的转录标记。其次，明确识别配体对于充分理解受体样激酶介导的信号通路至关重要。一个重要的方面是来自周围细胞的配体依赖性方向线索如何调节受体样激酶信号。我们将鉴定和定位ACR4受体样激酶的配体。第三，真核生物膜蛋白的三维结构只被非常有限地确定。我们将确定纯化的受体结构域蛋白的折叠和结构，并将其用于详细的分析。第四，蛋白质的暂时可逆磷酸化是最重要的翻译后修饰之一，具有调控功能，如控制转录变化。因此，我们将确定ACR4在主根和侧根发育过程中的底物。第六，利用我们将获得的关于配体受体样激酶信号传导的知识，以及在相同过程中对激素信号传导和转录网络的了解，我们将建立一个全面的模型。

Food security represents a major global issue, and it was put forward by the crop scientist Jonathan Lynch that a 'second green revolution' should be a priority. This should focus on root architecture, since root branching critically influences nutrient and water uptake efficiency. However, root architecture has not been a trait selected for by plant breeders in major cereal crops. In addition, in multicellular organisms, cell-cell communication plays a crucial role in patterning, growth and interaction with the environment. For example, a tight control of formative cell divisions - which are mainly asymmetric (stem) cell divisions - to produce tissues and organs and to prevent over-proliferation is crucial for the postembryonic growth and development of plants. This control of formative cell divisions is not only critical in plants, but also in animals to prevent irregular divisions or cancers. We recently identified a protein, the membrane-associated receptor-like kinase ACR4, which is crucial in the control of root architecture and which is a key regulator of formative cell divisions in the root of the model plant Arabidopsis thaliana. ACR4 has originally been described in maize for its role in other processes, and provides an obvious starting point for the detailed analysis of the role of receptor-like kinase signaling pathways in root architecture and in registering and conveying positional information. This research proposal aims to further characterize this ligand/receptor signaling mechanism that can integrate mobile signaling molecules to control formative cell divisions during organogenesis and, as such, provides an excellent tool to study short range, cell-cell communication during growth and development. First, we will identify those transcriptional changes that affect cell identity in the main and lateral root downstream of a ligand-driven cue from neighbouring cells. These data will provide us with a large number of transcriptional markers for other experiments. Second, unequivocal identification of the ligand is crucial to fully understand receptor-like kinase-mediated signaling pathways. One important aspect is how ligand-dependent directional cues from surrounding cells modulate receptor-like kinase signaling. We will identify and localize ligands for the ACR4 receptor-like kinase. Third, the three dimensional structure of eukaryotic membrane proteins has only been determined very limitedly. We will determine the folding and structure of purified receptor domain protein and use that for detailed analyses. Fourth, temporary and reversible phosphorylation of proteins is one of the most important post-translational modifications with a regulatory function, such as the control of transcriptional changes. Therefore, we will identify the substrates of ACR4 during main and lateral root development. Sixth, with the knowledge that we will gain on ligand-receptor-like kinase signaling and what is known about hormone signaling and transcriptional networks in the same processes, we will build a comprehensive model.