Cell Wall Signalling in Arabidopsis thaliana

复杂的多细胞生物体的发育如何通过协调的细胞增殖、分化和生长来完成是一个基本的生物学问题。在动物中，干细胞的维持和细胞特性的特化部分地由细胞外基质（ECM）控制。已知植物的刚性但动态的ECM（细胞壁）通过选择性限制细胞扩增来引导形态发生。为了控制生长，也为了响应外部扰动，细胞壁状态被认为处于与细胞内信号传导连接的细胞表面受体的持续监视下。然而，很少有人知道细胞壁的属性是如何感知的，信号是如何转导的，以及细胞壁介导的反馈信号如何与植物发育的调控机制相交。基于我们最近的发现，我们假设细胞壁信号通路通过控制细胞命运的维持在发育中发挥重要作用，这让人想起ECM在动物中的调节作用。我们发现了一种新的细胞壁信号通路，它依赖于质膜定位的受体样蛋白RLP 44。RLP 44与细胞壁的果胶成分相互作用，并通过与各自的受体复合物相互作用并促进其活性来连接两种众所周知的信号传导途径：油菜素类固醇（BR）信号传导和植物硫因子（PSK）信号传导。有趣的是，RLP 44促进PSK信号是必要的维持原形成层细胞的身份在根中，这一途径的新功能。模拟RLP 44的丢失，PSK相关的突变体在原形成层的位置显示异位木质部，而RLP 44突变体可以被外源PSK拯救。在此，我们主要想解决两个问题。首先，BRI 1-RLP 44-PSK信号模块如何促进原形成层身份？在广泛的初步结果的基础上，我们想检验PSK信号部分通过控制蛋白质翻译起作用的假设。此外，我们要解剖PSK信号如何与已知的原形成层身份，即相互抑制的生长素和细胞分裂素形态发生领域的监管机构相交。其次，RLP 44介导的细胞壁传感是否对调节生长和发育的细胞内网络有直接影响？为此，我们将利用我们的发现，即RLP 44直接与果胶酸相互作用，并评估细胞壁结合对信号传导读数以及受体复合物中蛋白质-蛋白质相互作用的影响。

How the development of complex multicellular organisms is accomplished through coordinated cell proliferation, differentiation, and growth is a fundamental biological question. In animals, stem cell maintenance and cell identity specification are in part controlled by the extracellular matrix (ECM). The rigid, yet dynamic ECM of plants, the cell wall, is known to guide morphogenesis through selective restriction of cell expansion. To control growth, but also to respond to extrinsic perturbations, cell wall state is believed to be under constant surveillance by cell surface receptors connected to intracellular signalling. However, very little is known about how cell wall properties are sensed, how signals are transduced, and how cell wall-mediated feedback signalling intersects with the regulatory mechanisms of plant development. Based on our recent discoveries, we hypothesize that cell wall signalling pathways play major roles in development by controlling the maintenance of cell fate, reminiscent of the regulatory role of the ECM in animals. We discovered a novel cell wall signalling pathways that depends on the plasma membrane localized receptor-like protein RLP44. RLP44 interacts with the pectate component of the cell wall and connects two well-known signalling pathways, brassinosteroid (BR) and phytosulfokine (PSK) signalling, by interacting with the respective receptor complexes and promoting their activity. Interestingly, RLP44-promoted PSK signalling is required for the maintenance of procambial cell identity in the root, a novel function for this pathway. Mimicking the loss of RLP44, PSK-related mutants show ectopic xylem in the position of procambium, whereas RLP44 mutants can be rescued by exogenous PSK. Here, we want to address mainly two questions. First, how does the BRI1-RLP44-PSK signalling module promote procambial identity? Building on extensive preliminary results, we want to test the hypothesis that PSK signalling acts in part through the control of protein translation. In addition, we want to dissect how PSK signalling intersects with the known regulators of procambial identity, namely the mutually inhibitory auxin and cytokinin morphogenetic fields. Second, does RLP44-mediated cell wall sensing have a direct effect on intracellular networks regulating growth and development? To this end, we will leverage our finding that RLP44 directly interacts with pectate and assess the influence of cell wall binding on signalling readouts as well as on protein-protein interactions in the receptor complexes.