Cell Wall Signalling in Arabidopsis thaliana

如何通过协调细胞的增殖、分化和生长来完成复杂多细胞生物体的发育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指定在一定程度上由细胞外基质(ECM)控制。植物坚硬而动态的ECM，即细胞壁，已知通过选择性地限制细胞扩张来指导形态发生。为了控制生长，也为了对外部干扰做出反应，细胞壁状态被认为受到与细胞内信号有关的细胞表面受体的持续监测。然而，关于细胞壁特性是如何被感知的，信号是如何被传递的，以及细胞壁介导的反馈信号是如何与植物发育的调控机制相交的，人们知之甚少。根据我们最近的发现，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，这让人想起细胞外基质在动物体内的调节作用。我们发现了一种新的细胞壁信号通路，该通路依赖于质膜上定位的受体样蛋白RLP44。RLP44与细胞壁的果胶组分相互作用，通过与各自的受体复合体相互作用并促进它们的活性，连接两个著名的信号通路，油菜素类固醇(BR)和植物硫氨酸(PSK)信号。有趣的是，RLP44启动的PSK信号是维持根中前形成层细胞特性所必需的，这是这一途径的一种新功能。与RLP44的缺失类似，PSK相关突变体在原形成层的位置表现为异位木质部，而RLP44突变体可以被外源PSK拯救。在这里，我们主要想解决两个问题。首先，BRI1-RLP44-PSK信号模块如何促进前共性认同？基于广泛的初步结果，我们希望检验PSK信号部分通过控制蛋白质翻译发挥作用的假设。此外，我们想要剖析PSK信号如何与已知的原形成原同一性的调节因子，即相互抑制的生长素和细胞分裂素的形态发生域交叉。第二，RLP44介导的细胞壁感知对调节生长和发育的细胞内网络有直接影响吗？为此，我们将利用我们的发现，即RLP44与果胶直接相互作用，并评估细胞壁结合对信号读数以及受体复合体中蛋白质-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.