Molecular mechanisms of sensing of and adaptation to K+ deprivation

感知和吸收钾对植物来说是必不可少的。土壤中K+的有效性在自然条件下波动很大，这使得K+限制条件成为经常遇到的环境胁迫。生物体的K+动态平衡是由一系列复杂的过程相互作用决定的，这些过程包括根内K+吸收、根内和从根到地上部的运输过程以及K+储存机制。植物具有广泛的适应反应机制，这些反应机制由感知K+有效性的传感系统触发，并随后触发不同的适应反应。然而，植物如何感知和适应波动的钾条件的分子机制才刚刚开始出现。K+转运的硬连接意味着K+通道和转运体的识别和调节，从而导致K+的摄取和分布。然而，如何以及在哪里机械地感知K+有效性的波动仍然知之甚少。此外，在组织和器官水平上，哪些信号和调节过程传递K+通量和内稳态的建立仍然是个谜。两位申请人以前的工作：(A)确定了根的器官尺度K+模式，(B)确定了K+快速下降和钙信号重合的分生组织后K+敏感生态位(KSN)，(C)确定了CIF肽激活的SGN3-LKS4/SGN1受体复合体的一个分叉的低K+信号轴，该复合体传递低K+触发的NADPH氧化酶RBOHC、RBOHD和RBOHF的磷酸化，(D)发现产生的ROS信号同时传递Hak5 K+吸收转运体诱导和加速的Casparian条带成熟。总而言之，这些发现揭示了植物如何同步发育分化和转录组重新编程，以维持K+稳态和优化根对营养的觅食。基于我们的初步数据，该项目的具体目标是：(I)确定K+在根中的分布格局和动态，(Ii)揭示在分生后K+敏感生态位(KSN)中产生K+信号的分子机制和成分，(Iii)探索KSN所生的钙/K+信号如何机械地传递增强的CIF2信号，(Iv)研究膜极化的分子功能和PM ATPase在LK信号和适应中的作用，以及(V)描述次生Ca~(2+)升高与ROS信号形成的功能相互关系，以及在LK诱导的NOX激活中产生特异性的机制。通过结合遗传方法、生物传感器分析和表型植物分析、生化方法和新型报告分析，我们打算识别和表征LK感应和信号转导的基本分子机制，以实现集成的适应反应。

Sensing and uptake of potassium is essential for plants. The availability of K+ in soils dramatically fluctuates in natural conditions making K+-limiting conditions a frequently encountered environmental stress. Organismic K+ homeostasis is determined by a complex interplay of processes that convey root K+ uptake, transport processes within the root and from root to shoot as well as K+ storage mechanisms. Plants possess a wide range of adaptive responses mechanisms, which are triggered by sensing systems that perceive K+ availability and subsequently trigger different adaptive reactions. However, the molecular mechanisms how plants sense and adapt to fluctuating potassium conditions are only beginning to emerge. The hardwiring of K+ transport meaning the identity and regulation of K+ channels and transporters that bring about K+ uptake and distribution of this ion is relatively well understood. However, how and where fluctuations in K+ availability are mechanistically sensed has remained far less understood. Moreover, which signaling and regulatory processes convey the establishment of K+ fluxes and homeostasis at the tissue and organ scale has remained enigmatic. Previous work of both applicants: (a) defined the organ scale K+ pattern of roots, (b) identified a postmeristematic K+-sensing niche (KSN) where rapid K+ decline and Ca2+ signals coincide, (c) identified a bifurcating low-K+ signaling axis of CIF peptide-activated SGN3-LKS4/SGN1 receptor complexes that convey low-K+-triggered phosphorylation of the NADPH oxidases RBOHC, RBOHD and RBOHF, (d) uncovered that the resulting ROS signals simultaneously convey HAK5 K+ uptake transporter induction and accelerated Casparian strip maturation. Collectively, these findings revealed how plants synchronize developmental differentiation and transcriptome reprogramming for maintaining K+ homoeostasis and optimizing nutrient foraging by roots. Based on our preliminary data the proposed project specifically aims to: (i) define the landscape and dynamics of K+ distribution in roots, (ii) uncover the molecular mechanisms and components that generate the K+ signal in the postmeristematic K+ sensing niche (KSN), (iii) explore how KSN-born Ca2+/K+ signals mechanistically convey intensified CIF2 signaling, (iv) investigate the molecular function of membrane polarization and the role of PM ATPases in LK signaling and adaptation, and (v) delineate the functional interrelation of the secondary Ca2+ elevation with ROS signal formation and of the mechanisms that bring about specificity in LK-induced NOX activation. By combining genetic approaches, biosensorics analyses and by using a combination of phenotypic plant analyses, biochemical approaches, and novel reporter assays, we intend to identify and characterize fundamental molecular mechanisms that underlie LK sensing and signaling to achieve integrated adaptation responses.