REGULATING THE FLOW: Uncovering How Roots Sense and Respond to Water Availability

气候变化导致土壤水分的减少，对英国和全球农业生产力都构成了威胁。因此，了解根系如何感知土壤水分有效性对于提高作物的气候适应能力至关重要。这一雄心勃勃的目标可以通过深入研究根-土壤水分传感的机制来实现。值得注意的是，关于根-水相互作用的传统研究主要集中在整个植物水平上，而忽略了许多发生在单个根尖局部的水感应过程。为了解决这一知识差距，我最近开发了一种优雅的生物测定法来研究个体根尖对瞬态水分胁迫的反应。这种生物分析使我能够发现“为什么根在土壤气隙中停止分支”的机制基础，这种现象被称为“干分支”（Mehra et al., 2022 Science）[1]。当生长的根尖失去与土壤水分的接触时，例如在气隙中，会引发干分枝反应，导致分枝抑制，直到根尖重新进入潮湿的土壤。最近，我发现干分枝利用水分胁迫激素脱落酸（ABA）来阻止根分枝。aba驱动的下游反应在干分支刺激后几个小时被触发。这一缓慢的时间框架令人费解，因为植物根系通常会迅速检测到水分不足，这表明aba介导的分支抑制是一种“响应机制”，而不是主要的“水感机制”。因此，在触发下游aba调节的反应之前，根必须首先感知外部水分供应的变化。作为发现号的一员，我的目标是发现和描述干分枝过程中涉及“水胁迫感知”的早期分子事件。离子通量（如Ca2+和K+）与水分胁迫信号的早期阶段密切相关。我对拟南芥钙信号突变体的初步实验揭示了离子信号在干分支过程中的明确作用。在这些发现的基础上，我的目标是研究离子通量在水感知中的功能意义，通过使用干分支生物测定筛选bbb80拟南芥离子通道/信号突变体（目的1）。此外，我的目标是利用高分辨率生物传感器成像和单细胞rna测序来确定根尖的水传感生态位（目标2）。通过利用这些最先进的方法，我的项目的第一阶段将发现涉及水感知和反应的新组件。接下来，我将研究离子通量如何在干分支过程中触发ABA的生物合成/释放（目的3）。最后，目标4将利用创新的基于细胞尺度拉曼的根系“水成像”来确定离子信号和水力通量之间的功能关系。从我的研究中产生的基本见解将加强对根系如何感知和响应细胞尺度上的水分可用性降低的理解，为未来旨在提高作物用水效率和耐旱性的转化工作奠定坚实的基础。在诺丁汉大学开始这项开创性的研究，我将有机会利用世界一流的研究环境，提供无与伦比的专业知识，跨学科的合作文化，杰出的导师和尖端的设施。这将使我能够发现植物根系用来感知水分供应的基本机制。主办机构和顶尖科学家网络的坚定支持，加上我的专业知识，将使我能够成功地执行这个项目，并在植物生物学研究的前沿产生重大影响。此外，这个项目将培养我独特的研究视野，磨练我的领导能力，使我成为未来根-水相互作用领域的领导者。

Climate change has led to a concerning decline in soil water availability, posing a threat to both UK and global agricultural productivity. Therefore, understanding how roots sense soil water availability is vital for improving climate resilience of crops. This ambitious goal can be realised by delving into the mechanisms underlying root-soil water sensing. Notably, traditional studies on root-water interactions have focused on the whole-plant level, disregarding many water-sensing processes that occur locally in individual root tips. To address this knowledge gap, I recently developed an elegant bio-assay to study individual root tip responses to transient water stress. This bio-assay enabled me to discover the mechanistic basis of 'why roots stop branching in soil air-gaps', a phenomenon termed as 'xerobranching' (Mehra et al., 2022 Science) [1].A xerobranching response is triggered when a growing root tip loses contact with soil moisture, such as in an air-gap, leading to suppression of branching until the root tip re-enters moist soil. Recently, I discovered that xerobranching employs the water-stress hormone abscisic acid (ABA) to block root branching. ABA-driven downstream responses are triggered several hours following a xerobranching stimulus. This slow time frame is puzzling as plant roots typically detect water deficit rapidly, revealing ABA-mediated branching suppression as a 'response mechanism' rather than a primary 'water-sensing mechanism'. Hence, roots must first perceive changes in external water availability before triggering downstream ABA-regulated responses. As a Discovery fellow, I aim to uncover and characterize the early molecular events involved in 'water stress perception' during xerobranching.Ionic fluxes (such as Ca2+ and K+) are closely linked with early stages of water stress signalling. My preliminary experiments using Arabidopsis calcium-signalling mutants reveal a clear role for ionic signalling during xerobranching. Building upon these findings, I aim to investigate the functional significance of ionic fluxes in water perception by screening >80 Arabidopsis ion channel/signalling mutants using the xerobranching bio-assay (Objective 1). In addition, I aim to identify the water sensing niche in root tips by utilizing high-resolution biosensor imaging and single-cell RNA-sequencing (Objective 2). By exploiting these state-of-the-art approaches, the first phase of my project will uncover novel components involved in water perception and response. Next, I will investigate how ionic fluxes trigger ABA biosynthesis/release during xerobranching (Objective 3). Finally, Objective 4 will determine the functional relationship between ionic signalling and hydraulic fluxes using innovative cell-scale Raman-based 'water imaging' of roots. The fundamental insights arising from my research will enhance understanding about how roots perceive and respond to reduced water availability at cell-scale, laying a strong foundation for future translational efforts aimed at improving water-use-efficiency and drought tolerance of crops.Embarking on this pioneering research at the University of Nottingham (UoN), I will have the opportunity to harness a world-class research environment that offers unparalleled expertise, a cross-disciplinary collaborative culture, outstanding mentorship, and cutting-edge facilities. This will enable me to discover the fundamental mechanisms plant roots employ to sense water availability. The unwavering support of the host institution and network of leading scientists, combined with my expertise, will empower me to successfully execute this project and make a significant impact at the forefront of plant biology research. Additionally, this project will enable me to nurture a unique research vision and hone my leadership skills, equipping me to emerge as a future leader in the field of root-water interactions.