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

气候变化导致土壤水分供应下降，这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的有效性对于提高作物的气候适应性至关重要。这一雄心勃勃的目标可以通过深入研究根系-土壤水分感应的机制来实现。值得注意的是，传统的关于根-水相互作用的研究主要集中在全植物水平上，而忽略了许多局部发生在个体根尖上的水分感知过程。为了解决这一知识鸿沟，我最近开发了一种优雅的生物测定方法来研究个体根尖对瞬时水分胁迫的反应。这种生物测定使我能够发现“为什么根在土壤气隙中停止分枝”的机制基础，这种现象被称为“旱作”(Mehra等人，2022年科学)[1]。当生长中的根尖失去与土壤水分的接触时，例如在气隙中，就会触发旱作反应，导致分枝受到抑制，直到根尖重新进入潮湿的土壤。最近，我发现旱作利用水分胁迫激素脱落酸(ABA)来阻止根的分枝。ABA驱动的下游反应在干旱刺激后几个小时被触发。这一缓慢的时间框架令人费解，因为植物的根通常会迅速检测到水分不足，这表明ABA介导的分枝抑制是一种“反应机制”，而不是一种主要的“水分感应机制”。因此，根必须首先感知外部水分的变化，然后才能触发下游ABA调节的反应。作为发现号的一名成员，我的目标是揭示和描述干旱胁迫过程中涉及到的早期分子事件。离子通量(如钙离子和钾离子)与水分胁迫信号的早期阶段密切相关。我用拟南芥钙信号突变体进行的初步实验表明，离子信号在干燥过程中起着明显的作用。在这些发现的基础上，我的目标是通过使用干旱生物测定筛选拟南芥离子通道/信号突变体，来研究离子通量在水分感知中的功能意义(目标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分感知生态位(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揭示涉及水感知和响应的新组件。接下来，我将研究离子通量如何在旱作过程中触发ABA的生物合成/释放(目标3)。最后，目标4将使用创新的基于拉曼的根部‘水成像’来确定离子信号和水力通量之间的功能关系。我的研究产生的基本见解将加强对根系如何感知和应对细胞级水分供应减少的理解，为未来旨在提高作物水分利用效率和抗旱性的转化努力奠定坚实的基础。利用诺丁汉大学(UON)的这项开创性研究，我将有机会利用世界级的研究环境，提供无与伦比的专业知识、跨学科的协作文化、卓越的指导和尖端设施。这将使我能够发现植物根部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不移的支持，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，这个项目将使我能够培养独特的研究视野和磨练我的领导技能，使我成为根-水相互作用领域的未来领导者。

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.