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

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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.