An Open And Shut Case

Food security represents an increasing global issue particularly as climate change, which is causing rainfall patterns to become much more erratic, impacts rain-fed crops. Plant roots play a critical role to reduce the impact of transient water stress. For example, roots cease branching when they lose contact with moist soil employing a mechanism called Xerobranching. Discovering how roots respond to transient water stress is therefore of vital importance for agriculture and 'future proofing' crops.

This research project will investigate how Xerobranching works to ensure new root branches only form when there is water available. Our research project attempts to 'fill in the gaps' between roots sensing the loss of water availability and then ceasing branching. To help our studies, we have developed an entirely new way to image water moving between plant cells, which will be instrumental for understanding what happens when roots are exposed to water stress. We have also identified plant hormone signals such as abscisic acid and auxin are important for Xerobranching. Several promising processes will be characterised including one that opens and shuts pores between root cells to enable hormone signals to move and regulate root branching. The knowledge gained from this study will provide new information about the key genes and processes controlling root branching in response to water availability, helping scientists design novel approaches to manipulate root architecture to enhance resource capture and yield in crops.

Water stress is an increasing problem in agriculture, given the impact of climate change. Discovering how abiotic stress signals like abscisic acid (ABA) control plant adaptive responses to fluctuating water stress is vital for future-proofing crops. Our team recently discovered an ABA-regulated response to transient water stress called Xerobranching (Orman et al [2018] Curr Biol), where root branching ceases in response to fluctuating soil moisture. Preliminary results suggest that ABA regulates Xerobranching by closing inter-cellular pores, termed plasmodesmata (PD), in root cells - disrupting delivery of the branching signal auxin to lateral root 'stem cells'. To discover how ABA controls root responses to fluctuating water stress we propose to characterise key genes, signals and mechanisms underpinning Xerobranching exploiting novel bioassays, hormone reporters and a cell-scale Raman water-imaging technique (Pascut et al [2021] Nature Comms).

Our proposal seeks to build on these promising results and techniques to discover how roots respond to transient water stress by addressing 4 objectives: OBJ1 exploits Raman imaging to map hydraulic fluxes across root tissues exposed to Xerobranching stimulus. OBJ2 uses hormone and Raman imaging approaches to reveal whether ABA co-mobilises with water fluxes during Xerobranching responses. OBJ3 addresses if ABA triggers closure of inter-cellular pores termed plasmodesmata. Finally, OBJ4 will discover whether plasmodesmata closure disrupts movement of branching signal auxin, which is needed to 'prime' lateral root 'stem cells' in inner root tissues. The knowledge generated about the new signals, genes and their regulatory pathways will underpin on going efforts to re-engineer root systems architecture and future proof crops. The expertise, resources and tools that have been assembled for this project at Nottingham with our international collaborators uniquely position us to successfully complete this project.