Sounding the all clear: investigating how and why plant cells deplete the stress hormone ABA

点击翻译按钮获取中文摘要

Drought stress is a major environmental stress that impairs crop production worldwide, but tolerance to drought and other stresses is a plant trait that varies greatly among cultivars and crop species. Tolerance of a plant to a stress condition is the result of coordinated action of many processes and thus rational improvement of crop stress tolerance will require a detailed and sophisticated understanding of plant stress biology. The plant hormone abscisic acid (ABA) plays a key role in controlling responses to environmental stress conditions like drought stress. ABA is also an important regulator in plant growth and development regulating processes such as seed dormancy and root growth. Plants have to adjust ABA levels constantly in order to match physiology and development to ever changing environmental conditions. It is known that ABA accumulated in cells during a stress condition is a temporary event that is followed by ABA depletion, maintaining a tight temporal regulation of ABA responses. Although three biochemical activities - breakdown, conversion to a storage form, and export from the cell - are known to lower cellular ABA levels, a quantitative understanding of how these combine to determine ABA depletion rates in plant cells remains elusive. A deeper understanding of these mechanisms and how they are controlled is important in improving the ability of crop plants to tune their development to suit their environment.The proposed research project aims to uncover dynamic ABA patterns in root cells and to understand how these dynamic patterns relate to ABA-dependent root development. The knowledge will be expanded to identify the mechanisms determining how root development responds to environmental nitrate availability. Biosensors that report concentrations of ABA by directly binding to ABA in cells have been used to measure dynamic ABA patterns in Arabidopsis thaliana, a reference plant for molecular biology research. Using time-course, microscopic imaging of growing Arabidopsis roots expressing ABA concentration and uptake sensors (ABACUS), we have already observed that ABA depletion rates vary in space and time. We now aim to understand how several biochemical activities combine to articulate ABA levels into dynamic patterns appropriate for a given environmental condition. Spatial and temporal depletion of ABA will be studied in detail using Arabidopsis mutants that are affected in ABA depletion activities, thus revealing the impact of each activity on ABA depletion rates. Root growth phenotypes of these mutants will be examined concurrently with ABA levels. Linking the maps of ABA depletion rates to corresponding root growth phenotypes will provide detailed hypotheses regarding how ABA impacts plant development. For example, ABA is thought to play a role in attuning root architecture to the levels of nitrate in the environment. Imaging ABACUS in root cells responding to nitrate availability will be carried out to pinpoint the specific cell-type and timing of ABA accumulations that control root nitrate responses. This type of detailed knowledge can then guide targeted interventions into crop plants to improve agricultural resilience to environmental stress. Another main objective of the project is to engineer next generation ABACUS sensors for improved high sensitivity visualisation of ABA dynamic patterning in roots and other plant tissues. In addition, a new biosensor - Sensor of Abscisic Acid-Glucose Ester (SAGE) - will be developed as a powerful tool to address the question of where and when ABA-glucose ester pools, inactive 'storage' forms of ABA, are important in development and environmental responses. Broadening the knowledge of spatio-temporal patterning of ABA will be important in understanding the mechanisms underlying physiological and developmental adjustments during environmental stresses that can prevent significant crop losses.