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

干旱胁迫是影响全球作物产量的主要环境胁迫，但对干旱和其他胁迫的耐受性是一种植物性状，在栽培品种和作物物种之间差异很大。植物对胁迫条件的耐受性是许多过程协调作用的结果，因此合理提高作物胁迫耐受性将需要对植物胁迫生物学的详细和复杂的理解。植物激素脱落酸（阿坝）在控制对干旱胁迫等环境胁迫条件的反应方面发挥着关键作用。阿坝也是植物种子休眠、根系生长等生长发育过程中的重要调节因子。植物必须不断调整阿坝水平，以使生理和发育适应不断变化的环境条件。已知在胁迫条件下细胞中积累的阿坝是一个暂时的事件，随后是阿坝耗竭，维持阿坝反应的严格时间调节。虽然已知三种生物化学活动--分解、转化为储存形式和从细胞中输出--会降低细胞阿坝水平，但对这些联合收割机如何结合以确定植物细胞中阿坝消耗速率的定量理解仍然是难以捉摸的。深入了解这些机制以及它们是如何被控制的，对于提高作物植物调整其发育以适应其环境的能力非常重要。拟议的研究项目旨在揭示根细胞中阿坝模式，并了解这些动态模式与ABA依赖的根发育的关系。知识将扩大，以确定机制，确定如何根的发展对环境硝酸盐的可用性。通过直接结合细胞中的阿坝来报告阿坝浓度的生物传感器已被用于测量分子生物学研究的参考植物拟南芥（Arabidopsis thaliana）中的动态阿坝模式。使用时程，表达阿坝浓度和吸收传感器（ABACUS）的拟南芥根生长的显微成像，我们已经观察到，阿坝消耗率在空间和时间上的变化。我们现在的目标是了解如何几个生化活动联合收割机阐明阿坝水平到动态模式适合于给定的环境条件。阿坝的时空消耗将使用拟南芥突变体的阿坝消耗活动的影响进行详细研究，从而揭示每个活动对阿坝消耗率的影响。这些突变体的根生长表型将与阿坝水平同时进行检查。将阿坝耗竭率的地图与相应的根生长表型联系起来，将提供关于阿坝如何影响植物发育的详细假设。例如，阿坝被认为在调节根结构以适应环境中的硝酸盐水平方面发挥作用。成像ABACUS根细胞响应硝酸盐的可用性将进行精确定位的特定细胞类型和阿坝积累的时间，控制根硝酸盐的反应。这种详细的知识可以指导对作物进行有针对性的干预，以提高农业对环境压力的适应能力。该项目的另一个主要目标是设计下一代ABACUS传感器，以提高根系和其他植物组织中阿坝动态模式的高灵敏度可视化。此外，一种新的生物传感器-脱落酸-葡萄糖酯传感器（SAGE）-将被开发为一个强大的工具，以解决何时何地ABA-葡萄糖酯池，阿坝的非活性“存储”形式，在发展和环境响应中很重要的问题。扩大阿坝的时空模式的知识将是重要的，在理解生理和发育的调整机制，在环境压力下，可以防止显着的作物损失。

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.