ABA-dependent control of plant hydraulics in acclimation to water deficit

水在陆地生态系统中起着至关重要的作用，植物是水循环的主要因素。通过控制从土壤到大气的水通量，植物蒸腾是陆地气候和碳循环的关键。除了其一般的生态重要性外，水的可获得性也是提高田间植物生产力的主要制约因素。当受到水分限制时，植物通过协调蒸腾作用和根系介导的水分吸收来维持其水分状况。这会导致气体交换的改变，从而提高叶片的水分利用效率。这是如何实现的，人们只是粗略地了解。看来，植物对水分限制的反应涉及到根和地上部之间的快速水力对话，而这种对话本身依赖于植物的基本生理机制。植物体内的水分通量由导水的水孔蛋白通道促进，水分利用效率和植物的气体交换受胁迫激素脱落酸(ABA)的控制，ABA是调节植物对干旱反应的关键因素。协调水分平衡需要细胞和植物器官不同的ABA敏感性和不同的ABA信号反应，超出这些原理的植物远距离协调水分平衡一直是一个挑战。在过去的十年里，这一领域的进展非常缓慢，因为在定义分子机制和在植物中测试它们方面存在实验上的困难。在ABA信号和植物水力控制领域的最新进展的推动下，法国和德国的联合研究团队感觉处于一个极好的地位，可以在这个谜团上实现突破。拟议的ABAqua项目将利用并产生对ABA信号通路和水孔蛋白调节的第一线理解，以阐明水分动态平衡是如何通过根和叶之间的沟通实现的。该项目的一个重点是回答ABA对根和保卫细胞水力的不同激素敏感性和作用是如何实现的，并传递给水传导水孔蛋白。针对水通道蛋白的原型ABA信号模块的详细分子分析将与磷蛋白质组学和拟南芥中非调控信号组件的表达相结合。全植物水平的分析将包括嫁接实验和ABA信号和水通道蛋白突变体的组织特异性互补。这些分析将揭示水分充足和干旱条件下植物体内关键的水力调节机制及其对气体交换的影响。植物水分动态平衡的新原理，影响气体交换和相应的水分利用变化，将为改进水分限制下的碳循环和植物生产力的预测提供机制基础。

Water plays a crucial role in terrestrial ecosystems with plants acting as a major factor in water cycling. By dominating the water flux from the soil to atmosphere, plant transpiration is key for terrestrial climate and carbon cycling. Besides its general ecological importance, water availability is the major constraint for higher plant productivity in the field. When subjected to water limitation, plants homeostase their water status by coordinating transpiration with root-mediated water uptake. This leads to altered gas exchange and can result in improved leaf water use efficiency. How this is achieved is only rudimentarily understood. It appears that the plant response to water limitation involves a rapid hydraulic dialog between roots and shoots which itself relies on fundamental plant physiological mechanisms. Water flux within the plant is facilitated by water-conducting aquaporin channels and water use efficiency as well as plant’s gas exchange are governed by the stress hormone abscisic acid (ABA) which is the key factor in adjusting plant responses to drought. Different ABA sensitivities and distinct ABA signalling responses of cells and plant organs are required for coordinated water homeostasis.Understanding the long distance-coordinated water homeostasis of plants beyond these principles has been a challenge. Progress in this field has been very slow over the last decade because of the experimental difficulties in defining molecular mechanisms and to test them in plants. Initiated by recent advances in the field of ABA signaling and the control of plant hydraulics, the joint French-German research team feels to be in an excellent position to achieve a breakthrough on this enigma. The proposed ABAqua project will use and generate frontline understanding of ABA signalling pathways and aquaporin regulation to elucidate how water homeostasis is achieved through communication between roots and leaves. An emphasis of the project is to answer how the different hormone sensitivities and actions of ABA on root and guard cell hydraulics are realized and relayed to water-conducting aquaporins. Detailed molecular analysis of prototypic ABA signaling modules targeting aquaporins will be employed in combination with phosphoproteomics and expression of deregulated signaling components in Arabidopsis. Analyses at the whole-plant level will include grafting experiments and tissue-specific complementation of ABA signaling and aquaporin mutants. These analyses will reveal the key hydraulic regulatory mechanisms and their impact on gas exchange in plants under well-watered condition and drought. The emerging principles of plant’s water homeostasis, affecting gas exchange and concomitant changes in water use, will provide a mechanistic basis for improved prediction of carbon cycling and plant productivity under water limitation.