Analysis of membrane traffic in adaptive stress tolerance in plants

胁迫介导的适应是植物适应长期或反复环境挑战的关键因素，对气孔补偿长期水分亏缺期间的气体交换尤为重要。植物叶片表皮中的气孔在调节光合作用的CO2交换，同时最大限度地减少叶片内部空气和大气之间的蒸腾水分损失方面起着至关重要的作用。气孔周围的保卫细胞吸收无机离子和水，当叶片中的二氧化碳耗尽时，保卫细胞的体积增加以打开气孔孔；当叶片中的二氧化碳耗尽时，保卫细胞失去离子、其他溶质和水，体积减小以关闭气孔孔，并在胁迫、黑暗和二氧化碳含量较高时保存叶片水分。可以说，气孔处于水供应危机的中心，这场危机预计将在未来20-30年内展开。在过去100年里，全球用水量增长了6倍，是人口的两倍，预计在2040年前还会再翻一番，这主要是由灌溉和农业推动的。显然，充分了解保卫细胞和气孔调节将对今后提高农作物水分利用效率的努力产生重大影响，从而使社会能够面对这些未来的挑战。事实上，我们对保卫细胞的细胞和分子生理学知道很多，特别是与脱落酸(ABA)、盐分和干旱有关的信息，这些信息的深度和广度有助于将保卫细胞系统提升到最了解的植物细胞模型之一。然而，几乎所有这些知识都集中在保卫细胞的短期反应行为上。相比之下，我们对保卫细胞调节气孔运动以适应长期环境胁迫的机制知之甚少。最近，本实验室观察到ABA触发了一个质膜K+通道的内室流量，该通道介导保卫细胞中的离子流量。该响应显示了在自适应调制信道群中的功能所必需的所有特征。这是对第二个发现的补充，即拟南芥突变体Atsyp121在质膜上存在一个主要的小泡运输蛋白的缺陷，选择性地削弱气孔‘记住’最近的逆境历史并保持关闭的能力(所谓的‘程序化’气孔关闭)。这些发现将保卫细胞的膜泡转运与[Ca~(2+)]i信号传递和适应联系在一起，并提示质膜和内室之间的K~+通道运输是保卫细胞适应的重要机制。我建议使用实验室现有的细胞和分子工具直接解决这个问题。这一结果将极大地扩展我们对植物中ABA信号和适应的理解，并将从根本上增加我们对真核细胞中膜运输和离子通道控制的动力学的了解。

Stress-mediated adaptation is a key factor in the ability of plants to cope under long-term or repeated environmental challenge, and is especially important for stomata to compensate for gas exchange during extended periods of water deficit. Stomata in the epidermis of plant leaves play a vital role in regulating CO2 exchange for photosynthesis while minimising transpirational water loss between the inner leaf air space and the atmosphere. Guard cells surrounding the stomata take up inorganic ions and water, increasing in volume to open the stomatal pore when CO2 in the leaf is depleted; and they lose ions, other solutes and water, decreasing in volume to close the stomatal pore and conserve leaf water under stress, in the dark and when CO2 is high. Arguably, stomata are at the centre of a crisis in water availability that is expected to unfold over the next 20-30 years. Globally, water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2040, driven mainly by irrigation and agriculture. Clearly, a full understanding of guard cells and stomatal regulation will have significant implications for future efforts to improve the water use efficiency of agricultural crops and, consequently, for society to face these future challenges. In fact, we know a great deal about the cellular and molecular physiology of guard cells, especially in relation to abscisic acid (ABA), salinity and drought that triggrer stomata to close, and the depth and breadth of this information has helped to elevate the guard cell system to that of one of the best understood plant cell models. However, virtually all of this knowledge centres on the short-term responsive behaviour of guard cells. By contrast, our knowledge is remarkably poor of the mechanisms by which guard cells adjust stomatal movements to adapt to longer-term environmental stress. Recently, this laboratory observed that ABA triggers the traffic to an internal compartment of one of the plasma membrane K+ channels mediating ion fluxes in guard cells. This response shows all the hallmarks essential for a function in adaptive modulation of the channel population. It complements a second discovery that the Arabidopsis mutant Atsyp121, which is defective in a major vesicle trafficking protein at the plasma membrane, selectively impairs the ability of stomata to 'remember' the recent history of stress and remain closed (so-called 'progammed' stomatal closure). These discoveries firmly tie membrane vesicle trafficking to [Ca2+]i signalling and adaption in guard cells, and suggest that K+ channel traffic between the plasma membrane and the internal compartment is an important mechanism for adaptation in these cells. I propose to address this idea directly using cellular and molecular tools now available in the laboratory. The outcome will greatly extend our understanding of ABA signalling and adaptation in plants, and should add fundamentally to our knowledge of the dynamics of membrane traffic and ion channel control in eukaryotic cells generally.