Engineering ion flux of the stomatal complex for enhanced photosynthesis and water use efficiency

气孔是开闭以平衡CO2进入叶片进行光合作用的需要与通过蒸腾减少水分损失和防止叶片干燥的需要的孔。气孔是未来20-30年水资源和作物生产危机的核心：在过去100年中，全球农业用水量增加了6倍，是人口增长速度的两倍，预计在20-30年之前将再翻一番。因此，气孔是努力提高作物性能的重要目标，特别是在全球气候变化的情况下。气孔开闭是由气孔周围保卫细胞的溶质和水分运输所驱动的。我们对这些过程的深入了解使保卫细胞成为最著名的植物细胞模型之一，并为设计气孔以改善作物水分利用的前景提供了真实的物质。相比之下，我们对表皮保卫细胞附近的周围细胞（有时称为附属细胞）知之甚少。周围细胞中离子含量的变化最初导致了溶质在周围细胞和保卫细胞之间“穿梭”的想法。有人认为，周围的细胞储存溶质-特别是K+ -用于保卫细胞在气孔开放过程中，并通过释放这种溶质，他们也缓解了膨压，反对保卫细胞扩张，促进气孔开放。因此，在原则上气孔复合体可以被认为是一个两细胞，两冲程的“泵”周围和保卫细胞之间的溶质转移，从而加速气孔动力学。然而，到目前为止，还缺乏研究气孔复合体中细胞功能的工具。在自然环境中，光线会发生波动，例如当云层经过时。大多数植物的气孔对光照的反应是通过打开气孔来增加光合作用的CO2进入，当光照强度下降和光合作用对CO2的需求下降时，气孔孔径会减小。光合作用通常跟踪光的波动，但气孔的反应要慢得多。当光照强度上升时，气孔响应较慢，限制了气体交换，减少了光合作用对碳的同化;当光照强度迅速下降时，气孔响应较慢，导致蒸腾作用而没有相应的同化作用。我们和其他人认为，如果气孔运动的速率能够更好地与光合需求的变化相匹配，同化作用和生物量的产生可以在植物水分利用减少的同时得到增强。最近，我们发现，通过引入光激活的K+通道BLINK 1，足以在模式植物拟南芥中增加生物量并将相关的用水量减少2倍。这些研究结果表明，加速气孔作为一种策略，以提高作物收益，同时保持水分的潜力。由光遗传学工具如BLINK 1提供的光控制也提供了一种手段来探测气孔复合体中周围细胞的功能，并可能进一步增强气孔动力学。如何周围的细胞参与气孔运动和翻译知识的气孔动力学在一个实际的示范与两个模式作物。我们将基于BLINK 1在拟南芥中的成功来实现这些目的。我们的总体目标是扩大迄今为止在拟南芥中取得的成果，通过对气孔复合体中周围细胞功能的新知识，作为提高作物产量和减少农业用水量的策略。

Stomata are pores that open and close to balance the requirement for CO2 entry to the leaf for photosynthesis against the need to reduce water loss via transpiration and prevent leaf drying. Stomata are at the centre of a crisis in water availability and crop production that is expected to unfold over the next 20-30 years: globally, agricultural water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is projected to double again before 2030. Thus stomata are an important target in efforts to improve crop performance, especially in the face of global climate change. Stomatal opening and closing are driven by solute and water transport of the guard cells which surround the stomatal pore. Our deep knowledge of these processes has made the guard cell one of the best-known plant cell models and gives real substance to prospects for engineering stomata to improve water use by crops.By contrast, we know very little of the surrounding cells, sometimes called subsidiary cells, adjacent the guard cells in the epidermis. Changes in the ion contents of surrounding cells originally led to the idea of a 'shuttling' of solute between surrounding and guard cells. It has been argued that the surrounding cells store solute - notably K+ - for use by the guard cells during stomatal opening and, by releasing this solute, they also relieve the turgor that opposes the guard cell expansion to promote stomatal opening. Thus, in principle the stomatal complex may be considered a two-cell, two-stroke 'pump' for solute transfer between surrounding and guard cells, thereby accelerating stomatal kinetics. Until now, however, tools to probe cellular function within the stomatal complex have been lacking.In the natural environment light fluctuates, for example as clouds pass over. The stomata of most plants respond to light by opening the stomatal pore to increase CO2 access for photosynthesis, and they reduce the pore aperture when the light intensity drops and the demand for CO2 by photosynthesis declines. Photosynthesis generally tracks light fluctuations, but stomata are much slower to respond. The slower response of stomata can limit gas exchange and reduce carbon assimilation by photosynthesis when light intensity rises, and it can lead to transpiration without corresponding assimilation when light intensity drops quickly. We and others have reasoned that assimilation, and consequently biomass generation, could be enhanced concurrent with an decrease in water use by the plant if the rates of stomatal movements could be better matched to variations in photosynthetic demand.Recently, we found that accelerating ion flux in stomatal guard cells by introducing a light-activated K+ channel, BLINK1, was sufficient to increase the biomass and reduce the associated water use by 2-fold in the model plant Arabidopsis. These findings demonstrate the potential of accelerating stomata as a strategy to enhance crop gains while conserving water. The photocontrol offered by optogenetic tools such as BLINK1 also offers a means to probing the function of surrounding cells in the stomatal complex and, potentially, to further enhancing stomatal kinetics.We propose here an interlinked effort to address this long-outstanding question of whether and, if so, how surrounding cells participate in stomatal movements and to translate the knowledge of stomatal kinetics in a practical demonstration with two model crops. We will build on the success with BLINK1 in Arabidopsis for these purposes. Our overarching aim is to extend the gains achieved to date in Arabidopsis, informed by new knowledge of surrounding cell function in the stomatal complex, as strategies for enhancing crop yields and reducing agricultural water consumption.