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

气孔是指气孔的打开和关闭，以平衡光合作用所需的二氧化碳进入叶片的需要，以及通过蒸腾减少水分损失和防止叶片干燥的需要。气孔是水资源供应和作物生产危机的中心，预计将在未来20-30年内展开：在全球范围内，农业用水量在过去100年中增加了6倍，是人口增长速度的两倍，预计到2030年将再翻一番。因此，气孔是提高作物生产性能的重要目标，特别是在面对全球气候变化的情况下。气孔的开闭是由气孔周围保卫细胞的溶质和水分运输驱动的。我们对这些过程的深入了解使保护细胞成为最著名的植物细胞模型之一，并为工程气孔改善作物水分利用提供了真正的物质前景。相比之下，我们对表皮保护细胞周围的细胞知之甚少，有时被称为附属细胞。周围细胞中离子含量的变化最初导致了周围细胞和保护细胞之间溶质“穿梭”的想法。有人认为，周围细胞储存的溶质-特别是K+ -供保卫细胞在气孔打开时使用，通过释放这种溶质，它们也缓解了反对保卫细胞扩张的肿胀，促进气孔打开。因此，原则上，气孔复合体可以被认为是一个两细胞、两冲程的“泵”，用于在周围细胞和保护细胞之间转移溶质，从而加速气孔动力学。然而，到目前为止，还缺乏探测气孔复合体内细胞功能的工具。在自然环境中，光线是波动的，例如当云层经过时。大多数植物的气孔对光的响应方式是打开气孔以增加光合作用对CO2的获取，当光照强度下降，光合作用对CO2的需求下降时，气孔孔径减小。光合作用通常会跟踪光的波动，但气孔的反应要慢得多。当光强上升时，气孔反应较慢，限制了气体交换，减少了光合作用的碳同化；当光强迅速下降时，气孔反应较慢，导致蒸腾作用没有相应的同化。我们和其他人推断，如果气孔运动的速率能够更好地与光合作用需求的变化相匹配，那么同化和因此产生的生物量可以在植物用水量减少的同时增强。最近，我们发现通过引入光激活的K+通道BLINK1加速气孔保护细胞中的离子通量，足以使模式植物拟南芥的生物量增加2倍，并将相关的水分消耗减少2倍。这些发现证明了加速气孔形成作为一种提高作物产量同时节约水资源的策略的潜力。BLINK1等光遗传学工具提供的光控制也为探测气孔复合体中周围细胞的功能提供了一种手段，并有可能进一步增强气孔动力学。我们在这里提出了一个相互关联的努力来解决这个长期悬而未决的问题，即周围细胞是否以及如果是这样，如何参与气孔运动，并将气孔动力学的知识转化为两种模式作物的实际演示。我们将以BLINK1在拟南芥中的成功为基础。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认识，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.