Stomatal-based systems analysis of water use efficiency

气孔是在植物叶片的不渗透角质层上提供气体交换的孔。它们打开和关闭以平衡光合作用对CO2进入的需求，以及减少水蒸气蒸腾和防止叶片干燥的需求。气孔蒸腾作用是水供应和作物生产危机的核心，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，预计在20 - 30年之前将再翻一番。因此，气孔是育种者在操纵作物性能方面的一个重要目标。气孔运动是由溶质运输-和随后的水的吸收/损失-穿过气孔周围的保卫细胞的细胞膜驱动的。值得注意的是，气孔的反应是缓慢的光合作用相比，在面对环境波动，特别是光。提高水分利用效率（=光合作用中固定的碳量/蒸腾的水量）应该是可能的，而不需要光合作用中同化的碳的成本，如果气孔响应的速度，特别是对光的响应，可以提高。然而，保卫细胞运输及其耦合到气体交换和蒸腾作用的复杂性，提出了一个强大的障碍，系统的逆向工程，旨在提高气孔响应通过遗传操作和其他measure.Quantitative系统分析提供了一个有效的途径，在silico探索微观基因功能和同化和蒸腾作用的宏观特征之间的联系。作为弥合这一理解差距的第一步，我们以前开发了OnGuard软件，用于对保卫细胞进行定量动态建模。OnGuard模型明确地建立在大量的分子、生物物理和动力学知识的基础上，这些知识涉及保卫细胞的运输和代谢，这些运输和代谢驱动气孔运动;它们适应不同植物物种的气孔，涵盖了迄今为止在实验室研究的各种条件;而且它们已经被证明具有真实的预测能力，可以指导细胞和生理水平的实验，这些实验从分子操作开始，silico。基于我们对气孔保卫细胞的深入了解，建立作物设计的计算机策略的下一个主要步骤将是建立和验证这种计算链接，以将叶片和整株水平的碳同化和水分利用效率结合起来。我们现在建议在叶片模型中开发这样的策略，并扩展到田间作物，捕获CO2吸收和蒸腾。我们将构建下一代OnGuard模型，其中包括CO2吸收和蒸腾，我们将采用计算统计方法来加速模型构建。最重要的是，这些模型将提供必要的微观-宏观联系，将分子功能与整个植物在水分利用和光合碳同化方面的生理特性联系起来，并将能够扩展到田间作物。我们将测试第二代OnGuard模型，并验证其输出，以检验长期存在的假设，即由于气孔和光合作用之间的动态环境响应不匹配，导致植物水分利用效率显著降低。此外，我们将探讨这些性状与已知发生在气孔孔径和信号事件（如cytosolic-free [Ca 2 +]）先前记录在细胞水平在单个保卫细胞的振荡的连接。所有的研究将集中在作物植物野豌豆，有很多数据在单细胞和全叶水平，和拟南芥，我们有明确的气孔动力学的影响突变体。

Stomata are pores that provide for gaseous exchange across the impermeable cuticle of plant leaves. They open and close to balance the requirement for CO2 entry for photosynthesis against the need to reduce the transpiration of water vapour and prevent leaf drying. Stomatal transpiration is 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 represent an important target for breeders interested in manipulating crop performance. Stomatal movements are driven by solute transport - and consequent uptake/loss of water - across the cell membrane of the guard cells which surround the stomatal pore. Significantly, stomatal responses are slow compared to photosynthesis in the face of environmental fluctuations, especially of light. Improving water use efficiency (=amount of carbon fixed in photosynthesis/amount of water transpired) should be possible, without a cost to carbon assimilated in photosynthesis, if the speed of stomatal responses, especially to light, can be enhanced. However, the complexity of guard cell transport and its coupling to gas exchange and transpiration has presented a formidable barrier to systematic reverse-engineering aimed at enhancing stomatal responses through genetic manipulation and other means.Quantitative systems analysis offers an effective approach in silico to exploring the link between microscopic gene function and the macroscopic characteristics of assimilation and transpiration. As a first step to bridging this gap in understanding, we developed previously the OnGuard software for quantitative dynamic modelling of the guard cell. OnGuard models build explicitly on the wealth of molecular, biophysical and kinetic knowledge for guard cell transport and metabolism that drive stomatal movement; they accommodate stomata of different plant species, over the full range of conditions studied in the laboratory to date; and they have been shown to incorporate the real predictive power needed to guide experiments at the cellular and physiological levels that start with molecular manipulations in silico. The next major step towards establishing in silico strategies for crop design, based on our deep knowledge of stomatal guard cells, will be to establish and validate this computational link to incorporate carbon assimilation and water use efficiency at leaf and whole-plant levels.We propose now to develop such a strategy in models of the leaf, and scaling to the crop in the field, that capture CO2 uptake and transpiration. We will build the next-generation OnGuard models that incorporate CO2 uptake and transpiration, and we will incorporate computational statistical methods to accelerate model construction. Most important, the models will provide the essential micro-macro link to connect molecular function with physiological traits of the whole plant in water use and photosynthetic carbon assimilation and will enable scaling to the crop in the field. We will test this second generation of OnGuard models and validate their outputs to examine the longstanding hypothesis that significant erosion in the efficiency of water use by plants arises because of the mismatch in dynamic environmental responses between stomata and photosynthesis. Additionally, we will explore the connection of these traits with oscillations known to occur in stomatal aperture and in the signalling events (e.g. cytosolic-free [Ca2+]) previously documented at the cellular level in single guard cells. All studies will focus on the crop plant Vicia for which there is much data at the single-cell and whole-leaf levels, and on Arabidopsis for which we have mutants with well-defined effects on stomatal kinetics.