Molecular Mechanisms of CO2 Signal Transduction in Plants

植物的叶表面有许多小开口或气孔(称为气孔)，植物通过这些气孔控制与大气的气体交换。植物也是通过气孔失去水蒸气的；超过95%的植物水分损失是通过气孔孔的蒸腾作用发生的。气孔孔是由一对保卫细胞形成的，它们(通过改变形状)控制气孔的大小，从而同时控制叶片失水的速度和大气中二氧化碳的扩散，这是光合作用和最终生长所需的。植物叶片中的二氧化碳水平在白天有很大的变化，这是由光合作用和呼吸作用引起的。从长远来看，大气中的二氧化碳水平正在上升；目前，二氧化碳水平比工业革命前高出40%，预计本世纪将翻一番。该项目将确定和描述植物感知二氧化碳水平的机制，并利用这一机制1)调节气孔的大小，2)控制叶片发育过程中形成的气孔孔的数量。气孔孔在同时控制二氧化碳交换和植物水分损失方面的作用，使它们在植物对大气二氧化碳持续增加和温度、干旱及其相关胁迫模式变化的反应中发挥核心作用。然而，对于介导二氧化碳控制气孔功能的细胞、分子、遗传和生物物理信号机制知之甚少。识别控制气孔开度和发育的分子网络，了解植物的生理功能，将有助于预测大气二氧化碳水平上升对植物的影响，并有助于未来作物工程，帮助避免叶片的热胁迫，提高叶片的水分利用效率。除了培训研究生和博士后研究员外，该项目还将为圣地亚哥普赖斯特许学校在科学和技术方面代表性不足的弱势群体的学生提供公开宣传和研究经验的机会。一系列信号转导机制感知和转导二氧化碳浓度的变化，从而调节植物的气孔运动和气孔发育，从而优化二氧化碳的内流、水分损失、避热和植物在胁迫下的生长。实现对二氧化碳刺激如何传递到气孔导度调节网络的机械性分子生物物理理解是本研究的长期目标。强健的二氧化碳信号突变体已经被确定，并对其作用机制进行了表征。然而，预测的细胞内碳酸氢盐传感器仍然未知。此外，该项目的最新进展表明，碳酸酐酶在通过提高二氧化碳水平抑制气孔发育方面发挥了关键作用，从而产生了一个二氧化碳输入气孔发育机制的模型。该项目将通过识别在二氧化碳诱导的气孔关闭中起作用的保卫细胞中的碳酸氢盐感知和信号机制来研究新的工作假说。利用异源表达系统对二氧化碳/碳酸氢盐信号进行功能性多组分重组，将被用来鉴定介导二氧化碳/碳酸氢盐反应的碳酸氢盐激活蛋白。该项目将探讨保卫细胞中光合作用对二氧化碳控制气孔运动的作用，以及保卫细胞/叶肉细胞淀粉代谢在二氧化碳控制气孔运动中的作用。将对系统水平细胞壁蛋白质组分析中新发现的CRSP蛋白水解酶和CRSP同源物的功能进行表征，并将使用数学模型和模型驱动的实验来确定二氧化碳调节气孔发育的新机制。二氧化碳对气孔导度的调节也将利用实验室最近开发的基因组规模的新的人工microRNA文库来研究。

Plants have many small openings or pores (termed stomata) on the surface of their leaves, by means of which plants control the exchange of gases with the atmosphere. It is through the stomata that plants also lose water vapor; over 95% of plant water loss occurs by transpiration from stomatal pores. Stomatal pores are formed by a pair of guard cells that (by changing shape) control the size of the pore and thereby simultaneously control the rate of water loss from the leaf and the diffusion into the leaf of carbon dioxide from the atmosphere needed for photosynthesis and ultimately growth. There are large changes in the levels of carbon dioxide in the leaves of plants during the day, caused by photosynthesis and respiration. In the longer term, atmospheric carbon dioxide levels are increasing; presently they are 40% higher than before the industrial revolution and are predicted to double during this century. This project will identify and characterize the mechanisms by which plants sense the level of carbon dioxide and use this 1) to regulate the size of the stomatal apertures and 2) to control the number of stomatal pores that form during leaf development. The role of the stomatal pores in simultaneously controlling carbon dioxide exchange and the loss of water from the plant place them in a role central to the response of plants to the continuing increase in atmospheric carbon dioxide and changing patterns of temperature, drought and their associated stresses. However, relatively little is known about the cellular, molecular, genetic and biophysical signaling mechanisms that mediate carbon dioxide control of stomatal function. Identification of the molecular network that controls stomatal aperture and development and understanding physiological function will help predict the effects of rising atmospheric carbon dioxide levels on plants and can contribute to future engineering of crop plants to help avoid heat stress of leaves and enhance their efficiency of water use. In addition to training of graduate students and postdoctoral fellows, the project will provide opportunities for public outreach and research experiences for students from disadvantaged groups underrepresented in science and technology from the Preuss Charter School in San Diego. A network of signal transduction mechanisms sense and transduce changes in carbon dioxide concentrations to regulate both stomatal movements and stomatal development in plants, thereby optimizing carbon dioxide influx, water loss, heat avoidance and plant growth under stress. Achieving a mechanistic molecular biophysical understanding of how the carbon dioxide stimulus is transmitted into the stomatal conductance regulation network is the long-term goal of this research. Robust carbon dioxide signaling mutants have been identified and their mechanisms of action characterized. However, the predicted intracellular bicarbonate sensors remain unknown. Furthermore, recent advances in this project have shown a key role of carbonic anhydrases in the repression of stomatal development by elevated carbon dioxide levels, leading to a model for carbon dioxide input into the stomatal development machinery. This project will investigate new working hypotheses by identifying bicarbonate sensing and signaling mechanisms in guard cells that function in carbon dioxide-induced stomatal closing. Functional multi-component reconstitution of carbon dioxide/bicarbonate signaling using heterologous expression systems will be used to identify the bicarbonate-activated proteins that mediate the carbon dioxide/bicarbonate response. The project will address the function of photosynthesis in guard cells for carbon dioxide control of stomatal movements and the functions of guard/mesophyll cell starch metabolism in carbon dioxide control of stomatal movements. The functions of the newly identified CRSP protease and CRSP homologs identified in a systems level cell wall proteome analysis will be characterized, and a mathematical model and model-driven experiments will be used to identify new mechanisms that function in carbon dioxide regulation of stomatal development. The carbon dioxide regulation of stomatal conductance will also be investigated using a genomic scale new artificial microRNA library recently developed in the laboratory.