Resolving CO2 regulation of the SLAC1 Cl- channel in guard cell ion transport and photosynthetic carbon assimilation

解决保卫细胞离子传输和光合碳同化中 SLAC1 Cl-通道的 CO2 调节

• 批准号: BB/W001217/1
• 负责人: Michael Blatt
• 金额: $ 80.18万
• 依托单位: University of Glasgow
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FW001217%2F1
• 关键词: Resolving; CO2; regulation; SLAC1; Cl

Stomata are pores that open and close to protect against leaf drying while enabling CO2 entry into the leaf for photosynthesis. They can limit photosynthesis by 50% or more when demand exceeds water supply and they exert a major control on water and carbon cycles of the world. Stomata are at the centre of a crisis in fresh water availability and crop production that is expected over the next 20-30 years. Global agricultural water usage has increased 6-fold in the past 100 years, twice as fast as the human population; even in the UK irrigation has expanded 10-fold in the past 30 years. The droughts of 2010-12 and 2018 cost UK farmers alone an estimated £1.2B and worldwide costs year-by-year are estimated in the hundreds of billions of pounds over the past five years.Stomata in most plants track the immediate demand for CO2 by photosynthesis in the leaf, opening in the light and closing in the dark. However, stomatal responses are slow by comparison with that of photosynthesis. Natural fluctuations in daylight, for example as clouds pass overhead, degrade photosynthetic carbon assimilation and water use efficiencies, principally because stomatal responses generally lag behind changes in light. We know that substantial gains in carbon assimilation and water use efficiencies are possible by accelerating stomatal movements, but we need to understand how CO2 affects guard cell mechanics and its integration with mesophyll-derived changes in CO2 in order to inform efforts in engineering stomatal kinetics.Guard cell transport is integral to controlling stomatal aperture. Guard cells surround the stomatal pore and respond to an array of extracellular signals, including light and CO2, to regulate stomatal aperture. Guard cells coordinate changes in the activities of a number of transporters, notably of ion channels that facilitate K+ and Cl- ion fluxes, and they remodel the cell membrane. Both the changes ion flux and membrane remodelling are needed for stomatal movements. Nonetheless, the challenge remains to understand how these changes arise and are coordinated, especially by CO2.We have discovered that the dominant Cl- channel, SLAC1, binds selectively within a multi-protein complex that incorporates a so-called SNARE protein, SYP121, that is vital for remodelling of the cell membrane, and with the carbonic anhydrase beta-CA4. The carbonic anhydrase is one of a small number of proteins known in the guard cells that bind with, and hence are capable of responding to CO2 directly. SYP121 also binds a subset of K+ channels to co-regulate K+ ion flux with membrane remodelling during stomatal movements. We find now that the assembly of SYP121 with beta-CA4 and SLAC1 confers a strong dependence of the Cl- channel on near-ambient changes in CO2.These are precisely the characteristics expected for the long-sought mechanism of CO2-mediated enhancement in Cl- flux and stomatal movements. They point to the multi-protein complex in coordinating Cl- as well as K+ flux with membrane remodelling and in conferring a CO2 sensitivity directly on these events. We propose here to resolve the mechanics of beta-CA4-SYP121-SLAC1 interactions in order to understand how CO2 regulates these events for stomatal closure. Thus, our primary goal is to develop a quantitative understanding of the mechanics of this novel SLAC1 supercomplex and the coordinate regulation it confers on the physiology of CO2 responses in guard cells. Among others, we want to resolve the key protein domains for binding of SYP121 with beta-CA4 and SLAC1, their impact on CA and SLAC1 activities, and their contributions to the CO2-dependence of SLAC1. The research proposed is for fundamental knowledge. It nonetheless holds longer-term relevance for crop improvement with benefits for producers, consumers, and the environment.

气孔是打开和关闭的毛孔，以防止叶子干燥，同时使二氧化碳进入叶子进行光合作用。当需求超过供水时，它们可以将光合作用限制 50% 或更多，并对世界的水和碳循环发挥重要控制作用。气孔是未来 20-30 年淡水供应和农作物生产危机的核心。过去 100 年来，全球农业用水量增加了 6 倍，是人口增长速度的两倍；即使在英国，过去 30 年灌溉面积也扩大了 10 倍。 2010-12 年和 2018 年的干旱估计仅英国农民就损失了 1.2 英镑，过去五年中全球每年的损失估计达数千亿英镑。大多数植物中的气孔通过叶子中的光合作用跟踪对二氧化碳的即时需求，在光照下打开并在黑暗中关闭。然而，与光合作用相比，气孔反应较慢。日光的自然波动，例如当云从头顶掠过时，会降低光合作用的碳同化和水的利用效率，这主要是因为气孔反应通常滞后于光线的变化。我们知道，通过加速气孔运动可以大幅提高碳同化和水利用效率，但我们需要了解二氧化碳如何影响保卫细胞力学及其与叶肉衍生的二氧化碳变化的整合，以便为工程气孔动力学工作提供信息。保卫细胞运输对于控制气孔孔径至关重要。保卫细胞围绕气孔，对一系列细胞外信号（包括光和二氧化碳）做出反应，以调节气孔孔径。保卫细胞协调许多转运蛋白（尤其是促进 K+ 和 Cl- 离子通量的离子通道）活动的变化，并重塑细胞膜。气孔运动需要离子通量的变化和膜重塑。尽管如此，理解这些变化是如何产生和协调的仍然是一个挑战，特别是通过 CO2。我们发现，主要的 Cl 通道 SLAC1 选择性地结合在一个多蛋白复合物中，该复合物包含所谓的 SNARE 蛋白 SYP121，该蛋白对于细胞膜的重塑至关重要，并与碳酸酐酶 beta-CA4 结合。碳酸酐酶是保卫细胞中已知的少数蛋白质之一，它与二氧化碳结合，因此能够直接响应二氧化碳。 SYP121 还结合 K+ 通道的子集，以在气孔运动期间共同调节 K+ 离子通量和膜重塑。我们现在发现SYP121与β-CA4和SLAC1的组装赋予了Cl-通道对近环境CO2变化的强烈依赖性。这些正是长期寻找的CO2介导的Cl-通量和气孔运动增强机制所预期的特征。他们指出多蛋白复合物可以协调 Cl- 和 K+ 通量与膜重塑，并直接赋予这些事件 CO2 敏感性。我们在此建议解决 beta-CA4-SYP121-SLAC1 相互作用的机制，以便了解 CO2 如何调节这些气孔关闭事件。因此，我们的主要目标是定量了解这种新型 SLAC1 超级复合物的机制及其对保卫细胞中 CO2 反应生理学的协调调节。其中，我们希望解决 SYP121 与 beta-CA4 和 SLAC1 结合的关键蛋白结构域、它们对 CA 和 SLAC1 活性的影响，以及它们对 SLAC1 的 CO2 依赖性的贡献。所提出的研究是针对基础知识的。尽管如此，它对作物改良具有长期意义，对生产者、消费者和环境都有好处。

项目成果

Engineering stomata for enhanced carbon capture and water-use efficiency.

• DOI: 10.1016/j.tplants.2023.06.002
• 发表时间: 2023-07
• 期刊: Trends in plant science
• 影响因子: 20.5
• 作者: Thu Binh-Ahn Nguyen;Cécile Lefoulon;T. Nguyen;M. Blatt;William Carroll