A SNARE-Aquaporin complex in stomatal hydraulics

气孔水力学中的 SNARE-水通道蛋白复合物

• 批准号: BB/X013383/1
• 负责人: Michael Blatt
• 金额: $ 88.39万
• 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: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FX013383%2F1
• 关键词: SNARE; Aquaporin; complex; stomatal; hydraulics

Stomata are pores that mediate gaseous exchange across the impermeable cuticle of plant leaves. They open for CO2 entry when photosynthesis depletes CO2 inside the leaf, and they close to reduce the transpiration of water vapour and prevent leaf drying when atmospheric humidity is low. Stomata are at the centre of a crisis in water availability and crop production that is beginning to unfold and can only escalate as the global demand, especially in agriculture, outstrips fresh water supplies. Thus stomata are an important target in efforts to enhance crop performance and efficiencies.Stomata of most plants track the immediate demand for CO2 by photosynthesis, responding to CO2 within the leaf, opening in the light and closing in the dark. However, stomatal responses are slow by comparison with that of photosynthesis. Fluctuations in daylight, for example as clouds pass overhead, degrade photosynthesis and reduce water use efficiency (WUE=amount of carbon fixed in photosynthesis/amount of water transpired), principally because stomata generally lag behind changes in light. Synthetic bioengineering has shown substantial gains in photosynthesis and WUE by accelerating the speed of stomatal response. We need now to understand how such gains might be achieved using the processes native to the stomata.Stomatal movement is driven by solute and water transport across the membrane of the guard cells that surround the stomatal pore. Guard cells harbour ion channel proteins to facilitate solute flux and aquaporins to mediate water flux, and they rely on a traffic of membrane vesicles to adjust cell surface area during stomatal movements. Thus, coordination of these three processes is essential for stomatal responses. From our previous work, we know that the dominant ion flux through K+ channels is coupled to membrane traffic by binding between subsets of channels and so-called SNARE proteins that facilitate vesicle traffic and are conserved across land plants. These interactions ensure solute flux and membrane traffic operate in 'lock-step' within guard cells. There is some evidence for a parallel coordination of water flux through aquaporins, but until now we have lacked an understanding of how this coordination might arise.Plasma membrane (PIP) aquaporins are found across all angiosperms. Three PIPs contribute to water flux in guard cells of the model plant Arabidopsis although one, PIP2;1, dominates. We recently uncovered a selective interaction between all three PIPs and the SYP121 protein, one of two principal SNAREs at the plasma membrane. These interactions depend on a cytosolic N-terminal region of SYP121 that is sequence-divergent, but functionally interchangable with other SNAREs and is widely recognised to regulate SNARE activity and vesicle traffic in all eukaryotes. Most exciting, we find that a chimeric SYP121 incorporating the same region of a non-interacting SNARE slows stomatal opening and closing when expressed in guard cells and suppresses WUE and growth when plants experience fluctuating daylight.Our findings are the first direct evidence for SYP121-PIP binding in stomatal movements, and they point to the SNARE subdomain responsible for this action in vivo. SYP121 also binds guard cell K+ channels, coordinating vesicle traffic with K+ flux. Thus, SYP121-PIP binding suggests a SNARE nexus in stomatal regulation; it begs questions about the coordination of PIP and K+ channel binding; and it challenges established dogma about the roles of vesicle traffic in aquaporin hydraulics that impact on WUE and plant biomass gain.We propose now to resolve the binding and function of SYP121 with the guard cell PIPs and to establish the consequences for the plant. This research is to understand the fundamental rules of life. Understanding this SNARE nexus nonetheless carries the promise of a potential target for future bioengineering to accelerate stomatal movements and enhance crop efficiencies.

气孔是介导植物叶子不渗透角质层气体交换的孔隙。当光合作用耗尽叶子内的二氧化碳时，它们会打开以供二氧化碳进入；当大气湿度较低时，它们会关闭以减少水蒸气的蒸腾并防止叶子干燥。气孔是水资源供应和农作物生产危机的核心，这场危机已经开始显现，并且随着全球需求（尤其是农业需求）超过淡水供应而加剧。因此，气孔是提高作物性能和效率的重要目标。大多数植物的气孔通过光合作用跟踪对二氧化碳的即时需求，对叶子内的二氧化碳作出反应，在光照下打开，在黑暗中关闭。然而，与光合作用相比，气孔反应较慢。日光的波动，例如云层从头顶掠过，会降低光合作用并降低水分利用效率（WUE=光合作用中固定的碳量/蒸腾的水量），主要是因为气孔通常滞后于光照的变化。合成生物工程通过加快气孔反应速度，在光合作用和 WUE 方面取得了显着的进展。我们现在需要了解如何利用气孔固有的过程来实现这种增益。气孔运动是由溶质和水穿过气孔周围的保卫细胞膜的运输驱动的。保卫细胞含有促进溶质通量的离子通道蛋白和介导水通量的水通道蛋白，并且它们依靠膜囊泡的流量来调节气孔运动期间的细胞表面积。因此，这三个过程的协调对于气孔反应至关重要。从我们之前的工作中，我们知道通过 K+ 通道的主要离子通量通过通道子集和所谓的 SNARE 蛋白之间的结合与膜运输耦合，这些蛋白促进囊泡运输并在陆地植物中保守。这些相互作用确保溶质通量和膜流量在保卫细胞内“同步”运行。有一些证据表明水通道蛋白的水通量存在平行协调，但到目前为止，我们对这种协调如何产生还缺乏了解。质膜（PIP）水通道蛋白存在于所有被子植物中。三种 PIP 对模式植物拟南芥保卫细胞中的水通量有贡献，但 PIP2;1 中的一种占主导地位。我们最近发现了所有三种 PIP 和 SYP121 蛋白之间的选择性相互作用，SYP121 蛋白是质膜上的两个主要 SNARE 之一。这些相互作用取决于 SYP121 的胞质 N 端区域，该区域具有序列差异，但在功能上可与其他 SNARE 互换，并且被广泛认为可调节所有真核生物中的 SNARE 活性和囊泡运输。最令人兴奋的是，我们发现嵌合 SYP121 包含非相互作用 SNARE 的相同区域，当在保卫细胞中表达时会减慢气孔的打开和关闭，并在植物经历波动的日光时抑制 WUE 和生长。我们的发现是 SYP121 的第一个直接证据PIP 与气孔运动结合，它们指向负责体内这一作用的 SNARE 子域。 SYP121 还结合保卫细胞 K+ 通道，协调囊泡运输与 K+ 通量。因此，SYP121-PIP 结合表明气孔调节中存在 SNARE 关系。它引出了有关 PIP 和 K+ 通道绑定协调的问题；它挑战了关于水通道蛋白水力学中囊泡运输作用的既定教条，影响 WUE 和植物生物量增益。我们现在建议解决 SYP121 与保卫细胞 PIP 的结合和功能，并确定对植物的影响。这项研究是为了了解生命的基本规则。尽管如此，理解这种 SNARE 关系仍然有望成为未来生物工程加速气孔运动和提高作物效率的潜在目标。