School of Biosciences, University of Sheffield, Western Park, Sheffield S10 2TN, UK.
Computational and Systems Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK.
Curr Biol. 2022 Jul 25;32(14):3170-3179.e4. doi: 10.1016/j.cub.2022.05.042. Epub 2022 Jun 7.
Stomata regulate plant water use and photosynthesis by controlling leaf gas exchange. They do this by reversibly opening the pore formed by two adjacent guard cells, with the limits of this movement ultimately set by the mechanical properties of the guard cell walls and surrounding epidermis. A body of evidence demonstrates that the methylation status and cellular patterning of pectin wall polymers play a core role in setting the guard cell mechanical properties, with disruption of the system leading to poorer stomatal performance. Here we present genetic and biochemical data showing that wall arabinans modulate guard cell flexibility and can be used to engineer stomata with improved performance. Specifically, we show that a short-chain linear arabinan epitope associated with the presence of rhamnogalacturonan I in the guard cell wall is required for full opening of the stomatal pore. Manipulations leading to the novel accumulation of longer-chain arabinan epitopes in guard cell walls led to an increase in the maximal pore aperture. Using computational modeling combined with atomic force microscopy, we show that this phenotype reflected a decrease in wall matrix stiffness and, consequently, increased flexing of the guard cells under turgor pressure, generating larger, rounder stomatal pores. Our results provide theoretical and experimental support for the conclusion that arabinan side chains of pectin modulate guard cell wall stiffness, setting the limits for cell flexing and, consequently, pore aperture, gas exchange, and photosynthetic assimilation.
气孔通过控制叶片气体交换来调节植物的水分利用和光合作用。它们通过可逆地打开由两个相邻保卫细胞形成的孔来实现这一点，而这种运动的极限最终由保卫细胞壁和周围表皮的机械性能决定。大量证据表明，果胶壁聚合物的甲基化状态和细胞模式在设定保卫细胞机械性能方面起着核心作用，该系统的破坏会导致气孔性能下降。在这里，我们提供了遗传和生化数据，表明细胞壁阿拉伯聚糖可以调节保卫细胞的柔韧性，并可用于构建具有改善性能的气孔。具体来说，我们表明，与保卫细胞壁中鼠李半乳糖醛酸聚糖 I 存在相关的短链线性阿拉伯聚糖表位是气孔完全打开所必需的。导致保卫细胞壁中长链阿拉伯聚糖表位新积累的操作导致最大孔径增加。我们使用计算建模结合原子力显微镜，表明这种表型反映了细胞壁基质刚度的降低，从而导致在膨压下保卫细胞的弯曲度增加，产生更大、更圆的气孔。我们的结果为结论提供了理论和实验支持，即果胶的阿拉伯聚糖侧链调节保卫细胞壁的刚度，从而限制了细胞的弯曲度，进而限制了孔径、气体交换和光合作用同化。
