Carl R. Woese, Institute of Genomic Biology, 1206 W. Gregory Drive, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
Center for Advanced Bioenergy and Bioproducts Innovation, 1206 W. Gregory Drive, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
J Exp Bot. 2024 Nov 15;75(21):6837-6849. doi: 10.1093/jxb/erae271.
Stomata regulate CO2 and water vapor exchange between leaves and the atmosphere. Stomata are a target for engineering to improve crop intrinsic water use efficiency (iWUE). One example is by expressing genes that lower stomatal density (SD) and reduce stomatal conductance (gsw). However, the quantitative relationship between reduced SD, gsw, and the mechanisms underlying it is poorly understood. We addressed this knowledge gap using low-SD sugarcane (Saccharum spp. hybrid) as a case study alongside a meta-analysis of data from 10 species. Transgenic expression of EPIDERMAL PATTERNING FACTOR 2 from Sorghum bicolor (SbEPF2) in sugarcane reduced SD by 26-38% but did not affect gsw compared with the wild type. Further, no changes occurred in stomatal complex size or proxies for photosynthetic capacity. Measurements of gas exchange at low CO2 concentrations that promote complete stomatal opening to normalize aperture size between genotypes were combined with modeling of maximum gsw from anatomical data. These data suggest that increased stomatal aperture is the only possible explanation for maintaining gsw when SD is reduced. Meta-analysis across C3 dicots, C3 monocots, and C4 monocots revealed that engineered reductions in SD are strongly correlated with lower gsw (r2=0.60-0.98), but this response is damped relative to the change in anatomy.
气孔调节叶片与大气之间的 CO2 和水蒸气交换。气孔是工程改良作物内在水分利用效率（iWUE）的目标。一种方法是表达降低气孔密度（SD）和气孔导度（gsw）的基因。然而，SD 降低、gsw 降低及其潜在机制之间的定量关系尚不清楚。我们以低 SD 甘蔗（甘蔗属杂种）作为案例研究，同时对来自 10 个物种的数据进行了荟萃分析，解决了这一知识空白。高粱 EPIDERMAL PATTERNING FACTOR 2（SbEPF2）的转基因在甘蔗中的表达使 SD 降低了 26-38%，但与野生型相比，gsw 不受影响。此外，气孔复合体大小或光合作用能力的替代指标没有变化。在低 CO2 浓度下进行气体交换的测量促进了完全气孔开放，以规范基因型之间的孔径大小，并结合解剖学数据对最大 gsw 进行建模。这些数据表明，当 SD 降低时，气孔孔径的增加是维持 gsw 的唯一可能解释。对 C3 双子叶植物、C3 单子叶植物和 C4 单子叶植物的荟萃分析表明，工程改造降低 SD 与 gsw 降低密切相关（r2=0.60-0.98），但与解剖学变化相比，这种反应受到抑制。
