Mekonnen Dereje Worku, Flügge Ulf-Ingo, Ludewig Frank
Botanical Institute II, Cologne Biocenter, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany.
Botanical Institute II, Cologne Biocenter, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany; Division of Biochemistry, Department Biology, University Erlangen-Nuremberg, Staudtstr. 5, 91058 Erlangen, Germany.
Plant Sci. 2016 Apr;245:25-34. doi: 10.1016/j.plantsci.2016.01.005. Epub 2016 Jan 23.
A rapid accumulation of γ-aminobutyric acid (GABA) during biotic and abiotic stresses is well documented. However, the specificity of the response and the primary role of GABA under such stress conditions are hardly understood. To address these questions, we investigated the response of the GABA-depleted gad1/2 mutant to drought stress. GABA is primarily synthesized from the decarboxylation of glutamate by glutamate decarboxylase (GAD) which exists in five copies in the genome of Arabidopsis thaliana. However, only GAD1 and GAD2 are abundantly expressed, and knockout of these two copies dramatically reduced the GABA content. Phenotypic analysis revealed a reduced shoot growth of the gad1/2 mutant. Furthermore, the gad1/2 mutant was wilted earlier than the wild type following a prolonged drought stress treatment. The early-wilting phenotype was due to an increase in stomata aperture and a defect in stomata closure. The increase in stomata aperture contributed to higher stomatal conductance. The drought oversensitive phenotype of the gad1/2 mutant was reversed by functional complementation that increases GABA level in leaves. The functionally complemented gad1/2 x pop2 triple mutant contained more GABA than the wild type. Our findings suggest that GABA accumulation during drought is a stress-specific response and its accumulation induces the regulation of stomatal opening thereby prevents loss of water.
生物和非生物胁迫期间γ-氨基丁酸（GABA）的快速积累已有充分记录。然而，在这种胁迫条件下，GABA响应的特异性及其主要作用却鲜为人知。为了解决这些问题，我们研究了GABA缺失的gad1/2突变体对干旱胁迫的响应。GABA主要由谷氨酸脱羧酶（GAD）催化谷氨酸脱羧合成，该酶在拟南芥基因组中有五个拷贝。然而，只有GAD1和GAD2大量表达，敲除这两个拷贝会显著降低GABA含量。表型分析显示，gad1/2突变体地上部生长受到抑制。此外，经过长时间干旱胁迫处理后，gad1/2突变体比野生型更早枯萎。早期枯萎表型是由于气孔孔径增加和气孔关闭缺陷所致。气孔孔径增加导致气孔导度升高。通过功能互补增加叶片中GABA水平，可逆转gad1/2突变体对干旱过度敏感的表型。功能互补的gad1/2 x pop2三重突变体比野生型含有更多的GABA。我们的研究结果表明，干旱期间GABA的积累是一种胁迫特异性反应，其积累诱导气孔开放的调节，从而防止水分流失。
