Department of Biology, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.
BMC Genomics. 2010 Mar 22;11:190. doi: 10.1186/1471-2164-11-190.
Glutamate plays a central position in the synthesis of a variety of organic molecules in plants and is synthesised from nitrate through a series of enzymatic reactions. Glutamate synthases catalyse the last step in this pathway and two types are present in plants: NADH- or ferredoxin-dependent. Here we report a genome wide microarray analysis of the transcriptional reprogramming that occurs in leaves and roots of the A. thaliana mutant glu1-2 knocked-down in the expression of Fd-GOGAT1 (GLU1; At5g04140), one of the two genes of A. thaliana encoding ferredoxin-dependent glutamate synthase.
Transcriptional profiling of glu1-2 revealed extensive changes with the expression of more than 5500 genes significantly affected in leaves and nearly 700 in roots. Both genes involved in glutamate biosynthesis and transformation are affected, leading to changes in amino acid compositions as revealed by NMR metabolome analysis. An elevated glutamine level in the glu1-2 mutant was the most prominent of these changes. An unbiased analysis of the gene expression datasets allowed us to identify the pathways that constitute the secondary response of an FdGOGAT1/GLU1 knock-down. Among the most significantly affected pathways, photosynthesis, photorespiratory cycle and chlorophyll biosynthesis show an overall downregulation in glu1-2 leaves. This is in accordance with their slight chlorotic phenotype. Another characteristic of the glu1-2 transcriptional profile is the activation of multiple stress responses, mimicking cold, heat, drought and oxidative stress. The change in expression of genes involved in flavonoid biosynthesis is also revealed. The expression of a substantial number of genes encoding stress-related transcription factors, cytochrome P450 monooxygenases, glutathione S-transferases and UDP-glycosyltransferases is affected in the glu1-2 mutant. This may indicate an induction of the detoxification of secondary metabolites in the mutant.
Analysis of the glu1-2 transcriptome reveals extensive changes in gene expression profiles revealing the importance of Fd-GOGAT1, and indirectly the central role of glutamate, in plant development. Besides the effect on genes involved in glutamate synthesis and transformation, the glu1-2 mutant transcriptome was characterised by an extensive secondary response including the downregulation of photosynthesis-related pathways and the induction of genes and pathways involved in the plant response to a multitude of stresses.
谷氨酸在植物中各种有机分子的合成中起着核心作用，并且是通过一系列酶促反应从硝酸盐合成的。谷氨酸合酶催化该途径的最后一步，植物中有两种类型：NADH 或铁氧还蛋白依赖性。在这里，我们报告了对 A.thaliana glu1-2 突变体叶片和根中发生的转录重编程的全基因组微阵列分析，该突变体在表达 Fd-GOGAT1（GLU1；At5g04140）时被敲低，这是编码铁氧还蛋白依赖性谷氨酸合酶的 A.thaliana 中的两个基因之一。
对 glu1-2 的转录谱分析显示，超过 5500 个基因的表达受到显著影响，叶片中近 700 个基因的表达受到显著影响。参与谷氨酸生物合成和转化的两个基因都受到影响，导致 NMR 代谢组分析揭示的氨基酸组成发生变化。谷氨酸水平在 glu1-2 突变体中的升高是这些变化中最显著的。对基因表达数据集的无偏分析使我们能够识别构成 FdGOGAT1/GLU1 敲低的次级反应的途径。在受影响最显著的途径中，光合作用、光呼吸循环和叶绿素生物合成在 glu1-2 叶片中总体下调。这与它们轻微的黄化表型一致。glu1-2 转录谱的另一个特征是多种应激反应的激活，模拟冷、热、干旱和氧化应激。类黄酮生物合成相关基因表达的变化也被揭示。大量与应激相关的转录因子、细胞色素 P450 单加氧酶、谷胱甘肽 S-转移酶和 UDP-糖基转移酶编码基因的表达在 glu1-2 突变体中受到影响。这可能表明在突变体中诱导了次生代谢物的解毒。
对 glu1-2 转录组的分析揭示了基因表达谱的广泛变化，揭示了 Fd-GOGAT1 的重要性，以及谷氨酸在植物发育中的核心作用。除了对参与谷氨酸合成和转化的基因的影响外，glu1-2 突变体转录组的特征还包括广泛的次级反应，包括光合作用相关途径的下调和参与植物对多种胁迫反应的基因和途径的诱导。
