Genetics Department, Institute for Plant Biotechnology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
Planta. 2012 Mar;235(3):553-64. doi: 10.1007/s00425-011-1525-6. Epub 2011 Oct 7.
Ascorbate (AsA) plays a fundamental role in redox homeostasis in plants and animals, primarily by scavenging reactive oxygen species. Three genes, representing diverse steps putatively involved in plant AsA biosynthesis pathways, were cloned and independently expressed in Solanum lycopersicum (tomato) under the control of the CaMV 35S promoter. Yeast-derived GDP-mannose pyrophosphorylase (GMPase) and arabinono-1,4-lactone oxidase (ALO), as well as myo-inositol oxygenase 2 (MIOX2) from Arabidopsis thaliana, were targeted. Increases in GMPase activity were concomitant with increased AsA levels of up to 70% in leaves, 50% in green fruit, and 35% in red fruit. Expression of ALO significantly pulled biosynthetic flux towards AsA in leaves and green fruit by up to 54 and 25%, respectively. Changes in AsA content in plants transcribing the MIOX2 gene were inconsistent in different tissue. On the other hand, MIOX activity was strongly correlated with cell wall uronic acid levels, suggesting that MIOX may be a useful tool for the manipulation of cell wall composition. In conclusion, the Smirnoff-Wheeler pathway showed great promise as a target for biotechnological manipulation of ascorbate levels in tomato.
抗坏血酸（AsA）在植物和动物的氧化还原平衡中起着至关重要的作用，主要通过清除活性氧物质来实现。本研究克隆了三个基因，它们代表了植物抗坏血酸生物合成途径中不同的步骤，并在番茄（Solanum lycopersicum）中独立表达，这些基因受 CaMV 35S 启动子的控制。研究靶向了酵母衍生的 GDP-甘露糖焦磷酸化酶（GMPase）和阿拉伯糖-1,4-内酯氧化酶（ALO），以及拟南芥的肌醇氧合酶 2（MIOX2）。GMPase 活性的增加伴随着叶片中抗坏血酸水平增加高达 70%，绿果中增加 50%，红果中增加 35%。在叶片和绿果中，ALO 的表达分别使生物合成通量显著向抗坏血酸方向移动，分别增加了 54%和 25%。在转录 MIOX2 基因的植物中，抗坏血酸含量的变化在不同组织中不一致。另一方面，MIOX 活性与细胞壁糖醛酸水平强烈相关，表明 MIOX 可能是操纵细胞壁组成的有用工具。总之，Smirnoff-Wheeler 途径有望成为生物技术操纵番茄抗坏血酸水平的目标。
