Lorence Argelia, Chevone Boris I, Mendes Pedro, Nessler Craig L
Department of Plant Pathology, Physiology, and Weed Science and Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
Plant Physiol. 2004 Mar;134(3):1200-5. doi: 10.1104/pp.103.033936. Epub 2004 Feb 19.
Two biosynthetic pathways for ascorbate (l-ascorbic acid [AsA]; vitamin C) in plants are presently known, the mannose/l-galactose pathway and an l-GalUA pathway. Here, we present molecular and biochemical evidence for a possible biosynthetic route using myo-inositol (MI) as the initial substrate. A MI oxygenase (MIOX) gene was identified in chromosome 4 (miox4) of Arabidopsis ecotype Columbia, and its enzymatic activity was confirmed in bacterially expressed recombinant protein. Miox4 was primarily expressed in flowers and leaves of wild-type Arabidopsis plants, tissues with a high concentration of AsA. Ascorbate levels increased 2- to 3-fold in homozygous Arabidopsis lines overexpressing the miox4 open reading frame, thus suggesting the role of MI in AsA biosynthesis and the potential for using this gene for the agronomic and nutritional enhancement of crops.
目前已知植物中抗坏血酸（L-抗坏血酸[AsA]；维生素C）的两条生物合成途径，即甘露糖/L-半乳糖途径和L-半乳糖醛酸途径。在此，我们提供了以肌醇（MI）作为初始底物的可能生物合成途径的分子和生化证据。在拟南芥生态型哥伦比亚的4号染色体（miox4）中鉴定出一个肌醇加氧酶（MIOX）基因，并在细菌表达的重组蛋白中证实了其酶活性。Miox4主要在野生型拟南芥植物的花和叶中表达，这些组织中AsA浓度较高。在过表达miox4开放阅读框的纯合拟南芥株系中，抗坏血酸水平增加了2至3倍，这表明MI在AsA生物合成中的作用，以及利用该基因进行作物农艺和营养改良的潜力。
