Myoinositol Oxygenase Controls the Level of Myoinositol in Arabidopsis, But Does Not Increase Ascorbic Acid
Myoinositol Oxygenase Controls the Level of Myoinositol in Arabidopsis, But Does Not Increase Ascorbic Acid
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DOI：
10.1104/pp.108.130948
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发表时间：
2009-02-01
期刊：
影响因子：
7.4
通讯作者：
Tenhaken, Raimund
中科院分区：
文献类型：
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作者：
Endres, Stefanie;Tenhaken, Raimund
抗坏血酸（阿萨）是一种重要的植物抗氧化剂。像vtc 1突变体显示出减少阿萨浓度，这证实了遗传证据先前提出的阿萨途径通过GDP的人。在这里，我们调查的作用类似动物的替代生物合成途径阿萨，从代谢产物D-葡萄糖酸，这是在植物中产生的肌醇加氧酶（Miox）。Miox过表达系具有超过30倍上调的转录水平和更高的酶活性，如通过增加的Miox衍生糖掺入细胞壁聚合物所示。此外，由于周转率提高，Miox过表达子在饲养实验中表现出较低的肌醇稳态水平和积累较少的肌醇。阿萨浓度在野生型和Miox过表达株系中保持相同。即使是具有胁迫的挑战性植物，其增加阿萨浓度4倍，也揭示野生型和Miox过表达系之间的阿萨生物合成没有差异。我们的结论是，D-GlcUA衍生自Miox反应中发挥的作用可以忽略不计的阿萨的生物合成。然而，Miox控制植物中肌醇的代谢物水平。
Ascorbic acid (AsA) is a major plant antioxidant. Mutants like vtc1 show a reduced AsA concentration, which confirmed by genetic evidence the previously proposed AsA pathway via GDP-Man. Here we investigate the role of an animal-like alternative biosynthesis route to AsA, starting from the metabolite D-GlcUA, which is produced in plants by myoinositol oxygenase (Miox). Miox-overexpressing lines have a more than 30-fold up-regulated transcript level and higher enzymatic activity as shown by increased incorporation of Miox-derived sugars into cell wall polymers. In addition, Miox overexpressors exhibit a lower steady-state level of myoinositol and accumulate less myoinositol in feeding experiments due to an enhanced turnover rate. The AsA concentration remains the same in wild-type and Miox overexpressor lines. Even challenging plants with stress, which increases AsA concentration 4-fold, reveals no difference in AsA biosynthesis between wild-type and Miox-overexpressing lines. We conclude that D-GlcUA derived from the Miox reaction plays a negligible role for AsA biosynthesis. However, Miox controls the metabolite level of myoinositol in plants.