OsMIOX, a myo-inositol oxygenase gene, improves drought tolerance through scavenging of reactive oxygen species in rice (Oryza sativa L.)

Myo-inositol oxygenase (MIOX), a unique monooxygenase, catalyzes the oxidation of myo-inositol to d-glucuronic acid. However, the protective role of MIOX in plants against oxidative stress or drought stress remains unknown. In this study, the functional characterization of MIOX obtained from the cDNA library of upland rice (Oryza sativa L. cv. IRAT109), was performed. OsMIOX was expressed predominantly in the roots and induced by drought, H2O2, salt, cold and abscisic acid. The transgenic rice lines overexpressing OsMIOX showed obviously improved growth performance in the medium containing 200 mM mannitol. Further, the survival rate of leaves from the transgenic rice lines was significantly higher than that of the wild type plants under polyethylene glycol treatment. It was discovered that the activity of ROS-scavenging enzymes and proline content, as well as the transcript levels of many ROS scavenging genes were significantly increased in transgenic plants compared to the wild type plants under drought stress conditions. Together, these data suggest that OsMIOX has a specific function in drought stress tolerance by decreasing oxidative damage .肌醇加氧酶（Myo-inositol oxygenase, MIOX）是一类独特的单加氧酶，可催化肌醇氧化生成D-葡萄糖醛酸。然而，MIOX在植物抵御氧化胁迫或干旱胁迫中的保护功能仍未明确。本研究对从旱稻（Oryza sativa L. cv. IRAT109）cDNA文库中获取的MIOX进行了功能表征。OsMIOX主要在根系中表达，且可被干旱、过氧化氢（H₂O₂）、盐胁迫、低温及脱落酸诱导。过表达OsMIOX的转基因水稻株系在含200 mM甘露醇的培养基中生长表现显著优于野生型植株。进一步实验显示，在聚乙二醇（polyethylene glycol, PEG）处理条件下，转基因水稻株系的叶片存活率显著高于野生型植株。研究发现，在干旱胁迫条件下，相较于野生型植株，转基因植株的活性氧（Reactive Oxygen Species, ROS）清除酶活性、脯氨酸含量以及众多ROS清除基因的转录水平均显著升高。综上，上述结果表明OsMIOX通过减轻氧化损伤，在水稻干旱胁迫耐受中发挥特异性功能。