College of Life Science, Henan Agricultural University, Zhengzhou, People's Republic of China.
PLoS One. 2012;7(5):e37383. doi: 10.1371/journal.pone.0037383. Epub 2012 May 31.
Sulfite oxidase (SO) plays an important role in sulfite metabolism. To date, the molecular mechanisms of sulfite metabolism in plants are largely unknown. Previously, a full-length cDNA of the putative sulfite oxidase gene from maize (ZmSO) was cloned, and its response to SO(2)/sulfite stress at the transcriptional level was characterized. In this study, the recombinant ZmSO protein was purified from E. coli. It exhibited sulfite-dependent activity and had strong affinity for the substrate sulfite. Over-expression (OE) of ZmSO in tobacco plants enhanced their tolerance to sulfite stress. The plants showed much less damage, less sulfite accumulation, but greater amounts of sulfate. This suggests that tolerance of transgenic plants to sulfite was enhanced by increasing SO expression levels. Interestingly, H(2)O(2) accumulation levels by histochemical detection and quantitative determination in the OE plants were much less than those in the wild-type upon sulfite stress. Furthermore, reductions of catalase levels detected in the OE lines were considerably less than in the wild-type plants. This indicates that SO may play an important role in protecting CAT from inhibition by excess sulfite. Collectively, these data demonstrate that transgenic tobacco plants over-expressing ZmSO enhance tolerance to excess sulfite through sulfite oxidation and catalase-mediated hydrogen peroxide scavenging. This is the first SO gene from monocots to be functionally characterized.
亚硫酸氧化酶（SO）在亚硫酸盐代谢中发挥重要作用。迄今为止，植物中亚硫酸盐代谢的分子机制在很大程度上尚不清楚。先前，已从玉米（ZmSO）克隆出假定的亚硫酸氧化酶基因的全长 cDNA，并在转录水平上对其对 SO2/亚硫酸盐胁迫的反应进行了表征。在这项研究中，从大肠杆菌中纯化了重组 ZmSO 蛋白。它表现出亚硫酸盐依赖性活性，并且对底物亚硫酸盐具有很强的亲和力。在烟草植物中超表达（OE）ZmSO 增强了它们对亚硫酸盐胁迫的耐受性。这些植物的损伤较小，亚硫酸盐积累较少，但硫酸盐含量较高。这表明通过增加 SO 表达水平增强了转基因植物对亚硫酸盐的耐受性。有趣的是，在用亚硫酸盐胁迫进行组织化学检测和定量测定时，OE 植物中的 H2O2 积累水平远低于野生型植物。此外，在 OE 系中检测到的过氧化氢酶水平降低明显少于野生型植物。这表明 SO 可能在保护 CAT 免受过量亚硫酸盐抑制方面发挥重要作用。总的来说，这些数据表明，过表达 ZmSO 的转基因烟草植物通过亚硫酸盐氧化和 CAT 介导的过氧化氢清除来增强对过量亚硫酸盐的耐受性。这是首次对单子叶植物中的 SO 基因进行功能表征。
