Qin Hua, Deng Zaian, Zhang Chuanyu, Wang Yayun, Wang Juan, Liu Hai, Zhang Zhili, Huang Rongfeng, Zhang Zhijin
Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
National Key Facility of Crop Gene Resources and Genetic Improvement, Beijing, 100081, China.
Plant Mol Biol. 2016 Feb;90(3):317-27. doi: 10.1007/s11103-015-0420-0. Epub 2015 Dec 29.
GDP-D-mannose pyrophosphorylase (GMPase) catalyzes the synthesis of GDP-D-mannose, which is a precursor for ascorbic acid (AsA) synthesis in plants. The rice genome encodes three GMPase homologs OsVTC1-1, OsVTC1-3 and OsVTC1-8, but their roles in AsA synthesis are unclear. The overexpression of OsVTC1-1 or OsVTC1-3 restored the AsA synthesis of vtc1-1 in Arabidopsis, while that of OsVTC1-8 did not, indicating that only OsVTC1-1 and OsVTC1-3 are involved in AsA synthesis in rice. Similar to Arabidopsis VTC1, the expression of OsVTC1-1 was high in leaves, induced by light, and inhibited by dark. Unlike OsVTC1-1, the expression level of OsVTC1-3 was high in roots and quickly induced by the dark, while the transcription level of OsVTC1-8 did not show obvious changes under constant light or dark treatments. In OsVTC1-1 RNAi plants, the AsA content of rice leaves decreased, and the AsA production induced by light was limited. In contrast, OsVTC1-3 RNAi lines altered AsA synthesis levels in rice roots, but not in the leaves or under the light/dark treatment. The enzyme activity showed that OsVTC1-1 and OsVTC1-3 had higher GMPase activities than OsVTC1-8 in vitro. Our data showed that, unlike in Arabidopsis, the rice GPMase homologous proteins illustrated a new model in AsA synthesis: OsVTC1-1 may be involved in the AsA synthesis, which takes place in leaves, while OsVTC1-3 may be responsible for AsA synthesis in roots. The different roles of rice GMPase homologous proteins in AsA synthesis may be due to their differences in transcript levels and enzyme activities.
GDP - D - 甘露糖焦磷酸化酶（GMPase）催化GDP - D - 甘露糖的合成，而GDP - D - 甘露糖是植物中抗坏血酸（AsA）合成的前体。水稻基因组编码三种GMPase同源物OsVTC1 - 1、OsVTC1 - 3和OsVTC1 - 8，但它们在AsA合成中的作用尚不清楚。OsVTC1 - 1或OsVTC1 - 3的过表达恢复了拟南芥中vtc1 - 1的AsA合成，而OsVTC1 - 8的过表达则没有，这表明在水稻中只有OsVTC1 - 1和OsVTC1 - 3参与AsA合成。与拟南芥VTC1相似，OsVTC1 - 1在叶片中的表达较高，受光照诱导，受黑暗抑制。与OsVTC1 - 1不同，OsVTC1 - 3在根中的表达水平较高，并在黑暗中迅速诱导，而OsVTC1 - 8的转录水平在持续光照或黑暗处理下没有明显变化。在OsVTC1 - 1 RNA干扰植物中，水稻叶片的AsA含量降低，光照诱导的AsA产生受到限制。相反，OsVTC1 - 3 RNA干扰株系改变了水稻根中的AsA合成水平，但在叶片中或光/暗处理下没有改变。酶活性表明，在体外OsVTC1 - 1和OsVTC1 - 3的GMPase活性高于OsVTC1 - 8。我们的数据表明，与拟南芥不同，水稻GPMase同源蛋白在AsA合成中呈现出一种新模式：OsVTC1 - 1可能参与叶片中的AsA合成，而OsVTC1 - 3可能负责根中的AsA合成。水稻GMPase同源蛋白在AsA合成中的不同作用可能是由于它们在转录水平和酶活性上的差异。
