普通小麦中双脱氢抗坏血酸还原酶(TaDHAR)基因的克隆与生化特性分析

Molecular and biochemical analysis of two genes encoding dehydroascorbate reductase in common wheat

利用同源克隆技术从六倍体普通小麦中获得了两个不同的双脱氢抗坏血酸还原酶(TaDHAR)基因的cDNA克隆。器官表达模式分析表明,这两个TaDHAR基因(暂时命名为TaDHAR1和TaDHAR2)在小麦根、茎、叶、幼穗以及开花后10d、20d和30d的种子中均有表达,为组成型表达基因。原生质体表达实验表明,两个基因的产物均可能定位在细胞质中。在细菌中表达并提纯了两个基因的重组蛋白。体外生化测定表明两个重组蛋白均具有将双脱氢抗坏血酸还原成抗坏血酸的能力,其最适pH为7.5,在37oC时的活性比25oC高,但25oC条件下pH6.0和7.0时,两个DHAR蛋白的活性显著不同。本研究的结果为进一步揭示TaDHAR基因在小麦抗坏血酸代谢中的生理作用奠定了基础。

Dehydroascorbate reductase （DHAR） plays an important role in the recycling of ascorbic acid. In this work, we isolated the full length cDNA clones of two different DHAR genes （tentatively named as TaDHAR1 and TaDHAR2, respectively） from common wheat. Semi-quantitative PCR experiments showed that TaDHAR1 and TaDHAR2 were transcribed in many vegetative and reproductive organs examined in this work. Transient expression analysis using wheat protoplasts indicated that the protein products of TaDHAR1 and TaDHAR2 may be located in the cytoplasm. The cDNAs of TaDHAR1 and TaDHAR2 were expressed in the bacterial cells, and resultant histidine tagged recombinant proteins could be efficiently purified using nickel chelate affinity chromatography. In vitro enzyme activity assays revealed that the recombinant TaDHAR1 and TaDHAR2 proteins could all convert dehydroascorbate （DHA） to AsA. The two proteins exhibited higher activity levels at 37℃ than at 25℃. Under the two temperature conditions, the optimal pH for TaDHAR1 and TaDHAR2 was both around 7.5. The major difference between TaDHAR1 and TaDHAR2 is the activity under pH 6.0 and 7.0 at 25℃. The results and resources obtained in this study may be useful for further research into the physiological role of TaDHAR genes in AsA metabolism in crop plants under normal or stressed conditions.