Abstract

Tocopherols, known collectively as vitamin E, are micronutrients with antioxidant properties synthesized only by photosynthetic organisms that play important roles in human and animal nutrition. The enzyme gamma-tocopherol methyltransferase (γ-TMT) converts δ- and γ-tocopherol to β- and α-tocopherol, which is a committed step to elevate vitamin E activity and nutrition value. Here, we presented the cloning, chromosome location and expression characterization of a cDNA from common wheat (Triticum aestivum L.) that encoded a putative γ-TMT. This gene (designated TaTMT, accession number: DQ139266) had a total length of 1288 bp with an open reading frame of 1098 bp, and encoded a predicted polypeptide of 365 amino acids with a molecular weight of 39.5 kDa and an isoelectric point of 7.2. The deduced amino acid sequence shared high similarity to those of the previously cloned γ-TMT genes from other plants and had a chloroplast transit peptide predicted by TargetP algorithm. Chromosome location of TaTMT based on sequence similarity and map position of the EST was mapped in wheat 6AL, 6BL and 6DL chromosomes. In silico, expression analysis revealed that TaTMT was constitutively expressed in various organs, whereas it was not detectable in callus, cell culture and sheath. Semi-quantitative RT-PCR showed that TaTMT was abundantly expressed in stem and leaf, but was showed very low expression level in root, indicating the expression of TaTMT was tissue specific in photosynthetic organs. However, the expression level of TaTMT was not regulated by high light oxidative stress and this was not surprising because γ-TMT can only convert tocopherol types but not the total volume of antioxidant tocopherols. These molecular analysis results provided fundamental and important information for genetic improvement of bread wheat vitamin E micronutrient quality.

Key words: Triticum aestivum, vitamin E, gamma tocopherol methyltransferase, gene cloning, gene expression.