Engineering tocopherol biosynthetic pathway in Arabidopsis leaves and its effect on antioxidant metabolism

With genetic manipulation, five genes (HPPD, VTE2, VTE3, VTE1, and VTE4), which encode enzymes involved in tocopherol biosynthesis, were over-expressed in model plant Arabidopsis thaliana, either alone or in couple combinations (VTE2 + VTE4 and VTE3 + VTE4), to value and compare the roles of enzymes played in tocopherol biosynthetic pathway under the same genetic background. Our results suggested that, elevated expression level of biosynthetic pathway gene affected either total tocopherol content or composition, it is recommended to choose two or more enzymes with different functions for genetic manipulation. It was also found that metabolic engineering of tocopherol biosynthetic pathway affected endogenous ascorbate and glutathione pools in leaves. Further study suggested that expression levels of genes encoding enzymes of Halliwell–Asada cycle were up-regulated, such as APX, DHAR and MDAR. These findings provide hints on the relationship of lipid-soluble antioxidant vitamin E and water-soluble antioxidants vitamin C and glutathione, which will help to perfect theory in plant physiology and give practical instruction for metabolic engineering.