Engineered drought-induced biosynthesis of α-tocopherol alleviates stress-induced leaf damage in tobacco

Tocopherols are members of the vitamin E complex and essential antioxidant compounds synthesized in chloroplasts that protect photosynthetic membranes against oxidative damage triggered by most environmental stresses. Tocopherol deficiency has been shown to affect germination, retard growth and change responses to abiotic stress, suggesting that tocopherols may be involved in a number of diverse physiological processes in plants. Instead of seeking constitutive synthesis of tocopherols to improve stress tolerance, we followed an inducible approach of enhancing α-tocopherol accumulation under dehydration conditions in tobacco. Two uncharacterized stress inducible promoters isolated from Arabidopsis and the VTE2.1 gene from Solanum chilense were used in this work. VTE2.1 encodes the enzyme homogentisate phytyltransferase (HPT), which catalyzes the prenylation step in tocopherol biosynthesis. Transgenic tobacco plants expressing ScVTE2.1 under the control of stress-inducible promoters showed increased levels of α-tocopherol when exposed to drought conditions. The accumulation of α-tocopherol correlated with higher water content and increased photosynthetic performance and less oxidative stress damage as evidenced by reduced lipid peroxidation and delayed leaf senescence. Our results indicate that stress-induced expression of VTE2.1 can be used to increase the vitamin E content and to diminish detrimental effects of environmental stress in plants. The stress-inducible promoters introduced in this work may prove valuable to future biotechnological approaches in improving abiotic stress resistance in plants.