Transgenic sweetpotato plants overexpressing tocopherol cyclase display enhanced alpha-tocopherol content and abiotic stress tolerance

Abstract

Oxidative stress caused by reactive oxygen species (ROS) under various environmental stresses significantly reduces plant productivity. Tocopherols (collectively known as vitamin E) are a group of lipophilic antioxidants that protect cellular components against oxidative stress. Previously, we isolated five tocopherol biosynthesis genes from sweetpotato (Ipomoea batatas [L.] Lam) plants, including tocopherol cyclase (IbTC). In this study, we generated transgenic sweetpotato plants overexpressing IbTC under the control of cauliflower mosaic virus (CaMV) 35S promoter (referred to as TC plants) via Agrobacterium-mediated transformation to understand the function of IbTC in sweetpotato. Three transgenic lines (TC2, TC9, and TC11) with high transcript levels of IbTC were selected for further characterization. High performance liquid chromatography (HPLC) analysis revealed that alpha-tocopherol was the most predominant form of tocopherol in sweetpotato tissues. The content of alpha-tocopherol was 1.6-3.3-fold higher in TC leaves than in non-transgenic (NT) leaves. No significant difference was observed in the tocopherol content of storage roots between TC and NT plants. Additionally, compared with NT plants, TC plants showed enhanced tolerance to multiple environmental stresses, including salt, drought, and oxidative stresses, and showed consistently higher levels of photosystem II activity and chlorophyll content, indicating abiotic stress tolerance. These results suggest IbTC as a strong candidate gene for the development of sweetpotato cultivars with increased alpha-tocopherol levels and enhanced abiotic stress tolerance.