Tocopherol as plant protector: an overview of Tocopherol biosynthesis enzymes and their role as antioxidant and signaling molecules

Tocopherols are vitamin E group of lipophilic antioxidant compounds, exclusively synthesized by plants. Mutant and transgenic approaches with loss or gain of function of Tocopherol pathway genes tends to provide insight into the role of this compound in plants. Tocopherols show fluctuation in their quantity under abiotic stresses, suggesting their critical role as antioxidant and as an indicator of stress tolerance in plants. From genetic approaches, it has been revealed that Tocopherols’ function is beyond antioxidant activities, as in some cases, it plays a major role in cell signaling as well. Though there is a lot of literature available about the enzymes function in the Tocopherol biosynthesis, but still the underlying mechanisms that regulate the entire pathway and fluctuation in Tocopherol content and composition during stress conditions remain less understood in plants. Understanding the induction mechanism under stress will help to develop methods to engineer plants with high Tocopherol contents. The main aim of this review is to reveal the responses of important Tocopherol biosynthesis enzymes under abiotic stresses to advance our genetic approaches and tools to unravel the functional mystery of Tocopherols in plants. In addition, the role of Tocopherols in cell signaling is also described in detail.