Vitamin E synthesis and response in plants

Abstract

Vitamin E, also known as tocochromanol, is a lipid-soluble antioxidant that can only be produced by photosynthetic organisms in nature. Vitamin E is not only essential in human diets, but also required for plant environment adaptions. To synthesize vitamin E, specific prenyl groups needs to be incorporated with homogentisate as the first step of reaction. After decades of studies, an almost complete roadmap has been revealed for tocochromanol biosynthesis pathway. However, chlorophyll-derived prenyl precursors for synthesizing tocochromanols are still a mystery. In recent years, by employing forward genetic screening and genome-wide-association approaches, significant achievements were acquired in studying vitamin E. In this review, by summarizing the recent progresses in vitamin E, we provide to date the most updated whole view of vitamin E biosynthesis pathway. Also, we discussed about the role of vitamin E in plants stress response and its potential as signaling molecules.

Keywords: VTE; biosynthesis; pathway; signal; stress; tocochromanol; tocopherol; vitamin E.

FIGURE 1

Plant tocochromanol biosynthesis pathway and sources of metabolites. Metabolite names were colored for recognizing different tocochromanol synthesis pathways. Abbreviations of metabolites: HPP, 4-hydroxyphenylpyruvate; HGA, homogentisate; Phytyl-P, phytyl-phosphate; PDP, phytyl-diphosphate; THGGPP, tetrahydrogeranylgeranyl pyrophosphate; GGDP, geranylgeranyl pyrophosphate; SPP, solanesyl pyrophosphate; MPBQ, 2-methyl-6-phytyl-1,4-benzoquinol; DMPBQ, 2,3-dimethyl-6-phytyl-1,4-benzoquinol. Abbreviations of enzymes: TAT1, tyrosine aminotransferase 1; TAT2, tyrosine aminotransferase 2; HPPD, 4-hydroxyphenylpyruvate dioxygenase; CLD1, chlorophyll dephytylase 1; PPH, pheophytin pheophorbide hydrolase; VTE, vitamin E biosynthetic enzyme.

FIGURE 2

Representative HPLC traces of Arabidopsis leaf tocopherols subjected to different growth conditions (high light, heat, and dark). Tocol is used as internal standard [based on Bao et al. (2020), with modification].

FIGURE 3

A proposed working model of the vitamin E in signal transduction Chilling stress can be sensed by COLD1 to regulate calcium signal and tocochromanol homeostasis for transcriptional reprogramming in the nucleus. Other stresses including high-light and heat can also transduce retrograde signaling between chloroplast and nucleus for miRNA biogenesis, via manipulating PAP (3′-phosphoadenosine-5′-phosphate) and tocochromanols.