Current strategies for vitamin E biofortification of crops

Abstract

Vitamin E refers to four tocopherols and four tocotrienols that are exclusively synthesized by photosynthetic organisms. While a-tocopherol is the most potent vitamin E compound, it is not the main form consumed since the composition of most major crops is dominated by g-tocopherol. Nutritional studies show that populations of developed countries do not consume enough vitamin E and that a large proportion of individuals exhibit plasma a-tocopherol deficiency. Following the identification of vitamin E biosynthetic genes, several strategies including metabolic engineering, classic breeding and mutation breeding, have been undertaken to improve the vitamin E content of crops. In addition to providing crops in which vitamin E content is enhanced, these studies are revealing the bottlenecks limiting its biosynthesis.

WRINKLED1 and ACYL‐COA:DIACYLGLYCEROL ACYLTRANSFERASE1 regulate tocochromanol metabolism in Arabidopsis

“…Previous studies have concluded that the availability of tocochromanol biosynthetic precursors is an important regulatory mechanism controlling vitamin E synthesis in plants (reviewed by Mène‐Saffrané & Pellaud, ). To date, only the HOMOGENTISATE DIOXYGENASE ( HGO1 ) gene controlling HGA availability has been shown to alter tocotrienol biosynthesis in soybean ( Glycine max ) (Stacey et al ., ).…”

“…In addition, it was shown that WRI1 pushes carbon into lipogenesis by stimulating the expression of late glycolysis and lipogenesis genes, respectively, while DGAT1 pulls carbon into lipogenesis by condensing diacylglycerol and acyl‐CoAs (Vanhercke et al ., ). Tocochromanol synthesis occurs in plastids as well and is initiated by the condensation of HGA and various prenyl pyrophosphates (Mène‐Saffrané & Pellaud, ). HGA derives from the degradation of tyrosine produced by the shikimate pathway which is located in plastids and is initiated by the condensation of PEP and erythrose‐4‐phosphate (Mène‐Saffrané & Pellaud, ).…”

“…Tocochromanol synthesis occurs in plastids as well and is initiated by the condensation of HGA and various prenyl pyrophosphates (Mène‐Saffrané & Pellaud, ). HGA derives from the degradation of tyrosine produced by the shikimate pathway which is located in plastids and is initiated by the condensation of PEP and erythrose‐4‐phosphate (Mène‐Saffrané & Pellaud, ). Tocochromanol prenyl side chains are mostly produced by the methyl erythritol phosphate (MEP) pathway, which is also located in plastids and is initiated by the condensation of PYR and glyceraldehyde‐3‐phosphate (Vranová et al ., ; Zhao et al ., ).…”

“…Among the organisms used to study tocochromanol biosynthesis in plants, Arabidopsis is by far the one that provided the most knowledge and resources and in which tocochromanol biosynthesis is the best characterized. Since pioneer works that identified the first tocopherol biosynthetic gene (Shintani & DellaPenna, ), 17 tocochromanol biosynthetic genes and many biosynthetic mutants have been described in this organism (reviewed by Mène‐Saffrané & Pellaud, ). Wild‐type Arabidopsis accessions naturally accumulate tocopherols and PC‐8.…”

“…Tocopherol and tocotrienol biosyntheses use phytyl pyrophosphate (PPP) and geranylgeranyl pyrophosphate (GGPP) as prenyl donors, respectively (DellaPenna & M ene-Saffran e, 2011). For both types of compound, most biosynthetic genes have been identified in several plant genomes (M ene-Saffran e & Pellaud, 2017). A third type of tocochromanol, plastochromanol-8 (PC-8), which results from the condensation of HGA and solanesyl pyrophosphate, was identified in numerous plant species (Kruk et al, 2014).…”