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

Abstract

SummaryPhotosynthetic organisms such as plants, algae and some cyanobacteria synthesize tocochromanols, a group of compounds that encompasses tocopherols and tocotrienols and that exhibits vitamin E activity in animals. While most vitamin E biosynthetic genes have been identified in plant genomes, regulatory genes controlling tocopherol accumulation are currently unknown.We isolated by forward genetics Arabidopsis enhanced vitamin E (eve) mutants that overaccumulate the classic tocopherols and plastochromanol-8, and a tocochromanol unknown in this species. We mapped eve1 and eve4, and identified the unknown Arabidopsis tocochromanol by using a combination of analytical tools. In addition, we determined its biosynthetic pathway with a series of tocochromanol biosynthetic mutants and transgenic lines.eve1 and eve4 are two seed lipid mutants affecting the WRINKLED1 (WRI1) and ACYL-COA:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1) genes, respectively. The unknown tocochromanol is 11 0 -12 0 c-tocomonoenol, whose biosynthesis is VITAMIN E 1 (VTE1) -and VTE2-dependent and is initiated by the condensation of homogentisate (HGA) and tetrahydrogeranylgeranyl pyrophosphate. This study identifies the first two regulatory genes, WRI1 and DGAT1, that control the synthesis of all tocochromanol forms in seeds, and shows the existence of a metabolic trade-off between lipid and tocochromanol metabolisms. Moreover, it shows that Arabidopsis possesses a tocomonoenol biosynthetic pathway that competes with tocopherol synthesis.

Beyond pathways: genetic dissection of tocopherol content in maize kernels by combining linkage and association analyses

“…Furthermore, we found that natural variations in fatty acid pathway genes affect phenotypic variation in tocopherol content, which is supported by at least four points of evidence. The first was that five of the 32 genes affecting tocopherol content in AMP508 also showed a significant association with oil content in the same panel (Table S7), including DGAT, which has recently been shown to affect tocopherol content in Arabidopsis (Pellaud et al ., ). The second point of evidence was that the five genes that were significant for both oil and tocopherol were located within tocopherol QTLs, and one gene— DGAT —also fell within a QTL for oil content (Yang et al ., ).…”

“…In addition, a mutation in LACS , a gene from the fatty acid metabolism pathway, resulted in an altered tocopherol profile (Figure ). Moreover, the influence of DGAT , another fatty acid pathway gene that was found to affect tocopherol content in this study, was recently shown to affect tocopherol content in Arabidopsis (Pellaud et al ., ). Together, these results suggest the existence of complicated cross‐talk between fatty acid and tocopherol metabolic pathways.…”

“…Studies in other species, such as tomato, have also greatly enhanced our understanding of the biosynthetic pathways of tocopherols (Lira et al, 2016;Quadrana et al, 2013). Recent studies suggest that the tocopherol metabolic pathway is not completely understood (Lin et al, 2016;Zhang et al, 2014), and genes influencing tocopherol content in higher plants continue to be identified (Adato et al, 2009;Enfissi et al, 2010;Hey et al, 2017;Karlova et al, 2011;Liao et al, 2017;Pellaud et al, 2018;Van Eenennaam et al, 2004). These findings indicate the complexity of the tocopherol biosynthetic pathway and raise the possibility that there are additional genes that have not been discovered.…”

Metabolic Origins and Transport of Vitamin E Biosynthetic Precursors

“…The tocomonoenol prenyl precursor THGGPP is an intermediate of the reductive pathway converting GGPP into PPP ( Kruk et al, 2011 ; Pellaud et al, 2018 ). This process is mediated by a geranylgeranyl reductase (GGR) that sequentially converts both geranylgeranylated chlorophyll a and GGPP into phytylated chlorophyll a and PPP, respectively ( Keller et al, 1998 ; Takahashi et al, 2014 ).…”

“…Tocochromanol biosynthesis is initiated by the condensation of two biosynthetic precursors, the polar homogentisate (HGA) and a lipophilic polyprenyl pyrophosphate that varies according to the type of tocochromanol. The polyprenyl precursor of tocopherols is phytyl pyrophosphate (PPP), geranylgeranyl pyrophosphate (GGPP) for tocotrienols, solanesyl pyrophosphate (SPP) for PC-8, and tetrahydrogeranylgeranyl pyrophosphate (THGGPP) for tocomonoenols ( Figure 1 ; Pellaud et al, 2018 ). The core tocochromanol biosynthetic pathway has been widely investigated and is now well-characterized ( Mène-Saffrané and DellaPenna, 2010 ; DellaPenna and Mène-Saffrané, 2011 ; Mène-Saffrané and Pellaud, 2017 ).…”