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Genetic and biochemical basis for alternative routes of tocotrienol biosynthesis for enhanced vitamin E antioxidant production.
- Source :
-
Plant Journal . Feb2013, Vol. 73 Issue 4, p628-639. 12p. 2 Color Photographs, 1 Diagram, 7 Graphs. - Publication Year :
- 2013
-
Abstract
- Vitamin E tocotrienol synthesis in monocots requires homogentisate geranylgeranyl transferase ( HGGT), which catalyzes the condensation of homogentisate and the unsaturated C20 isoprenoid geranylgeranyl diphosphate ( GGDP). By contrast, vitamin E tocopherol synthesis is mediated by homogentisate phytyltransferase ( HPT), which condenses homogentisate and the saturated C20 isoprenoid phytyl diphosphate ( PDP). An HGGT-independent pathway for tocotrienol synthesis has also been shown to occur by de-regulation of homogentisate synthesis. In this paper, the basis for this pathway and its impact on vitamin E production when combined with HGGT are explored. An Arabidopsis line was initially developed that accumulates tocotrienols and homogentisate by co-expression of Arabidopsis hydroxyphenylpyruvate dioxygenase ( HPPD) and Escherichia coli bi-functional chorismate mutase/prephenate dehydrogenase (TyrA). When crossed into the vte2-1 HPT null mutant, tocotrienol production was lost, indicating that HPT catalyzes tocotrienol synthesis in HPPD/TyrA-expressing plants by atypical use of GGDP as a substrate. Consistent with this, recombinant Arabidopsis HPT preferentially catalyzed in vitro production of the tocotrienol precursor geranylgeranyl benzoquinol only when presented with high molar ratios of GGDP: PDP. In addition, tocotrienol levels were highest in early growth stages in HPPD/TyrA lines, but decreased strongly relative to tocopherols during later growth stages when PDP is known to accumulate. Collectively, these results indicate that HPPD/TyrA-induced tocotrienol production requires HPT and occurs upon enrichment of GGDP relative to PDP in prenyl diphosphate pools. Finally, combined expression of HPPD/TyrA and HGGT in Arabidopsis leaves and seeds resulted in large additive increases in vitamin E production, indicating that homogentisate concentrations limit HGGT-catalyzed tocotrienol synthesis. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 09607412
- Volume :
- 73
- Issue :
- 4
- Database :
- Academic Search Index
- Journal :
- Plant Journal
- Publication Type :
- Academic Journal
- Accession number :
- 85652537
- Full Text :
- https://doi.org/10.1111/tpj.12067